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~AQA GCSE CHEMISTRY Unit 3 NEW SPEC 20th May+ POLL~READ 1st POST watch

  • View Poll Results: What do you think the 6 marker will be?
    Titration
    59
    37.58%
    Haber process
    68
    43.31%
    Evaluate fuel cells
    24
    15.29%
    Knowledge based evaluation
    13
    8.28%
    Other (please comment)
    6
    3.82%

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    Official thread for the chem exam:

    Please VOTE in the above poll on the 6 mark question.

    If you post on here any exemplar six mark question answers, PM me and I will paste them on here for other users.

    -Please keep discussion to this exam only, general science exam discussion can be found at http://www.thestudentroom.co.uk/show....php?t=2296889

    Please read the site's exam rules before posting.

    Example 6 mark answers:

    1. The early ideas about the Periodic Table (Newlands and Mendeleev)
    Mendeleev and Newlands classified elements in order of their atomic weights.
    Newlands came up with the 'law of octaves', he noticed that every eighth element seemed to have similar properties. This pattern broke down going further down the table. The modern name of this is the 'law of periodicity'
    Mendeleev left gaps for undiscovered elements and estimated their properties. In this way, the pattern in the table carried on for more elements.


    2. Water - hardness and softness, then purification

    Water can either be hard or soft. Hardness in water is caused by dissolved calcium or magnesium ions.
    Hard water reacts with soap (sodium stearate) to form scum. This causes high costs since all calcium and magnesium ions need to have reacted before the soap can form a lather. This means more soap needs to be purchased.
    Hard water does have some advantages; it has been proven to help prevent heart disease and it contains calcium which is necessary for healthy teeth and bones.
    There are two types of hard water; permanent or temporary. Permanent is caused by calcium sulfate in the water, whereas temporary is caused by the calcium hydrogencarbonate ion, HCO3-
    Water becomes hard when it travels over rocks in streams. Gypsum (calcium sulfate) dissolves in the water to form permanent hard water. Calcium carbonate is not soluble in water, however as rain falls it reacts with carbon dioxide, forming an acidic solution. This falls in the rivers and causes them to become slightly acidic. Calcium carbonate reacts with this acidic solution.
    Water can be softened in several different ways. Firstly, boiling. Only temporary hard water is softened by boiling. The HCO3- ion undergoes thermal decomposition:
    2HCO3- -> CO2 + H2O + CO3-
    Then, the CO3- (carbonate) ion reacts with Ca+ ions
    CO3- + Ca+ -> CaCO3
    The CaCO3 is known as scale in this situation. Scale is a nuisance since it reduces the efficiency of kettles as it is a poor thermal conductor.
    You can also soften water by sodium carbonate (washing soda). The calcium and magnesium ions in the water react with the carbonate ions in the soda, forming calcium and magnesium carbonate precipitates. These can be filtered out of the water. Sodium ions remain dissolved in the water.
    Water can also be softened by passing it through an ion exchange column. In the resin, there are sodium and hydrogen ions which are swapped for calcium and magnesium ions in the hard water, softening it.
    Many people have self-filtering jugs which use carbon, silver and an ion exchange column to soften water. Silver prevents growth of bacteria and carbon reduces chlorine levels.
    (Probably too much)

    3. Titration and neutralisation (example)

    First add 20cm3 of NaOH (choosing this as an example) to a flask using a pipette. Next, add some methyl orange indicator to the NaOH; it should turn yellow to indicate an alkali. Add 20cm3 of HCl to a burette. Set up the burette on a stand and release 1cm3 of HCl at a time and stir thoroughly with a glass rod. Carry on doing this until the methyl orange turns red. When this happens, record the volume of HCl required to neutralise the 20cm3 of NaOH.
    Neutralisation reactions happen between an acid and alkali, and always form a salt and water. They are exothermic too


    4. Forensic analysis of an unknown substance


    CURRENTLY EMPTY...

    ....Need someone to write one...

    5. Compromise conditions in the Haber Process

    The haber process uses conditions of 450 degrees celsius and pressures of 200 atmospheres. Both these conditions are compromises to make the process as efficient as possible at a relatively low cost.
    The haber process reaction is: N2 + 3H2 -> 2NH3
    As you can see, there are four reactant molecules and two product molecules. So a high pressure will favour the forward reaction. However, extremely high pressures are very expensive to sustain and expensive equipment and machinery is necessary for this. The compromise of 200 atmospheres is to maintain a relatively fast rate of forward reaction at a reasonable cost.
    The forward reaction of the process is exothermic. So essentially, an increase in temperature would decrease the rate of forward reaction. However, a with a low temperature the rate of reaction would be extremely slow. The temperature of 450 degrees is a compromise to make sure that the reaction happens relatively fast (more collisions of particles).


    January 2012:

    C1 Higher:

    Question Paper | Mark Scheme

    C1 Foundation:

    Question Paper | Mark Scheme

    June 2012:

    C1 Higher:

    Question Paper | Mark Scheme

    C1 Foundation:

    Question Paper | Mark Scheme

    C2 Higher:

    Question Paper | Mark Scheme

    C2 Foundation:

    Question Paper | Mark Scheme

    January 2013:

    C1 Higher:

    Question Paper | Mark Scheme

    C1 Foundation:

    Question Paper | Mark Scheme

    C2 Higher: (2013 MS link currently doesnt work)

    Question Paper | Mark Scheme

    C2 Foundation:

    Question Paper | Mark Scheme

    Specimen Papers:

    C1 Higher:

    Question Paper | Mark Scheme

    C1 Foundation:

    Question Paper | Mark Scheme

    C2 Higher:

    Question Paper | Mark Scheme

    C2 Foundation:

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    C3 Higher:

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    • Thread Starter
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    Poll being added soon
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    Poll added
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    Thank you for making this group! Any ideas of what grade boundaries will be like?
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    (Original post by memoona123456)
    Thank you for making this group! Any ideas of what grade boundaries will be like?
    High.

    In reality probably a bit lower than unit 2 but not as low as 3
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    I'm not fully sure what the 6 mark question will be as there are quite a lot of possibilities.. Titrations would be quite a nice one because as long as you've learned the method it's quite easy to get the marks. But it was in the specimen so they might not want to have it as a 6 mark. But maybe a 4 or 5 mark question could come up? (I saw that in one of the practice papers we did.) I can imagine a question with some titration calculations, maybe explaining about why we have to do titrations and then a longer mark question on how to carry it out.

    I really hope fuel cells doesn't come up as I haven't really revised that very much and don't even remember doing about it in class. But they like to try and catch people out with putting stuff that people might not know as much, so I need to revise that.

    What about the trends in the periodic table? I don't know how they would phrase the question, but there's quite a lot to say about the different groups and the properties that the elements have..
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    (Original post by Dougieowner)
    I'm not fully sure what the 6 mark question will be as there are quite a lot of possibilities.. Titrations would be quite a nice one because as long as you've learned the method it's quite easy to get the marks. But it was in the specimen so they might not want to have it as a 6 mark. But maybe a 4 or 5 mark question could come up? (I saw that in one of the practice papers we did.) I can imagine a question with some titration calculations, maybe explaining about why we have to do titrations and then a longer mark question on how to carry it out.

    I really hope fuel cells doesn't come up as I haven't really revised that very much and don't even remember doing about it in class. But they like to try and catch people out with putting stuff that people might not know as much, so I need to revise that.

    What about the trends in the periodic table? I don't know how they would phrase the question, but there's quite a lot to say about the different groups and the properties that the elements have..
    Perhaps they would give you several elements and you asked to explain their relationship, but I think this is unlikely
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    I reckon it will be Haber process as in the old spec they always did titrations as 6
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    The C2 link for the january higher mark scheme is currently incorrect. Do you have access to the correct mark scheme?
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    Ok, I will try to find a working link
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    If the six markers is going to be haber process, what would it be on?
    (Original post by bbadonde2)
    I reckon it will be Haber process as in the old spec they always did titrations as 6
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    (Original post by veniceswan)
    If the six markers is going to be haber process, what would it be on?
    They will give you a blank diagram or something and ask you to explain the processess
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    Chemistry thread.....
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    (Original post by Captain Anonymous)
    Chemistry thread.....
    Hiiiiiiii
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    Anyone got any revision notes on the computer they'd like to share? Or any questions would do
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    how's everyone feeling for this exam? what do you need for your grades and what do you think is bound to come up?
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    How are you lot revising triple chemistry?? It's so hard!


    Posted from TSR Mobile
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    I've made notes twice over for chemistry. Think I need 80 for A*
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    (Original post by Jams97)
    How are you lot revising triple chemistry?? It's so hard!


    Posted from TSR Mobile
    I think it's really hard to revise for chemistry and physics because they're not knowledge questions they're data questions so you can't QnA with people...
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    Chemistry you just need to learn the info and in physics you have to have background knowledge
 
 
 

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