AQA AS Chemistry Paper 1 2018 Unofficial Mark Scheme

Original post by nyxnko_

Other way around. Na has few protons than F so it has a smaller nuclear charge.
They don't have the same number of electrons but they do have the same number of orbitals and because F has a bigger nuclear charge, it pulls these orbitals closer so that F has a smaller atomic radius.

But Fs proton number is 9 and Nas is 11, I’m so confused?!😬

Reply 22

HR77

My one personally was so bad . Looking at these answers make me even more stressful . Does anyone think that the grade boundaries will go down??

Reply 23

nyxnko_

OP

20

Original post by Clarareeves2001

But Fs proton number is 9 and Nas is 11, I’m so confused?!😬

Sorry, I edited my reply so you must not have seen that yet :colondollar:

I got that q wrong..

Reply 24

hannah.moonlight

2

Original post by Clarareeves2001

The last question about the effect of lone pairs on bond angles was to do with lone pair lone pair repulsion being threaten than lone pair bonding pair repulsion so it would decrease the angle in a tetrahedral to 104.5 (bent)

i asked my chemistry teacher and he said it was linear 120

Reply 25

jelwyn

3

Original post by HR77

My one personally was so bad . Looking at these answers make me even more stressful . Does anyone think that the grade boundaries will go down??

dude same
i guess since last year you needed 50/80 for an A it would be somewhat similar to that.
i personally found it difficult. don't sweat it since if enough people found it hard grade boundaries would be like 47/80 for an A

Reply 26

can you add the marks to questions
any any predictions on grade boundaries

Reply 27

SaraFreire14

3

Original post by nyxnko_

Disclaimer: These are my own answers and I have no idea whether they are right or not. I also can’t remember the order of the questions very well. Please bear with me.

Thank you to: @Clarareeves2001, @Vanilla Twilight

1))
I said that there is a positive nucleus in the atomic model but the plum pudding model suggests that the entire atom is positive. I also said that electrons surround the nucleus in orbitals/shells in the atomic model whereas the plum pudding model states that the electrons are dotted within the atom.
Can’t remember the next part.
R was nitrogen. I think it was Be2N3?

2))
1210ppm
Something along the lines of 2300ppm
I think 0.831-ish kg?
Were there any more parts?

3))
Can’t remember

4))
6-mark q
I think most people will have missed the fact that they were solid samples. You had to add water to make them aqueous.
Carbonate: Add HCl and observe fizzing
Na2CO3 (aq) + 2HCl (aq) —> CO2 (g) + 2NaCl (aq) + H2O (aq)
Fluoride and Chloride: Add acidified AgNO3. DO NOT ACIDIFY WITH HCl, white ppt formed with chloride, no ppt formed with fluoride
AgNO3 (aq) + NaF (aq) —> AgF (aq) + NaNO3 (aq)
AgNO3 (aq) + NaCl (aq) —> AgCl (s) + NaNO3 (aq)

5)) 6)) 7)) 8)) 9))
Can’t remember the specific order

Equilibria q:
3 minutes. b/c equilibrium is when rate of forward and backward reactions are the same so the concentrations of the reactants and products is CONSTANT.
T2 was higher because eqm shifted right, and because it was an endothermic reaction, it shifted right to lower the temperature, meaning the temperature must have increased from T1

Mass spec q:
time: 6 point something times 10^-4. It was of the same order as the time for the 79Br+ ion.
It’s detected because the ions hit a negative plate that gives the ions electrons. The number of electrons given corresponds to relative abundance of that ion.

The Syringe q:
Mr was like 74/5-ish?
The Mr would be bigger because the volume of gas would have decreased so no. of moles would decrease but the mass would be greater so overall, the Mr would be bigger than actual.

Bonds q:
KrF2 was supposedly linear. Bond angle: 180 Drawn with 2 bond pairs and 3 lone pairs. (I put down trigonal bipyramidal and bond angle: 86, which is wrong but I can hope they'll 'accept' or 'condone' it :tongue:

)
Can’t remember exact q but it was something about a V-shaped molecule and you had to say something about the lone pairs and that the angle would be reduced to 104.5

The Hydrated Salt q:
x was 5.68
Can't remember the next bit...

A q about Intermolecular forces in SiF4..
Should have been van der Waals b/c although Si-F bond is polar, SiF4 is a symmetrical molecule so polar charges cancel.

A q about Atom Sizes:
Na is smaller than F because it has a larger nuclear charge. They have the same number of electrons so they have the same orbitals but b/c Na has a larger nuclear charge, it pulls the electrons closer to the nucleus so that the atomic radius of Na is smaller.

chlorine q: Cl2 + H2O —> HCl + HClOOxidation half-eq: Cl2 + 2H2O —> 2HClO + 2H⁺ + 2e^-Reduction half-eq: Cl2 + 2H⁺ + 2e^- —> 2HCl There was a next part but I can't remember it

Yeah, I can’t remember them very well but if anyone does remember anything, please comment below.

For the first question wasn't it Be3N2? Honestly im not to sure with that paper ://

Reply 28

u missed the question on what could be improved with hydrated salt i said add lid prevents mass escaping probs wrong

Reply 29

Clarareeves2001

Original post by mathsguy5503

u missed the question on what could be improved with hydrated salt i said add lid prevents mass escaping probs wrong

I said heat for longer time cos was only heated for 1 minute so may not have been completely dehydrated, not sure if that’s right tho

Reply 30

Original post by mathsguy5503

u missed the question on what could be improved with hydrated salt i said add lid prevents mass escaping probs wrong

It was heat to a constant mass; so u continue to heat until the sample’s mass is no longer decreasing as This means water has evaporated

Reply 31

Also did anyone else get -2 Kj mol^-1 for the Change in Enthalpy because that’s what I got and I feel like it’s wrong

Reply 32

Original post by 12tastani

It was heat to a constant mass; so u continue to heat until the sample’s mass is no longer decreasing as This means water has evaporated

Spoiler

Reply 33

Vanilla Twilight

13

Original post by Chloet5827

Yeah

can you remember any of the multiple choice I think we should put some answers together for those now :smile:

Can't remember any of them sadly

Reply 34

i mean but if you dont have a lid woudnt some of your solid escape :frown:

Reply 35

Original post by mathsguy5503

Spoiler

That’s unlikely because the solid would have had a much higher mp/bp as it is soluble in water; not to mention water boils at very low temp (373 K)

But don’t rely on this being the only answer I might be wrong

Reply 36

well then i probs about 30 marks maybe even 20 who knows chemistry was a nightmare this year

Reply 37

username2912782

13

On the Mr question it asked what the definition of relative molecular mass is (in the same part of the question that asked you the 74 bit)

Reply 38

idk because on chem revise it said what you also said but what i also said about the lid

Reply 39