what was learnt due to AS past papers chemistry

What to do when comparing the size of atoms

Look at the electron configuration but also the number of protons as more protons (with the same electron configuration as other atom) means smaller atom as more protons attract outer electrons closer

Metal carbonate add acid word equation

Metal carbonate and acid = salt and water and carbon dioxide

Concentrations in equilibrium

Constant not equal

How to form oxidation/reduction half equations

Identify the change (only put all the reactants and the specific product), balance the oxygen, then hydrogen, then charge

Relative formula mass

The ratio of the average mass of one formula unit of a compound to 1/12th of the mass of an atom of carbon-12.

Remember to look for

Molar ratios

Visible change when iodide ions are oxidised to aqueous iodide (I2)

Forms a brown solution/black ppt

Visible change when bromide ions are oxidised to aqueous iodide (Br2)

Orange solution

Visible change when chloride ions are oxidised to aqueous iodide (Cl2)

Pale green/yellow bubbles/gas

Change in enthalpy equation, and about it

Products - reactants, doesn’t matter if of formation or combustion as this is for enthalpy in general, on,y use other formulae if about bond enthalpy

Equation for mass and the units (no moles)

Mass(g) = Mr/avogadros constant

How to fund the gas of a mixture after a reaction at constant temp and pressure

Find balanced equation and molar ratio, find limiting reagent, use the limiting reagent to find how much reacted, carry on calculations

Trend of first ionisation energies

Increases from LHS to RHS

What can you dilute and not dilute in a titration

Can dilute conical flask but not pipettes

Equation for percentage uncertainty, and how to affect it

(Uncertainty of apparatus/measured value)x100, so to reduce percentage uncertainty, want to increase the titre volume and have a larger denominator

Percentage uncertainty and indicators

Using a different indicator won’t affect the percentage uncertainty as it doesn’t affect the maths, only how easy it is to read

how hydrogen bonding is formed

Dipoles form on the same molecule, on one covalent bond, there is an available lone pair on the F/O/N atom, intermolecular hydrogen bonding forms

Strength of intermolecular forces

Van der waals are not stronger than dipole dipoles, but they can be depending on size and shape of the molecule you are comparing (in a symmetrical molecule, the dipoles cancel)

Where are van der waals

Between all molecules

How does a catalyst affect rate/yield

Increases the rate of the forward and backwards reaction equally

Amount of substance questions about equilibrium mixtures - what to do and what to be aware of

May not need RICE tables, just use the Kc equation, and remember to use powers when substituting, be aware if the molar ratio is accounted for or not

When to use molar ratios

Initial values and one equilibrium value, stoichiometry (how much of x is needed to make y moles of z?)

When not to use molar ratios

Values at equilibrium

Equation for reverse Kc and the units

Reverse Kc = 1/Kc, and flip the units

Test for ammonium ion and why the first step

Add NaOH and warm, hold damp red litmus paper at the mouth of the tube and it turns blue, must add NaOH to release the gas being tested

Formula of ammonium ion

NH4+

What to look at for unpaired electron questions

Electron configuration, compare to Hund’s rule

First ionisation energy - what to take until account when deciding stability

Hund’s rule (look for unpaired electrons), electron repulsion (not if full outer shell, even though there is some), the number of shells and how many electrons in them

What to do when looking for coordinate bonds

Draw it out and be careful of ions (the charges link to the number of electrons)

What materials can carry charge and why

Ionic compound (when molten), metallic bonding (sea of delocalised electrons), graphite (delocalised electrons)

What happens to lone pairs in a compound

Lone pairs of electrons are fixed in a compound, and they won’t move to conduct heat or electricity they can only move in reactions

Halide ions as reducing agents with an example

Halide ions increase in their ability as reducing agents as you go down the group, so bromide ions are weaker reducing agents than iodide ions so will not reduce iodine

Chloride ions vs sulfuric acid

Chloride ions are not strong enough reducing agents to reduce sulfuric acid

Independent variable

What changed in the experiment

Dependant variable

What is measures as an outcome

In a question about the rates of reaction from an experiment, how to calculate the temperatures

Measure the temp at the start and end of the reaction and find the mean

Rate of reaction graphs - why a small increase in temp causes a large increase in the rate of reaction

Because many more particles will have energy equal to or greater than the activation energy, therefore there is a greater frequency of successful collisions

Position isomers

Molecules with the same molecular formula but with the functional group attached to a different carbon atom on the same carbon skeleton

E/Z isomerism eligibility

For a molecule to exhibit E/Z (cis-trans) isomerism, each carbon atom in the double bond must be attached to two different groups

Is asked for x isomer of y, what can you not do

Cannot write y, as they want a different version of y, not the original

Chain isomers

Molecules with the same molecular formula but a different arrangement of the carbon skeleton

What to do when drawing chain isomers

Keep the functional groups the same - keep the C=C in the same place

What isomer is it when there is a change of carbon skeleton (branching)

Chain

What isomer is it when there is a change of double bond position

Position

What isomer is it when there is a change of the double bond to a ring (e.g. cyclohexane)

Functional group

Functional group isomer

Molecules with the same molecular formula but with atoms arranged to give different functional groups

Structural isomers

Molecules with the same molecular formula but a different structural formula

Equation for percentage yield

Percentage yield = (actual yield/theoretical yield)x100

The termination step - what to write

Not always just chlorines, need to decide what two radical to react together to get the desired product, it is always two radicals form a non radical

Carbons in complete combustion

In complete combustion, every carbon atom in the fuel molecule turns into one molecule of CO2 (e.g. C3H6O will form 3CO2)

What is q, and the units

The heat energy transferred, in Joules (J)

What is deltaH, and what can it represent

Change in enthalpy, can represent combustion/formation

What to make sure you do when writing out mechanism

Show every step with charges, lone pairs, and curly arrows, don’t skip the middle step

Unsaturated - type and formula

Alkene, CnH2n

Addition polymers

Formed from monomers with C=C double bonds

Process of addition polymers

Double bond opens up to link with the next monomer

Product(s) of addition polymers

The polymer us the only product - 100% atom economy

Example of addition polymers

Poly(ethene), poly(propene), PVC

Condensation polymers

Formed from monomers with two different functional groups

Process of condensation polymers

Monomers join and a small molecule (usually water or HCl) is released at each link

Product(s) of condensation polymers

You get two products, the polymer and the small molecule

Examples of condensation polymers

Polyester (Terylene) and polyamides (Nylon and proteins)

‘Total amount at equilibrium’ meaning

Amount of products AND reactants

Does this reaction result in a change in the shape around a carbon atom: substitution

Almost never

Does this reaction result in a change in the shape around a carbon atom: Addition

Almost always

Does this reaction result in a change in the shape around a carbon atom: Combustion

Always - for both types

Does this reaction result in a change in the shape around a carbon atom: Oxidation

Usually

Does this reaction result in a change in the shape around a carbon atom: Reduction

Usually

Does this reaction result in a change in the shape around a carbon atom: Elimination

Always

What is a product of complete combustion

CO2

‘In excess’ meaning with combustion

Complete combustion

How are ketones produced and what happens

By the oxidation of secondary alcohols, the hydroxyl group (OH) is converted into s carbonyl group (=O) at the same carbon position

What type of reaction is alcohol + acidified potassium dichromate

Oxidation

When does an alcohol form a mixture of alkenes when dehydrated

If the alcohol is unsymmetrical around the carbon atom attached to the (OH) group