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AQA GCSE Chemistry Unit 2 24 May 2012

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    (Original post by PriyankaP)
    I think i've got 25-28 marks.. what grade is that?
    I think i got 25-28 as well. I think its a strong B so like 75 UMS above
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    (Original post by MissGeek)
    Here are most of the questions from the unofficial markscheme I created to help you, I think this mark scheme may need a little bit of finishing off.

    Why are chloride ions attracted to the positive electrode? (1)
    Opposite charges attract/chloride ions have a negative charge
    I can't remember, I think it was something on ions, or alkalis? (1)
    Why is hydrogen formed? (1)
    Hydrogen is less reactive than sodium
    Draw the diagram (Hydrogen and Chlorine) (I THINK) (1)
    Both must have a full outer shell.
    What type of bonding is it? (1)
    Covalent

    What type of ions make the solution pH 1? (1)
    Hydrogen

    What type of ions make the solution alkali? (1)
    Hydroxide

    Calculate the number of ? in 1 mol^3 of ? (gas canister question) (1)
    I did 53.? - 51.? (I don't know if this is right though)

    Calculate the mean mass of gas results. (2)
    Miss out anomaly to get answer, however, if you showed your workings, you could still get 1 mark.

    Suggest 2 causes of this experimental error (2)
    I put weighing error in measuring gas canister, human error, recording error, may have been a systematic error (unsure, please correct me if I'm wrong)

    Why should they repeat the test more (1)
    Make it more reliable
    Allows them to spot any anomalies
    Allows them to calculate a mean/average

    What type of acid makes the magnesium hyrdoxide react to form calcium chloride? (1)
    Hydrochloric acid

    Explain how the magnesium hydroxide (I think) can be separated from the calcium chloride. (1)
    I can't remember what I put.

    Suggest how the calcium chloride can be made into a solid? (1)
    Evaporation

    What is oxidation? (1)
    Electrons are lost.

    Explain why the best yield is produced when the pressure is higher (1)
    There are more (gaseous) reactant molecules than (gaseous) product molecules.

    Explain why, in terms of particles, the rate of reaction increases when temperature increases. (2)
    The particles gain energy, they move faster and collide more frequently.

    Explain why the pressure is not higher than 200 atmospheres in the Haber process (1)
    It would be more expensive.

    Explain why a temperature of 450 is suitable (can't remember exactly how it was worded) (1)
    The forward reaction is exothermic

    Explain why it doesn't matter if a low yield of ammonia is produced in the Haber process (2)
    The unreacted hydrogen and nitrogen are reacycled and can be used and reacted again to form ammonia again.
    The reaction is reversible.


    Calculate the mass of ammonia that can be made from 2g of nitrogen (3)
    2.4g (1 d.p.)

    In Haber Process, a maximum of 80kg can be produced. 12 kg is produced. Calculate the percentage yield. (2)
    15%

    Diamond is hard. Explain why it is hard, refer to structure and properties in your answer (3)
    Each carbon atom is covalently bonded to 4 other carbon atoms. The bonds are strong and a lot of energy is required to break the bonds. There are no delocalised electrons in diamond due to each carbon atom being covalently bonded to 4 other carbon atoms.

    Calculate the relative formula mass of C3H8. C=12, H=8 (2)
    44g

    Explain the structure of gold. (3)
    There is metallic bonding in gold. There are fixed positive ions and delocalised electrons which are free to move around. There are electrostatic forces of attraction between the electrons and positive ions.

    Explain why gold is a good conductor of electricity (1)
    It has delocalised electrons

    yay i'm all happy now according to that mark scheme I got 34 , looks like all that revision finally paid off
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    I get 33 if im being ungernerous and 36 if i am being generous :L
    So on adverage im thinking 34ish marks which im pretty sure will be an A so im happy
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    (Original post by alicea12)
    you're missing a question where it says 20dm3 is used for hydrogen, work out how much is used for nitrogen. (1)
    It was 60 right??
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    (Original post by alicea12)
    That's what I put, as I assumed you do 3x20
    Yepp gdgd
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    Well according to the latest unnoficial mark scheme I got 35-37, so I'm pretty happy , now I just need to find one for C3, somehow I don't think I've done as well on that one :/.
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    I wrote "crystalisation" for the question to make calcium chloride solution into solid. Will I get the mark ?
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    (Original post by hoanganhbeo96)
    I wrote "crystalisation" for the question to make calcium chloride solution into solid. Will I get the mark ?
    Yep I put that too, you can put either evaporation/crystallisation =)
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    i thought it was easier than the one i did in january 2012 - i got 88ums (a) and the grade boundaries were quite high 36-a* 32-a etc... but, i think many people would have made more common mistakes on the one today, e.g- ammonia question.
    i reckon 35-a* 31-a 29-b
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    does anyone know if there is a mark scheme for c3??
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    (Original post by MissGeek)
    Here are most of the questions from the unofficial markscheme I created to help you, I think this mark scheme may need a little bit of finishing off.
    I agree with most of your answers, but there are a few I would change/add too.
    Suggest 2 causes of this experimental error (2)
    I put weighing error in measuring gas canister, human error, recording error, may have been a systematic error (unsure, please correct me if I'm wrong)
    AQA only accepts specifics, such as 'Some gas may have escaped' or 'the measuring cylinder may not have been completely filled with water'. Vague answers like 'human error' don't get credit.

    Explain how the magnesium hydroxide (I think) can be separated from the calcium chloride. (1)
    I can't remember what I put.
    Filtration.

    Explain why the best yield is produced when the pressure is higher (1)
    There are more (gaseous) reactant molecules than (gaseous) product molecules.
    The question was 'why does decreasing the temperature increase the yield of ammonia?'

    The answer is simply 'the reaction is exothermic'. Mentioning the forward reaction is great, but past mark schemes only need the word 'exothermic'.

    Explain why, in terms of particles, the rate of reaction increases when temperature increases. (2)
    The particles gain energy, they move faster and collide more frequently.
    A third option is the fact that more collisions are successful, due to the increased energy of the particles.

    Explain why it doesn't matter if a low yield of ammonia is produced in the Haber process (2)
    The unreacted hydrogen and nitrogen are reacycled and can be used and reacted again to form ammonia again.
    The reaction is reversible.
    I'm not sure 'the reaction is reversible' is credited. There may be a mark for 'the process is continuous' although I imagine there'd have to be some sort of qualification for it - e.g. products go back into the reactor, so no need to worry about energy.


    Diamond is hard. Explain why it is hard, refer to structure and properties in your answer (3)
    Each carbon atom is covalently bonded to 4 other carbon atoms. The bonds are strong and a lot of energy is required to break the bonds. There are no delocalised electrons in diamond due to each carbon atom being covalently bonded to 4 other carbon atoms.
    Reference to electrons will be ignored. Marks given for:

    three from:
    structure: (max 2)
    • giant structure / macromolecule
    / all the atoms are joined
    together
    • covalent (bonds)
    • strong bonds / bonds difficult to
    break
    • each carbon atom forms 4 bonds.

    explanation: (max 2)
    • a lot of energy needed to break
    the bonds
    • strength of bonds makes the diamond hard.
    Explain the structure of gold. (3)
    There is metallic bonding in gold. There are fixed positive ions and delocalised electrons which are free to move around. There are electrostatic forces of attraction between the electrons and positive ions.
    Also credited: Lattice structure, regular sheets of gold atoms, electrons coming from the outer shell.
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    i thought this exam was very hard, made some stupid mistakes i think, but by the looks of the answers everyone else has put i hope i did ok!
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    (Original post by elsher)
    The question based on Equlibrium.... the first i put exothermic, then there was questions about particles, then was a question how increasing pressure increases yield.... i put favours endothermic reaction
    I think it's that there were less gaseous molecules on that side cos it is 2NH3(ammonia) and the reactants are N2 and 3H2 so that equals 4
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    (Original post by R.P.Everything.)

    I'm not sure 'the reaction is reversible' is credited. There may be a mark for 'the process is continuous' although I imagine there'd have to be some sort of qualification for it - e.g. products go back into the reactor, so no need to worry about energy.
    Can you say... Because a catalyst is used the reaction is complete at a fast rate each time, and the Nitrogen and Hydrogen is recycled?? Thanks
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    (Original post by maxtate)
    Can you say... Because a catalyst is used the reaction is complete at a fast rate each time, and the Nitrogen and Hydrogen is recycled?? Thanks
    Its right, but as I've never seen a past paper question with similar wording, I can't give a confident judgement on whether they credit it or not.
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    (Original post by tssf_skye)
    For the one about why a higher pressure wasn't used, i didn't say expensive i don't know if that's correct.
    How many people wrote that?
    I'm pretty sure it's something about affecting the yield?
    Very expensive
    Extremely high risk of explosion
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    (Original post by BBBT)
    But the it was a solution and had the symbol (aq) which shows it's dissolved in water so surely you evaporate??
    Are you completely sure it said (aq) because usually when they ask they ask it in a different way like how would you obtain solid ..... they said how would you make a solution of ... into solid.... im sure if you cool/freeze something it turns into a solid like water and melted metal and things like that. Anyway I hope your wrong
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    (Original post by alicea12)
    you're missing a question where it says 20dm3 is used for hydrogen, work out how much is used for nitrogen. (1)
    The percentage yield question was worth 1 mark. The second to last question about why gold conducts electricity was also worth 1 mark.
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    (Original post by Hollykins)
    I should think so, I put there were 4 moles of reactants and 2 moles of product.
    I dont think so because the amount of products doesnt affect ror when pressure increase having less GASEOUS molecules is what is affected by pressure increase
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    (Original post by R.P.Everything.)
    Its right, but as I've never seen a past paper question with similar wording, I can't give a confident judgement on whether they credit it or not.
    K ty

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