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    (Original post by omarkhaled)
    Nope sorry 9c is not 60g, I got it mixed up with the other magnesium question
    No problem
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    (Original post by U-GradeStudent)
    How did you get 1920? Just interested cause I had no idea
    0.08 (moles) x 24 000 cm³ (moles of Gas at RTP)
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    (Original post by U-GradeStudent)
    How did you get 1920? Just interested cause I had no idea
    0.08 X 24000 =1920cm3
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    I got 50g for Q) 9c, can anyone tell me how the answer is 60g?
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    (Original post by GCShElpme)
    Predictions for grade boundaries.
    The last couple of grade boundaries are as follows;
    2015- A*: 60, A: 50, B: 40, C: 30
    2014- A*: 62, A: 52, B: 41, C: 31
    2013- A*: 54, A: 45, B: 36, C: 28
    [Links: "]http://www.ocr.org.uk/i-want-to/convert-raw-marks-to-ums/ ]
    Despite my own opinion on the difficulty of the paper, the vast majority thought that this paper was relatively difficult, more so than past papers. On account of the comparative easiness of the first paper, I'd say that these grade boundaries will be lower than 60, though no lower than, say, 55.
    Predictions for 2016- A* 56, A: 46, B: 38, C: 30.
    Hope this helps. I appreciate feedback!
    Thank you for the mark scheme! Do the marks needed for each grade boundary take into consideration the extra ten marks in section D?
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    (Original post by TSR-Radioactive)
    I got 50g for Q) 9c, can anyone tell me how the answer is 60g?
    It is 50g - I will update my mark scheme with it
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    (Original post by some-student)
    It is 50g - I will update my mark scheme with it
    Thanks buddy!
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    (Original post by _anonymoususer)
    Thank you for the mark scheme! Do the marks needed for each grade boundary take into consideration the extra ten marks in section D?
    Yes. The listed boundaries for previous years include section D and the predictions for this year also include section D.
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    (Original post by some-student)
    Starting the mark scheme for C4 C5 C6.

    How did you all find it? I found it pretty difficult but not as bad as Biology.
    I need some help for the question which referred to current and time, on my graph I thought it was 7.6, so therefore I got 60.8. Will they still allow this?
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    (Original post by some-student)
    Starting the mark scheme for C4 C5 C6.

    How did you all find it? I found it pretty difficult but not as bad as Biology.
    Your mark scheme is so good! Better make on for physics!
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    (Original post by CandC)
    I need some help for the question which referred to current and time, on my graph I thought it was 7.6, so therefore I got 60.8. Will they still allow this?
    That will be fine, and may even be better than 7.5 - the graphs were really hard to read off.
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    (Original post by Gymnast7)
    Yes. The listed boundaries for previous years include section D and the predictions for this year also include section D.
    Great! Thank you!
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    (Original post by CandC)
    Your mark scheme is so good! Better make on for physics!
    Thank you ! and yes I am intending to make one for P4 P5 P6 too
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    (Original post by some-student)
    that will be fine, and may even be better than 7.5 - the graphs were really hard to read off.
    thank you!
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    I think 16)c)i) was mass of animals used and it was 1,260,000,000g if I remember right
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    (Original post by some-student)
    OCR Gateway Chemistry B
    C4 C5 C6 + Section D
    Unofficial Mark Scheme
    Monday 20 June 2016

    Module C4 - 25 marks
    1) Table of atoms
    a) Complete the table [3]
    atomic number: 12 (1)
    can't remember this one
    electronic configuration: 2.4 (1)

    b) Atoms W and X are both chlorine atoms but different. Name what types of atom they are and explain why [2]
    isotopes (1)
    same atomic number but different mass number (or equivalent in terms of neutrons/protons) (1)

    2. Superconductors
    a) Write about two advantages [2]
    any two of
    • loss free power transmission (1)
    • super-fast electronic circuits (1)
    • powerful electromagnets (1)

    b) Explain one disadvantage [1]
    it is very hard / expensive to get them to the low temperatures required (1)

    3. Chlorine fluoride (formula: ClF)
    a) covalent, dot and cross [2]
    shared pair of electrons between Cl and F atoms (1)
    Cl and F atoms both having 6 other outer electrons (1)

    b) it is a simple molecular structure - predict two properties [2]
    any two of
    low boiling / melting point (1)
    does not conduct electricity (1)
    gas or liquid at room temperature (1)

    4. Testing for ions [6 QWC]
    Marking points
    balanced symbol equation: 3AgNO3 + FeCl3 -> 3AgCl + Fe(NO3)3

    compound A: copper(II) chloride (CuCl2) - Cu2+ ions in sodium hydroxide solution form a blue precipitate; Cl- ions in silver nitrate solution make a white precipitate

    compound B: iron(II) bromide (FeBr2) - Fe2+ ions in sodium hydroxide solution form a green precipitate; Br- ions in silver nitrate solution make a cream precipitate

    5. Group 7 elements
    a) Complete the table [3]
    can't remember this completely
    iodine: grey solid (1)

    b) Explain the reactivity in group 7 [2]
    as you go down the group: increased atomic radius / more nuclear shielding (1)
    therefore less attraction from the nucleus to electron to be gained (1)

    c) Describe how Mendeleev contributed to the periodic table [2]
    any two of
    order of atomic mass (1)
    left gaps for undiscovered elements (1)
    in vertical groups, elements had similar properties (1)

    Module C5 - 25 marks
    6. Water testing [3]
    Sample A: bromide (Br- ions) as cream precipitate formed in lead nitrate (1)
    I can't remember if the precipitate was cream (Br- ions) or white (Cl- ions)

    Sample B: iodide (I-) ions as yellow precipitate formed in lead nitrate, and sulfate (SO42- ions) as white precipitate formed in barium chloride (1)
    Sample C: sulfate (SO42- ions) as white precipitate formed in barium chloride (1)

    7. Strong and weak acids
    a) Explain the difference between strong and weak acids [2]
    • acid strength is a measure of thedegree of ionisation of the acid (1)
    • acid concentration is a measure of the number ofmoles of acid in one dm3 (1)

    b)i) Explain why the reaction is faster for the strong acid [1]
    in hydrochloric acid the hydrogen ions have a higher collision frequency with reactant particles as they are in a higher concentration (1)

    b)ii) Explain why the same volume of strong and weak acids used in a reaction will still produce the same amount of carbon dioxide gas [1]
    the amount of products is determined by the amounts ofreactants present not the acid strength / all the atoms in the gas are from the calcium carbonate (1)

    8. Contact process
    a) List another condition apart from the pressure or temperature [1]
    V2O5 catalyst (or any equivalent name) (1)

    b) Explain all the conditions used in the contact process [3]
    • increasing the temperature moves the positionof equilibrium to the left and increases rate ofreaction so a compromise temperature is used (1)
    • addition of catalyst increases rate but does notchange position of equilibrium (1)
    • even at low pressure, the position of equilibriumis already on right so expensive high pressure isnot needed (1)

    9. Reaction/calculations
    a)i) How much gas is produced? [1]
    75 (1) I can't remember if it was this

    a)ii) How long did the reaction take before it stopped? [1]
    51 - 53 (1) I think it was in this range

    b) Draw on the graph to show the reaction for 0.005g of magnesium [2]
    line half height of original line (1)
    correct shape of line (1)

    c) Calculate the mass of magnesium sulfate produced with 0.5g magnesium, explaining your answer [2]
    calculation (1)
    correct answer: 50g (1)

    d)i) Calculate the number of moles [1]
    0.08 mol (1)

    d)ii) Calculate the volume of gas [1]
    1920 dm3 (1)

    10. Titration [6 QWC]
    Marking points
    graph: when 20cm3 of acid has been added, neutralisation occurs - this is also the end-point

    concentration of sodium hydroxide
    calculating number of moles of acid: when the reaction occurred (neutralisation), 20cm3 of acid had been used, which is 0.02dm3 (20 / 1000)

    c = n / v
    n = c × v = 0.1 × 0.02 = 0.002 mol

    as the equation was balanced, there were the same amount of moles of acid as alkali

    25cm3 of alkali = 0.025dm3

    c = n / v = 0.002 / 0.025 = 0.08 mol/dm3

    Module C6 - 25 marks
    11. Fats
    a) What type of molecule is a fat? [1]
    ester (1)

    b) Molecular formula of glycerol [1]
    C3H8O3(1)

    c)i) Explain why the given diagram is unsaturated [1]
    carbon to carbon double bond (1)

    c)i) Explain how it would be checked if it was unsaturated, and the results expected to be seen [2]
    • addition reaction takes place at the carbon-carbon double bond with addition of bromine water
    • a colourless dibromo compound is formed (1)

    d) Explain how margarine is made [2]
    hydrogen gas is bubbled in (using a nickel catalyst at 200°C) (1)
    breaking some of the bonds, hardening the oil (1)

    12. Displacement reaction [6 QWC]
    Marking points
    word equation: copper(II) sulfate + iron -> iron(II) sulfate + copper

    balanced symbol equation: CuSO4 + Fe -> FeSO4 + Cu

    oxidation: Fe - 2e- -> Fe2+ - electrons are lost(iron is the reducing agent as it causes copper's reduction - see below)

    reduction: Cu2+ + 2e- -> Cu - electrons are gained (copper is the oxidising agent as it causes iron's oxidation - see above)

    13. Ozone layer depletion
    a) Pick the reaction to show UV rays breaking down ozone [1]
    reaction 4 (1)

    b) Explain how a CFC molecule can create a chlorine atom, in terms of bonding and electrons [2]
    (UV light) breaks a C-Cl bond (1)
    forming a chlorine free radical with an unpaired electron (1)

    c) Explain how a single chlorine atom can destroy many ozone molecules, using the reactions given [2]
    any two of
    reaction 2 produces chlorate radical (1)
    which makes a chlorine atom again in reaction 3 (regeneration) (1)
    chain reaction in terms of the reactions 2 and 3 (1)

    d) Explain why it took a long while for scientists to recommend the ban of CFCs [2]
    • initial enthusiasm for the use of CFCs based upon their inertness (1)
    • later discovery of ozone depletion and link topresence of CFCs (1)

    14. Water hardness [2]
    soap affected as lather only 30cm3 with calcium hydrogen carbonate, while for distilled water it is 60cm3 (1)
    washing up liquid not affected as lather only 60cm3 with calcium hydrogen carbonate and distilled water (1)

    15. Reaction
    a) How much magnesium is made after 30 minutes (current: 10.3A)? [1]
    7.5g (1)

    b) Predict how much magnesium is made - current: 20.6A, time: 120 minutes [2]
    7.5 × 2 × 4 (1)
    60g (1)

    Section D - 10 marks
    16. Pollutants
    a) Work out, from the graph, the amount of fertilisers used [1]
    37 million tonnes (1) I can't remember so this may be wrong

    b) Explain why the nitrate restrictions have had an effect from the graph [1]
    sudden decrease after 1977 (1)

    c)i) Calculate the mass of fertilisers used[1]
    I can't remember

    c)ii) Explain why a country with a much smaller agricultural area would use more fertilisers[2]
    there are likely many answers to this question
    more efficient farming (1)
    to provide enough food for the population (1)

    17. Greenhouse gases
    a) Explain which gas is most likely to be produced by the use of fertilisers [2]
    nitrous oxide (1)
    88% is contributed by farming (in comparison to other gases) (1)

    b) Explain why farming has a much higher impact on greenhouse emissions than residential uses [3]
    calculation of (average) percentage for farming (1)
    calculation of (average) percentage for residential uses (1)
    comparison to show farming's greater impact (1)
    THANKS SO MUCH FOR THIS! SO USEFUL! Feel like an A* is a possibility because I got around 73/85 which should be 100% UMS BUT I have an issue: my coursework was only 38/48 and I haven't been able to find mark scheme for the first paper but I did s*** - probably around 52-56 out of 75 - so many silly mistakes. just wondering if I could still get an A* and if you have a mark scheme for the first paper? Thanks
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    The missing thing from Q1 is the number of neutrons^^^
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    (Original post by _anonymoususer)
    Thank you for the mark scheme! Do the marks needed for each grade boundary take into consideration the extra ten marks in section D?
    Indeed they do!
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    1 (b) was 4.
    9 (a) (i) and (ii) are both correct.
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    (Original post by omarkhaled)
    I think 16)c)i) was mass of animals used and it was 1,260,000,000g if I remember right
    Ok thank you I have updated my mark scheme
 
 
 
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