5- Rates, Equalibrium, PH, Energy, Transition Elements Flashcards
Oxidation is ….. of electrons
Loss
Reduction is …. Of electrons
Gain
What is a redox reaction
Reduction and oxidation happening simultaneously
What is an oxidising agent
Accepts electrons amd gets reduced
What is a reducing agent
Donates electrons and gets oxidised
What can be combined to make a full redox equation
An oxidation half equation can be combinded with a reduction half equation
What needs to be the same for half equations can be combined
The electrons
What are the only things your allowed to add to half equations
Electrons
H+
Water
What is the oxidation of iron, half equation
Fe2+ to Fe3+
Fe2+ —-> Fe3+ + e-
What is the reduction of manganateequation
MnO4- +8H+ +e- —> Mn2+ 4H2O
What elements are good at changing oxidation statex
And so therefore are good at what
Transition elements
This makes them usefull oxidising and reducing agents - as they readily give out and receive electrons
What colour is MnO4-
Purple
What is the colour change + why
Acidified potassium manganite (vll) redox
Purple to colourless
As the (Mn(H2O)4) 2+ Is colourless
What is the colour change + why
Acidified potassium dichromate redox
Orange
(Cr(h2o)6)3+ is violet (but usually looks green)
So a colour change looks orange to green
Tritations using transition element ions are what
Redox tritations
How to carry out a redox reaction
(Of manganite (vlll) ions)
first you measure out a quantity of the reducing agent eg.
aqueous Fe2+ ions, using a pipette, and put it in a conical flask
2 You then add some dilute sulfuric acid to the flask
- this is an excess, so you don’t have to be too exact.
(This acid is added to make sure there are plenty of H+ ions to allow the oxidising agent to be reduced)
- Now you gradually add the aqueous MnO4- (the oxidising agent) to the
Reducing agent using a burette, swirling the conical flask as you do so.
You stop when the mixture in the flask just becomes tainted with the coloe
of the MnO4- and record the volume of the oxidising agent added
Run a few tritiations and then calculate the mean volume or MnO4-
T or f
In a redox tritiations
You add the known concentration to the substance of the unknown concentration
T
What can you do during a redox tritiations wot make the colour change Easier to spot
You could use a coloured reducing agent and a coloured oxidised agent - so you’d be looking for the moment the colour of the flask dissapears
Doing the reaction inffont of a white surface
Ensure you can do redox tritations calculations
👍
What is the definition of rate of reaction
The change in conc of reactants ( or products ) per unit time
What are the units of rates of reaction
Mol dm -3 s -1
What is activation energy
The minimum amount of energy a particle needs in order to react
The energy ( enthalpy) difference between the reactants and the transition state
What does rate of reaction describe
How quickly reancys are used up or how quick products are formed
What 2 diff rates can we look at when looking at rate of reaction;
The average rate for the entire reaction
Or
The rate at a specific point ( instantaneous rate )
What 4 ways can you measure rate
Vol of gas given of
Changes in PH (Ph probe )
Colour change ( use of colorimeter)
Loss of mass ( gas given off in an open system )
Make sure you know what the first, zero and second order graphs look like (6)
Check
What are the observations for the iodine/thiosulfate tritiations
CuI precipitation ( white)
Iodine - brown solution
What are the 3 main used of iodine / thiosulfate tritiations
Used to determine the clo- conctent in household bleach
Used to determine the cu2+ content in cu((ll) compound
Used to determine the cu content in copper alloy
In iodine / thiosulfate tritations
What are the oxidising agents oxidiseing
I- to I2
What is the iodine tritated against
Standard solution of sodium thiosulfate (S2O3 2- ion )
SO2O3 2-
In iodo thiosulfate tritations half equation goes to
S4O6 2-
What is the best way to balence the thiosulfate half equation
Look at charges not oxidation number
What is the molar ratio ot thiosulfate ion to iodide
2 : 1
What do you see in the iodine and thiosulfate tritations
Iodide -brown , fades to straw colour
When no iodine left colourless
( you can make this colour change easier to see by adding starch when it turns straw yellow)
What is rate of reaction usually measured in terms of
How fast the conc of One of the reactants is falling
T or f
Moles in the equation don’t effect the rate equation
T
What is rate of reaction proportional to
The rhe concentration of a particular reactant raised to a power
For each reactant in the rate equation
The power =
The order of reaction for that reactant
What orders are there in the rate equation
Zero
First
Second
How are orders determine in the rate equation
Experimentally
What is the overall order
The sum of the individual orders of reacts in the rate equation
Describe zero order
If the conc. changes, rate doesn’t change rate is proportional to [A]^0 = 1
Describe first order
Conc double, rate will double
Rate is proportion to [A]^1
Describe second order
Conc double, rate inc. by factor 2^2 = 4
Rate is proportional to [A]^2
What is K in the rate equation
Rate constant for a reaction
Is the rate constant differnt for differnt reactions
Yes
What are the units for the rate constant
The units depend on the order of the reaction
What is the value of the rate constant effected by
Temp
Presence / change of a catalyst
What does the rate equation provide lots of info about
The mechanism for the reaction
Iodine-sodium thiosulfate tritations are a way of finding the concentration of a …
Oxidising agent
How does iodine sodium thiosulfate work
STAGE 1: Use a sample of oxidising agent to oxidise as much iodide as possible.
1) Measure out a certain volume of potassium iodate(V) solution (KIO,) (the oxidising agent) - say 25.0 cm
2) Add this to an excess of acidified potassium iodide solution (KI).
STAGE 2: Find out how many moles of iodine have been produced.
You do this by titrating the resulting solution with sodium thiosulfate (Na,S,°s).
(You need to know the concentration of the sodium thiosulfate solution.)
How do you carry out the titration of iodine with sodium thiosulfate
1) Take the flask containing the solution that was produced in Stage 1.
2) form a burette add sodium thiosulfate solution to the flask drop by drop
3)It’s hard to see the end point, so when the iodine colour fades to a pale yellow (this is close to the end point), add 2 cm’ of starch solution (to detect the presence of iodine). The solution in the conical flask will go dark blue, showing there’s still some iodine there.
4) Add sodium thiosulfate one drop at a time until the blue colour disappears.
5) When this happens, it means all the iodine has just been reacted.
6) Now you can calculate the number of moles of iodine in the solution.
What is the reaction rate
The change in the amount of reactants or products per unit time
What are some ways to follow the rate of a reaction
Measure the volume of gas evolved
Measure the loss of mass as a gas is evolved
Use a colorimetry to measure the colour change of a reaction
Measure the ph change of a reaction
How can you find the rate from a concentration time graph
The rate at any point is given by the gradient at that point on the graph
How can you measure inital rates based on reactant concentration
1) carry out the reaction , continuously measuring one reactant
Use this to draw a concentration-time graph.
2) Repeat the experiment using a different initial concentration of the reactant
Repeat the experiment using a different initial concentration of the reactant.
Keet herations her eactats the same. Draw another concentration-time graph.
3) Use your graphs to calculate the initial rate for each experiment using the method above.
1) Repeat the proces for each reactant (different reactants may affect the rate differently).
5) Woulse on 19 how you can go on to look at how the different initial concentration safe ties
How can clock reactions be used to find inital rates
Clock Reactions not sea to Simplify the Initial Rate Method
The method described rathe & graphs. the last praction working out initial rates is a bit of a fat - Tob if measuring and drawing grapes, In clock reactions, the initial rate can beal stated.
1) In a clock reaction, you measure now the time taken for a set amount of produy to form changes as you vary the concentration of one of the reactants
There is usually an easily observable endpoint, such as a colour change, to tell you when the desired amount of product has formed.
3) The quicker the clock reaction finishes, the faster the initial rate of the reaction.
You need to make the following assumptions:
• The concentration of each reactant doesn’t change significantly over the time period of your clock reaction.
• The temperature stays constant.
• When the endpoint is seen, the reaction has not proceeded too far.
5) As long as these assumptions are reasonable for your experiment, you can assume that the rate of reaction stays constant during the time period of your measurement. So the rate of your clock reaction will be a good estimate for the initial rate of your reaction.
What is the iodine clock reaction
H,02 (ag) + 21(ag) + 2H1(ag) → 2H,00 + 12(00)
• A small amount of sodium thiosulfate solution and starch are added to an excess of hydrogen peroxide and iodide ions in acid solution.
(Starch is used as an indicator — it turns blue-black in the presence of iodine.)
• The sodium thiosulfate that is added to the reaction mixture reacts instantaneously with any iodine that forms:
2S2O32- + I2 —> 2I- + S4O62-
To begin with, all the iodine that forms in the first reaction is used up straight away in the second reaction But once all the sodium thiosulfate is used up, any more iodine that forms will stay in solution, so the starch indicator will suddenly turn the solution blue-black. This is the end of the clock reaction.
Varying iodide or hydrogen peroxide concentration while keeping the others constant will give different times for the colour change.
What does an order of reaction with respect to a particular reactant tell you
How the reactants concentration affects the rate
If you double the reactants concentration and the rate stays the same
What is the order
0
If you double the reactants concentration and the rate also doubles
What is the order
1
If you double the reactants concentration and the rate x4
What is the order
2
What is the reactions overall order
The sum of the orders of all the differnt reactants
What is rhe only way to find the orders of reaction
form experiment
What 2 ways experimentally can you find out orders of reactions
1) continuously monitor the change in concentration of A against time to construct a rate concentration graph
2) use an initial rates method to find out how the inital rate changes as you vary the concentration of A
How can you turn a concentration time graph to rate concentration graph
Find. The gradient at various points along the concentration time graph . This gives a set of points for the rate conc graph
What does rhe shape of a conc time graph or rate time graph show you
The order
What does a zero Order conc-time graph look like
Straight line down
What does a first order conc-time graph look like
Curved down
What does a zero order rate-conc graph look like
Horizontal line
What does the first order of the rate conc graph look like
Straight line through origin
Proportional
What does the second order rate- conc graph look like
A curve upwards
What does rhe rate equation tell you
How rate is affected by the concentrations of reactants
If the overall reaction is first order, then the rate constant is….
On a rate - conc graph of that reactant
Equal to the gradient
What is the half life of a reaction
The time is takes from half of the reactant to be used up
The half life of a first order reaction is …
Independent of the concentration
So each half life is rhe same length
What can the half life of a first order reaction be read off
It’s conc time graph by seeing how long it takes to halve the reactant concentration
What equation can you use if you know the half life of a first order reaction
To work out the rate constant
ln2
K = ——
t 1/2
Of all the half lives are equal what Order is it
1st
If a reaction has a series of steps, do all the steps have the same rate
No
If a reaction has a series of steps, what is the overall rate decided by, what is the called
The step with the slowest rate , the rate-determining step
The rate equation helps you work out the mechanism of a chemical reaction, to pick out wich reactions are involved in rate determining step
What are the rules:?
- if a reactant appears in the rate equation, it must affect the rate, so this reactant, or so,etching derived for, it must be in the rate determining step
-if the reactant isn’t in the rate equation it isn’t involved in the rate determine step at a
Can the rate determining step be anywhere in the mechanism
Yes
T or f
The reaction mechanism can usually be predicated from just the chemical equation
False they can’t usually
What does the order of a reaction with respect to a reactant show about the rate determining step
The number of molecules of that reaction wich are involved in the rate determining step
When nitrogen oxide and oxygen decompose
2N2O5 —> 4NO2 +O2
You may suggest that its second order with reseptors to n2o5
Yet expermenralt its found its first Oder with respect to n2o5.
What is a possible equation that fits with thus
N2O5 ——> NO2 + NO3 (rate determing step)
NO3 + N2O5 —-> 3NO2 + O2
Why do reactions oftern happen in a series of small change
Too complicated
Collisions with more than 2 species are unlikely
Chemical reacations only happen as fast as what ?
The slowest step
What is the slowest step called in a chemical reaction
Rate determining step
When you measure the rate of reaction what are you actually measuring
The rate determining step
What. Is a clue a mechanism is a multi step
Look at the stoichiomety in the rate eq and overall if they don’t match its most likely a multi step
What does the rate equation only show
Reacting species involved in the RDS
What does rhe order in the rate equation match in the RDS
The number of species
What is molecularity
Link between order and stochiometry
How does a temp increase effect K and how does it also effect rate
Inreases
Also increases
What is the Arrhenius equation for
Formula for temp dependence on the rate equation
What does rhe A stand for in the Arrhenius equation
A pre exponential factor
What does the pre exponential factor in the Arrhenius equation take I ot account
Frequency of collision
Orientation of molecules
What is activation in the Arrhenius equation measured in
J mol -1
What is temp measured in the Arrhenius equation
K
What does the R stand for in the Arrhenius equation
Ideal gas constant
What does the information after A in the Arrhenius equation equvioamt to
The number of molecules with energy above or equal to the activation energy
Do K and A in the Arrhenius equation have the same unit
Yes
Describe the link between K and Ea in the Arrhenius equation
If a reaction has a high Ea the. Rate of reaction is slow
Shown in the Arrhenius equation
- if Ea is high the fraction is larger so e raised to a larger negative value so K will have a smaller value so a slower rate
Describe the link between K andT in the Arrhenius equation
If reaction has high T rate is fast
Shown in the Arrhenius equation
If T is higher, denominator is larger so raising e to a smaller negative so K will have a
Larger value
How can the Arrhenius equation be expressed
lnK = - Ea/ RT + lnA
How can the natural log of the Arrhenius equation be written to be represent on a graph
LnK = - Ea/R x 1/T + lnA
LnA = C
1/T = x
-Ea/R = m
LnK = y
A graphs for the Arrhenius equations shows a relationship between what
Rate constant
Temp
What does the rate constant apply to
A particular reaction at a certain temperate
When is a system said to be in dynamic equilibrium
The rate of th forward reaction is the same as the rate of the reverse reaction
(Conc are constant )
When can a closed system only happen
In a closed system at a constant temperature
Explain how bromine can set an equilibrium in a physical system
When liquid bromine is shaken in a closed flask, some of it changes to orange bromine gas, after a while, equilibrium is reached - bromine liquid is still changing to bromine gas and bromine gas is still changing to bromine liquid but they are changing at the same rate
What does the equilibrium constant show
The ratio of products and reactants at dynamic equilibrium
What is homogeneous equilibrium
All the reactants and products in a reaction are in the same state
What are the heterogenous equilibrium
The reactants and products in a reaction are in differnt states
If the mixture is homogenous what is put into the Kc expressions
All reactants and products are put into the expression
If the mixture is heterogenous what is put into the Kc expression
Only he gazes and aqueous substances)
(Solids and liquids get left out)
What is the exception for not including liquids or solid in heterogenous equilibrium in the Kc expression
If the solvent isn’t aqueous you need to include any water in the Kc expression
Check example 1 /2 /3 on page 128 and 129
Write
A(g) + 2B(g) = C(g)
In a Kp expression
p(C)
= —————-
p(A).p(B)^2
Mole fraction equation
Number of moles of gas
————————————
Total number of moles of gas in gas mixture
What should the sum of all mole fractions add up to
1
What is partial pressure
The contribution that the gas makes towards the total pressure
Partial pressure equation
Mole fraction X total pressure
What should the sum of all partial pressures add up to
The total pressure
What is the total pressure of a gas mixture
The sum of all the partial pressures of the individual gases
Ensure you can work out partial pressure maths Qs
What is a mole fraction
The proportion of a gas mixture that is a particular gas
What changes for a Kp expression for heterogenous equilibrium
Don’t include solids or liquids
The larger the value of Kc , what does this tell u about equilibrium
The equilibrium lies to the right , more products relative to reactants
What is the only thing that effects the value of Kc and kp
Temperature
Why doesn’t concentration changes effect Kc or kp
The value of the equilibrium is fixed at a given temperature
So if the conception of a one thing in the equilibrium mixture changes then the concentrations of the others must change to keep the value of Kc the same
How does catalysts effect equilibrium
Approaches equlibrium faster
But has no effect on position or the value of Kc or kp
How and why does temp effect K values
( if forward direction is exothermic)
K decreases with increasing temperature
Position of equilibrium, shifts to the left
More reactants, less products
If K decreases the system us no longer at equilibrium so the product reactant ratio must become smaller by the numerator decreasing and denominator increasing
A + B = C
Explain what happening in terms of equilibrium and value of Kc
When A conc is increased
Increase denomination so ratio smaller, Kc can’t change so Poe shirt sright to favour C conc to also increase numerator and decrease A conc
So Kc stays constant
When pressure increases what happens to the species partial pressures
All of them increase
A + B = C
If pressure increases explain what happens to kp
Greater increase so expect kp to decrease by kp is uneffected
So Poe shits to right ( fewer moles) so p (c) inc and p( b) and p ( a ) decrease
What are brønsted-Lowry acids
Release hydrogen ions when they are mixed with water
You never get H+ ions by themselves in water
What are they always combined with to form what
H2O
To form hydroxonium ions, H3O+
HA (aq) + H2O. —> ……
H3O+ (aq) + A- (aq)
What are brønsted Lowry bases
Protons acceptors
When they’re in solution, they grab hydrogen ions form water
(brønsted Lowry bases)
B(aq) + H2O(l) —>…?
BH+ (aq) + OH- (aq)
how many protons can HCl and HNO3 release into solutions and what are they called
One protons
monobasic acids
Give 2 examples of acids that release more than one proton
H2SO4
H3PO4
Sulfuric acid releases …. Protons so it’s …..
2
Dibasic acid
Phosphoric acid releases…. Protons so is called ….
3
tribasic
Acids and bases form what ?
Conjugate pairs
What are conjugate pairs
Species that are linked by the transfer of a proton.
They’re always on opposite sides of the reaction equation
(Conjugate pairs)
The species that has lost a proton is the ……… and the species that has gained a proton is the ……….
Conjugate base
Conjugate acid
when brønsted-Lowry acids and bases react together
Give a general Eq for it
And which ones are conjugate pairs
HA ( acid) + B ( base) = BH+ (acid) + A- (base)
HA and A- are conjugate pairs
And B and BH+
HA ( acid) + B ( base) = BH+ (acid) + A- (base)
In the forward direction what donated a proton
HA acts as an acid and donated the proton
HA ( acid) + B ( base) = BH+ (acid) + A- (base)
In the reverse reaction what accepts the proton
A- act as as a base and accepts a proton form the BH+ ion to from HA
Why is water a special case when reaction with acids or bases
It reacts with acids to from a conjugate acid ( H3O+)
And reacts with a base to from a conjugate base ( OH-)
Water + acid general Eq
HA (aq) + H2O = A- (aq) + H3O+ (aq)
Water and base general Eq
B(aq) + H2O(l) = BH+ (aq) + OH- (aq)
How do reactive metals react with acids
Release hydrogen gas
Metal atom donates electron to the H+ ions in the caud solution
The metal atoms are oxidised and the H+ ions are reduced
What are alkalis
Bases that release hydroxide ions in water
They react with acids to form water
Most insoluble bases are ….
Metal oxides
Insoluble base + acid ionic Eq
2H+ (aq) + O^2- —> H2O (l)
What did Lavoisier Belive about the acid base theory
Lavoisier thought it was all to do with oxygen…
Lavoisier came up with the first theory of acids and bases in the 18th century. He didn’t know the tormulas of compounds like hydrochloric acid but he did know that suluric acid had the formula H2SO4m and nitic acid had the formula HNO3,. So he proposed that acids had to have oxygen in them. It was later shown that acids like hydrochloric acid (HCl and hydragen sulfide (H2S) don’t have any oxygen in them at all.
Who replaced Lavoisier acid base theory and with what
Arrhenius thought it was about H+and OH -…
Al the end of the 19th century, a chemist called Arrhenius suggested that acids release protons in aqueous solution, whilst bases release hydroxide ions. He said that when acids and bases react together they form water and a salt. This is true for loads of examples but doesn’t work for bases such as ammonia (NH3) which don’t contain any hydroxide ions.
what theory did brønsted-Lowry come up with and who’s work was it based on
Brønsted and Lowry came up with their dietinition of acids and bases independently one another . It’s clearly based on Arrhenius theory, but broadens the direction of a base to be a proton acceptor. They also came up with the idea that acids and bases react to form conjugate pairs, rather than a salt and water. This definition currently explains most of our observations, so is one of the theories we still use today — around 100 years later
Uses of acids
Industrial processes
(Fertilizer manufacture, dyes, drugs)
Bases use
Household cleaning products, soap, manufacture of fertilisers
Brønsted and Lowry
Deifnion of an acid
Proton donors
Brønsted and Lowry
Deifnion of a base
Proton acceptors
When an acid loose a H+ it becomes ….
A base
When a basic substance gains a H+ it becomes …
An acid
When an acid is present does a base need to be present
Yes
What name is given to H3O+
Hydronium ion
What is the definition for conjugate pairs
Conjugate acid - base pairs contains two species that can be interconnected by transfer of a proton
What is another word for monoprotic
Monobasic
The H+ ions from acids in water are often bonded to….
atoms that are electrgonetve ( o , f ,cl
What is PH a measure of
How acidic or basic something is
Measures the concentration of hydrogen ions in solution
Why is a logarithmic scale (PH scale) used
Conc of h ions can vary enormously
PH = in terms of logs
-Log10[H+]
What do you need to know to calculate the Ph of a solution
Hydrogen ion concentration
If you know the PH of a solution, what can you find out and how
Hydrogen ion concentration
You need the inverse of the PH formula
What is the inverse of the PH formula
[H+] = 10 ^-ph
What does monobasic mean
One mole of acid produces one more of hydrogen ions
Strong acids ionise fully in solution ( eg, hcl) and is monobasic. What does this mean for the H+ conc
The same as the acid concentration
For 0.1 mole dm -3 of HCl
What is the conc of H+
Also 0.1
Water dissociates into hydroxonium ions and hydroxide ions
How is this more simply written
H20 = H+ + OH-
The equilibrium constant for the dissociation of water is called what …
And what is the simple
The ionic product of water
Kw
What are the units of Kw always
Mol^2dm^-6
Does it matter whether water is pure of part of a solution for the Kw constant
No , this equlibrium constant is always happening
What is the Kw expression
Kw = [H+][OH-]
For pure water what is the ratio of H+ and OH- due to it’s dissociation
1:1
For pure what what can Kw also be written as and why
[H+]= [OH-]
So
Kw = [H+]^2
If you know Kw of pure water at a certain temp, what can you calculate
[H+] which can be used to find PH
How does changing conc of either [H+] or [OH-] effect Kw
The value of Kw doesn’t change, as the equilibrium will shift, changing concentration of the other substances to keep the value of Kc the same
How does changing temp of solution change the value of Kw
The dissociation of water is an endothermic process, so for example, warming the solution shifts the equilibrium to the right and Kw increase
T or f
Kw always have the same value of pure water of aq solution at a given temp
T
What happens to NaOH and KOH in water
They are strong bases that fully ionise in water
NaOH and KOH donates …… per mole of base
What does the mean for the link between conc of base and oh-
One mole of OH- ions
They have the same conc
How do you work out PH for, known base conc
Base conc gives OH- conc
OH- conc links to H+ conc with Kw
h+ gives PH
What the PH formula
-Log[H+]
What the rearranged ph formula to find H+ conc
[H+] = 10^-Ph
How many dp should you give Ph to
2
What happens to PH when diluting strong acids
The same number H+ ions in a larger volume of solution
Conc dec, so PH inc
Where does the equilibrium lie of the dissociation of weak acids
The left
What is the general Ka equation
[H+] [A]
Ka= ———————-
[HA]
Unit for Ka
In mol dm - 3
How does Ka change in respects to the strength of an acid
Increases the stronger the acid
As dissociated more so more H+ so the numerator in the expression increases so an increase in Ka
If tempt increases what happens to Ka
And why
Increases
As equilibrium shifts right ( it’s an endothermic reaction)
What 2 assumptions are made to use the Ka expression
[Ha] inital = [HA]equilibrium
[H+] = [A-]
When is [H+] = [A-] assumption valid
Of there are no other reactants added
Why does [Ha] inital = [HA]equilibrium work
Very little dissociation
When is this less reliable
[Ha] inital = [HA]equilibrium
The stronger the acid the less reliable the assumption
[H+]= [A-]
What is this ignoring
H+ from water
Why is pKA used
As the value of Ka for weak acids is almost always very small
So to create a more usable scale pKA is used
pKa =
Formula
-log Ka
Ka = …
Formula
10^-pka
pKa units
None
The weaker the acid the….. the value of pKA
Larger
Why is [H+] not the same conc as the acid when it is a weak acid
The weak acids down fully ionise in solutions
What constant do you use for ph of a weak acid
Ka
What does Ka apply to
A particular acid at a specific temperature regardless of concentration
Be able to use Kpa , Ka, H+ and Ph to calculate weak and strong acids
Is the dissociation of water exo or endo
Endo
What does Kc[H2O] =
Kw
Kw expression
Kw = [H+] [OH-]
In pure water what assumption can you make
[H+] = [OH-]
What is the PH of pure water at rtmp
7
What does Kw=
Simplified
[H+] ^2
What is the Kw value for pure water at rtmp
1x10^-14
Mol2dm^-3
What do all aqueous solutions contain
H+
OH-
In pure water and neutral solutions
What is the link between H+ and OH-
They are equal
In acidic solutions
What is the link between H+ and OH-
[H+] > [OH-]
In alkaline solutions
What is the link between H+ and OH-
[H+] < [OH-]
What is another way of writting the dissociation to water
2H20 = H3+0. + OH-
What happens to Ph of water as temp increases and why
Dissociation of water is endothermic so increasing the temp would push Poe to the right
Inc Kw, inc H+ ions and so lowering PH
If temp increases, PH decreaes
How is water still neutral
As OH- have also increased
Neural solution is defined as equal number of moles of H+ and OH- not ph of 7
What is strength of a base measured on
Dissociation in solution to Oh- ions
Show NH3 is a weak base
NH3 + H2O = NH4+. + OH-
Ensure you can calc PH around strong bases
What key info do you need
Kw
—- = [H+]
[oh-]
How to work out neutralisation PH Qs
Balenced Q
Starting moles
Find limiting reactant
Find final moles
Find new vol
Find concentration
Multiply to account for it being monoptoric or disprotic
chmage to H+ if in OH-
The PH
What is a buffer
A solution that is able to resist changes in PHwhem small volumes of acids and bases are added
Uses of buffers
1) store enzymes which change shape if PH changes too much
2) soap in shampoo raide the ph and cause skin irritation so buffers are used
3) induturial dye processes and manufacture of pharmaceuticals are controlled using buffers
4) baby lotion is buffered to inhibit growth of bacteria which can cause nappy rash
Why does blood contain buffers
Exersize releases Latic acud
Blood should stay between 7.35 and 7.45 so buffered to keep in range
What is buffered formed form
1) an acud and its salt
2) excess weak acid and a strong base with partial nutrilaisation
What must buffers contain
HA
A-
(Weak acid and conjugate base)
Why can’t a strong acud be used when making a buffer
It completly dissociates so no HA
Why can’t you use a weak acid alone when making a buffer
Only slightly dissociates so not high enough A-
Use 2 equations to show how buffers are made form acid and corresponding salt
1) CH3COOH = CH3OO- + H+
this only partially dissociates so leaving a high reserve of HA ( CH3COOH)
2) CH3COO-NA+ —> CH3COO- + NA+
The ch3coo- is in reservoir as the salt fully dissociates
How do buffers work when H+ ions are added
System opposes the change as POE shifts left to lower H+
There is a reservoir of A- to react with so HA increases
How do buffers work when OH- are added
They react with H+ ion to make water , the system opposes the change by POE shifts right to restore H+
There is a reservoir of HA so can dissociates into H+
How to make a buffer from partial neutralisation (use Eq)
Weak acid and strong base
CH3COOH + NAOH —> CH3COO-NA+ + H2O
as a general rule add half amount of moles of bases as you add to ensure partial neutralisation
This means CH3COOH left ( leave a reservoir of HA)
The product CH3COO-NA+ which dissociates into CH3COO- which is in reservoirs
when dealing with buffers do we assume
[H+] = [A-]
No that wouldn’t be a buffer
When are buffers most effective
When [HA] = [A-]
Ka for buffers with assumption
Ka = H+
What is the pKA of buffer
PKA = PH
What does buffers operate over
2 PH units centred at pKa
rearrange Ka
To make H+ subject
= Ka [HA] / [A-]
What is a buffer
Solution that minimises changes in OH when small amounts of acid or base are added
Do. Buffers stop PH from changing
No , it makes the change very slight
Buffers only work for what
Small amounts of acid or base.
Too much and they won’t be able to cope
What are the types of buffers you can get
Acidic
Basic
What equilibrium is set up for an acidic buffer no matter how it’s made
( ethanoic acid as an example)
CH3COOH = H+ + CH3COO-
What does an acidic buffer equilibrium system contain
lots of undissociated HA
Lots of the acids conjunctive base A-
enough H + ion to make the solution acidic
How is thePH of the blood controlled
using a carbonic acid-hydrogen carbonate buffer system
What two equilibrium reactions occur in blood
H2CO3 = H+ + HCO3-
H2CO3 = H2O (l) + CO2
what PH does blood need to kept between
7.35 and 7.45
How are the levels of H2CO3 controlled in blood
Respiration
When breathing Out CO2 the H2CO3 is reduced as it moves the equilibrium to the right
What are the levels of HCO3- controlled by in the blood
By the kidneys wich excess being excreted in urine
When calculation PH of acidic buffer s
What assumptions can you make
1) the salt of the conjucgate base is fully dissociates so we assume the equilibrium conc of A- us the same as Initial conc of the salt
2) HA is only slightly dissociated, so assume that it’d equilibrium conc is the same as its initial conc
Ensure you can do buffer calls
Describe using a PH probe
Usefull instruments to monitor PH changes during a tritiations
- record PH at regular intivals ( more frequently when PH changes rapidly )
- plot a graph of PH against total volume of aq base
- attain a tritiaioncurve
What are the key features of a tritiations curve
Slight change at first as either acid or base in excess
PH then changes more rapidly
Rapid chmage with small volume addition at vertical section of PH curve
Equivelnce point
After equivalence point - PH chmages slightly as either base or acid in excess
What do tritations curves help choose
Appropriate indicatiors
What is the equivalence point
The centre point of the verticillium section - the volume For one solution that exactly reacts with the volume of another solution
T or f
Equvelence point is the neural point
F
Know the 4 tritations curve shapes
What does weak acid and strong base tritiations curve have that the rest don’t
Buffer zone
What is the EQ p of strong acid and string base
7
What is the EQ p of weak acid and strong base
PH> 7
What is the EQ p of strong aci and weak base
PH<7
What PH curve has no visible verticals section
Weak acid and weak base
Why does weak acid strong base have a resulting solutions of PH >7
CH3COOH + NAOH = CH3COO-Na+. + H2O as an example
Acid and alkaline in same conc , there would be 25 ml ( example) of each for neutralisation to occur)
However resulting solutionPH>7 as ethamoate ions from salt would bond with H+ from water leaving OH-, raising the PH
Why does strong acid and weak base have PH < 7B
HCL + NH3 - > NH4CL as an example
NH4C are proton donors and will form H3O+ hence reducing PH slightly
What is the half neutralisation point
And how to use it
The point at which exactly half of acid has reacted to from A-
So
HA = A-
Then work out PH of weak acid using
[H+] [ A-]
Ka = ————. As HA =A
[HA]
KA = H+ SO PKa = PH
Allowing u to identify the weak acid
What do indicators do
Detect presence of H3O+
Properties of indicators
Two distinct colours in acid and base
Intensely coloured when only few drops are added
Soluble in water
An end point that lies in the range of the equivelnce point
Define end point
The point in a tritations where the indicator changes colour, the end point indicates when the reaction is just complete
Define equivalence point
The point. In a tritations at which the volume of one solution has reached exactly the volume of the second solution
Define indicator
A substance that changed colours at a particular PH
What 2 ways can u write an indicator EQ
HA = A- + H+
HIN - IN- + H+
How do indicators work
The position of equilibrium shift towards weak acid in acid and A- in basic
They are weak acid that have a differnt colour to its conjugate base
Give an example of 2 indicators
Phemophaline
Methyl orange
What is the phenopjaline colour change
Colourless in acid
Pink in alkaline
Describe phenopthaline in acid conditions
HA = A- + H+
(Colourless) ( pink)
the H+ present will push POE left so colourless in acid
Describe phenopthaline in alkaline conditions
HA = A- + H+
(Colourless) ( pink)
OH- will react and remove H+ causing Poe to shift right so pink in alkaline
How does the colour in methyl orange work
At end point, indicator contains equal conc of HA and A-, the colour will be in between two examples
How do you chose the right indicator
An indicator wich has an endpoint in a range which closely matches the potential equivelnce point
How would u calibrate a PH probe
Place the bulb of the PH probe into distilled water and allow the reading to settle. Now adjust the reading so that it reads 7
Do the same with a standard solution of PH4 and zPH10, make sure to rinse probe with distilled water between each reading
What do u need your indicator to do during a tritations
Change colour exactly at the end point of your tritiations
So the PH range of change. Of colour of the indicator needs to happen on the verticals part of
The PH Curve
Methyl orange and phenophaline
What can u use for strong acid and strong base
Methyl orange and phenophaline
Methyl orange and phenophaline
What can u use for strong acid and weak base
Methyl orange
Methyl orange and phenophaline
What can u use for weak acid and strong case
Phenophaline
Methyl orange and phenophaline
What can u use for weak acid and weak base
No sharp ph change so neither
What is the approximate change for methyl orange
3.1 - 4.4
What is the approximate colour change for phenophaline
8.3 - 10
ENERGY …..
How is bond dissociation linked to enthalpy atomisation
Bond dissipation is twice enthalpy of atomisation
This only works if the elements gasses and covalently bonded in standard states
The greater the lattice enthalpy the …… the ionic bonding
Stronger
What does strength of an ionic bond depend on
Size and change of ions
What combination leads to the strongest ionic bonding so larger enthalpy of lattice formation
Small size and higher charger
Can you find lattice enthalpies experimentally
No
What do the 2 routes involve in the born haber cycle
Route one- enthalpy of formation
Route 2 -enthalpy of atomisation, ionisation wnergy, electron affinity, lattice enthalpy
On a born haber cycle what direction do exothermic arrows point in
Downwards
On a born haber cycle what direction do endothermic arrows point in
Upwards
Is ionisation endothermic or exothemric
Endothermic
Is enthalpy of lattice dislocations endo or exo
Endo
Is enthalpy of lattice formation endo or exo
Exo
Is 1st enthalpy og electron affinity endo or exo
Exo
Is 2nd enthalpy oh electron affinity endo or exo and why
Endo
Adding a negative e- to a 1- ion so needs energy
What is standard lattice enthalpy a measure of
Ionic bond strength
The more negative the lattice enthalpy the stronger the bonding
What affect lattice enthalpy and why
The higher the charge on the ions the more energy is released when an ionic lattice forms. This is due to stronger electrostatic forced between the ions
As more energy released so lattice enthalpy will be more negative
The smaller the ionic radius, the more exothermic the lattice enthalpy. As smaller ions have a high change density and their smaller ionic radii mean that the ions can sit closer together in the lattice. Both these things means that attractions between th ions are stronger
What do you have to use to calculate lattice enthalpy
Born-Haber cycle
Know how to do born harber cycles
What changes if you are doing a born-harber cycle with group 2 elements
Eg, mgcl2
There are 2 moles of chlorine ions in each mole of mgcl2 so times atomisation energy by 2
Group 2 elements form 2+ ions so inculde second ionisation energy
And double first electrom affinity for chlorine as 2 moles
What happens when solids dissolve in water
+ and - ions formed
Polar water forms dipole interactions with the ions
Oxygen to positive ions and H to negative ions
Is standard enthalpy change of solution Endo or exo
Either
It’s the balnece between energy needed to break up lattice and energy needed to form ion dipole forces
Is standard enthalpy change of hydration endo or exo
Exo due to formation of ion-dipole forces
What factors affect size of hydration enthalpy
Size of hydration enthalpy depends on the strength of the attraction between the ions and water molecules
Smaller ions = stronger attraction ( so more exothermic hydration enthalpy ) due to higher charge density . Greater charge but similar size have stronger attractions
What is entropy a measure of
Disorder
What order to the states if matter go
Least entropy to most entropy
Solid < liquid < gas
What letter represents entropy
S
Units of entropy
JK^1mol^-1
Know how to draw a graph of entropy against temperature
+S
Has entropy increased or decreased
Inc
-S
Has entropy increased or decreased
Dec
How do you do an entropy chmage calculation
Add up all entropies of the products in a system and substrate the sum of entropies od the reactants
Are entropies of elements included in entropy chmage calculation
Yes as they aren’t 0
What is starndard entropy of a substance
Entropy of one more of a substance under standard conditions
Standard entropies are always …..
Positive
What is gibbs free energy represenated by
Delta G
Units of gibbs energy
KJmol^-1
Delta G calculation equation
Delta H - TdeltaS
What calculation gibbs energy what do you need to convert
Delta S to KJ
What units of temperature are used in gibbs equation
k
Are feasible reactions exo or endo
Either
What does it mean that a reaction is feasible
It can occur without continue energy supply
What does free energy ( delta G) depend on
Delta H and TdeltaS
When is a reaction feasible
When delta G <0
What is gibbs free energy
Leftover energy available to do chemcial work
A negative delta G therefore means leftover energy
What can we use to calculate temperature at wich recation is feasible
G = 0
What 2 things happen when solid ionic lattice dissolved in water
1) bonds between the ions break to give gaseous ions
2) bonds between the gaseous ions and water are made
What is enthalpy change of hydration
The enthalpy change when 1 mole of gaseous ions dissolves in water
What is enthalpy change of solution
The enthalpy chmage when 1 mole of solute dissolves in water
When do substances only dissolve ( generally )
When the energy released is roughly the same ot greater than the energy taken in
Soluble Substances then to have …… enthalpies of solution
Exothermic
Knwo how to draw a enthalpy cycle to work out enthalpy change of solution/hydration
Why do ions with a greater change have a greater enthalpy of hydration
ions with a higher charge are better at attracteing water molcules than those with lower charges, the electrostatic attraction between the ion and water molecule is stronger. Thus means more energy is released when the bonds are made giving them a more exothermic enthalpy of hydration
Why do smaller ions have a greater enthalpy of hydration
Smaller ions have a higher change density than bigger ions, they attarct the water molecules better and have a more exothermic enthalpy of hydration
What is entropy
a measure of the number of ways that particles can be arranged and the number of ways that the energy can be shared between particles
The more disordered the particles are, the ……. The entropy
Higher
What 2 things effect entropy
physical state
More particles
how does physical state affect entropy
Solid particles, hardly any randomness so lowest entropy
Gas particles, most random arrangements so highest entropy
Why does more particles mean more entropy
more particles more ways they and their energy can be arranged
Why do substances like disorder
They are more energetically stable
Particles will move to try and……. Their entropy, so some reactions are ……
Increase
Feasible
When a substance reaches it maximum entropy state, it’s said to be ?
Thermodynamically stable
It won’t react any further without input of energy
How can you calculate entropy change of reaction
Entropy if products - entropy of reactants
Reactants with a positive delta S are ….. likely to be feasible
More
For feasible reactions delta G must be ….
Negative or zero
What 3 things is the tendency of a process to take place is dependent on
The entropy
The enthalpy
The temperature
What is the equation; to calculate free energy
Delta G = Delta H - TxDeltaS
The temperature at which a reaction becomes feasuble can be calculated by doing what
Making delta G =0
When delta H is negative and delta S is posustive delta G will always be ….
Negative
When delta H is positive and delta S is negative delta G will always be ….
Positive
Why does a negtaive delta G not always guarantee a reaction
Might have a really high activation energy
Or so slowly that you wouldn’t notice it happening
How can you calculate delta H
q = mcdelatT
Then divide q by numbe of moles of reactant.
What is the electrochemical series
Ranking series, the post powerful reducing agents at the stop, and good oxidising agents at the bottom, they are assigned as standard electrode potentials, which allows us to predict the direction of redox reaction
What are voltaic cells
Electrochemical cells which convert chemical energy into electrical energy
What are voltaic cells also known as
Galvanic cells
What are voltaic cells made by
connecting two different half cells which enables the flow of electrons
what does a half cells contain
A half cell contains the chemcial species present in a redox half equation eg. A metal strip in a solution of its ions
Why must the half cells by kept apart
otherwise heat energy is released instead of electrical energy
A solution in a standard half cells will have a concentration of …
1 mol dm -3
Half cel
Zinc as solid and Zn2+ as Aq
What is the notation
Zn ( s) | Zn 2+ (aq)
Zn(s)IZn2+(aq)
What does the line represent
What would it represent if it was ||
phase boundary as (s) —> Aq
|| salt bridge
What does redcat+ mean
reduction at cathode wich is positive
What is used to measure cell potential
High resistance voltmeter
what doing full notation of cells
What is the rule for the order
Solids tend to be on the ends
The lowest oxidation umbers go on the outside
What do standard electrode potentials compare
The tendency of metal to form its ions with the tendency of hydrogen to form ions
Definition of standard electrode potential
The EMF ( electromotive force) of a half cell connected to a standard hydrogen half cell under standard conditions
Why is platinum oftern used in cells
inert so won’t react with the redox system
SHE = ?V
So the voltmeter tells you standard electrode potential
0
Why is it Important for the voltmeter to be high resistance voltmeter
The voltmeter needs to be a very high resistance to stop the current form flowing in the circuit
In this state it is possible to. Measure the maximum possible potential difference
The reactions will not be occurring because the very high resistance voltmeter stops the current from flowing
Why is the salt bridge required
The salt bridge is used to connect the circuit
The free moving ions conduct charge
What is the salt Bridge usually made of
A slat bridge is squally made form a piece of filter paper soaked in a salt solution, usually potassium nitrate
The salt should be unreactive with the electrodes and electrode solution
The half cell with the more postitve potential is set up at the ….
Right hand electrode
In cell notation what is used between substances in the same phase
Commas
What is emf ( calculation )
E°cell = E°right -E°left
The potential of the right hand electrode minus the potential of the left hand potential
The SHE is difficult to use why
And what is oftern used instead
involves use of a gas, and one thats flammable
Oftern a differnt standard is used which is easier to use
What is a standard electrode that has been calibrated against the primary standard
Secondary standard
What is rhe redox process in the cell
Metal atoms lose electrons at the one electrode, the electrons travel through the wire to the other electrode reducing it
Equation to figure out Ecell value ( voltage )
E( positive electrode / right ) - E ( negative electrode / left )
What electrode goes on the left
Negative
Sign on volatage is the sign of the ….. electrode
Right hand
In chemical cells e- flow from …… electrode to ……
Negative
Positive
Where does reduction take place in electrochemical cells
Cathode
Where does. Oxidation take place in electrochemical cells
Anode
When considering a pair of equations in electrochemical cells a reaction is feasible when….
The redox of an oxidising agent has a more positive standard elcectrde potential value than the reducing agent
Limitations if electrochemical cells
We can predict the feasibility of a reaction but this gives no indication of the rate of reaction
Varying concentration of solution will affect electrode potential values
Remember that standard electrode potentials apply to aqueous equilibria- many reactions that take place are not aqueou
What is an electrochemical cells made from
Two different metals dipped in salt solution of their own ions and connected by a wire
Describe what happens in a zinc / copper electrons chemical cell
1) zinc looses electrons more easily than copper, so in the hall cell, zinc is oxidised to form zn2+. This released e to the external surface
2) in the other half cell, the same number of electrons are taken form the external circuit, reducing the cu2+ ions to copper atoms
So electrons flow through the wire form the ….. reactive metal to the …..
Most
Least
What does rhe voltmeter in the external circuit show
The voltage between the two half cells . This is the cell potential or e.m.f or E cell
Can you have a half cell with a of2 aq ions of the same element
Yes
The conversion between the two ions happens on the surface of a platinum electrode
Can electrochemical cells be made form non-metals
Yes
Such as gases, the gases can be bubbled ober a platinum electrode sitting in a soltion of its aqueous ions
The reaction at each electrode are reverisble, so how do you know which direction each reaction goes in
It depend on how easily each metal loses electrons
Hoe easily a metal is oxidised is measured using …
Electrode potentials
A metal that’s easily oxidesed has a very ……. Electrode potential
Harder to oxides has a …… electrode potential
Negative
Positive
If one metal is more negative does that mean it is oxidised or reduced
Oxidised ( the reaction go3s backwards)
The cell potential will always be
Positive
You can measure electrode potential of a half cell against a ,,…
Standard hydrogen electrode
The standard electrode potential of a half cell
The voltage measured under standard conditions when the half cell is connected to a standard hydrogen electrode
What are the standard conditions for a electrochemical cell
Conc of solutions 1 mol dm-3 or equimolar
Temp 298K
Pressure 100kpa
The standard hydrogen electrode is always on the ….
It doesn’t matter whether or not the half cell is more positive
Left
The stanard hydrogen electrode half cell has a value of …..
0.00V
Does changing the equilibrium position changes the cell potential
Yes
That’s why you use standard conditions
The more reactive a metal the more ….
More reactive metals have a more ….
It wants to lose electrons to form a positive ions
Negative standard electrode potential
The more reactive a non metal is, the more …
More reactive non metals have more ….
It wants to gain electrons to form a negative ion
Postives standard electrode potential
Why can the prediction of if a E cell is posible under standard conditions be wrong
- Not under standard conditions
- The reaction kinetics are not favourable ( rate of reactions may be so slow that the reactions might not appear to happen , if a reaction has a Hugh activation energy)
How can changing conc of the solution cause the electrode potential to change
( with example zinc and copper )
If you increase the conc of zn2+ the equilibrium will shift left reducing the ease of electrons loss. The electrode potential of zinc becomes less negative and the whole cell poteneitls will be lower
If you increase the conc of cu2+ the equilibrium will. Shift right , increasing the ease of electrode gain. The electrode potential of cu become more positive and the whole cell postienital will be higher
What is a Primary battery
non rechargeable
Electrical energy released by oxidation and reduction at the electrode
Eventually chemicals are used up and reaction can’t be reverse
What is a secondary battery
Rechargeable - the cell reaction can be reverse
What is a fuel cell
Fuel and oxygen flow into the fuel cel , products out, electrolyte remains in cell
How long can a fuel cell work
Can operate continuously to produce voltage as long as fuel and oxygen are supplied
Ensure you can draw a hydrogen fuel cell ( acidic) and alkali
What happens in hydrogen acidic fuel cells
Hydrogen looses electrons
H+ through electrolyte
O2 gains E-
What happens in alkali hydrogen fuel cells
Hydrogen and hydroxide to produce water and electrons
O2 accepts electrons and water to produce hydroxide
Explain how a fuel cells works
1) at the anode rhe platinum catalyst splits the H2 into protons and electrons
2) the polymer electrolyte membrane only allows H+ across and this forced e- to travel around the circuit to get to the cathode
3) am electric current is created in the circuit which is used to power something
4) at the cathode oxygen combines with H+ from the anode and the e form the circuit make H2O, this is the only waste product
Advantages of electrochemical cells
More efficient at producing energy than combustion as energy is wasted as heat
They produce less pollution as water is the only waste product
Negatives of using electrochemical cells form energy
The production of cells involves use of toxic chemicals , which need to be disposed of once the cell has reached the end of its life span
The chemcials used to make the cells are also very flammable
TRANSITION METALS
T or f
Transition metals have typical metal properties
T
uses of
Cu/ag/ni/ zn
Coinage
Use of fe
Construction
Use of cu
Electrical cables and water pipes
Use of Ti
Aerospace industry / medical applications
What subshells are filled in transition metals
4s and 3d
What is the aufbau principle
Lower energy orbitals fill first
What is hunts rule
Orbitals will fill singularly first then electrons pair up
What. Are the other rules for filling up orbitals
No atomic orbital can hold more than 2 3-
4s fill before 3d
Which two transition metals are “special cases” and what are their electron configurations?
in chromium the 4s1 and 3d5 structure is adopted because the repulsion between 2 paired electrons in the 4s orbital is more than the energy difference between the 4s and the 3d subshells
It is therefore more stable to have unpaired electrons in the higher 3d …
Define a transition metal.
a transition element is one that forms at least one stable ion with a partially filled d shell of electrons
State three properties of transition metals.
variable oxidation’s states, these arise because the 4s and 3d subshells are so close in terms of energy, each oxidation state oftern has a characterised colour
- Formations of coloured compounds Used as catalysts
What are complex ions
In solution, transition elements form complex Ions. A complex ion is formed when a
Central transition metal ion is surrounded by coordinately bonded molecules or ions called ligands
What are ligands
Molecules or ions that form coordinate bonds with the transition metal ion
What is a coordinate bond
A covalent bond in which both electrons in the shared pair come form the same atom
What is a coordinate number
Number of coordinate bonds to ligands that surround a Transition metal ion
What does coordinate number depend on
The number of them depends on size and electron configuration if that cation , and also the size and change of that ligands
List some ligand examples
H2O, NH3, Cl-, OH-, CN -
Which coordination numbers are you most likely to come across
2,4,6
What are the shapes associated with transition metal complexes , for 6 coordinate bonds
Octahedral
What are the shapes associated with transition metal complexes , for 4 coordinate bonds
Tetrahedral occasionally a square planar exception
What are the shapes associated with transition metal complexes , for 2 coordinate bonds
Linear
What catalysis is used in the contact process
V2O5
What calculation can be used to figure out the oxidation state of the metal ion in TM
Total oxidation state of complex - sums of oxidation states of ligands
Any transition metal is surrounded by …… water when aq
6
What goes in the bracket when doing TM
Everything in the []
Ligand in the ()
What would you call
[Fe(H2O)6]2+
Hexa aqua iron (ll)
What shape does Ligands connected to pt tend to be
Square planar
Bond angles in square planar
90°
Diammine silver complex ion in solution is also known as…
Tollens
Are all elements in the d block transition elements
no, most are
A transition element definition
A d-block element that can form at least one stable ion with an incomplete d subshell
A transition element must form at least one ion that has between how many electrons in the d subshell
1 and 9 electron s
Which elements in period 4 d block aren’t transition elements
Scandium and zinc
Why arnt scandium and zinc transition elements
Hey cant form stable ions with an incomplete d subshell
Sc only forms sc3+ , which has an empty d subshell
Zn only forms zn2+, which has a full d subshell
COLOURS
What colour is manganese in +7 oxidation state
( MnO4-)
Purple
What colour is manganese in +6 oxidation state
(MnO4 2-)
Green
What colour is manganese in +2 oxidation state
Mn2+
Pale pink
What colour is titanium in Ti+3
Purple
What colour is titanium in Ti+2
Violet
What colour is vanadium in +5 oxidation state
Vo2. +
Yellow
What colour is vanadium in +4 oxidation state
VO. 2+
Blue
What colour is vanadium in V3+
Green
What colour is vanadium in V2+
Violet
What colour is chromium in +6 oxidation state
Cr2O7. 2-
Orange
What colour is chromium as Cr3+
Green
What colour is iron as Fe3+
Yellow
What colour is iron as Fe 2+
Pale green
What colour is cobalt in Co2+
Pink
What colour is nickel as Ni2+
Green
What colour is copper in cu2+
Pale blue
How do the elements show variable oxidation states ?
The energy levels of the 4s and 3D sub shells are very close to one another, so differnt numbers of electrons can be gained or lost using fairly similar amounts of energy
Why do transition metals and their compounds make good catalysts
They can change oxidation states by gaining or loosing electrons within their d orbitals , this means they can transfer electrons to speed up reactions
Transition metals are also good as adsorbing substances into their surfaces to lower the activation energy of reactions
What is the catalyst of zinc with acid
CuSO4
What is the catalyst of decomposition of hydrogen peroxide
Mno2
What catalyst is used in the harber process
Iron
Why are catalysts good for industry and the environment
They allow reactions to happen faster and at lower temperatures and pressure reducing energy usage
Negatives of using transition elements as catalysts
They can pose health risks as many of the metals and their compounds are toxic
Eg, long term copper exposure can damage liver and kidneys
And exposure to manganese can cause psychiatric problems
When you mix Aq solution of transition elements ions with aq sodium hydroxide or aq ammonia. What do you get
Coloured hydroxide precipitate
Copper as an aqueous soltion and hydroxide
What is the colour change
Pale blue to a blue precipitate
[Cu(H2O)6]2+ + 2OH- —>?
[Cu(OH)2(H2O)4] + 2H2O
[Cu(H2O)6]2+ + 2NH3 —>?
[Cu(OH)2(H2O)4] + 2NH4+
In excess NH3 [Cu(OH)2(H2O)4] reacts further to form ….
[Cu(NH3)4(H2O)2]2+
Which is dark blue
Aq iron (ll) with hydroxide what is the colour chnageb ( or ammonia)
Pale green solution to a green precipitate which darkens upon standing
Aq iron (lll) with hydroxide colour change ( or ammonia )
Yellow soltion to an orange precipitate which darkens upon standing
Manganese (ll) with hydroxide or ammonia colour change
Pale pink solution to a pink/buff precipitate which darkens upon standing
Aq Chromium (lll) wuth hydroxide or ammonia
Green solution to a grey-green precipitate
Aq chromium (lll) reacts further with sodium hydroxide to form ….. with colour …..
cr(OH)6. 3-
Dark greeen
Aq chromium (lll) reacts with excess ammonia further to form ,…. Which is …..
[cr(NH3)6]3+ purple
What is a complex ion
Metal ion surrounded by coordinately bonded ligands
When is the coordination number 6
If the ligands are small, like H2O, CN-, NH3, 6 can fit around the central metal atom/ion.
When is the coordinate number 4
If ligands are larger, such as Cl-, only 4 can fit around the central metal atom / ion
6 coordinate bonds means what shape
An octahedral shape
4 cooordiante bonds usually means what shape
Tetrahedral shape
Give an example of 4 coordinate bonds that for, a square planar shape
[ NiCl2(NH3)2]
What must a ligand have
At least one lone pair of electrons
Ligands with one lone pair available for bonding are called ,,,,,
Monodentate
Ligands with two lone pair available for bonding are called ,,,,,
Bidentate
How many coordinate bonds can bidentate liganss form with a metal ion
2
Ligands that form 2 or more coordinate bonds are called …..
Multidentate
When can optical isomers happen with complex ions
When an ion can exist in two non superimposable mirror images
This happens in octehedral complexes when three bidente ligands are attached to the central ion
When can complex ions show cuz/trans isomerism
Square planar and octahedral complex ions that have at least two pairs of ligands show it.
Cis isomerism have the same groups on the same side, trans opostite sides
Descirbe cis-platin
A complex platinum (ll) with two chloride ions and two ammonia molecules in a square planar shape
What is cis-platin used as
Anti-cancer drug.
Can bind to DNA Im cancer cells
How does cis platin work
1) the two chloride ligands are very easy to displace. So the cis-platin loses them, and bonds to two nitrogen atoms on the DNA molecules inside th cancerous cell instead.
2) this block on its DNA prevents the cancerous cellls from, reproducing by division. The cell will die, since it is unable To repair the damage
What is the downside of cis platin
Also prevents normal cells form reproducing, including blood, which can suppress the immune system and increase the risk of infection.
Cis platin may also cause damage to the kidneys
Desicbe the interconvension between Fe2+ and Fe 3+
Fe2+ pale green is oxidised to Fe3+ yellow
By acidified potassium manganite (Vll)
Manganese reduced
Iron oxidised
Fe3+ hello is reduced to Fe2+ pale green by iodide ions
Describe the interconvesion between Cr3+ and Cr2O7 2-
Cr3+ in [Cr(OH)6]3- dark green is oxidised to the yellow chromate (Vl) solution CrO4 2-,by warming with hydrogen peroxide, in alkaline conditions
Adding dilute sulphuric acid to the chromate (Vl) solution produces the orange dichromate (vl) solution Cr2O7 2-
Which can reduced to Cr3+ by acidified zinc
Desicbe the reduction if Cu2+
Pale blue cu2+ is reduced to the off white precipitate copper (l) iodide by iodide ions
Desicbe the disproportionation of Cu+
Spontaneous disproporionation to produce cu and cu2+
How can transition element ions present in a mixture be identified
Using aq sodium hydroxide
They from coloured precipitates
Add NaOH dropwise form a pipettes to a test tube containing the unknown collusion and record the colour of any precipitate formed
One ligand can be swapped out for another ligand, what is thus called
Ligand substitution
What happens if there is a ligand substitution of the same size
Then the coordinate number of the complex ion doesn’t change and neither does the shape
What happens if there is a ligandsubsitiuiton and the ligands are differnt sizes
There is a chmage of coordinate number and a change of shape
can you have a partial ligand subsitutuon
Yes
[Cr(H2O)6]3+ +6NH3 = ?
[Cr(NH3)6]3+ + 6H2O
[Cu(H2O)6]2+ + 4Cl- =?
[CuCl4]2- + 6H2O
[Ch(H2O)6]2+ + 4NH3 = ?
When does thus reaction only happen and what happens if you only add a bit of NH3
[Cu(NH3)4(H2O)2]2+ +4H2O
Only happens if nh3 is in excess
If only a bit of NH3 added [Cu(H2O)4(OH)2] blue ppt
When doing an unfamiliar ligand subsitutuon what do you need to take note of
If they are the same size ligands
And their change
What is haem
A multidentate ligand
Desicbe the structure of heamoglobin
Fe 2+ ion forms 6 coordinate bonds
4 of the long pairs come form nitrogen atoms within the circular part of the molecule called heam
A fifth lone pair comes form a nitrogen atom on a protein ( globin)
The last position has. Water ligand attached to the iron
How does heamoglobin carry oxygen
In The lungs the oxygen concentration is High so the water ligand is substituted for an oxygen molecule forming oxyheamoglobin .
When it’s taken to where it is needed the oxygen is substituted for a water again
What happens if CO is inhaled
The haemoglobin swaps its water ligand for a carbon monoxide ligand. Forming carboxyheamoglon. The carbon monoxide is a strong ligand and doesn’t really exchange with oxygen or water ligands, meaning haemoglobin can’t transport oxygen
How do you make complex ions
- number of ligands
- name of ligands
Name of metal ion (ending changes to ate if complex ion is negatively charged)
State oxidation number
How do you name the ligand H2O
Aqua
How do you name the ligand OH-
Hydroxo
How do you name the ligand NH3
Ammine
How do you name the ligand Cl-
Chloro
What order do you put ligands in when naming if multiple
Alphabetical
What transition metals give square planar complexes
Pt2+ and Dp2+
What transition metals give linear complexes
Ag+
What is heam
It’s a multidenete ling and that forms 4 coordinate binds with Fe
What are the popular ligands that are bidente
NH2CH2CH2NH2
C2O4 2-
What is a multidentate ligand
Up to 6 coordinate bonds to central metal ion as they have multiple lone pairs
What is the most common multidentate ligand
EDGA 4-, forming 6 coordinate bonds
What type of isomerism is present in transition metals and why
Optical
And
Cis/trans , not E/Z as that is based on a double bond
When is it cis
Ligands are 90° apart
When is it trans
Ligands are 180° apart
When is cis / trans shown
Square planar or octahedral with 2 differnt ligands
