LAST MINUTE CHEM Flashcards
What’s avagardos number (the number of particles in one mole)?
6.02x10^23
How do you work out number of moles when given amount of particles?
Moles = Number of particles you have / number of particles in one mole (6.02x10^23)
Be careful that if working out how many atoms in a molecule, you have to multiply answer by the amount of atoms in the molecule
Formula for moles involving mass?
Moles = mass / RFM
Formula for moles involving gases?
Moles = volume in dm^3 / 24 dm^3
What’s the ideal gas equation?
pV = nRT
p = pressure in pascals V = volume in m^3 (1cm^3 = 1 x 10^-6 m^3, and 1dm^3 = 1 x 10^-3 m^3) n = number of moles T= temperature in Kelvin
How do you work out the empirical formula and then the molecular formula?
You will be given the elements in compound and there masses or percentages
Divide each percent or mass by the elements RFM
Divide everything by smallest value to get everything into whole number ratio
Then to find molecular you will given the total RFM of compound and then see how much you have to multiply the empirical to reach the RFM this will give you the molecular formula
How do you write ionic equations?
Write the full equation down
Split everything that’s (aq) into into it’s ions
Cross out any ions that appear on both sides
How do you work out moles of water in a water of crystallisation question?
Find number of moles lost by doing:
Find mass of water by doing mass of Hydrated salt - mass of anhydrous salt, and dividing that value by RFM of water
Find moles of ANHYDROUS salt, using moles = mass/rfm
Find how ratio when there is one mole of anhydrous salt how many there will be of water
Acid, base, alkali?
Release H+ ions in solution, proton donor
Proton acceptor
Base and releases OH- ions in solution
How do you work out number of moles when given concentration?
Moles = concentration (mol dm^-3) x volume (dm^3)5
What’s the percentage yield?
(Actual yield (experimental) / theoretical yield)) x 100
Theoretical yield is what you get from working it out from the equation
Atom economy?
RFM of desired product / RFM of all products
What is an ionic bond?
The electrostatic attraction between 2 oppositely charged ions
Covalent bond definition?
Strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms
What do you do if there is a double bond when predicting the shape of a molecule?
Treat them the same as single bonds
What does 2 electron pairs around the central atom produce?
Linear molecule
180 degrees
What does 3 bonded pairs around the central atom produce?
Trigonal planar
120 degrees
4 bonded pairs around central atom?
Tetraherdral (Tripod shaped, use lined wedge and filled in wedge)
109.5 degrees
3 bonded pairs and one lone pair around central atom?
Lone pair at the top, everything bellow same structure as tetrahedral
107 degree bond angle
2 bonded pairs and 2 lone pairs around central atom?
nonlinear shape (V shaped) 104.5 degrees
5 bonded pairs around central atom?
Trigonal bipryamidal
Around central atom there is a straight line going through, and perpindicular to this there is a triangle of atoms (use both wedges in this)
Producing 90 degree angles and 120 degree angles)
6 Bonded pairs around central atom?
Octahedral (Use 2 lined wedge, and 2 filled in wedge)
All angles 90 degrees
However there are 2 exceptions in the rule that ionisation energy increases along a period between group 2 to 3 and group 5 to 6 explain why?
The outer electrons in group 3 elements is a p orbital, rather than an S orbital, which means it’s further away from the nucleus, and has additional shielding from s orbital, theses factors overide the increased nuclear charge
In the group 5 elements, the electron is being removed from a singly-occupied orbital, in group 6 being removed from orbital containing 2 electrons. The repulsion means between 2 electrons in a orbital makes it easy to remove from shared orbitals
How do you test for halogens?
Add silver nitrate solution and then dilute ammonia and then conc ammonia
Chloride ions form AgCl which is a white precipitate, dissolves in dilute NH3
Bromide ions form AgBr which is a cream preicpitate, dissolves only in conc NH3
Iodide ions form AgI which is a yellow precipitate, and doesn’t dissolve in conc NH3
What’s a chlorate ion?
ClO-
How do you make bleach?
React chlorine gas with cold dilute aqueous sodium hydroxide in a disproportionation reaction
How is chlorine used to kill bacteria in water?
Cl2 + H2O =(reversible reaction) HCl + HClO
HClO + H2O = (reversible reaction) ClO- + H3O+
Chlorate ions kill bacteria
Alternatives to treat water?
Ozone strong oxidising agent for killing bacteria, but expensive and short half life
UV light- Kills bacteria by damaging their DNA but inefective in cloudy water
How do you test for sufates?
With HCl and Barium Chloride
White precipitate formed if it’s present
How do you test for ammonium ions?
Add NaOH and warm mixture, if ammonia is given off then ammonium ions were present
What order should you do tests to avoid false negatives?
Test for carbonates - no CO2, so no barium carbonate precipitate can form
Test for sulphates - no sulphate to react with silver nitrate to form silver sulphate
Test for halides
What happens to KBr (colourless) when in aqueous or organic solution and Chlorine water, Bromine water, and Iodine solution are added?
In aqueous solution:
Chlorine water added: Goes yellow from Br2
Bromine water added: no reaction
Iodine solution added: no reaction
In organic solution:
Chlorine water added: Goes orange from Br2
Bromine water added: no reaction
Iodine solution added: no reaction
What happens to KI (colourless) when in aqueous or organic solution and Chlorine water, Bromine water, and Iodine solution are added?
In aqueous solution:
Chlorine water added: Goes orange/brown as I2 displaced
Bromine water added: Goes orange/brown as I2 displaced
Iodine solution added: no reaction
In organic solution:
Chlorine water added: Goes purple as I2 displaced
Bromine water added: Goes purple as I2 displaced
Iodine solution added: no reaction
What does le Chatelier’s principle state?
If there’s a change in concentration, pressure or temperature the equilibrium will move to help counteract the change
What happens if you increase the pressure in a gaseous equilibrium?
It will shift the equilibrium to the side with the fewer moles of gas
What happens if you increase the temperature in a dynamic equilibrium?
The equilibrium shifts in the endothermic (positive enthalpy change) direction
So if the forward reaction is exothermic it will shift left
If the forward reaction is endothermic it will shift to the right
Formula for Kc the equilibrium constant if the reaction is aA + bB (reversible reaction) = cC + dD and how you work Kc out?
Kc = ({C}^c x {D}^d ) / ({A}^a x {B}^b)
Just put in concentrations to find Kc
To find units use that each concentration has the units moldm^-3 and then use indices rules to find the units
Enthalpy change definition?
ΔH, the heat energy transferred in a reaction at constant pressure
Units are kj mol^-1
What are the standard conditions?
298 kelvin (25 degrees) 100kPa (1 atm) Standard states (1moldm^-3 in solutions)
What’s the standard enthalpy change of formation
Δ(f)H, enthalpy change when 1 mole of compound is formed from it’s elements in their standard states under standard conditions
What’s the standard enthalpy change of combustion?
Δ(c)H, enthalpy change when 1 mole of a substance is completely burned in oxygen under standard conditions
What’s the standard enthalpy change of neutralisation?
Δ(neut)H, enthalpy change when an acid and an alkali react together under standard conditions to form 1 mole of water
What is enthalpy change in terms of bond forming and breaking?
The overall affect of both of them occuring
Average bond enthalpy of breaking bonds - average bond enthalpy of forming bonds
How do you calculate enthalpy changes using a formula?
Heat losss or gained in joules = mass of water in grams x 4.18 x change in temperature
Put all values into equation
Convert answer from joules to kJ by dividing by 1000
Work out how many moles of fuel produced this heat
Divide answer by the amount of moles to find standard enthalpy change (kJmol^-1) also make it negative
How to work out enthalpy change using enthalpies of formation?
Write out the reactants equalling the products, then bellow write out all the elements in their natural states that you require
Draw arrows from the natural state elements to the reactants and products, then look how many moles are made and of which substance to work out the enthalpy changes of formation for reactants and products
(if element stay the same won’t be an enthalpy change, remember to multiply by the amount of moles)
Work out total distance from the reactants to products, bearing in mind the first arrow is going in the wrong direction
How can enthalpy changes be worked out using the enthalpy change of combustion?
Same method before, however the direction of arrows have changed and so has what’s on the bottom
On the bottom have water and CO2 and both the lines will be going downwards with an amount of oxygen next to them to balance the equation
Work out total distance taking into account second line is going to wrong way
How to draw a Boltzman distribution?
Number of particles on y axis
Kinetic energy on x axis
Draw a line with a gradient of 1 going up into a smoth curve which then goes down into an asmyptote
Draw a line near the end to show the activation energy
What is the reaction rate?
The change in the amount of reactants or products per unit time
Units are mol dm^-3 s^-1
What assumptions do you need to make when doing a clock reaction?
The concentration of each reactant doesn’t change significantly over time period of clock reaction
Temperature stays constant
When the endpoint is seen, that the reaction hasn’t proceeded too far
Explain the iodine clock reaction?
H2O2 (aq) + 2I- (aq) + 2H+ (aq) = 2H2O (l) + I2(g)
Small amount of Sodium Thiosulfate solution and starch are added to an excess of H2O2 (Hydrogen peroxide), and Iodide ions in acid solution (H+)
Starch is an indicator and turns blue/black in presence of iodine
Sodium thiosulfate instantly reacts with any Iodine that forms making it go back to iodide ions
So once the set amount of Sodium thiosulfate is used up solution will go blue/black, so can vary iodide or H2O2 concs to give you different times
Straight diagonal line going down from y axis
Straight diagonal line going down from y axis
What’s the shape of a Concentration-Time graph of a 1st order reaction?
Curved line with diagonal gradient from y axis, reaching an asymptote near x axis
What’s the shape of a Rate-Concentration graph for a 0 order reaction?
Horizontal line from Y axis, as changing concentration doesn’t affect rate
What’s the shape of a Rate-Concentration graph for a 1st order reaction?
Positive gradient for y=x, through the origin
Rate is proportional to concentration
What’s the shape of a Rate-Concentration graph for a 2nd order reaction?
Positive curve going through the origin, Rate is proportional to concentration^2
How would you write the rate equation if A + B = C + D?
Rate (mol dm^-3 s^-1) = k x (A)^m x (B)^n k= rate constant m= order of reaction of A n = order of reaction of B (A)= concentration of A (B)= concentration of B
What is half life?
The time taken for half the reactant to be used up
What’s the half life for a first order reactant?
Constant, will always be the same amount of time for reactant to half
Meaning it’s half life can be read off it’s Conc-Time graph
How do you work out the rate constant of a first order reaction if you know it’s half life?
k = ln2 / half life Units = s^-1
What’s the half life for a second order reaction?
Not constant
What’s the rate determining step?
Is the slowest step in a multi step reaction, which determines the overall rate
Probably the first step in the multi-step reaction, and the orders show how many molecules of each there is
What’s the Arrhenius equation in ln form?
ln k = -Ea/Rt + ln A
How do you use ln form of equation to create a Arrhenius plot and find activation energy and the pre exponential factor?
Plotting ln K on y axis so ln K is substituted for y
Plotting 1/T on x axis so 1/T is substituted for x
y = mx + c
LnK = -Ea/R x + lnA
Creating a graph with a gradient of -Ea/R and a y intercept of lnA
Calculate the gradient and make it equal to -Ea/R then solve for Ea
Find the y intercept and make it equal to ln A and solve for A, or just put Ea into equation
(Make sure graph is well proportioned, doesn’t need to show Y intercept)
What’s the rule for finding Kc if reaction is heterogenous?
Only aqueous and gaseous reactants and products go into formula (water needs to go in it if the solvent isn’t aqueous)
How to use a table to work out equillibrium concentrations?
Draw your table with at top the chemical equation with column for each chemical
At side have initial concentration, conc change, and equillibrium concentration
Fill in table with everything you know, the products initial concentration will always be 0
Whatever the decrease is for the products to equillibrium concentration from initial, will be the increase for the products
Remember to take moles into account
How do you find the total pressure of a gas mixture?
It’s the sum of all the partial presures
How do you find the partial pressure of a gas?
First find mole fraction of the gas in the mixture using Number of moles of gas / total number of all moles of gas in mixture
The multiply the mole fraction of gas by the total pressure of the mixture
So if they have the same amount of moles in equation will have the same partial pressure
What’s the equation for Kp?
if aA(g) + bB(g) ⇋ cC(g) + dD(g)
Then Kp = p(C^c) x p(D^d) / p(A^a) x p(B^b)
Use the partial pressures instead of concentrations
Units are kPa
Which out of temperature, pressure, catalyst and changing concentrations effects Kc?
Only temperature
Describe the equilibrium set up by an acid reacting with a base in terms of conjugate pairs?
HA(acid) + B(base) ⇋ BH+(acid) + A-(base)
In forward reaction HA acts as acid as donates a proton to B
In reverse reaction A- acts as base to accept proton from BH+
HA and A- are a conjugate pairs, HA being conjugate acid and A- being conjugate base
B and BH+ are a conjugate pairs, BH+ being the conjugate acid, and B being conjugate base
Will have A1 and B2 on one side, and B1 and A2 on the other
numbers link them
Formula for pH if you know it’s H+ concentration?
pH = -log10 (H+)
If you know the pH of solution how do you find it’s H+ concentration?
(H+) = 10^-pH
What’s an important rule for monobasic acids or bases?
H+ concentration = Concentration of acid
OH- concentration = Concentration of base
How do you find the ionic product of water Kw?
Kw = (H+)(OH-)
If water is pure then ratio between them is 1:1, so Kw is the same as (H+)^2
What’s important about a weak acid?
Don’t fully ionise in solution so H+ conc isn’t the same as acid concentration
Also it’s concentration is the same at start and at equillibrium
Formula for Ka the acid dissociation constant?
Ka = ((H+) x (A-)) / (HA)
Or Ka = (H+)^2 / (HA)
(Ka units are moldm^-3)
Formula to find pKa?
pKa = -log10 Ka
Formula to find Ka when you know pKa?
Ka = 10^-pKa
What do acidic buffers contain?
A weak acid and it’s conjugate base
Eg CH3COOH(aq) ⇋ H+(aq) + CH3COO-(aq)
What are the 2 ways to form an acidic base?
Mix a weak acid with the salt of it’s conjugate base
Mix an excess of weak acid with a strong alkali
How do acidic buffers resist changes in pH?
If you add a small amount of acid the H+ ion increases,, meaning the position of equilibrium shifts to the left reducing H+ ion concentration. pH doesn’t change much
If Alkali is added OH- ion concentration increases, they react with H+ to form water, removing H+ ions from solution. Causing equilibrium to shift right so more CH3COOH dissociates, H+ ion concentration increases, pH doesn’t change much
What are the 2 buffer systems that occur in our blood?
H2CO3 ⇋ H+ + HCO3-
H2CO3 ⇋ H2O + CO2
How to calculate the pH of a buffer solution?
Assume that initial concentration of salt is the same the equilibrium value of A-
HA initial concentration is the same as it’s equilibrium concentration
Use and rearrange the Ka formula if necessary
So trying to solve for H+ as that is what tells us what can tell us what the pH is
What’s the vertical part of a pH plot?
The equivalence point
The point where the acid is neutralised and (OH-)=(H+)
Describe features f Methyl orange indicator?
Colour at low pH is red
Colour at high pH is yellow
Approx pH of colour change is between 3 and 4.5
So useful for strong acid/ strong base and strong acid/ weak base
Describe phenolphthallein?
Colour at low pH is colourless
Colour at high pH is pink
Approx pH of colour change is 8 to 10
So useful for strong acid/ strong base and weak acid/ strong base
Why can indicators be thought as weak acids?
They have differently coloured conjugate pairs, so as H+ or OH- concs change the equilibrium positions also do
phenolphthallein-H (colourless) ⇋ phenolphthallein-(pink) +H+
Methyl orange-H (red) ⇋ Methyl orange- (yellow) + H+
What is the standard lattice enthalpy?
The enthalpy change when one mole of an ionic lattice is formed from it’s gaseous ions under standard conditions (always exothermic)
How to draw a born haber cycle?
At the very bottom have the ionic lattice
Then above it have the elements of the ionic lattice in their standard states, with line going downwards showing energy change of formation
Then do the atomisation energy of each of the elements, the solids will go to gases, and any diatomic molecules will be come singular, the lines are going upwards
Do the ionisation energies of what was the metal, gives +1 charge to the metal gaseous ion and produces an electron, lines go up
Do the electron affinitys of the other element, decreasing it’s by 1 and removing an electron until you reach it’s gaseous ions, arrow may go up or down, look to see if value is positive or negative
Lattice enthalpy goes from ions to salt, so to calculate it work out value of all the other arrows going in the correct direction to the salt from the gaseous ions
How do you work out enthalpy change of solution if given the enthalpy change of hydration and lattice enthalpy?
Draw an arrow from the salt to it’s aqueous ions, this line is the enthalpy change of solution
Bellow it have the gaseous ions
Draw arrow from the gaseous ions to the salt, this is the lattice enthalpy
Then draw arrow from gaseous ions to aqueous ions,this is enthalpy change of hydration
Add hydration and lattice enthalpy to find the one of solution
What is entropy?
A measure of disorder of particles, the higher it is the more disordered the particles
Is effected by state and amount of molecules (in equations)
Has to be positive for a reaction to be feesible
How do you calculate entropy?
Entropy = Entropy of products - Entropy of reactants
So entropy has to increase during a reaction for it to be feesible
Formula for the free energy change ΔG?
ΔG = ΔH - TΔS
ΔH = enthalpy change (J mol^-1) T= temperature in Kelvin ΔS= entropy change in (J K^-1 mol^-1)
If positive, reaction isn’t feesible and can make equal 0 to work out when a reaction
How would you separate redox reactions into half equations?
Split it into a oxidation half equation (electrons are lost so on product side)
and a reduction half equation (electrons are gained so are on reactant side)
If trying to find an unknown half equation, can add H2O, H+ and e- to balance
The reactions that occur at each electrode are? And what is the standard notation?
Reversible
Always put e- on the reactant side
What do you use to know how easy a metal is to oxidise?
E⦵ value, the more negative it is the easy it is to oxidise
So the more negative E⦵value reaction goes backwards
And the more positive E⦵ goes forwards
How do you calculate the E⦵ value of a cell?
E⦵ = E⦵ of more positive side - E⦵ of more negative side
So E⦵ will always be positive
Standard electrode potential definition?
E⦵ of a half cell is the voltage measured under standard conditions when the half cell is connected to a standard hydrogen electrode (0.00v)
How to predict whether or not a chemical reaction will happen or not?
Write down both half equations with electrons on the standard left size
Look at the E⦵ value, the more positive one the reaction goes forwards (left to right)
The more negative one goes backwards (right to left)
Combine the 2 half equations remembering to multiply if uneven amount of electrons
Check to see if the combination of half equations matches what has been asked in the question
If it does then it’s feasible, if doesn’t match it’s not
Explain changes that may occur in a E⦵ cell prediction if conditions are not standard?
If you increase the concentration of Zn(2+) equillibrium shifts left, reducing the ease of electron loss, so the electrode potential of Zn/Zn(2+) becomes less negative and the whole cell potential will be lower
If you increase the concentration of Cu(2+), the equillibrium will shift right, increasing the ease of electron gain, the electrode potential of Cu(2+)Cu becomes more positive and the whole cell potential becomes higher
Describe how fuel cells generate electricity?
At the anode the platinum catalyst splits the H2 into protons and electrons (H2 = 2e- +2H(+))
The polymer electrolyte membrane only allows the H+ across and forces the e- to travel around the whole circuit to get to the cathode
An electric current is created in the circuit, which is used to power something
At the Cathode, O2 combines with the H+ from the anode and the e- from the circuit, to form H2O which is the only waste product
What are the 2 half equations for the redox titration of Acidified Potassium manganate oxidising Fe(2+) to Fe(3+) and the colour change and what does this titration tell us?
5Fe(3+)
Once the reaction has finished will see a colour change from purple to colourless as MnO4(-) is pink and {Mn(H2O)6}(2+) is colourless
How much Oxidising agent we need to reduce the species
MY OCTPUS 8 HIS 5 EARS “MUNCH” 4 HIPPOS 5 FISH, 5 FERRETS AND 5 EARS
What are the 2 half equations for Potassium dichromate solution K2Cr2O7 oxidising Zn to Zn(2+) and the colour change and what does this titration tell us?
Cr2O7(2-) + 14H+ + 6e- = 2Cr(3+) + 7H2O
3Zn = 3Zn(2+) +6e-
So equals Cr2O7(2-) + 14H+ + 3Zn = 2Cr(3+) + 7H2O + 3Zn(2+)
Colour change when reaction is finished will be orange to green as Cr2O7(2-) is orange and {Cr(H2O)6}(3+) looks green
How much Oxidising agent we need to reduce the species
All the steps and equations for a sodium thiosulfate titration to find the concentration of an oxidising agent?
Use a certain volume Potassium Iodate solution to oxidise an excess of KI
IO3(-) + 5I(-) + 6H+ = 3I2 + 3H2O
Find out how many moles of iodine have been produced, by titrating the resulting solution with a known concentration of Sodium Thiosulfate (Na2S2O3), when the solution goes pale yellow showing it’s near to the end point, add starch solution, which will show that Iodine is still present by being blue/black, will know reaction is finished when blue/black dissapears
I2 + 2S2O3(2-) = 2I- + S4O6(2-)
Find the moles of Iodine from second equation, then input it into first equation to find moles of oxidising agent ( divide by 3) and then can find concentration
Definition of a transistion element?
A d block element, that can form at least one stable ion with an incomplete d sub shell
So scandium and Zinc aren’t transition elements
Which transition elements are exceptions to the electron configuration filling up rules?
Chromium- prefers to have one electron in each orbital of the 3d subshell and just one in the 4s subshell, makes it more stable
Copper- prefers to have a full 3d subshell, and only one electron in the 4s subshell
What happens when you mix Copper(II) with NH3 (including equations)?
Cu2(+) + 2OH- = Cu(OH)2 goes from pale blue solution to a pale blue precipitate
OH is there as NH3 is a weak alkali
Then in excess NH3,Cu(OH)2 dissolves to form {Cu(NH3)4(H2O)2}2+ which is a dark blue colour
So the reaction is 4NH3 + {Cu(H20)6}2+ = (reversible) {Cu(NH3)4(H20)2}(2+) + 4H2O
What happens when you mix Iron(II) with NH3 (including equations)?
Fe(2+) + 2OH- = Fe(OH)2 pale green solution to a green precipitate, OH there as NH3 is a weak alkali
What happens when you mix Iron(III) with NH3 (including equations)?
Fe3+ + 3OH- = Fe(OH)3 goes from yellow solution to an orange precipitate, OH there as NH3 is a weak acid
What happens when you mix Manganese (II) with NH3 (including equations)?
Mn(2+) + 2OH- = Mn(OH)2 goes from pale pink solution to a light brown precipitate
What happens when you mix Chromium (III) with NH3 (including equations)?
Cr(3+) + 3OH- = Cr(OH)3 goes from a purple solution to a grey-green precipitate
Then in excess NH3, Cr(OH)3 dissolves to form {Cr(NH3)6}(3 +)which is a purple solution
So the equation is {Cr(H2O)6} + 6NH3 =(reversible) {Cr(NH3)6}(3+) + 6H20
What’s a complex ion?
A metal ion surrounded by coordinately (dative bond, both electrons are from the same atom) bonded ligands
When can optical ismomerism occur in complex ions?
Occurs when an ion can exist in 2 non-superimposable mirror images (don’t match each other when put on top of each other)
So occurs when in octahedral complexes, when 3 biodentate ligands are attached to the central ion
Draw by reflecting in a mirror line
How can cis-trans isomerism occur in complex ions?
When there’s only 2 different groups involved
The Cis isomers have the same groups on the same side (so are close together as they can be)
Trans have the same groups on opposite side
What is Cis platin?
A complex of platinum(II), with 2 chloride ions and 2 ammonia molecules in a square planar shape
Treats cancer by chloride ligands being displaced, binds to cancerous cell DNA (at Nitrogens) stops it reproducing, can’t fix damage, dies
To prove if a reactant is first or second order from a graph need to?
Work out the half life, and show it;s constant or not constant
What type of brackets should be used in Kp?
Not square
