Topic 5 - Physical Chemistry and Transition Elements Flashcards
Kc =
[products] / [reactants]
[ ] =
equilibrium concentrations in moldm^-3
If the equation is aA + bB cC + dD, what is the Kc equation?
Kc = ([C]c x [D]d) / ([A]a x [B}b)
What is Kc?
Kc is a constant but is temperature dependent
How does temp do to Kc on an exothermic forward reaction?
Temp increase so concentration of reactants increase and products decrease so Kc drops
Temp decrease so concentration of reactants decreases and products increases so Kc rises
Size of Kc meaning?
Large Kc, equilibrium on the right
Small Kc, equilibrium on the left
If an equilibrium mixture is homogeneous, what does this mean? and what happens to Kc?
If an equilibrium mixture is homogeneous (all the reactants and products are in the same physical state) all the species go into the Kc expression
If an equilibrium mixture is heterogeneous, what does this mean? and what happens to Kc?
If an equilibrium mixture is heterogeneous (reactants and products are in different physical states) only gaseous and aqueous species go into the Kc expression
When writing Kc expressions for heterogeneous equilibria we leave out any species which are solid or liquid as …
… Their concentrations are essentially constant
For gaseous equilibria it is more convenient to use ______ ________ of reactants and products instead of equilibrium concentration in moldm-3
partial pressures
if aA(g) + bB(g) cC(g) + dD(g), then Kp =
((pC)c x (pD)d) / ((pA)a x (pB)b)
If N2(g) + 3H2)g) 2NH3(g), then Kp =
Kp = (pNH3)2 / ((pN2) x (pH2)3)
In Kp, what is ‘p’?
P = partial pressure in Pa/kPa
If Kp>1 there are …
… more of the products to reactants at equilibrium
If Kp<1 there are …
… more of the reactants to products at equilibrium
Partial pressure is the …
… individual pressures of the components in the mixture
Kp is a constant at …
constant temperature
How does temperature effect Kp in an exothermic reaction?
Suppose temperature increases, an increase in temperature favours the endothermic reaction, which in this case is the reverse reaction, so the equilibrium responds by moving to the left hand side, in other words the partial pressure of the products drop, this drops the value of Kp.
Suppose temperature decreases, a decrease in temperature favours the exothermic reaction, which in this case is the reverse reaction, so the equilibrium responds by moving to the right hand side, in other words the partial pressure of the reactants drops, this increases the value of Kp.
How do we know partial pressure is proportional to the mole fraction?
A(g) + B(g) C(g) at a fixed volume and constant temperature
pV = nRT
Partial pressure =
mol fraction x total pressure
Mole fraction =
mol / total moles
What is Kp?
the equilibrium constant in terms of partial pressure
Why is equilibria involving gases are usually expressed in terms of Kp?
This is because it is easier to measure the pressure of gas rather than the concentration
The mole fraction of a gas is the same as its …
… proportion by volume to the total volume of gases in a gas mixture
For gas A in a mixture: Mole fraction (A) =
moles (A) / total number of moles in gas mixture
Mole fraction of gases in the air?
Air has approx. 78% N2 , 21% O2 and 1% other gases
Mole fraction of N2 x(N2) = 78/100 = 0.78
Mole fraction of O2 x(O2) = 21/100 = 0.21
Mole fraction of other x(other) = 1/100 = 0.01
Sum of mole fractions always =
1
Calculating Mole Fraction from Gas Volumes?
Volume = moles x 24
This shows that volume is proportional to the moles of gas
Sum of partial pressures =
total pressure
How are the units for Kp found?
in the same way as Kc
Nitrogen, hydrogen and ammonia coexist in a homogeneous equilibrium ;
N2 (g) + 3 H2 (g) 2 NH3 (g)
An equilibrium mixture at 400 oC contains 18 mol N2, 54 mol H2 and 48 mol of NH3. The total equilibrium pressure is 200 atms. Use this information to calculate the value of Kp.
Step 1 : find the mole fraction of N2, H2 and NH3.
Total number of gas moles = 18+54+48 = 120 mol
x(N2) = 18/120 = 0.15 x(H2) = 54/120 = 0.45 x(NH3) = 48/120 = 0.40
Step 2 : find the partial pressures of each gas.
p(N2) = 0.15 x 200 = 30 atms p(H2) = 0.45 x 200 = 90 atms p(NH3) = 0.40 x 200 = 80 atms
Step 3 : Calc Kp Kp = p(NH3)2 = 802 = 2.9 x 10-4 atms-2
p(N2) x p(H2)3 30 x 903
Units = (atm)2 = 1 = atm-2
(atm) x (atm)3 atm2
Describe and explain how you find kP in heterogeneous equilbria
Equilibrium contains different phases (solid and gas)
Equilibrium: CaCO3(s) ⇌ CaO(s) + CO2(g)
Kp expression contains only gaseous species
Kp = p(CO2)
Solid species are omitted
(solids have no gas pressure)
Therefore, if a question arose that said:
In the equilibrium mixture, CO2 has a partial pressure of 2.5 x 10-2 atm at 600oC. Calculate Kp.
Kp = p(CO2) = 2.5 x 10-2 atm.
K is a constant and only changed by
A change in temperature
Equilibrium is achieved within a system when
the concentrations/partial pressures of the species at equilibrium give the value of K for that temperature when placed in the equilibrium constant expression
For forward exothermic reactions what happens when temp increases in terms of Kp?
As temperature increases, Kp values decrease, showing that the equilibrium position shifts to the left
For forward endothermic reactions what happens when temp increases in terms of Kp?
As temperature increases, Kp values increase, showing that the equilibrium position shifts to the right
Why is there no change in K for changes in concentration or pressure?
as the equilibrium moves to keep the equilibrium constant at the same value
Explain how a change in pressure effects Kp?
For a change in pressure, if the pressure is increased, when looking at K equation, the part of the fraction that will be most affected by a change in the system will be the part with the highest powers. This increase in pressure will increase the value of Kp and mean that the system is no longer in equilibrium, to restore Kp to its value for that temperature, the partial pressure of the substance with less powers need to increase so the equilibrium shifts in that direction.
What is a reaction rate?
Chemists define the rate of reaction as the rate at which a reactant(s) is used up or the rate at which a product formed
when we look at concentration and rates of reaction it is important to state which substance we are following, why?
.For example if we consider the reaction A + 2B C
.The concentration of reactants A and B decrease with time and the concentration of product C increases with time
.The reaction tells us that for every A that reacts two Bs are required
.So the concentration of B decreases twice as fast as the concentration of A
.We talk about the amount of reactants or products in terms of their what?
Concentration
.Concentration is measured in what?
mol dm-3
.We use the symbol [ ] to write about what?
Concentration
if we were looking at the concentration of A we would write what?
[A]
.Chemical equations tell us what?
what is involved in the reaction
the stoichiometric values tell us what?
the quantitative relationship between the different reactants and products
chemical equations gives us no information about what?
whether the reaction will actually happen or how fast it will occur
.The rate of a chemical process can depend on several factors, what are they?
– temperature of the reaction – concentration of the reactants – the surface area • only relevant with solid reactants – the presence of a catalyst
.The chemical kinetics of a reaction allow chemists to what?
control reactions by altering the conditions
.The reaction rate is what?
the change in concentration of a reactant (or product) per unit time
The reaction rate describes what?
– describes how quickly reactants are used up
– or how quickly products are formed
.We can look at the __________ for an entire reaction or look at the rate a specific point during the reaction – __________________
Average rate
the instantaneous rate
.The average rate is what?
the total change in concentration of reactants (or products) divided by the time taken for the reaction to take place
.The instantaneous rate of a reaction is what?
the rate of change occurring at a specific time in the reaction
.One method to calculate the rate of change at a given point is to what?
find the gradient of the tangent at the point you are interested in
The units for a rate of reaction is
mol dm-3s-1
Rate of reaction =
change in concentration / time
.In the reaction: A → B, we can calculate either …
… the average rate of A being used or the average rate of B being produced
.Rate is always a positive value so a minus sign can be added to [A] as the change in concentration is …
… negative
.The instantaneous rate of reaction is …
… the amount of change in concentration of a product or reactant at a specific time during a reaction
.A graph can be used and the rate determined by …
… drawing a tangent to the graph at any time and finding the slope of that tangent
.Calculate the gradient by
dividing the change in y by the change in x
.Changing the concentration often changes the what?
rate of a reaction
.The rate of reaction is proportional to the …
… concentration of a particular reactant raised to a power
.For example, for reactant [A] and power n, rate is proportional to …
… [A]^n
.For each reactant, the power is (in reference to order of reaction)
the order of reaction for that reactant
.In a reaction, different reactants can have different orders and each may affect the rate in different ways
.Common orders are:
zero order (0), first order (1), second order (2)
Tell me about the zero order
.When the concentration of a reactant has no effect on the rate, the reaction is zero order with respect to the reactant
.With zero order, rate is proportional to [A]0
.In a zero order reaction:
- Any number raised to the power zero is 1
- Concentration does not influence the rate
Tell me about the first order
.A reaction is first order with respect to a reactant when the rate depends on its concentration raised to the power of one
.With first order, rate is proportional to [A]1
.In a first order reaction:
- If the concentration of A is doubled, the reaction rate increases by a factor of 21 = 2
- If the concentration of A is tripled, the reaction rate increases by a factor of 31 = 3
Tell me about the second order
.A reaction is second order with respect to a reactant when the rate depends on its concentration raised to the power of two
.With second order, rate is proportional to [A]2
.In a second order reaction:
- If the concentration of A is doubled, the reaction rate increases by a factor of 22 = 4
- If the concentration of A is tripled, the reaction rate increases by a factor of 32 = 9
.The rate equation gives the what?
mathematical relationship between the concentrations of the reactants and the reaction rate
.For two reactants, A and B, the rate equation is:
- Rate = k [A]m [B]n
.The rate constant k is the what?
proportionality constant, it is the number that mathematically converts between the rate of reaction and concentration and orders
Outline the principles in Le Chatelier’s principle
- Conc increase of a species, equilibrium moves in direction to reduce that concentration
- Pressure increase favors side with the least number of molecules
- Temperature increase favors the endothermic direction
- At constant temperature, K does not change if you change …
… pressure, concentration or use a catalyst
- K will only change if …
… the temperature is changed
For an exothermic reaction, Kp decreases with increasing temperature and the equilibrium position shifts to the left, why?
an increase in temperature favors the endothermic backward reaction
Essentially, why does temperature cause the equilibrium to shift?
A change in the K value, which is caused by a change in temperature, has to be met by a change in the concentrations or partial pressures of the reactants and products - which means the equilibrium is shifting
Effect of Increasing Temperature on Equilibrium
Exothermic
K decreases
Equilibrium shifts to the left
Effect of Increasing Temperature on Equilibrium
Exothermic Endothermic
K increases
Equilibrium shifts to the right
Explain Why K Doesn’t Change with Concentration using :
.N2O4 (g) 2 NO2 (g)
.At constant temperature, [NO2] = 0.4 moldm-3 [N2O4] = 0.01 moldm-3
as an example
Kc = [NO2 (g)]2 = 0.4002 = 16.0 mol dm-3
[N2O4 (g)] 0.010
If [N2O4] increased to 0.02 then Kc = 0.4002 = 8.0 mol dm-3
0.02
The system is now no longer in equilibrium.
.To return the value of Kc ratio back to 16.0 mol dm-3 then [NO2] must increase & [N2O4] must decrease (top bigger bottom smaller)
.N2O4 (g) 2 NO2 (g) the equilibrium shifts to the right
.Using Le Chatelier’s principle, we would expect the equilibrium to shift to the right so that the equilibrium can decrease the [N2O4] if extra is added.
.Le Chatelier’s principle only works because Kc controls the relative concentration of reactants and products present at equilibrium to maintain a constant value.
Explain Why K Doesn’t Change with Pressure by using :
.N2O4 (g) 2 NO2 (g)
.Le Chatelier : increase in pressure favours shift to the left due to lower number of molecules
.At constant temp; p(NO2) = 9.6 atms p(N2O4) = 0.24 atms
as an example
.Kp = p(NO2)2 = 9.62 = 384 atms
p(N2O4) 0.24
.If total pressure doubled p(NO2) doubled to 19.2 atms and p(N2O4) = 0.48 then Kp = 19.22 / 0.48 = 768 atms
.To reduce Kp back to 384, p(NO2) must decrease and p(N2O4) must increase (top smaller / bottom bigger), so equilibrium shifts from right to left
.The shift to the left (fewer gaseous molecules) is directed by the value of Kp being restored
Increasing Pressure on Ammonia Production, explain what happens with reference to K values?
.N2 + 3 H2 2 NH3
.Increase pressure favors shift from left to right
. Kc = [NH3]2 If pressure increased at constant temperature, then Kc must remain constant
[N2] x [H2]3
.As pressure increased then the concentration of N2, H2 and NH3 will increase (same moles in smaller volume)
.As denominator (bottom) power x4 / numerator (top) x2 then value of Kc will decrease as [ ]’s increase
.To restore Kc back to original value i.e., maintain constant Kc then equilibrium will shift to increase top [NH3] and reduce bottom [N2][H2] – shift from left to right
Effect of catalysts on K values
.Equilibrium constants are unaffected by catalysts
.They affect the rate of a reaction, not equilibrium position (speed up both forward and back reaction by same factor)
If a species is zero order:
- It means that changing the concentration of a substance has no effect on the rate
- If the concentration doubles, the rate stays the same
- If the concentration triples, the rate stays the same
If a species is first order:
- It means that changing the concentration of a substance changes the rate to the power 1
- If the concentration doubles, the rate doubles (21 = 2)
- If the concentration triples, the rate triples (31 = 3)
If a species is second order:
- It means that changing the concentration of a substance changes the rate to the power 2
- If the concentration doubles (x2), the rate quadruples (x4) (22 = 4)
- If the concentration triples (x3), the rate increases by 9 (32 = 9)
A + 2B + C D + E
[A] is zero order, [B] is 1st order, [C] is 2nd order
Rate =
Overall rate =
K [B] [C]2
1 + 2 = 3
What does ICE stand for?
Initial
Change
Equilibrium
2NO2 2NO + O2
0.56 moles of NO2 are left to decompose in a vessel with a volume of 0.5dm3. 0.48 moles of NO are formed. What is the value of Kc?
17.28M
How to work out K and the units for K
Rearrange the rate equation and input values from the table to work out the value of K
Write the units of each part of the equation for K and work out the units by cancelling etc.
What is Kc?
a mathematical representation of the ration of products:reactants
What do homogeneous and heterogenous mean?
Homogeneous – same state
Heterogeneous – different states
The concentrations of pure solid and pure liquids are excluded from equilibrium expressions, why?
as their concentrations are constant
What is the unit of rate constant for an overall order of reaction of 0
Mol dm-3 s-1
What is the unit of rate constant for an overall order of reaction of 1
s-1
What is the unit of rate constant for an overall order of reaction of 2
Mol-1 dm3 s-1
What is the unit of rate constant for an overall order of reaction of 3
Mol-2 dm6 s-1
What is the unit of rate constant for an overall order of reaction of 4
Mol-3 dm9 s-1
.For gaseous equilibria, it is more convenient to use ________ of reactants and products instead of equilibrium concentrations in mol dm-3
partial pressures
Generic Kp formula –
aA + bB cC + dD
Kp = ((pC)c x (pD)d) / ((pA)a x (pB)b)
Haber process equation and Kp formula
N2 + 3H2 2NH3
Kp = (pNH3)2 / ((pN2) x (pH2)3)
What is p in Kp?
p = partial pressure in Pa/kPa
If Kp > 1 there are
more products than reactants
If Kp < 1 there are
more reactants than products
What is partial pressure
The partial pressure is the pressure of an independent component of the equilibria
Like Kc, Kp is constant at what?
a constant temperature
In the haber process, Suppose the pN2 is doubled, how does the equilibrium respond?
The denominator will be bigger, so Kp will get smaller, so to get bigger again it increases the numerator, so pNH3 increases, so the equilibrium moves to the right
Effect of temperature –
Delta H = -92 kJmol-1
what would happen in a temperature increase?
Suppose a temperature increase, it would favour the endothermic reaction, so the equilibrium would shift to the left, so Kp would get smaller
Effect of temperature –
Delta H = -92 kJmol-1
what would happen in a temperature decrease?
Support a temperature decrease, it would favour the exothermic reaction, so the equilibrium would shift to the right, so Kp would get larger
A + B C
Fixed volume at a constant temperature
Why is partial pressure proportional to the number of moles?
pV = nRT
Partial pressure is proportional to the what?
mole fraction
The sum of the mole fractions equals what?
1
Partial pressure =
mol fraction x total pressure
Kp is what?
The equilibrium constant in terms of partial pressures
Equilibria involving gases are usually expressed in terms of what?
Kp
.It is easier to measure ____ of gas rather than concentration
pressure
.Concentration & pressure are __________ to each other
directly proportional
.Under the same conditions, the same volume of different gases will contain the same number of __________
moles of gas molecules
.The mole fraction of a gas is the same as its proportion by volume what?
to the total volume of gases in a gas mixture
mole fraction x(A) =
number of moles of A / total number of moles in gas mixture (N)
Partial pressure, p, is what?
the contribution of a gas towards the total pressure
Why do mol fractions have no units?
- Mol fractions are calculated with moles on the top and bottom of the equation, so the units cancel out
Partial pressure, p, is the what?
contribution of a gas towards the total pressure
Partial pressure (p) =
mole fraction x Total pressure (P)
To work out the order of the reaction for the concentration, you have to use experimental data, to get this you have two options, what are they?
- Continuously monitor the change in concentration of A against time
- Use initial rates method to find out how the initial rate changes as you vary the concentration of A
Concentration-time graphs can be plotted by ______________________________________________________________________, it is called continuous monitoring
continuously monitoring the concertation of a reactant through the course of the reaction
How can you gain the concentration of a reactant through the course of the reaction?
Can use loss in mass, gas syringe, or measuring cylinder
Also can use pH changes or colorimetry
Can’t use every method for every experiment
What can the shape of concentration time graphs tell us?
The shape can be used to tell you the order for that particular reactant
For concentration time graphs, a zero order reaction produces ….
a straight line with a negative gradient, the reaction rate does not change at all through the course of the reaction
For concentration time graphs, a first order reaction produces …
a downward curve with decreasing gradient over time, as the gradient decreases with time, the reaction gradually slows down
For concentration time graphs, a second order reaction has a …
downward curve but steeper at the start and tailing off more slowly
For concentration-time graphs, you can find the rate using: gradient =
delta (y) / delta (x)
How to find gradient of concetration-time graphs
.For zero orders, draw a triangle to the start and end
.For first order, draw a triangle touching the curve at one point (a tangent)
Apart from rate, what else can you find from conc-time graphs?
K
How can you tell between first and second order conc-time graphs?
.We can tell if we have a first order curve by measuring half life
Half life (t1/2) is the time taken for half of the reactant to be used up
First order reactions have a constant half-life independent of the initial concentration
This pattern is called exponential decay
what does ln(2) / t1/2 equal?
k
Equilibria involving gases are usually expressed in terms of what?
Kp – constant in terms of partial pressure
Easier to measure pressure of ___ rather than concentration
gas
_________ and pressure are directly proportional to each other
concentration
Mole fraction x(A) =
number of moles of A / total number of moles in gas mixture (N)
Volume = mole x __
24
Partial pressure is what?
the contribution of a gas towards the total pressure
Partial pressure (p) =
mole fraction x total pressure (P)
Kp is similar to Kc but …
… partial pressures are used instead of concentration
Briefly explain le Chatelier
.Conc increase of a species equilibrium moves in direction to reduce that conc
.Pressure increase favours side with the least number of molecules
.Temperature increase favours the endothermic reaction
.Le Chatelier works because of what?
equilibrium constants
k=1, k<1, k>1 meaning
.k=1 equilibrium half way
.k=100 equilibrium lies will over to products (to the right)
.K=0.01 equilibrium lies well over to the reactants (to the left)
.At constant temperature, K does no change if
you change pressure, conc, or use a catalyst
.K will only change if
the temperature is changed
How changes in conc and pressure affect equilibrium constants
.The value of the equilibrium constant K is unaffected by changes on concentration and pressure.
.This may seem strange as you know from Le Chatelier’s principle that the position of the equilibrium can be shifted by changing concentration or pressure.
.The equilibrium shift actually takes place from the very fact that the equilibrium constant does not change
Increasing pressure on ammonia production exam answer
.Increase pressure favors shift from left to right. If pressure increased at constant temp, then Kc must remain constant. As pressure increased then the concentration of N2, H2 and NH3 will increase (same moles in smaller volume). As denominator (bottom) power x4 / numerator (top) x2 then value of Kc will decrease as [ ]’s increase. To restore Kc back to original value i.e., maintain constant Kc then equilibrium will shift to increase top [NH3] and reduce bottom [N2][H2] – shift from left to right.
.Equilibrium constants are _________ by catalysts. …
unaffected
…. they affect the rate of a reaction, not equilibrium position (speed up both forward and back reaction by same factor).
Define acid
dissociates in water and releases H+ ions
Define alkali
dissociates in water to release OH- ions
Neutralisation equation
H+ + OH-1 H2O
Bronsted Lowry Acid:
Proton donor
Bronsted Lowry Base:
Proton acceptor
pH = 1 (x 10 the concentration of H+ ions) pH =
2
What makes an acid strong?
It fully dissociates
As a Strong acid fully dissociates, pH of a strong acid can be calculated from
concentration of acid
pH =
-log10[H+]
Sulphuric acid is dibasic, what does this mean?
H2SO4 2H+ + SO42-
[H+] =
10-pH
Weak acids form an acid dissociation constant called
Ka
Ka =
[products] / [reactants]
[H+] =
for weak acids
root([HA] Ka)
[HA] is what?
concentration of weak acid
A+B C
What happens when you Increase pressure?
equilibria moves to the side with fewer molecule/moles, 2 moles on RHS and 4 on LHS, equilibria moves to the right
A+B C
What happens when you Lowering Temperature?
Forward reaction is exothermic (negative energy change), lowering temperature moves equilibria to exothermic reaction (RHS)
A+B C
What happens when you Increase A and B?
Equilibria removes addition of A and B, equilibria moves to RHS to remove this extra concentration of A and B
A+B C
What happens when you Decrease C?
Equilibria moves to make more of what is removed, equilibria moves to RHS to make more C
Meaning of Kc>1?
means more products, equilibria is towards the RHS
Meaning of Kc<1?
means more reactants, equilibria towards the LHS
Meaning of Kc=1?
means LHS=RHS
.When a reversible reaction establishes an equilibria at a certain temperature, K will not change if, ________, _______,
____________ are changed/added
concentration, pressure, or a catalyst
.K is only changed by ________
temperature
In the equation 2SO2 + O2 2SO3
delta H = -197
As temperature increases Kp decreases, why does this happen?
Kp = p(SO3)2 / ( p(SO2)2 x p(O2) )
Partial pressure of products decrease and reactants increase
Equilibria moves to the left
Using N2O4 2NO2 as an example, explain why Kc and Kp do not change due to concentration, pressure or addition of a catalyst?
.If N2O4 concentration was increased at same temperature, Kc value would be lowered (denominator increased), equilibria moves to the RHS and Kc returns to normal (numerator increase, denominator decrease)
.If we increased partial pressure then the numerator would be increased more than the denominator due to the difference in powers, this would cause Kp value to increase (system not at equilibria), equilibria moves left to increase value of the denominator (N2O4) and restore the value of Kp, system would be back in equilibrium
.Catalyst does not change equilibria (Kc/Kp = same) as both forward and reverse reaction rates are changed the same, this means position of equilibria does not move
What does the Arrhenius theory define bases and acids as?
The Arrhenius theory of acids and bases defines acids as a substance that releases protons in solution, and bases as a substance that releases hydroxide ions.
How can we test for acids?
We can test for acids using universal indicator paper which turns red or orange depending on the strength of the acid
Blue litmus paper also turns red in the presence of an acid
HCl + H2O –>
H3O+ + Cl-
What is H3O+
A hydronium ion, also known as an oxonium ion
What is water acting as in the equation:
HCl + H2O H3O+ + Cl-
a base
What is a bronsted-lowry base?
A Bronsted Lowry base is a substance which accepts protons in solution
What is a bronsted-lowry acid?
A Bronsted Lowry acid is a substance which releases or donates protons in solution
What does a bronsted-lowry acid-base reaction involve?
the transfer of a proton from one base to another
What does ammonia do in water? include equation
Ammonia, in water, accepts a proton
NH3 + H2O NH4+ + OH-
In the equation,
NH3 + H2O NH4+ + OH-, what is water acting as?
An acid
For a bronsted-lowry base, what is the pH of an acid?
So for the Bronsted Lowry theory, a base does not need to have a pH>7
What are substances that can act as either a base or an acid called?
Substances that can act as either an acid or a base are amphoteric
What are some old defnitions of acids?
.The definition of acids has developed since the time of the ancient Greeks
.Simpler ideas involved substances that had a sour taste, contained hydrogen, hydrogen ions or had a pH lower than 7
.When a chemical reacts with an acid it is the __________ from the acid which is driving the reaction forward
hydrogen ion, H+,
HCl (aq) + NaOH (aq)
NaCl (aq) + H2O (l)
How did the Bronsted-Lowry name come about?
Johannes Nicolaus Bronsted and Martin Thomas Lowry did not work together but both chemists formulated the idea that acids are proton donors and bases are protons acceptors
The Brønsted–Lowry acid–base theory is a development of these earlier ideas and states that:
.An acid is a proton donor
.A base is a proton acceptor
.How many protons, neutrons and electrons does a Hydrogen ion, H+ have?
.A hydrogen ion is just a proton
We know that HCl forms a covalent bond between the hydrogen and chlorine so what happens when it dissolves in water to become hydrochloric acid?
.HCl(g) + aq H+(aq) + Cl-(aq)
HCl(g) + aq H+(aq) + Cl-(aq)
.On closer inspection is?
HCl(g) + H2O(l) H3O+(aq) + Cl-(aq)
.H3O+(aq) is known as the hydronium ion, also known as _______ ion
hydroxonium
.In this equation:
HCl(g) + H2O(l) H3O+(aq) + Cl-(aq)
what is HCl and H2O acting as?
The HCl is a proton donor (a Brønsted–Lowry acid)
.The H2O is a proton acceptor (a B-L base)
In the reverse equation of HCl(g) + H2O(l) H3O+(aq) + Cl-(aq) what happens to the roles?
.In the reverse equation, the roles reverse:
H3O+(aq) + Cl-(aq) HCl(g) + H2O(l)
once an acid has ‘donated’ a proton it would become able to ‘accept’ a proton back and hence act as a base, what is this called?
We call these pairs of chemicals conjugate acid-base pairs
Give an example of a conjugate acid-base pair?
HCl and Cl- = Acid and conjugate base
What are the acid base pairs in HCl + H2O H3O+ + Cl-
HCl = acid 1 Cl- = base 1
H2O = base 2 H3O+ = acid 2
What are the acid base pairs in CH3COOH + H2O CH3COO- + H3O+?
CH3COOH = acid 1 CH3COO- = base 1
H2O = base 2 H3O+ = acid 2
What are the acid base pairs in NH3 + H2O NH4+ + OH-?
Base 2 Acid 1 Acid2 Base 1
What are the acid base pairs in HCO3- + HCl H2CO3 + Cl-?
Base 2 Acid 1 Acid 2 Base 1
Complete the equation for the conjugate acid-base pair: CH3CH(OH)COOH + CH3CH2CH2COOH
CH3CH(OH)COO- + CH3CH2CH2COOH2+
List the roles of H+ in reactions
spectator ions:
Acid + metal salt + hydrogen
Solid carbonates and soluble carbonates:
Acid + carbonate Water + carbon dioxide
base (metal oxides): Acid + base salt + water
Alkali: H+ + OH- H2O
What did Soren Sorenson do?
introduced simple numbers to represent the colours of indicators using an electrochemical cell to measure the hydrogen content
What did Soren Sorenson find?
.He found the ion concentration had a very large range of values of powers of 10 (10-1 to 10-14)
What is a strong acid? With general equation
.A strong acid is one which completely dissociates into ions in a solution
HA H+ + A-
So for a strong acid, [H+] =
concentration of the acid ([HA])
pH =
-log10[H+]
What does the equation pH = -log10[H+] tell us?
.It tells us the relative hydrogen ion concentration of a given solution
What must we remember with the equation pH = -log10[H+]?
.THIS ONY WORKS FOR STRONG ACIDS
.An increase in H+ x10, it reduces the pH by how much?
1
What is pH of 1M HCl?
0
What is Sorenson’s pH scale?
.The logarithmic scale means that a shift of one pH unit means a 10x change in the acidity and alkalinity of the solution
.Theoretically there is no limit to the pH scale
What type of acid is HCl, what does this mean?
monobasic = [H+]
What type of acid is H2SO4, what does this mean?
dibasic = 2[H+]
What type of acid is H3PO4, what does this mean?
tribasic = 3[H+]
[H+] =
10-pH
What is the [HCl] of a solution with pH 1.8?
0.016 moldm-3
What is the [H2SO4] of a solution with pH 1.8?
0.008 moldm-3 as dibasic acid
50cm^3 of 0.1M HCl is diluted to 100cm^3 with water, what is the change in pH?
Before dilution, pH = 1
0n dilution, HCl conc is halved to 0.05M
After dilution, pH = 1.30
Change = 0.3
rate-concentration graphs can be plotted using two different methods, what are they?
- Continuously monitor the change in concentration of a substance over time and work out the gradient at set point on the graph
- Use initial rates method to find out how the initial rate changes as you vary the concentration of A
We can produce a rate-concentration graph by producing a concentration time graph for the experience at different concentrations and then what?
using a tangent to work out the initial rate (the rate at t=0)
We can also use an initial rate reaction called a what?
clock reaction
The shape of rate-concentration graph can tell us what?
the order of the reaction
Describe a zero order rate-concentration graph
.Produces a horizontal line with zero gradient
.This shows the rate doesn’t change
.Rate = k
.To work out the rate constant, it is the intercept on the y axis
Describe a first order rate-concentration graph
.Produces a straight line through the origin
.This shows the rate is directly proportional to the concentration
.Rate = k[A]
.To work out the rate constant you should work out the gradient of the straight line
Describe a second order rate-concentration graph
.Produces an upward curve with increasing gradient
.Rate = k[A]2
.This curve doesn’t actually confirm its second order, just that it’s not 0 or 1
.You have to plot another graph from this one to show its 2nd order
.This means you can’t work out the rate constant directly from this curve
How to work our rate constant from second-order rate-concentration graph?
.To work out the rate constant you would need to plot a second graph of rate against concentration squared
.If I is truly second order it should produce a straight line
.To work out the rate constant you would work out the gradient of the line (like first order)
What is a clock reaction?
.A clock reaction is a more convenient way of obtaining initial rate
.We use a reaction with a visual change – usually a colour change
.We time from the start of the experiment to the visual change
.We repeat the experiment each time with different concentration meaning the time for the colour change each time
For a clock reaction, what is assumed?
.We assume that the average rate of the reaction is the same as the initial rate
For a clock reaction, the initial rate is proportional to what?
.The initial rate is proportional to 1/t
What is an iodine clock?
.This is a clock reaction which relies on the formation of iodine
.Aqueous iodine is orange brown so we can measure the colour change
.We usually use an indicator (starch) as that is a intense black-blue colour with iodine so it is very easy to see the colour change
How can you work out the order of hydrogen perioxide in a reaction using an iodine clock?
.Hydrogen Peroxide (H2O2) reacts with iodide ions in an acid solution to form iodine
H2O2 + 2I- + 2H+ I2 + 2H2O
.Lets say we start with 0.05M of H2O2
.We would add some acid (to provide the H+ ions) and some KI to provide the I ions
.We would also add some starch (for the indicator) and some sodium thiosulfate, Na2S2O3, to provide S2O32- ions
Reaction 1:
H2O2 + 2I- + 2H+ I2 + 2H2O
Reaction 2:
2S2O3 2- + I2 S4O6 2- + 2I-
.We time how long it takes to see a colour change (the blue-black to start to appear), this occurs when all of the sodium thiosulfate has been used up
.We would then repeat this for the next concentration (e.g. 0.04 mol dm-3 and so on)
You would end up with a table of results with concentration of H2O2 and time
.You can then use the principle that initial rate = 1/t
.So we work this out and add to the table
You can then plot a graph of [H2O2] against 1/t, and from that work out its order
How accurate is the iodine clock?
.In the clock reaction we are measuring the average rate over a period of time, the shorted the amount of time, the less the rate will change over that time
.The clock reaction is classed as accurate as long as less than 15% of the reaction has taken place (in terms of time)
What is a reaction mechanism?
A reaction mechanism describes the one or more steps involved in a reaction in a way which makes it clear how certain bonds are broken and made
What is the rate determining step?
The slowest step is called the rate determining step
What is The overall rate of reaction (the one you could measure if you did some experiments) controlled by?
the rate of the slowest step
What can the rate equation tell you in terms of rate determining steps?
.If the species is in the rate equation it is taking part in the rate determining step
.If the species is not in the rate equation it is not taking part in the rate determining step
.The power on the substance in the rate equation is the number of that substance in the rate equation
The steps involved in the reaction must add up to what?
the overall equation in the reaction
Rate = k[NO2]2 Overall = NO2 + CO NO + CO2
what are the two steps involved?
R.D.S = NO2 + NO2 NO3 + NO
Other step = NO3 + CO NO2 + CO2
In any chemical reaction, some bonds are broken and new ones are made
Often these changes are too complicated to happen in one single stage, instead, the reaction may involve what?
a series of smaller steps one after the other
BrO3- + 6H+ + 5Br- 3Br2 + 3H2O
why must this reaction take multiple steps?
it is unlikely that all the ions will collide at the same time
This reaction happens in two steps, the steps also happen at different rates, one step is slow and one step is _____
fast
Rate = k [Cl.][O3]
Overall equation = O3 + O 2O2
what are the two steps involved?
RDS = Cl. + O3 ClO. + O2
Other Step = ClO. + O O2 + Cl.
What is a strong acid?
A strong acid is one which completely dissociates into ions in a solution
WHat does pH = -log10[H+] only work for?
ONLY WORKS FOR STRONG ACIDS
[H^+] equation for changing concentraation
[H+] = [H+]old x (old volume / new volume)
How are weak acids different to strong ones?
.Weak acids do not dissociate fully like strong acids
What happens when a weak acid dissociates?
An equilibrium is established between the ions and the acid
As an equibrlium is established when weak acids dissociate, what can we calculate?
we can calculate an equilibrium constant Ka (Acids dissociation cons tat)
What does Ka equal for, HA H+ + A-?
Ka = ( [H+] [A-] ) / [HA]
For the Ka equation what two assumptions need to be made?
.A pure acids will split evenly into equal quantities of [h+] and [A-]
.The concentration of the acid doesn’t change as the equilibrium lies so far to the left it can be considered equal
does [H+] = [H+ aq]?
yes
.A sample of ethanoic acid of concentration 0.04 moldm-3
.What is the value of Ka?
2.5x10-9 moldm-3
Steps to calculating pH of weak acid
.Step 1: Calculate [H+] from ka and [HA]
.Step 2: Calculate pH
Are the approximations for weak acids justified?
.The first approximation assumes that the dissociation from water is negligible
.[H+(aq)]eqm = [A-(aq)]eqm - if pH>6 then water dissociates and [H+] from water will be more significant than from dissociation of acid
.This approximation breaks down for very weak acids or very dilute solutions
.Second approximation assumes that the concentration of the acid [HA] is much greater than the [H+] concentration at equilibrium
.[HA]start»_space; [H+]eqm [HA]eqm = [HA]start – [H+]eqm so [HA]eqm = [HA]start
.Not valid as acid gets stronger as [H+] becomes more significant and real difference between [HA]eqm = [HA]start – [H+]eqm
.Not justified for stronger weak acids / very dilute solutions.
.The value of Ka for weak acids is almost always very small and difficult to compare numbers with negative indices, how do we get around this?
create a scale of more useable numbers we often use the value of pKa, when talking about the aciditing of weak acids
What is pKa often used for?
to compare acids in biological systems
pKa equation
pKa = -log10Ka
What do the values of pKa mean?
The higher the value of pKa, the weaker the acid
The lower the value of pKa, the stronger the acid
How does wine show behaviour of typical dibasic and tribasic acids?
Wines often contain traces of sulphurous acid, H2SO3, added as a preservative
.Sulphurous acid is dibasic and its dissociation is shown as:
H2SO3 H+ + HSO3 - (pKa = 1.92)
HSO3 - H+ + SO3 2- (pKa = 7.18)
.For the first dissociation, H2SO3, acts as a weak acid
.From the pKa values, HSO3, is a far weaker acid than H2SO3
.The behaviour is typical of dibasic and tribasic acids
What can increase the rate of a reaction?
.Increase temperature .Increase concentration/pressure .Increase surface area .Catalyst .Increase temperature .Increase concentration/pressure .Increase surface area .Catalyst
What needs to happen for a successful reaction?
.The particles must collide
.Have sufficient energy
.Be in correct orientation
What must you remember when drawing a maxwell-boltzman distribution?
SHOULD NEVER TOUCH X AXIS
Why should the maxwell-boltzman distribution go through the origin?
no molecules with no energy
Is the rate constant actually a constant?
.The rate constant is only actually constant if we change the concentration of reacantn
.If we change other factors then it changes
How can we show that the rate constant can change?
This can be shown mathematically with an equation, called Arrhenius:
K = A(e^(-Ea/RT))
What are the different parts of the Arrhenius equation?
.K = rate constant .A = pre-exponential frequency factor .e = natural log constant .Ea = activation energy .R = gas constant (8.31) .T = temperature (K)
what is e^(-Ea/RT) called?
the exponential factor
what does e^(-Ea/RT) represent?
This represents the proportion of particles that exceed Ea and have sufficient energy to take place
In the Arrhenius equation, what does A do?
‘A’ takes into account the frequency of collisions with the correct orientation, it does increase slightly with temperature but is essentially constant over a small temperature change
How can we show the effect of temperature by using the Arrhenius equation?
.You can use the arrhenius equation to describe the effect of temperature on the rate equation
.Make up some numbers plug them into the equation to get a value for the exponential factor
.Increase the temperature value by 10
.State the effect that this has had on K, and consequently the rate
.This links to the Boltzmann distribution, as the increase in temperature shifts to distribution to the right, the number of particles above Ea increases, the particles move faster and they collide more frequently at the correct orientation.
Increasing temperature effects reactions by increasing the number of particles above Ea, but also increasing the number of collisions - which has the larger effect?
.There is more effect of temperature caused by more particles exceeding Ea than from increased collisions
How can we show the effect of a catalyst by using the Arrhenius equation?
.You can use the arrhenius equation to describe the effect of a catalyst on the rate equation
.Make up some numbers plug them into the equation to get a value for the exponential factor
.Decrease the activation energy value (as catalysts offer an alternate pathway, and so lower the Ea)
.State the effect that this has had on K, and consequently the rate
Summarise how using the Arrhenius equation can show the effect of changing temperature and catalyst presence
.Increasing the temperature increases the rate constant and therefore increases the rate
.Decreasing the activation energy (by using a catalyst) increases the rate constant and therefore increases the rate
What is the logarithmic form of Arrhenius?
ln(k) = -Ea/RT + ln(A)
What is a major use of the Arrhenius equation?
We can use this equation to determine Ea and A graphically
If we plot a graph of ln(k) against 1.T we will get a straight line of the type y=mx+c
How does the Arrhenius equation link to y=mx+c
ln(k) = -Ea/RT + ln(A) ln(k) = y -Ea/R = m 1/T = x Ln(A) = c m = gradient so working it out gives -Ea/R c = intercept on the y axis
Steps to plotting an Arrhenius graph
.Work out ln(k) and 1/T
.Plot a graph of ln(k) against 1/T
.Workout the gradient, and consequently the activation energy
.Calculate A from the intercept ( ln(A) )
How to work out stuff from Arrhenius graph if its a broken scale?
Use the equation
Where strong acids completely dissociate to release all H+ ions into solution, weak acids only partially dissociate, explain this in terms of equations
Strong: HA → H+ + A-
Weak: HA ⇌ H+ + A-
As weak acids form an equilibrium their dissociation can be represented by the acid dissociation constant, Ka, whats the equation for this?
Ka = “[H+(aq)][A-(aq)]” /”[HA(aq)]”
Explain why a larger value for Ka means a lower pH
.The larger the value for Ka the more the equilibria lies to the right and so the lower the pH i.e. higher [H+]
What alters Ka?
Temperature
.As the values for Ka are very small it is easier to give their negative logarithm, pKa, instead, what is the equation for this?
pKa = - logKa
pKa = - logKa, what is the inverse equation for this?
The inverse for this equation is: Ka = 10-pKa
This means that the weaker an acid the:
._____ Ka
._____ pKa
.Smaller Ka
.Larger pKa
.The [H+] of a weak acid depends on the value of what?
Ka and [HA]
.The equilibrium concentrations, [ ]eqm, can be used to determine a value for Ka, what is the equation for this?
Ka = “[H+]eqm [A-]eqm” /”[HA]eqm”
There are two approximations that need to be made when calculating Ka, what are they?
.HA dissociation forms equal [H+] and [A-]
.The change in [HA] is negligible so [HA]eqm = [HA]start
Using the approximations, Ka can be determined by what equation?
Ka = “[H+]eqm 2” /”[HA]start”
How can pH be calculated for a weak acid?
[H+] = √(“Ka x [HA]” ) → pH = -log[H+]
.A value for Ka can be determined experimentally, how?
by using a pH meter to get the pH of a standard solution
.The larger the value for Ka, the greater the _________
dissociation
When calculating values for Ka there are issues with the approximations made, what are these issues?
• At pH values >6 water dissociation is significant
Therefore doesn’t work for very weak acids or very dilute solutions
• If [H+] concentration is significant there will be a difference between [HA]eqm and [HA]start
Therefore doesn’t work stronger weak acids with Ka > 10-2 mol dm-3 or very dilute solutions
All aqueous solutions contain which ions?
H+ and OH- ions
H2O
H+ + OH-
In ____ [H+] > [OH-]
In ____ [OH-] > [H+]
In ____ [H+] = [OH-]
In acids [H+] > [OH-]
In alkalis [OH-] > [H+]
Neutral [H+] = [OH-]
For every 500,000,000 H2O molecules, only _ dissociates
1
For every 500,000,000 H2O molecules, only 1 dissociates, what does this mean for the equilbrium?
the equilibrium is on the left hand side
Do the Kc equation for water equilibrium
Kc = ([H+][OH-]) / [H2O]
[H2O] x Kc =
[H+] x [OH-]
[H2O] is such a large excess it can be classed as a ____
constant
What is Kw?
ionic product of water
Kw = [H2O] x Kc, so replace [H2O] x Kc with Kw in the correct equation
Kw = [H+] x [OH-]
At 298K, Kw =
1x10-14 mol2dm-6
Why is the pH of pure water at 298K, 7?
Kw = [H+] x [OH-] 1x10-14 = [H+] x [OH-] The concentrations are the same and so it can be written as: 1x10-14 = [H+]2 1x10-7 = [H+] pH = 7
Effect of temperature on Kw
The dissociation of water is endothermic
Temperature increase will move the equilibrium to the right, and so Kw will increase
Temperature decrease will move the equilibrium to the left, and so Kw will decrease
Water will always remain neutral at all temperatures, pH may change with temperature, but [H+] = [OH-] all the time and so it is neutral
.Water ionises very slightly, acting as both an acid and as a base – setting up an ________
equilibrium
.Water dissociates a very, very small amount according to the equation – it must do, otherwise it would not _____________
conduct electricity
.1 dm3 (1000g) of water is mainly ________ H2O
undissociated
. [H2O(l)] = 1000/18 = 55.6 mol dm-3 (a constant), why?
.1 dm3 (1000g) of water is mainly undissociated H2O
.If we know the concentration of hydroxide ions we can rearrange Kw to give us the value of what?
[H+]
What is the pH of 0.4 mol dm-3 NaOH?
Kw = [H+][OH-] = 1.00 × 10–14 mol2dm–6 (1.00 × 10_14 )/([0.4])=[H+] = 2.5 x 10-14 mol dm-3 pH = -log10[H+] = -log10[2.5 x 10-14 ] = 13.60
What is the pH of a solution with [OH-] = 2 x 10-2 mol dm-3 at 25oC ?
Step 1 : calculate [H+] from Kw and [OH-]
Kw = [H+][OH-] = 1.00 x 10-14
[H+] = Kw = 1.00 x 10-14 = 5.00 x 10-13 mol dm-3
[OH-] 2.00 x 10-2
Step 2 : Use calculator to find pH
pH = - log [H+] = -log (5.00 x 10-13) = 12.30
What are the concentrations of H+ (aq) and OH- (aq) in a solution of pH 3.25 at 25oC ?
Step 1 : Use calculator to find [H+(aq)]
[H+] = 10-pH = 10-3.25 = 5.62 x 10-4 mol dm-3
Step 2 : Calculate [OH-] from Kw and [H+]
Kw = [H+][OH-] = 1.00 x 10-14
[OH-] = Kw = 1.00 x 10-14 = 1.78 x 10-11 mol dm-3
[H+] 5.62 x 10-4
For pH values that are whole numbers, it is easy to work out the [H+] and [OH-] concentrations as the indices add up to what?
-14
.The pH of weak bases can be calculated via a similar method to that used for ______
weak bases
.In an aqueous solution, there will always be both H+ (aq) and OH- (aq) ions present such that ________
[H+ (aq)][OH- (aq)] = Kw
.A solution is ______ when [H+ (aq)] > [OH- (aq)]
.A solution is ______ when [H+ (aq)] = [OH- (aq)]
.A solution is ______ when [OH- (aq)] > [H+ (aq)]
.A solution is acidic when [H+ (aq)] > [OH- (aq)]
.A solution is neutral when [H+ (aq)] = [OH- (aq)]
.A solution is alkaline when [OH- (aq)] > [H+ (aq)]
.So a solution that is acidic will still contain __ ions, it is just that there are more __ions (and vice versa in an ______ solution)
OH-
H+
Alkaline
.The value of Kw controls the ______ of each ion
Concentrations
• Kw can also tell us the pH of ______
pure water
• As the water splits into equal concentrations of OH- and H+ ions we can make what assumption?
Kw = [H+][OH-] = 1.00 × 10–14 mol2dm–6 = [H+]2 = 1.00 × 10–14 = [H+] = 1.00 × 10–7 pH = -log10[H+] = -log10[1.00 x 10-7 ] = 7
When is neutral not neutral?
.A neutral solution is defined by a equal number of moles of H+ ions and OH- NOT by a pH of 7 as you may have been taught
.Whilst this value is 7 at approximately 298K, the value of Kw increases with temperature
.The pOH scale measures what?
the concentration of hydroxide ions
.Therefore you can solve fpr pH, pOH and [OH-] given just ___
[H+]
pH + pOH =
14
.Kw = [H+][OH-] =
1x10-14
Define Enthalpy of reaction ΔrH
enthalpy change that accompanies a reaction in the molar quantities shown in a chemical equation under standard conditions, with all reactants and products in their standard states
Define Enthalpy of formation ΔfH
enthalpy change when one mole of compound is formed from its constituent elements under standard conditions
Define Enthalpy of combustion ΔcH
enthalpy change when one mole of substance is burnt completely in excess oxygen under standard conditions
Water slightly ionises, what equation will show this?
H2O(l) H+(aq) + -OH(aq)
Ka of :
H2O(l) H+(aq) + -OH(aq)
=
[H+][-OH] / [H2O]`
Ka x [H2O] =
Kw
Kw =
[H+][-OH]
What is Kw?
Kw is the ionic product of water, at 25’C it equals 1x10-14 mol2dm-6
How does ionic bonding work?
- Loss of an electron(s) by an element
- Gain electrons by a second element
- Attraction between positive and negative ions
Na + Cl, ionisation electron addinity and latice equations
Ionisation Energy – Na e- + Na+ +496kJmol-1 Electron Affinity – e- + Cl Cl- -349kJmol-1 Lattice Enthalpy – Cl- + Na+ NaCl -766kJmol-1
What is electron affinity?
.The enthalpy change when one mole of electron is added to one mole of atoms in the gaseous phase to form one mole of -1 ions
Is repulsion between two electrons exothermic or endothermic, why?
.Repulsion between two negatively charged things requires energy so exothermic
What is lattice enthalpy?
.ΔHlatt is the enthalpy change when 1 mole of ionic substance is formed from its gaseous ions under standard conditions
.The strength of the ionic bond is related to the lattice enthalpy, how?
more exothermic the greater the ionic bonding
Lattice enthalpy can’t be measured, why?
Cannot be measured directly as cannot form one mole of ionic lattice from gaseous ions
What are the factors affecting lattice enthalpy? How?
Charge –
.The greater the charge on the ions, the stronger the attraction – therefore, more exothermic lattice enthalpy
Size –
.Smaller ions can pack together more tightly, therefore there is greater attraction and more exothermic lattice enthalpy
Why, when moving down group two, do the temperatures required to break the lattice increase?
.They have decreasing charge densities
.Mg2+ is a smaller ion than Ba2+ , so the +2 charge occupies a smaller volume – this means Mg2+ has a higher charge density than Ba2+
.Mg2+ can distort the electron clouds within the CO32- ion (called polarisation), this weakens the covalent bonding in the ion and reduces its decomposition temperature
What is a buffer?
a solution that minimises pH change when a small amount of acid or alkali is added
What two types of buffers are they?
Weak Acid and Salt of Weak Acid
Excess Weak Acid and Strong Base
Suggest and explain a Weak Acid and Salt of Weak Acid buffer
Weak Acid – Ethanoic Acid –
CH3COOH(aq) CH3COO-(aq) + H+(aq)
Salt of Weak Acid – Sodium Ethanoate –
CH3COONa(s) + (aq) CH3COO-(aq) + Na+(aq)
¬Buffer Contains –
CH3COOH(aq) CH3COO-(aq) + H+(aq)
When add H+, H+ reacts with conjugate base, equilibrium will move to the left to reduce the amount of H+, pH is constant
Adding –OH (alkali) –
-OH + H+ H2O
Conc of H+ decreases, equilibrium moves to the right to increase the conc of H+, pH is constant
Suggest and explain an excess Weak Acid and strong base buffer
CH3COOH(aq) + NaOH(aq) –> CH3COONa(aq) + H2O(l)
CH3COONa(aq) CH3COO-(aq) + Na+(aq)
CH3COOH(aq) CH3COO-(aq) + H+(aq)
When add H+, H+ reacts with conjugate base, equilibrium will move to the left to reduce the amount of H+, pH is constant
Adding –OH (alkali) –
-OH + H+ H2O
Conc of H+ decreases, equilibrium moves to the right to increase the conc of H+, pH is constant
Excess methanoic acid is reacted with potassium hydroxide, explain how a buffer solution is produced and how pH is controlled when 5cm3 of HCl is added.
The solution now contains HCOOK(aq) HCOO- (aq) + K+(aq) and HCOOH(aq) HCOO-(aq) + H+ equilibriums in solution – the buffer. When 5cm3 of HCl is added, it dissociates into H+ and Cl-, the H+ ions increase the concentration of the H+ already in the solution, so the HCOOH(aq) HCOO-(aq) + H+ point of equilibrium moves to the right – decreasing the conc of H+ in solution, and so keeping the pH constant.
Ka x ( [HA]/[A-] ) = ?
what does each part mean?
[H+] = Ka x ( [HA]/[A-] ) [HA] = concentration of weak acid [A-] = concentration of conjugate base
50cm3 of 1.2M NaOH reacts with 250cm3 of ethanoic acid (1M), Ka = 1.74x10-5, what is the pH?
CH3COOH CH3OO- + H+ CH3COOH + NaOH CH3COO- + Na+ + H2O 1. Moles weak acid = 250x1 / 1000 = 0.25mol 2. Moles NaOH = 50x1.2 / 1000 = 0.06mol 3. Moles A- = 0.06mol 4. Moles HA = 0.19mol 5. [H+] = Ka ([HA] / [A-]) = 1.74x10-5 x (0.19/0.06) = 5.51x10-5 6. pH = 4.26
Equation to work out lattice enthalpy from born haber cycle
L.E = FORMATION – sum(ATOM + I.E + E.A)
or
L.E = FORMATION – sum(REST)
What are Born Haber Cycles used for?
Born Haber cycles can be used to calculate a measure of ionic bond strength based on experimental data
Draw the born haber cycle for NaCl
check notes or google
Draw the born haber cycle for MgCl2
check notes or google
Draw the born haber cycle for CuO
check notes or google
Blood must contain a pH of what?
Blood must contain a pH of 7.40 +- 0.05
What is the most important buffer in blood?
the carbonic acid – hydrogencarbonate
Carbonic acid dissociation equation
H2CO3 H+ + HCO3-
If blood becomes too acidic (acidosis), what presents?
fatigue, shortness of breath, shock, death
If blood becomes too alkaline (alkalosis), what presents?
spasms, light-headed, nausea
What happens if the body produces more acidic products?
.The H+ concentration in the blood will increase, the equilibrium of the hydrogencarbonate dissociation will shift to the left, the H+ ions will be used up to form more hydrogencarbonate, the H+ concentration will return to normal, the pH will have had minimal change
.If the acid level continued to rise, fatigue, shortness of breath, shock, or death would eventually set in
.This would occur when we have ran out of HCO3- ions
Carbon dioxide dissolves in water to form what? What is the equation for this?
carbonic acid:
CO2 + H2O H2CO3
Inhalation of high levels of CO2 means what?
Inhalation of high levels of CO2 mean that the equilibrium in the blood must shift to the right to form more H2CO3, this means that the level of H2CO3 in the blood increase, so in the equilibrium H2CO3 H+ + HCO3- the equilibrium shifts to the right to counter this, this forms more H+ ions in the blood, making it more acidic, and resulting in acidosis which would lead to fatigue, shortness of breath, shock, and eventual death. Increased [H+] means enzymes would also be denatured.
Define enthalpy of solution, with an example
DeltasolutionH is the enthalpy change when one mole of ionic compound is completely dissolved in water under standard conditions.
e.g. NaCl(s) Na+(aq) + Cl-(aq)
What is enthalpy of hydration with example
- Delta Hhydration¬ is the enthalpy which takes place when one mole of gaseous ions is dissolved in water forming one mole of aqueous ions under standard conditions
- Na+(g) + aq Na+(aq)
Why is enthalpy of hydration always exothermic?
These are exothermic as bonds are formed between the ions and water molecules
Factors Affecting Enthalpy of Hydration
Charge – the higher charge on the ion, the greater the attraction for the H2O molecules, therefore a more exothermic hydration
Size – smaller ions have a greater charge density compared to the larger ions, this creates a greater attraction for H2O molecules, therefore a more exothermic hydration
Draw the general cycle of enthalpy of solution, hydration and lattice enthalpy
check notes
Equation that links lattice enthalpy, enthalpy of solution, and enthalpy of hydration
lattice enthalpy + enthalpy of solution = sum of the enthalpy of hydrations
Draw the titration curve for when HCl is added to NaOH
check notes
Draw the titration curve for when NaOH is added to HCl
check notes
Draw strong acid strong base titration curve
check notes
Draw strong acid weak base titration curve
check notes
Draw weak acid strong base titration curve
check notes
Draw weak acid weak base titration curve
check notes
The shape of the titration curve depends on what?
- Substance being titrated i.e. acid or base
- Type of acid or base i.e. strong or weak
Describe and explain parts of titration curve
- Excess of base: pH decreases as acid added
- Vertical section: acid base concentration similar, pH alters rapidly
- Excess of acid: pH decreases slightly as acid is added
- The equivalence point: halfway up the vertical section
What is the equivalence point?
The point halfway between the two horizontal lines on the titration curve
The equivalence point is the volume required to have completely reacted the acid and base toetehr, stoichiometric volumes
The pH at the equivalence point depend son the type of acid and base
Where is the equivalence point on each titration curve?
Equivalence point = 7 on SA-SB
Equivalence point < 7 on SA-WB
Equivalence point > 7 on WA-SB
No equivalence point on WA-WB
Why is the equivalence point 0 on SASB titration curves?
- H+ ions completely neutralised by OH- ions, so only water and salt present, neutral
Why is the equivalence point < 7 on SAWB titration curves?
- A weak base, like NH3, will have a strong conjugate acid, NH4+ , which will react with water to produce H3O+ so the pH is less than 7
Why is the equivalence point > 7 on WASB titration curves?
- A weak acid, HA, will have a strong conjugate base, A-, which can react with water to produce OH- ions, so the pH is more than 7
What are acid-base indicators?
Acid-Base indicators are weak acids that have different coloured conjugate bases
In acidic conditions the indicator equilibrium is shifted towards the weak acid (HIn)
As the system becomes more basic the equilibrium shifts towards the conjugate base (In-), altering the colour
What is the end point?
The end point is when equal [HIn] and [In-] are present, the colour will therefore lie between both extremes
Each indicator will have a different pH value for the end point as they each have different ka values
HIn
H+ + In-
How is an acid-base indicator chosen?
The indicator required for a titration must have a colour change that lies within the vertical section of a titration curve
A chemical reaction will proceed when?
A chemical reaction will proceed if the products are energetically more stable than the reactants
What is entropy?
Entropy is a measure of the dispersal of energy in a system, the more disordered a system the greater the dispersal of energy = higher entropy
we define entropy as a measure of disorder
What happens to entropy over time?
Entropy must increase over time
When is a system in a state of high entorpy?
When its degree of disorder is high
As order within a system increases, its entropy decreases, why?
This can be explained in terms of probability: disordered states are simply more likely to exist (or emerge) than ordered states.
The spontaneous direction of change is from a less probable to a more probable state
What does entropy always do?
The total entropy always increases, and the process is irreversible
What is the unit for entropy
S
in JK^-1mol^-1
Why is S (entropy) alwasy potisive?
All substances process some degree of disorder because particles are always in constant motion
How does the entropy of each state differ?
Solid has lowest entropy, and gas has the highest
Draw a graph of waters change in enthalpy as temperaurer increases
check notes
Systems that are more chaotic have a _____ entropy value
higher
(s) (s) + (g) , what is delta S
+
(g) 2(g) , what is delta S
+
What is delta S?
C2H5OH(l) C2H5OH(g)
+
What is delta S?
C2H2(g) + 2H¬2(g) C2H6(g)
-
What is delta S?
NH4Cl(s) + aq NH4Cl(aq)
+
What is delta S?
4Na(s) + O2(g) 2Na2O(s) deltaS
-
Define the standard entropy change
The standard entropy change is the entropy change that accompanies a reaction in the molar quantities expressed in the equation, under standard conditions
Sum for delta S^theta
delta S^theta = sum(S^theta products) – sum(S^theta reactants)
Why are exothermic reactions more preferable in nature?
as the products are more stable than reactants
the key is not the decrease in energy but the associated increase in entropy of the surroundings.
deltaSsurroundings is proportional to what?
-deltaHsystem
deltaSsurroundings =
(-deltaHsystem)/T
deltaStotal =
deltaSsystem + deltaSsurroundings
deltaStotal >
0
What can we learn about the entropy of the sun by the photosynthesis equation?
6CO2(g) + 6H2O(l) UV light C6H12O6(s) + 6O2(g)
Negative entropy change
Entropy change in sun must be so positive it outweighs every plant on earth
What is gibbs free energy equation?
deltaG = deltaH – T deltaS < 0
How do you get to gibbs free energy equation?
deltaStotal¬ = deltaSsystem + deltaSsurroundings > 0
deltaStotal¬ = deltaSsystem – (deltaHsystem)/T > 0
T deltaStotal = T deltaSsystem – deltaHsystem > 0
-T deltaStotal = -T deltaSsytem + deltaHsystem < 0
deltaG = deltaH – T deltaS < 0
Using deltaG explain when a reaction is and is not feasible
deltaG must be negative (<0) for a reaction to be feasible i.e. proceed
If deltaG is positive (>0) then a reaction is not feasible
What is deltaG at the points of feasibility?
At the point of feasibility, we can say deltaG = 0 (assume that deltaH and deltaS don’t vary with temperature)
At low temperatures what does deltaGsystem equal? why?
- At low temperatures, deltaGsystem = deltaH (-T deltaS becomes negligible) so for a reaction to occur it needs to be exothermic
At high tempertaures deltaGsystem ewuals what? why?
- At high temperatures, deltaGsystem = -T deltaS (deltaH becomes negligible) so for a reaction to occur it needs to have a positive deltaS as – T deltaS needs to be less than 0
Limitations to deltaG equation
just because the value is negative and so feasible it doesn’t mean it occurs, the reaction rate might be incredibly slow or the activation energy too high
What is an oxidation number?
An oxidation number shows the charge of an atom if all of its bonds were considered totally ionic
What are the oxidation number rules?
- Elements in their natural state = 0
- The total oxidation states in a molecule = 0
- The total oxidation states in an ion = the charge
Groups 1, 2, 3 -
State +1, +2, +3
Fluorine -
State -1
Hydrogen -
State +1
-1 in metal hydrides
Oxygen -
State -2
-1 in peroxides
Chlorine -
State -1
+ (varies) in chlorates
What is an oxidising agent?
takes electrons from what is oxidised
What is a reducing agent?
gives electrons to what is reduced
Write the half equations and full equation for
4Na + O2 2Na2O
4Na 4Na+ + 4e-
O2 + 4e- 2O2-
4Na + O2 4Na+ + 2O2-
Write the half equations for
Cu2O + H2SO4 Cu + CuSO4 + H2O
Cu+ Cu2+ + e-
2Cu+ Cu + Cu2+
Steps of a redox titration using iron sulphate and sulphuric acid and potassium manganate (VII)
- Make up a 150cm3 standard solution using 7g of iron sulphate by weighing by difference in a volumetric flask, record your mass measurements in a table
- a. Pipette 25cm3 of the standard solution into a conical flask
b. Add 10cm3 of 1M H2SO4 to the conical flask
c. Fill the burette with a standard solution of 0.02M potassium manganate (VII)
d. Carry out the titrations until the ed point is reached, the first permanent pink colour, record your results in a table
e. Repeat until you have two concordant results
f. Calculate the mean titre
Reduction: MnO4- + 8H+ + 5e- Mn2+ + 4H2O
Oxidation: Fe2+ Fe3+ + e- or 5Fe2+ 5Fe3+ + 5e-
MNO4- + 8H+ + 5Fe2+ Mn2+ + 4H2O + 5Fe3+
What is the oxidising and reducing agent?
Fe2+ is the reducing agent
MnO4- is the oxidizing agent
Mass of impure hydrated iron II sulphate = 6.97g
25cm3 of hydrated iron (II) sulphate used taken from a 250cm3 volumetric flask full of the dissolved iron tablets
Mean titre of 0.02M potassium manganate (VII) = 23.4cm3
Calculate the percentage purity of the impure sample of FeSO4.7H2O
93.3%
What are the redox equations for the iodine/thiosulphate titrations?
I2 + 2e- 2I-
2S2O32- S4O62- + 2e-
I2 + 2S2O32- 2I- + S4O62-
What colour is iodine?
Iodine is a yellow brown solution
What colour is iodide?
Iodide is a straw colour
How do you know when an iodine/thiosulphate titration is complete?
Iodine is a yellow brown solution
Iodide is a straw colour
The above colour change is the indication for the redox reaction to be complete
Is an anode positive or negative?
Positive
Is a cathode positive or negative?
Negative
Draw a general cell
check notes
What is a cell? What is it made of? What does it do?
- A cell has two half cells
- The two half cells must be connected with a salt bridge
- Simple half cells will consist of a metal (acts as an electrode) and a solution of a compound containing that metal
o For example, Cu and CuSO4 - These two half cells will produce a small voltage if connected into a circuit (become a battery or cell)
Draw the standard hydrogen half-cell
Check notes
What is the standard hydrogen half-cell?
- H+/H2 half-cell is chosen to produce standard potentials
- H+ + e- ½H2
- 1/2H2 H+ + e-
- Conditions
o 298K
o 1atm
o 1M H+ - Both equations have a voltage of 0.0 volts
Why is platinum used in the standard hydrogen half-cell?
Platinum is inert and so does not take part in the reaction
How can you find the value of any electron potential?
If the standard hydrogen half-cell is connected to another cell,
you can find the value of any electron potential (as the standard is
0.0 volts).
Why a salt bridge? Using potassium chloride and copper as an example
- The salt bridge is used to connect up the circuit
- The free moving ions conduct the charge
- A salt bridge is usually made from a piece of filter paper (or material) soaked in a salt solution, usually potassium nitrate
- The salt should be unreactive with the electrodes and electrode solutions
o For example, potassium chloride would not be suitable for copper systems as chloride ions can form complexes with copper ions, a wire is not used because the metal wire would set up its own electrode system with the solutions
What is standard electrode potential?
The emf of a half cell compared with a standard hydrogen electrode at standard conditions of 298K, concentration 1.0M and 1 atm of pressure.
What is emf?
The emf is the difference in the positive and negative sides of the cell.
Describe a two ion cell system?
Both of the ions in the equation will be at a concentration of 1M, platinum electrode is used as it is INERT.
2 aqueous ions in a half equation, means they both have to be 1.0M solutions in the same half cell
Draw a manganese/lead system
check notes
General properties of d-block elements
The d-block elements have high melting and boiling points.
The d-block elements are good conductors of both electricity and heat.
What elements have been used in coinage for many years?
copper, silver, nickel, and zinc
What element is used extensively in construction and production of tools?
Iron
What element is used for electrical cables and water pipes?
Copper
Titanium has great strength, what are the elements applications?
It has many aerospace and medical applications (for example joint replacement).
Sc orbital configuration
[Ar] 4s2 3d1
Fe orbital configuration
Fe – [Ar] 4s2 3d6
Ni orbital configuration
Ni – [Ar] 4s2 3d8
Zn orbital configuration
Zn – [Ar] 4s2 3d10
Cr orbital configuration
Cr – [Ar] 4s1 3d5
Cu orbital configuration
Cu – [Ar] 4s1 3d10
How do copper and chromium minimize repulsions?
Copper and chromium minimize repulsions by being half full or full, chromium has 4s and 3d orbitals half full, copper has 3d full
Fe2+ orbital configuration
Fe2+ - [Ar] 4s0 3d6
Fe3+ orbital configuration
Fe3+ - [Ar] 4s0 3d5
Cu2+ orbital configuration
Cu2+ - [Ar] 4s0 3d9
Cr3+ orbital configuration
Cr3+ - [Ar] 4s0 3d3
Mn2+ orbital configuration
Mn2+ - [Ar] 4s0 3d5
Mn4+ orbital configuration
Mn4+ - [Ar] 4s0 3d3
Sc3+ orbital configuration
Sc3+ - [Ar] 4s0 3d0
Zn2+ orbital configuration
Zn2+ - [Ar] 4s0 3d10
Define a transition element
A transition element is a d-block element that forms at least one ion with an incomplete d sub-shell.
Which ‘d’ block elements do not fit the transition element definition?
- Scandium and zinc
What are some characteristic properties of transition metals and there compounds, with examples. (not conduction, melting, boiling etc.)
- They form compounds in which the transition element has different oxidative states
o Fe2+ = +2
o Fe3+ = +3 - They form colored compounds
- The elements and their compounds can act as catalysts
o Fe in Haber process
o Ni in hydrogenation of alkenes
A species containing a transition element in its highest oxidation state is often a what?
strong oxidizing agent
What does the observed colour of a solution depend on?
The observed colour of a solution depends on the wavelengths absorbed
Why does copper sulphate solution appear blue?
Copper sulphate solution appears blue because the energy absorbed corresponds to red and yellow wavelengths, wavelengths corresponding to blue light aren’t absorbed.
Draw the exam colour chart
check notes
If the colour we observe is red, what colour has been absorbed?
Cyan
What colour is cu2+
white
What colour is [Cu(H2O)6]2+
blue
Transition metals form complex ions or ?
coordination compounds
WHat do transition metals form when they make complex ions?
ligand forms bonds with the central transition metal ion
Examples of complex ions
[Cr(H2O)6]3+ [CuCl4]2-
What is a ligand?
a molecule or ion that can donate a pair of electrons with the transition metal ion to form a coordinate bond
What does monodentate mean?
Monodentate ‘one tooth’ means each ligand donates just one pair of electrons.
Examples of ligands and how many loan pairs they have
H2O (oxygen has two loan pairs) NH3 (nitrogen has a loan pair) Cl- (chloride has a loan pair)
CN- (carbon has a loan pair) OH- (oxygen ha a loan pair)
Draw [Cu(H2O)6]2+
check notes
Describe the structure and bonding in [Cu(H2O)6]2+
- The central ion is Cu2+
- The ligands are water molecules
o Each molecule donates a pair of electrons from the O atom to the Cu2+ to form a co-ordinate bond - The co-ordination number is 6
o This indicates the number of coordinate bonds to the central metal ion
What is the oxidation of Co in [Co(H2O)5Cl]+
+2
How to name complex ions?
- The name gives the metal ions and its oxidation state last, and the name/number of ligands before
- Pre-fixes di, tri, tetra, penta, hexa used
- Ligands are listed alphabetically, with prefixes not allowed to alter this order
[Cr(H2O)4Cl2]+ name
¬¬Tetraaquadichlorochromium (III) ion
[Co(H2O)5Cl]+ name
Pentaaquamonochlorocobalt (II) ion
If the complex ion is an anion, what do you do?
the suffix ‘-ate’ follows the metal
Name of [Fe(CN)6]4-
Hexacyanoferrate (II) ion
What does cobalt become in an anion complex ion?
cobaltate
What does aluminium become in an anion complex ion?
aluminate
What does chromium become in an anion complex ion?
chromate
What does vanadium become in an anion complex ion?
vanadate
What does copper become in an anion complex ion?
cuprate
What does iron become in an anion complex ion?
ferrate
What does nickel become in an anion complex ion?
nickelate
What does the value of pKa show?
The higher the value of pKa, the weaker the acid
The lower the value of pKa, the stronger the acid
Equation for finding hydrogen ion concentration in buffer
[H+] = ka x ([HA]/[A-])
In an electrochemical cell, where does oxidation happen?
the half-cell with the most negative standard electrode potential
What is the relationship between electrode potential and metal reactivity?
More negative electrode potential = more reactive the metal
Which equation links E (cell), E(positive electrode), and E(negative electrode)
E (cell) = Eo (positive electrode) – Eo (negative electrode)
The more reactive a metal is, the more likely it is to what?
to lose electrons and form a positive ion
More reactive metals have more negative electrode potentials and vice versa for what?
Non-metals
in general if the electrode potential for the reaction is positive it is regarded as being what?
feasible
What is the problem with predicting the feasibility of electrode reactions?
- The value of E says something about the feasibility of the reaction under standard conditions only
- The value of E says something about the feasibility of the reaction, but does not say anything about the rate of the reaction
What is the anticlockwise rule?
Arrange the redox half equations so that:
- The electrons are on the left
- The largest negative electrode potentials are at the top
- The reaction will then take place anticlockwise around the half equations
- E (cell) = E (bottom) – E(top)
When does predicting feasibility of electrode reactions go wrong?
When the conditions are not standard, this includes:
- A change in concentration
- If the half equations are in equilibrium
If the kinetics are not favorable:
- The rate of reaction may be slow so reaction does not appear to happen
- If the reaction has a high activation energy
Define catalyst
a substance that increases the rate of a chemical reaction by providing an alternative reaction pathway of lower activation energy (Ea)
What happens when Al3+, Ca2+, Mg2+
Add NaOH or KOH or NH4OH
white precipitate
Description of solution, observation with NaOH, and equation for Copper Cu2+
Transparent blue Pale blue precipitate
Insoluble in excess Cu2+(aq) + 2OH-(aq) Cu(OH)2(s)
Description of solution, observation with NaOH, and equation for Iron(II) Fe2+
Pale green Dark green precipitate
Turns brown on contact with air
Insoluble in excess Fe2+¬(aq) + 2OH-(aq) Fe(OH)2(s)
Description of solution, observation with NaOH, and equation for Iron(III) Fe3+
Orange/brown Orange/brown precipitate
Insoluble in excess Fe3+(aq) + 3OH-(aq) Fe(OH)3(s)
Description of solution, observation with NaOH, and equation for Chromium(III) Cr3+
Violet Grey-green precipitate
Soluble in excess giving dark green solution Cr3+ + 3OH-(aq) Cr(OH)3(s)
Cr(OH)3(s) + 3OH-(aq) [Cr(OH6]3-(aq)
Description of solution, observation with NaOH, and equation for Manganese(II) Mn2+
Pale pink Off white precipitate
Rapidly turning brown on contact with air
Insoluble in excess Mn2+(aq) + 2OH-(aq) Mn(OH)2(s)
- Cu2+(aq) + 2e- Cu(s)
If we increase the concentration of Cu2+ ions then:
- Equilibrium moves to oppose the charge
- Electrons are removed from the system
- The electrode potential becomes more positive
What shape are four coordinate complex ions usualy? with examples
- Tetrahedral is the most common shape
- E.g. [CuCl4]2- and [CoCl4]2-
When not tertrahedral, what shape are 4 coordinate complexes, with examples
- Some 4 co-ordinate complex ions are square planar in shape, with the ligands arranged at the corners of a square
- E.g. [Ni(NH3)2Cl2] (cis and trans)
When does a square planar shape take place in complex ions? example
- These occur in complexes with 8-d electrons in the d subshell.
- E.g. Pt(II), Pd(II), Au(III)
What is cis platin used in?
- Cancer treatment in testicular cancer and useful for ovarian, head and neck, and lung cancer
- Extremely toxic
Why did they change from cisplatin to carboplatin?
- Improved chemical stability relative to cisplatin due to chelation by cyclobutane dicarboxylic acid
- Essentially equivalent antitumour activity to cisplatin
WHat is oaplatin used in?
treatment of colorectal cancer
Types of cancer therapy
- Surgery
- Radiotherapy
- Chemotherapy
o Cytotoxic
o Targeted
Anti-endocrine
Novel targeted agents - Immuno-therapy
- Gene therapy
What is mustard Gas? What came about because of mustard gas?
- Potent vesicant agent that burns eyes, skin and respiratory tract
Mustard Gas = war gas
Nitrogen Mustard = anticancer drug
How does cisplatin treat cancer?
- The cisplatin binds to DNA and causes a critical structural change n the DNA – a bend of 45 degrees
- This stops cell replication and leads to apoptosis (cell death)
Key points of lactic acid
- 2-hydroxy propanoic acid
- Also known as lactic acid
- The second carbon is a chiral center
- The mirror image is non-superimposable
o One is found in sour milk
o The other is found in anaerobic respiration
What is a fuel cell?
a fuel cell is a device that converts chemical energy into electrical energy, water, and heat through electrochemical reactions.
How ddoes a fuel cell work? Are there many or one usually and why?
• Fuel and air react when they come into contact through a porous membrane (electrolyte) which separates them
• This reaction results in a transfer of electrons and ions across the electrolyte from the anode to the cathode
• If an external load is attached to this arrangement, a complete circuit is formed and a voltage is generated from the flow of electrical current
The voltage generated by a single cell is typically rather small (< 1 volt), so many cells are connected in series to create a useful voltage.
Differences between a fuel cell and a battery
Hydrogen Fuel Cell –
• Open system
• Anode and cathode are gases in contact with a platinum catalyst
• Reactants are externally supplied, no recharging required
Galvanic Cell (Battery) –
• Closed system
• Anode and cathode are metals
• Reactants are internally consumed, need periodic recharging
Differences between a fuel cell and an internal combustion engine
Fuel Cell – • Output is electrical work • Fuel and oxidant react electrochemically • Little to no pollution produced Internal Combustion Engine – • Output is mechanical work • Fuel and oxidant react combustively • Use of fossil fuels can produce significant pollution
Similarities between a fuel cell and in internal combustion engine
- Both use hydrogen-rich fuel
- Both use compressed air as the oxidant
- Both require cooling
Draw an alkaline fuel cell
check notes
What are the half equations, volatages, cell potential, and overall equation for an alkaline fuel cell?
Half Equations –
2H20 (l) + 2e- H2 (g) + 2 OH- (aq) E = -0.83V
½ O2 (g) + 2e- 2 OH- (aq) E = +0.40V
Cell Potential –
= 0.4- -0.83 = 1.23V
Overall Equation –
H2 + ½ O2 H2O
Why Methanol not Hydrogen?
Some new fuel cells use methanol rather than hydrogen as the fuel because
- Liquid methanol is easier to store then hydrogen gas
- Methanol can be generated from biomass
Define electrochemical reaction
A reaction involving the transfer of electrons from one chemical substance to another
Define electrode
An electrical terminal that conducts an electric current into or out of a fuel cell (where the electrochemical reaction occurs).
Define electrolyte
A chemical compound that conducts ions from one electrode to the other
What is an electrochemical cell consisted of?
An electrochemical cell consists of 2 electrodes + 1 electrolyte
What is rhe equation for the number of optical isomers
- The number of isomers follows the equation: 2n, where n is the number of chiral centres
Why are optical isomers called such?
The isomers are called optical isomers as they can rotate plane-polarized light (light which only travels in one plane)
WHat makes a 6 co-ordinate compound cis or trans?
The bond angle between the two ligands which are different, e.g. 90’ cis, 180’ trans
What is a bidentate ligand? Example
Bidentate – ‘two tooth’ ligands
Most common is ethane-1, 2-diamine
Draw [Ni(NH2CH2CH2NH2)3]2+
Check notes
Describe and explain EDTA4-
A Hexadentate Ligand
- EDTA4- has 6 lone pairs, each of which can form a co-ordinate bond
- 1 EDTA ion reacts with 1 metal ion
- Ethylenediaminetetraacetic acid (EDTA)
What is ligand substitution?
The addition of another ligand to a solution containing the aqua transition metal ion results in a substitution reaction
What occurs for ligand substitution?
- One or more ligands is exchanged for another
- A change in colour of the solution is observed
- Sometimes the complex ion changes shape/coordinate number
Colour of [Cu(H2O)6]2+, and its colour with dropwise and excess, ammonia and hydrochloric acid
Complex Ion
[Cu(H2O)6]2+
Pale blue solution
Addition of Ammonia
Dropwise: Pale blue precipitation of copper(II) hydroxide
Excess: Blue precipitate redissolves, forming a deep blue solution
Addition of Concentrated HCl
Dropwise: Begins to turn green
Excess: Begins to turn yellow
Colour of [Cr(H2O)6]3+, and its colour with dropwise and excess, ammonia
Complex ion
[Cr(H2O)6]3+
Violet solution
Ammonia
Dropwise: Grey/green precipitate
Excess: Precipitate redissolves to produce a purple solution
Equation for addition of NaOH to [Cu(H2O)6]2+
[Cu(H2O)6]2+ + 2OH- [Cu(H2O)4(OH)2]2+ + 2H2O
Equation for addition of NH3 to [Cu(H2O)6]2+ in dropwise and excess
[Cu(H2O)6]2+ + 2NH3 [Cu(H2O)4(OH)2]2+ + 2NH4+
[Cu(H2O)6]2+ + 4NH3 [Cu(NH3)4(H2O)2]2+ + 4H2O
Equation for addition of HCl to [Cu(H2O)6]2+
[Cu(H2O)6]2+ + 4Cl- [CuCl4]2- + 6H2O
Equation for addition of ammonia to [Cr(H2O)6]3+
[Cr(H2O)6]3+ + 6NH3 [Cr(NH3)6]3+ + 6H2O
What is the stability constant?
Kstab – the equilibrium constant existing between a transition metal ion surrounded by water ligands and the complex formed when the same ion has undergone a ligand substitution reaction
Like KC but for equilibrias including complex ions
Colour of Sc3+
Colourless
Colour of Ti2+
colourless
Colour of Ti3+
lilac
Colour of Ti+4
colourless
Colour of Ti5+
colourless
Colour of V2+
lilac
Colour of V3+
green
Colour of V4+
blue
Colour of V5+
yellow
Colour of Cr2+
blue
Colour of Cr3+
green
Colour of Cr4+
colourless
Colour of Cr5+
colourless
Colour of Cr6+
orange
Colour of Mn2+
pale pink
Colour of Mn+3
colourless
Colour of Mn4+
dark purple
Colour of Mn5+
colourless
Colour of Mn6+
green
Colour of Mn7+
lilac
Colour of Fe2+
pale green
Colour of Fe3+
pale yellow
Colour of Fe4+
colourless
Colour of Fe5+
colourless
Colour of Fe6+
colourless
Colour of Co2+
Pink
Colour of Co3+
green
Colour of Co4+
colourless
Colour of Co5+
colourless
Colour of Ni2+
green
Colour of Ni3+
colorless
Colour of Ni4+
colourless
Colour of Cu1+
colourless
Colour of Cu2+
blue
Colour of Cu3+
colourless
Colour of Zn2+
colourless
[Cu(H2O)6]2+ colour
blue solution
Cu(OH)2 colour
Blue precipitate
[Cu(NH3)4(H2O)2]2+ colour
Deep blue solution
[CuCl4]2- colour
Yellow solution
HCl + Cu2+(aq) reaction colour and why
the complex can look green as the reaction is reversible so both blue and yellow species present
[Fe(H2O)6]2+ colour
pale green solution
Fe(OH)2 colour
Green precipitate, if left in air a reddy brown colour appears (Fe2+ oxidizes to Fe3+)
[Fe(H2O)6]3+ colour
Yellow solution
Fe(OH)3 colour
Reddy brown precipitate
[Mn(H2O)6]2+ colour
Very pale solution
Mn(OH)2 colour
Light brown precipitate which darkens in air
[Cr(H2O)6]3+ colour
Violet solution
Cr(OH)3 colour
Grey/green precipitate
[Cr(OH)6]3- colour
Green solution
[Cr(NH3)6]3+
Purple solution
[Cu(H2O)6]2+ + 4NH3
[Cu(H2O)6]2+ + 4NH3 [Cu(NH3)4(H2O)2]2+ + 4H2O
Blue solution Deep blue solution
[Co(H¬2O)6]2+ + 6NH3
[Co(H¬2O)6]2+ + 6NH3 [Co(NH3)6]2+ + 6H2O
[Cu(H2O)6]2+ + 4Cl-
[Cu(H2O)6]2+ + 4Cl- [CuCl4]2- + 6H2O
Blue solution Yellow/green solution
[Co(H2O)6]2+ + 4Cl-
[Co(H2O)6]2+ + 4Cl- [CoCl4]2- + 6H2O
Pink solution Blue solution
Cu2+ + 2OH- Cu(OH)2 colours
Cu2+ + 2OH- Cu(OH)2
Blue solution blue precipitate
Mn2+ + 2OH- Mn(OH)2 colours
Mn2+ + 2OH- Mn(OH)2
Very pale pink solution pale brown precipitate
Fe2+ + 2OH- Fe(OH)2 COLOURs
Fe2+ + 2OH- Fe(OH)2
Green solution green precipitate
Fe3+ + 3OH- Fe(OH)3 colours
Fe3+ + 3OH- Fe(OH)3
Yellow/brown solution brown precipitate
Cr3+ + 3OH- Cr(OH)3 colours
Cr3+ + 3OH- Cr(OH)3
Green solution green precipitate
[Mn(H2O)6]2+ + 2NH3
[Mn(H2O)6]2+ + 2NH3 Mn(H2O)4(OH)2 + 2NH4+
[Fe(H2O)6]3+ + 3NH3
[Fe(H2O)6]3+ + 3NH3 Mn(H2O)3(OH)3 + 3NH4+
Cr(H2O)3(OH)3 + 3OH-
Cr(H2O)3(OH)3 + 3OH- [Cr(OH)6]3- + 3H2O
Green precipitate green solution
Cr(H2O)3(OH)3 + 3H+
Cr(H2O)3(OH)3 + 3H+ [Cr(H2O)6]3+
Green precipitate green solution
Cr(OH)3(H2O)3 + 6NH3
Cr(OH)3(H2O)3 + 6NH3 [Cr(NH3)6]3+ + 3H2O + 3OH-
Green precipitate purple solution
Cu(OH)2(H2O)4 + 4NH3
Cu(OH)2(H2O)4 + 4NH3 [Cu(NH3)4(H2O)2]2+ + 2H2O + 2OH-
Blue precipitate deep blue solution
