AQA AS Chemistry Paper 1 2018 Unofficial Mark Scheme

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I thought it was that Na was smaller because even though there was the same number of electrons, Na has a higher nuclear charge, meaning he attraction is higher, lowering the atomic radius

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, @SaraFreire14, @mathsguy5503, @MissMilkshake. Huge thanks to @Cirsium for the MCQs.

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 Be3N2 or something like that...?

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 )
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
The next bit asked why the calculated value was less than 10. It was b/c not all of the water would have evaporated from the salt so you had to heat for longer.

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 + HClO
Oxidation 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

MCQs:
10. Ammonium chloride contains all three kinds of bonding (covalent between N and three H, dative between NH3 and the 4th H and ionic between the ammonium ion and the chloride ion)
11. 6g of N gas is 0.429 mol of atoms, each with 7 protons. So 0.429 x 7 x Avo = 1.8 x 10^24
12. Melting point? Cos atomic radius consistently goes down, electronegativity consistently goes up, and first ionisation energy would have dips for Al and S
13. Haven't got enough Fluorine for all the nitrogen to react. Fluorine decreases from 60cm3 to 0. 2/3 of the Nitrogen will react so from 30cm3 to 10cm3. The reaction will make 2/3 of the amount of NF3 as fluorine, so 40cm3. So the total final volume will be 50.
14. Magnesium is used to reduce TiCl4
15. Barium sulfate is insoluble so you can use it for X-rays of intestines etc
16. H2SO4 acts as an oxidising agent. (Br ions aren't reduced: ox state goes from -1 to 0; there's no hydrogen bromide formed - though there would be HF or HCl made if it were sodium fluoride or sodium chloride; and there's no hydrogen sulfid formed)
17. Magnesium hydroxide is taken for indigestion
18. Phosphorus has the highest 1st IE (dips for Al becaus of 3p and sulf because of pairing electrons)
19. 150g of ammonia is 150/17=8.824 mol. Then double it cos it's in 500cm3
20. Invert the volumetric flask (ensure your solution is homogenous)
21. Rinse the conical flask with water: you'll still have the same number of mols of H+ in the flask when you put your acid in and no leftovers
22. Improve uncertainty by using less concentrated alkali in burette
23. Gloves for battery acid
24. Red to yellow

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

Hi do you have any places you can tell me to revise from? You seem to know certain small facts that help your understanding but I have no idea where to get this knowledge from, my base knowledge needed to understand the subject well is not good - any tips on strengthening the foundations of my understanding? In general - what do you use to revise? Thanks

there is a increas in shelding

that's true regarding the fact that its a na + ion