Year 12s: what will be the first way you research your future options? >>

Chemistry iGCSE AQA unofficial mark scheme (part of)

Heya, not sure how much I can remember/ what question numbers things were, so if you have anything to add please say and I'll write up a full one :smile:

Question 1:

Water and oxygen are needed for rusting to occur.

Zinc on ships is sacrificial protection.

It works because zinc reacts with water and oxygen instead of iron.

Question 7 :frown:

6 marks)

Electricity is passed through so sodium chloride and water form ions. Sodium is more reactive than hydrogen so remains in solution, hydrogen is reduced and forms hydrogen atoms, chloride is a halide so is oxidised and given off at atoms and OH- stays in solution, then Na+ and OH- bond because they're oppositely charged and they form a solution as there is still water there.

Question 8:

A catalyst provides AN ALTERNATIVE PATHWAY for the reaction with A LOWER ACTIVATION ENERGY.

H H
| |
- C - C -
| |
H ?? n

I can't remember what ?? was, and the bonds on the left and right go outside the brackets, and the n outside the brackets.

Some random ones that I remember:

Magnesium and fluorine bond by magnesium giving one electron to one fluorine and another electron to another fluorine (from the outer shell) so they're all stable.

Ionic compounds have high boiling points because there are strong electrostatic forces of attraction between oppositely charged ions that take a lot of energy to overcome.

Hydrogen and Chlorine bond by covalent bonding, they share a pair of electrons (from outer shell) giving them full outer shells.

Potassium is more reactive than lithium because it has more energy levels, so the electron that it needs to lose on the outer shell is further away from the nucleus, so it less strongly attracted to the nucleus, meaning it is more easily lost in bonding.

I think that's all I can remember, if anyone remembers any more answers, or questions but not the answers, just say and I can answer them :smile:

Hope it went well for everyone! I will be doing the same for igcse aqa physics next week, and all science paper 2s, so look out for those! (I will also answer any maths or science related GCSE questions)

Reply 1

Monideep

what did you get for the equilibrium questions?

Reply 2

alirs

I talked to my friends and I got them the wrong way round lol. Other than that it was pretty easy

Reply 3

Monideep

Original post by alirs

I talked to my friends and I got them the wrong way round lol. Other than that it was pretty easy

DOes it shift to the right or left?

Reply 4

alirs

for the pressure one: right (i think, this topic and energy is the hardest topic for me) I didn't revise it enough. Paper 2 is gonna be hard, titrations plus all the boring shiz like chromatography

Reply 5

Salain

The colour one, equilibrium shifts to the right because at higher temperatures it favours the endothermic reaction ( the enthalpy change for the forward reaction was positive)

For The pressure one, equilibrium shifts to the left because there are fewer moles on the left hand side of the equation than the right.

Trends in boiling points of alkanes - weak intermolecular forces which get stronger with increasing size of the molecule and hence the boiling point increases from methane to hexane

Reply 6

chessmaster123

Pressure decreased for this one I believe so equilibrium shifts to the right due to more moles of gas

Reply 7

kart1400

Yes I totally agree. Decreasing pressure favours the direction of reaction producing the most moles so for that question it has to be the right hand side.

Reply 8

Salain

Original post by chessmaster123

Pressure decreased for this one I believe so equilibrium shifts to the right due to more moles of gas

Original post by kart1400

Yes I totally agree. Decreasing pressure favours the direction of reaction producing the most moles so for that question it has to be the right hand side.

Yep you are correct, I forgot the question was for decrease in pressure rather than increase, in which case yes it's the opposite shift. I was recalling it from memory after seeing the paper at a glance (I'm a chemistry teacher).