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    Thanks to CandidateZero for help putting this together.



    C7 Unofficial Mark Scheme

    1. Fill in the word equation and symbol equation (2 marks)
    Sodium chloride (1)
    NaCl (1)

    2. How does the reaction explain the gas in her stomach (2 marks)
    Carbon dioxide is formed (1)
    Which can not escape (1)
    Because there is lots of acid in her stomach, it will constantly be being produced (1)

    3. Calculating concentration and mass (4 marks)
    10g/dm3 (2) - 1 mark for converting volume into dm3
    0.25g (2) - 1 mark for converting volume into dm3.

    4. Explain how you would carry out a method to make a standard solution (6 marks)
    • Calculate the amount of solute needed
    • Place the beaker onto the scale and record the weight of the beaker.
    • Add in the amount of solute, until the correct amount has been added.
    • The total weight should be the mass of solute and weight of beaker.
    • Put some distilled water into the beaker, and stir until the solute is dissolved.
    • Using a funnel, pour the solution into the volumetric flask to ensure that none spills out.
    • Use the rod to rinse out the beaker, and pour this back into the volumetric flask to ensure that no solute is left in the beaker. Repeat 2-3 times.
    • Fill the volumetric flask up with distilled water, to 250cm3 taking a reading from the bottom of the meniscus.
    • When you are getting close to this volume, use a pipette to add it in drop by drop.


    5. Explain why hydrogen is a good fuel, but not when made from water (6 marks)
    • Hydrogen combustion is an exothermic reaction because the reactants had more energy than the products. This reaction has a low activation energy therefore less energy is needed to break bonds to start the reaction. If less energy is needed, less fossil fuels have to be burnt. If less fossil fuels have to be burnt, there is less gases, such as carbon dioxide, produced.
    • Production from water is endothermic because the products had more energy than the reactants. This is not a sustainable one because it had a greater activation energy and therefore more energy is needed to break the bonds to start the reaction



    6. Draw the other molecule that forms (2 marks)
    Drawing (1)
    Butane (1)


    7. Question about sharing data (2 marks)

    To compare the effectiveness of each factor, to decide which to choose (1)
    To carry out peer review(s), to assess the repeatability of the data that is shared (1)
    It increases confidence in their data (1)
    Can compare results to see if others got same pattern (1)


    8. Question about why modern process involves more green chemistry (3 marks)

    There are two feedstocks that must be cracked from fossil fuels, in comparison to just one (1)
    There is a larger yield to be purified (1)
    No extra chemicals added as sulfuric acid isn’t needed (1)


    9. Question about the highest boiling point of ethanol or ethene (2 marks)

    Ethanol (1)
    Is liquefied as it passes through the cooler/condenser (1)
    Whereas ethene remains in a gaseous state (1)

    10. Question about atom economy of the two processes (2 marks)

    The data indicates that the old method produces waste whereas the new method does not (1)
    The new method produces by-products, which are classified as useful products - hence higher atom economy (1)

    11. Something about using the formula to explain why it must be recycled (2 marks)

    It is a reversible reaction (1)
    There is a set % of products that can be formed, and if it goes past this, the products get turned back into reactants (1)
    So some product re-reacts to form the reactants, which must be recycled to increase the yield (1)

    12. Why use phosphoric acid and 70 atms (2 marks)

    Phosphoric acid is a catalyst which reduces activation energy (1)
    Using a higher atmospheric pressure favours the forwards reaction: more molecules on LHS than RHS (1)

    13. Why compromise with temperature (2 marks)

    Higher temperature shifts the equilibrium in favour of the backwards reaction because the forward reaction is exothermic (1)
    But using a higher temperature increases the rate of reaction (1)

    14. Why are his titrations unreliable (3 marks)

    They have a large range, so a true value cannot be estimated (1)
    Results are not concordant/inconsistent (1)
    Results contain an outlier: titration 4 (1)
    There is no reason for there to be so much variation in the values (1)

    15. Compare the two reactions (6 marks)
    • The first reaction formed water, whereas the other one formed hydrochloric acid.
    • The first reaction formed ethyl ethanoate whilst the second one formed ethyl propanoate.
    • Both reactions involved reacting ethanol.
    • Both processes produce an ester and another product.
    • Could compare atoms present eg hyodrgen/carbon/Cl ect


    16. How could he put the alkali into the beaker more precisely? (1 mark)
    Pipette (1)

    17. Explain what else they could consider in investigating making a process greener (2 marks)
    The raw materials (1)
    The energy costs eg high temperatures and pressures (1)

    18. Tick box about enzyme catalysts (2 marks)
    One about optimum temperature (1)
    One about certain pH (1)

    19. Tick boxes about octane and something and both (3 marks)
    1st column
    2nd column
    3rd column
    1st column

    20. Balancing equation (2 marks)
    CO2 and H2O (1)
    9CO2 and 10H2O (1)

    21. Working out the mean (2 marks)
    23.5 (2)

    22. Explain whether this is 5% concentrated. Use ideas about significant figures (2 marks)
    23.5/5 = 4.7 (1)
    Therefore, it is 5% to one significant figure (1)
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    Aw coulda sworn that question 6 would have been hydrogen, oh well
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    Thank you!
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    Looking at this, think I got around 50
    Hopefully that's an A*
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    for the recycling question - does the ethene not need to be reused because if they condense that alongside the ethanol, it won't be a pure ethanol solution?

    thanks for the ms
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    Begging that 40 gets an A*.....pls...
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    (Original post by danielwinstanley)
    Begging that 40 gets an A*.....pls...
    Hah, we can all dream eh? Truth is, 52 for an A* last year and the grade boundaries have gone up every year. Doesn't look too hopeful. Probably 45-49 for A*
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    what is the predicted grade
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    What do u think the grade boundraries will be
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    (Original post by TheExtremeGoat)
    Hah, we can all dream eh? Truth is, 52 for an A* last year and the grade boundaries have gone up every year. Doesn't look too hopeful. Probably 45-49 for A*
    I made so many stupid mistakes - eg naming the wrong ester for the 6 marker because I forgot to take away the carbons for the ethanol so I got ethyl pentanoate rather than propanoate.

    It's harder than all the past papers I've done, though.
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    (Original post by danielwinstanley)
    I made so many stupid mistakes - eg naming the wrong ester for the 6 marker because I forgot to take away the carbons for the ethanol so I got ethyl pentanoate rather than propanoate.

    It's harder than all the past papers I've done, though.
    That final six mark question was awful. First two, however, were indeed a God send. At the max, you'll lose 2 marks for incorrectly naming the esters, although it could even just simply be ignored.
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    (Original post by CTolley)
    Aw coulda sworn that question 6 would have been hydrogen, oh well
    It was - the answers are not in the order of the questions.
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    Wasn't 16 how to measure the vol of the acid or did I get it completely wrong 😒
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    (Original post by nish2910)
    Wasn't 16 how to measure the vol of the acid or did I get it completely wrong 😒
    It could have been, although regardless 'pipette' would have been awarded as it can measure to a greater accuracy than a measuring cylinder, given in the stem of the question.
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    Grade boundary predictions:

    A* - 46/47
    A - 40/41
    B - 33
    C - 27
    D - 19
    E - 15

    Basing my predictions on the grade boundaries for the 2014 C7 exam, which was the closest to this year's difficulty and thus had lower boundaries - 45 was an A*, and in 2013, 37 was an A*. Today's was undoubtedly more challenging than the 2013 one, but 2013 was the first year of testing.

    EDIT: It could even be 45 or lower this year for an A*, as today's exam is harder than the 2014 one so people will have dropped more in places.
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    (Original post by CandidateZero)
    It could have been, although regardless 'pipette' would have been awarded as it can measure to a greater accuracy than a measuring cylinder, given in the stem of the question.
    i said burette :/
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    (Original post by nish2910)
    i said burette :/
    The specification references both pipettes and burettes, so you may well still get the mark.
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    (Original post by danielwinstanley)
    Begging that 40 gets an A*.....pls...
    What do you think of odds of that are? Also there is anywhere with predicted grade boundaries like there was for Maths?
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    16. How could he put the alkali into the beaker more precisely? (1 mark)

    you could use a balance too? as 1g = 1cm3

    15. Compare the two reactions (6 marks)

    both reactions were irreversible, I think. As the arrow did not go both ways. and normally OCR show ester reactions as reversible.
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    I flunked the last 6 marker so bad
    Barely had 5 minutes to answer it
 
 
 
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