UNOFFICIAL MARK SCHEME C2 AQA 25th May 2011

Poll

what mark do you think you got out of 45?

Rose.1994

going to start a mark scheme, as I think it will be useful

1. question about nanoparticles and socks
a. silver kills bacteria (1 mark)
b. nanoparticles are very small compared to normal sized particles (1 mark)
c. nanoparticles have a larger surface area to volume ratio (1 mark)
d. if the silver is trapped then it is less likely to escape and therefore will not go into rivers and kill fish (2 marks)

2a. they are gases, so can escape easily (1 mark)
b. 80 (1 mark)
c. 80% (2 marks?)
d. 3.2g (1 mark)
e. 3.3 recurring (1 mark)
f. make it more precise by measuring to 2 decimal places rather than 1 decimal place (1 mark)
g. errors in measurements: (add answers for this) (2 marks)
- not all reactants converted to products
- some of the copper was lost/ not extracted
- it was not heated for long enough
-Errors in weighing the copper.
-Weighed the copper before the reaction had finished/been completed.
- an anomalous result

3. the reaction is faster when the temperature is increased as particles gain energy which means they can move faster, this means that collisions of particles are with more force and more collisions are successful (2 marks)
b. increase the concentration of the sulfuric acid
OR
use a catalyst (in order to make the reaction quicker )
OR
increase the pressure
OR
increase the surface area of the rock (1 mark)

4a. electrons (1 mark)
ions (1 mark)
b. copper (1 mark)
ii. it is the least reactive positive ion, so will not react on the way to the electrode and it is the positive electrons that will be attracted to the negative electrode as opposite charges attract ( 2 marks)
c. the chloride is oxidised as it has lost electrons (1 mark)
d. equation : 2H2+2e- = H2 (2 marks)

5a. an exothermic reaction is one which gives out heat (1 mark)
b. activation energy (1 mark)
c. diagram. both shells complete. 2-8 (1 mark)
d. ion bonds are held together strongly due to the electrostatic bondings, the ions are attracted together, the positive ions are attracted to the negative ions (1 mark)

diagram: a circle and cross at each link with the hydrogen and 4 extra crosses on the other element (1 mark)
balanced equation : 4 (1 mark)
low boiling point because the intermolecular forces between the bonds are very weak and therefore not a lot of energy is required to break the bonds. (2 marks)

Empirical formula : Pb3O4 (4 marks, 3 marks obtained from working)

LAST QUESTION : ai) hydrogen is obtained from natural gas (1 mark)
aii) nitrogen obtained from the air (1 mark)
b) 450 degrees used as the forward reaction is exothermic, so greater yield at lower temperatures, however decreasing the temperature means a slower rate of reaction so 450 is a compromise between a greater yield and the rate of reaction, (3 marks)
c) mine would have shut down as they made the fertiliser sodium nitrate but the haber process makes ammonia which can be made into the fertliser ammonium nitrate. This is a cheaper and quicker method, and takes place all over the world so people do not need the sodium nitrate anymore
ammonia is certain to be made, sodium nitrate is less reliable (2 marks)

the one about which acid would be used : nitric (1 mark) (sorry cant remember where that goes)
actually cant remember the questions so if you guys remind me then I will add them, also I know that the answers I have put so far may not be accurate so feel free to question me

(edited 12 years ago)

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Reply 1

Blob2491

f) not all reactants converted to product
some of the copper was lost/not extracted

Reply 2

Rose.1994

cheers, have added them
can you remember the other questions?

Reply 3

shewhomustnotbnamd

for 2f i also put not heating it for long enough or hot enough but thats probably wrong :/

Reply 4

Blob2491

3a) exothermic - reaction in which energy, usually in the form of heat, is given out to surroundings
b) activation energy

Reply 5

shewhomustnotbnamd

empirical formula one...and the one with the ship but that might have been c3

Reply 6

prada1234

here are some other q's i can remember...
the one on empirical fomula,
unsaturated hydrocarbons
moles and concentration
the one about the expirement with why do the gases escape or something like that

Reply 7

Rose.1994

Original post by prada1234

the unsaturated hydrocarbons are c3?

Reply 8

Blob2491

3b could also be catalyst?

Reply 9

prada1234

could you also say increase the pressure instead of concentration?

Reply 10

Blob2491

Last question
nitrogen - air
hydrogen - water? natural gas

nitric acid

Mine shut down because expensive to ship sodium nitrate and pay workers to mine. Ammonium nitrate is a better fertiliser than sodium nitrate

Reply 11

Rose.1994

Original post by Blob2491

3b could also be catalyst?

oh yeah yeah I was thinking that in the exam!
think you're right, so have added it :smile:

Reply 12

Popey94

3b could also be increasing the surface are of the 'rock'? Sorry, can't remember what it was.

Reply 13

laurel1

Last one was raw materials for Haber process - air & methane (I think) 1 mark for each
Then why 450 degrees - because it's a compromise blah blah blah 3 marks
Then something else but I can't remember :/