UNOFFICIAL MARK SCHEME - AQA AS Chemistry 13/01/2012 (UPDATED)

Don't worry about it - I go to a really good school with people who got 6A* - 11 A*s in their GCSE's and they came out of the chemistry exam with their hands on their faces

don't worry, I imagine a lot of people will be resitting, and by the time you've done CHEM2, CHEM1 will seems like a breeze...or so I'm told

Join da club

Looks a bit like the Fibonacci sequence without the 1 at the beginning.. Could it just be?!

Heptane has 8 isomers, octane has 13 oh the joys of mathematics!

Oi, don't be stealing my credit yeh!

That's my beautiful mathematical mind that figured that out

Sorry, I'm almost as bad as 'Buttercup'

Sorry, I'm almost as bad as 'Buttercup'

Where was the question where you had to write the equation for the first ionisation of Krypton????? Ie which number???

Dead. If you think editing a UNOFFICIAL mark scheme, is wrong, why you even reading it? Since, its so morally wrong and I should go spiritually replenish my soul.

It was part of the very last question.

**** there goes my 100UMS I'm retaking.
For those thinking I'm a cock for wanting 100UMS in chemistry it's because I want to do it as a degree at Uni :P
****ed up on the first question. Arghhh.

This is a prediction I have adapted and changed, so don't panic if your questions vary and questions are not in right order but I ensure you the marks are all there, if not this is all from memory remember, play nice and enjoy
[*] - Indicated my side comments

1) State this bond & How it is formed;
Covalent bond (1 mark) Shaped pair of electrons *between non-metal atoms (1 mark)

2) Shapes of Molecules questions;
- BF3 (should resemble a trigonal planar shape, incorporated with two lone pairs) (1 mark)
- Angle *There is debate with this so these are what most people have said
- 120 (115-120) OR 90 (85-90) (1 mark)

- BrF4 (Should resemble Square Planar Shape, incorporated with two lone pairs) (1 mark)
- Angle: 90 (1 mark)

3) Why does KbrF4 have a higher melting point?, explain in terms of bonding.
*Therefore including structure wouldn’t gain/loose any marks if added
- Ionic bonding (1 mark) electrostatic forces/attraction between oppositely charged ions (1 marks) require a lot of energy to overcome (1 mark)

4) Volume question, to be converted from cm3 to dm3 NOT m3
PV = nRT or V = nRT/P (1 mark)
Correctly changing 101kpa to 101,000 pa (1 mark) (however you may also need to correctl have converted the volumes to dm3, to get this mark)
Answer is 0.0175 (1 marks)
*Myself and others put 0.0260, and I can hapilly admit that is wrong people, since we had to convert it to dm3 and we made it to m3 which is usually asked. However, you get marks for working out, so all is not wrong

. Calculation questions for Volume of Nitric acid = 0.0524 dm3

*my working out:
8.14 / 207.2 = 0.0393
Then to get moles of n02 you times by 8/3 (due to 3:8 ratio)
so 0.0393 x 8/3 = 0.1048 moles of n02 ( 2 marks - for correct working out)

then 0.1048/ 2.00 (conc) to get volumes = 0.0524 dm3 (1 mark for correct answer and unit)

5) Which element in group 2, has the largest atomic radius?
- Lithium (1 mark)
*I assure you, they did not ask why or why there was a trend, ignore any unofficial mark scheme which say so.

6) How would HCL be labelled?
Irritant/Corrosive/Toxic (1 mark)

7) Electron Configuration; 1s2 2s2 2p6
. (N) 3- (1 mark)
. (F) - (1 mark)

*I also included the proton number/atomic number, if you also did so I highly doubt they will penalise marks for addition information, as long as it does not contradict.

. Why does Fluorine have a low melting Point?
Simple Molecular ( 1 mark)
Weak van de Waals forces between molecules


8).Name/State Formulae for Lithium Nitride
Li3N (1 mark)

. Calcium Nitride Empirical Formulae
Correctly stating percentage of Nitrogen (1 mark)
Correct method used ( 1 mark)
Ca3n2 (1 mark)

9) Balance Equation for Lead Nitrate
2___ + 2___ -----> 4___ + 1___
* You did not need to include 1 in front of the 02 at the end as this goes without saying.

10) Sulphur Compounds impact on Environment?
- (Contributed to) Acid Rain (1 mark)

11) Equation to show how CO & NO is removed in a Catalytic Converter
2NO + 2CO -> N2 + 2CO2 ( 1 mark)

12) Equation to show how Si3N4 is formed (1 mark)

3Si + 2N2 -> 3SiN4
OR
1/5 Si2+ N4 --> Si3N4
*There is debate in this however multiples are definitely allowed.


13) Atom Economy Question
Correct method (2 marks)
Correct Answer 76.4% (1 mark)
* Cant remember to what decimal place but it 76.??

14) Why does Carbon have a high melting point?
Macromolecular (1 mark)
Each carbon is covalently bonded to four other carbons (making a tetrahedral shake), networking throughout structure (1 mark)
Strong Covalent bonds ( 1 mark)
Alot of energy is required to overcome/break bonds (1 mark)

15) Completing Graph for Nitrogen
Nitrogen should be plotted with an X, lower than all other elements but NOT on 0.
( 1 mark)

16) What raw material is Hexane Obtained from?
Crude Oil ( 1 mark)

17)
. What substance/material would be used to remove Sulphur
CaO (Calcium Oxide) or CaCO3 (Limstone) ( 1 mark)
. Why is this used?
If you used CaO - It neutralised acid in Sulphur impurity (there is debate for this, I didnt personally use Ca0 so cannot give judgement) (1 mark)
. If used CaCO3 - Limestone can be easily accessed/high in abundance/ there is high supply (1 mark)

18) Draw how H-F molecules interact..
Partial Charges correctly indicated (1 mark)
3 Lone pairs of Fluoride ( 1 mark)
Hydrogen Bond (- - - -) Between Delta Plus H and Delta Minus F on different molecules ( 1 mark)

19) Which type of Cracking produces high % of Alkenes?
- Thermal Cracking ( 1 mark)
State conditions required
- High Temperate and Pressure ( 1 mark)
*You could also gain these marks if you said the actual temperature and pressure required

20) State why Zeolite/Catalyst is used in Catalytic converters
- (Extremely) Large surface area for reaction to take place (1 mark)

21) How many isomers does Hexane have
5 (1 mark)

22) Name the Compound shown
2,2-dichloro-3-methlypentane

.Type of Isomer shown?
Chain Isomerism/Isomer ( 1 mark)

23) Empirical forum ale for compound
C3H6CL (1 mark)

24) How is Krypton Ionised
Electron Gun (1 mark)
bombards/hits Krpton Sample ( 1 mark)
Knocking off electrons forming possitive ions/1+ ions/2+ions ( 1 marks)

25) Ar of Krpton
For correct method (2 marks)
Correct answer to one decimal place 84.0 (1 mark)

26) Equation for 1st IE of Krypton.

Kr(g) + e- -> Kr+(g) + 2e-

Or

Kr(g) -> Kr+(g) + e-

For correct state symbols (1 mark)
for Correct equation (1 mark)

27) Which element deviates from Period 2, general trend, from Li to N
Boron (1 mark)
*If you said Oxygen this would be wrong since they've given you a boundary of from Lithium to Nitrogen

.Explain why
Outer electron is 2p Orbital, Higher energy level than Be in 2s ( 1 mark)
More shielding (as more inner main energy shells) (1 mark)

28) Processed used to obtain Hexane from Crude Oil
Fractional Distillation ( 1 mark)

29) Why it is not possible to get pure N0 on its own? (1 mark)
*There is debate with this answer; I have been suggested the most and make the most logical sense

- NO reacts with water (vapour) in air to form H2N03 (Nitric Acid)
OR
-

(- The reason why 'N0 escpaing into air' wont be accepted is because, you havent explained how that makes it impure? If the question was why can N0 not be 100% obtained/collected which is the next question then that answer would would but its talking about purity.)

. Why is it not possible to get 100% yield of N0 (1 mark)
- Not high enough Temperature/Pressure for Lead Nitrate to completely decompose
- N0 make escape into air, due to being a gas

30) Explain peak at 42
- (When Krpton sample ionised) a 2+ ion charge/double charged ion was created ( 1 mark)

I thought the standard unit you always have to use in the ideal gas equation was m^3.

And on chemguide, it says '

Volume, V

This is the most likely place for you to go wrong when you use this equation. That's because the SI unit of volume is the cubic metre, m3 - not cm3 or dm3.

1 m3 = 1000 dm3 = 1,000,000 cm3'

I've lost 3/4 marks definately. Probably more from careless answering and silly mistakes. I'm happy now!

Yes it is, but the question asked for it in Dm3, which is where we all went wrong, including myself since our mind were telling us m3.

but dont worry you get marks, as ive already stated in my mark scheme
for PV = nRT and changing Kpa to PA