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CHY3H Unofficial Mark Scheme June 2012

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    how many marks would 88ums be
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    (Original post by umar ali)
    how many marks would 88ums be
    34 or 35 marks considering this exam was pretty easy
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    Here's my full answers, let me know what you think

    1a) The water is hard because it contains magnesium ions. When sodium carbonate is added it reacts with the magnesium sulphate to form a precipiate of magnesium carbonate. Because the magnesium is removed from the water it's soft and the and the sdoium ions displace the magensium ions (3)
    b) Result is anomalous(1)
    ii) 68 degrees C (1)
    iii) because the water would evaporate at 100c (1)
    c) Because it isn't a curve and as the temperature increases the solubility doesn't always increase. Also, the solbuility increases to 68 C and then falls when it should continue going up (2)
    2 a) They are metals and they all have one electron in their outer shell (2)
    b) He put two elements in same box more than one for example he put Di and Mo in the same box. Also, it wasn't accepted as he put metals and non metals in the same group, for example he put gold and oxygen in the same group and also he put elements in groups with elements that they don't react similarly to for example he put copper and lithium in the same groups(3)
    c) He considered undiscovered elements and left gaps for them so that they could easilly fit into his period table (2)
    3 a) Transition metals are strong,malleable and don't corrode easily (2)
    b) The electrons of transition metals fill up the 3rd enegry level after there are two in the 4th shell, meaning that they usually have the same number of electrons in their outer energy level, making them have similar properties (2)
    4 a) H+(1)
    b) pH of weak acid higher and the pH of a strong acid is lower as it's fully ionised in water so there is more hydrogen ions in solution so they have lower pH (2)
    c) 0.61 mol/dm3 (3)
    ii) 12g (2)
    5 a) i) Bubble gas through limewater and limewater should go cloudy (2)
    ii) Wrong, as ammonia gas did not form when sodium hydroxide was added (2)
    iii) Right , as white precipitate formed after silver nitrate added (2)
    b) i) Atom Absorption Spectroscopy (1)
    ii) Measure smaller amounts (1)
    6. Chlorine atoms are smaller so the electrons in the outer energy level are closer to the postive nucleus, so they are more strong sttracted to the positive nucleus. Also, in chlorine, the electrons are less sheilded from the positive charge on the nucleus so they are ore strongly attracted to the positive nucleus. Because of this there are more strongly attractied to the nucleus so any electron that would be added to the outer energy less is gained more easily (3)
    7 a) -810 kJ/mol (3)
    b) Because the energy released from new bonds forming is more than the enrgy required to break the existing bonds(1)
    c) Because it provides the activation energy (1)

    I think i got 36/45 :/

    I think i dropped marks here

    iii) because the water would evaporate at 100c (1)-Lose 1
    c)Because it isn't a curve and as the temperature increases the solubility doesn't always increase. Also, the solbuility increases to 68 C and then falls when it should continue going up (2)-Lose 1
    3 a) Transition metals are strong,malleable and don't corrode easily (2)-Lose 1
    ii) Wrong, as ammonia gas did not form when sodium hydroxide was added (2)-Lose 2
    iii) Right , as white precipitate formed after silver nitrate added (2)-Lose 2
    b) i) Atom Absorption Spectroscopy (1)-Lose 1 as i mispelt it
    ii) Measure smaller amounts (1)-Lose 1

    Can you see where i've dropped or gained marks compared to what i've put please?
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    (Original post by umar ali)
    thanks 4 that why do u divide by 4
    1000/250 = 4

    (Original post by umar ali)
    how many marks would 88ums be
    Around 33.
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    (Original post by umar ali)
    thanks 4 that why do u divide by 4
    48g is in a litre

    the question asks for 250ml

    so divide by 4

    because 250ml is 1/4 of a litre
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    5) a) iii) You've put the wrong thing. Although chloride does form a white precipitate after silver nitrate solution is added, the student had kept the hydrochloric acid (from test 1) in the mixture, so you are unable to tell whether the chloride was in the original substance or whether the white precipitate was a result of the chloride in the hydrochloric acid.
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    (Original post by umar ali)
    **** for the 12g i put 3.33...
    well all my class got 3.33 grams?????


    how do you work it out pleasssseee help
    I got that too! Thank god I'm not the only one... although I think it might be wrong
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    For the 100 degrees question, I said he already had enough data to see a trend... Think I mighhhtt just get the mark, or is it too off?
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    (Original post by Student95)
    I got that too! Thank god I'm not the only one... although I think it might be wrong
    lol
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    Could anyone post the CHY2H June 2012 unofficial mark scheme please :? :-
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    hi guys i made some stupid mistake on the bond energy question and got -990. i wanted to know what the 3 marks were for because i think i did the calculations correct but maybe entered it wrong on my calculator ??

    thanks
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    (Original post by RaeesaP)
    For the 100 degrees question, I said he already had enough data to see a trend... Think I mighhhtt just get the mark, or is it too off?
    That's what I put, I'm not counting it as a mark.
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    for 5bi (i think that was the q) i put gas-liquid chromatography... am i wrong? it was so annoying, i could remember Atmomic Absorbtion S.... but i couldnt remember Spectroscopy, so annoying -_-
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    (Original post by PhoenixLament)
    0.8 x 60 = 48

    48 / 4 = 12g

    Just in a really simple form
    ooh i didnt use this method, but i did moles = 250/1000 x 0.80 = 0.2 moles

    then i did mass = moles x Mr ( unit 2 days hehe) to get mass = 0.2 x 60

    = 12g

    so different methods same answer
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    (Original post by LucyW456)
    for 5bi (i think that was the q) i put gas-liquid chromatography... am i wrong? it was so annoying, i could remember Atmomic Absorbtion S.... but i couldnt remember Spectroscopy, so annoying -_-
    Gas-liquid chromatography is wrong cos that only tests for stuff that can be easily vaporised? it is an elements test so i assume it could be correct, but mark schemes tend to say 'ignore chromatography' so i dunno
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    (Original post by v.007)
    hi guys i made some stupid mistake on the bond energy question and got -990. i wanted to know what the 3 marks were for because i think i did the calculations correct but maybe entered it wrong on my calculator ??

    thanks
    oi think marks will be for getting the correct energy values for both products and reactants and then for subtracting one from the other to get +- 810 kJ
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    (Original post by Cubic)
    That's what I put, I'm not counting it as a mark.
    Aah fair enough, thanks anyway
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    The question about test for chlorides is wrong as hydochloric acid was added not nitiric and hydrochloric alride has chloride ions so a white precipatate would be given.
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    wtf energy answer is -118, they tricked ya suckers like in da past paperrr!
    (even my CHEM TEACHER said it is -118)

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