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Chemistry HL, P1, P2, TZ2 2012

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    (Original post by MAMDS1993)
    I didnt like the carbon dating I mean what the hell for 3 marks? I just wrote used to determine age of plant and animal fossils..apparently it had to do with half-lives!
    Exactly! I lost 3 marks there probably.. Was hoping for a 7 but now i feel like it's between a 6 and a 7
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    Yeah I knew I-130 is used for tracing and diagnosing! And because its radioactive and emits gamma radiation its obvious effect would be its penetrating effect on cells!
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    I found the carbon dating ridiculous.... Apparently not many people got it other than the people who took physics. That's not chemistry! Also did anyone did the acid and base option in section B? I got ph of 11. Something and buffer ph of 9.25 I think 14-4.75
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    In question 9 has anyone managed to understand the last part of the question. First of all they gave you temperature and k graph you then had to state what k and A stands in Aarrhenius equation, then they asked you to calculate activation energy and the last to marks were for finding A - how do you find A I was so confused, so I somehow cramed some numbers in my calculator and a random value appeared it looked fine so I wrote it in.

    Overall the paper was mediocre, though it could have been much worse. Question 1 was pretty good however I could't figure out how to write redox equations for oxidation of hydrogen peroxide. Question 2 was also not bad as they asked to find a limiting reactant, I got .003 moles for magnesium and .03 moles for hydrochloric acid - you sneaky IB trying to confuse people. And then they asked why experimental value of hydrogen is lower than theoretical - I hate the application questions as IB tends to come up with very specific reasons. Question 3 was lattice enthalpies and it was OK, I especially enjoyed the diagram. Question 4 Lewis structures for XeF4 and the nitrate ion NO3- - thank you IB for this question !!!!!!!. Question 5 was about isotopes, I couldn't think anything about carbon 14 so I sort of waffled on about.......something. And of course question 6 - salt hydrolysis...I couldn't remember any equations so I just explained it. Part B was equally OK.

    Though paper 1 was strangely easy - made me worried last night.
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    Paper was was fine, paper 2 was pretty rubbish. All my friends agreed that it was the more difficult one out of the two. I was hoping for a 6, but it looks like I'm going to get a 5 now. :l
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    (Original post by momentalus)
    In question 9 has anyone managed to understand the last part of the question. First of all they gave you temperature and k graph you then had to state what k and A stands in Aarrhenius equation, then they asked you to calculate activation energy and the last to marks were for finding A - how do you find A I was so confused, so I somehow cramed some numbers in my calculator and a random value appeared it looked fine so I wrote it in.
    I think you were just meant to rearrange the Arrhenius equation- since you'd calculated Ea at a specific temp, then you just sub the values in and rearrange. I got something like e^16, though not so sure about that....
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    (Original post by arthurhoe123)
    I found the carbon dating ridiculous.... Apparently not many people got it other than the people who took physics. That's not chemistry! Also did anyone did the acid and base option in section B? I got ph of 11. Something and buffer ph of 9.25 I think 14-4.75
    Yeah I remember getting 11.46 so rounded to 11.5! Buffer yep you're right I got the same thing! What did you put for the indicator pKA and pH range relationship and the property..the property I said was its ability to exist in different colours in acid and in base dissociated and undissociated form!
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    I got the same values for the pH I rounded to 11.5 too. For the indicator I put the pKa value is in between the range of the pH values therefore in the range of pH valus given, the H+ ion concentration is large enough to drive the forward/backward reaction allowing a colour change. However, at other values it is not. Well at least that is what I remember putting. Do you remember what you got for the q=mcdeltaT bit?
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    Well, for the Pka and ph relationship. I am pretty sure is that... well heres what i did. I wrote that assume Hln is the indicator. It is a weak acid then Hln dissociate into H+ and ln- ions in equilibrium and they exist in two colours A and B. Because they are two distinct different colours, the colour change would occur when Ln- = Hln which would bring ph=pka and that would be the range whereby the first colour change would occur.
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    (Original post by momentalus)
    In question 9 has anyone managed to understand the last part of the question. First of all they gave you temperature and k graph you then had to state what k and A stands in Aarrhenius equation, then they asked you to calculate activation energy and the last to marks were for finding A - how do you find A I was so confused, so I somehow cramed some numbers in my calculator and a random value appeared it looked fine so I wrote it in.

    Overall the paper was mediocre, though it could have been much worse. Question 1 was pretty good however I could't figure out how to write redox equations for oxidation of hydrogen peroxide. Question 2 was also not bad as they asked to find a limiting reactant, I got .003 moles for magnesium and .03 moles for hydrochloric acid - you sneaky IB trying to confuse people. And then they asked why experimental value of hydrogen is lower than theoretical - I hate the application questions as IB tends to come up with very specific reasons. Question 3 was lattice enthalpies and it was OK, I especially enjoyed the diagram. Question 4 Lewis structures for XeF4 and the nitrate ion NO3- - thank you IB for this question !!!!!!!. Question 5 was about isotopes, I couldn't think anything about carbon 14 so I sort of waffled on about.......something. And of course question 6 - salt hydrolysis...I couldn't remember any equations so I just explained it. Part B was equally OK.

    Though paper 1 was strangely easy - made me worried last night.
    I got 3.04X10^(-3) or I think moles and volume I got 74. something cm^3. The salt hydrolysis qn, I just explained that the Cr Nitrate comes from a strong acid and a weaker base so the salt will be slightly acidic the other one was neutral made from two weak acid and bases. What did you get for question 7, in the heat energy in KJ what I did is find number of moles and then multiply that by the KJmol value given. And the heat energy one a few qns later was just mc delta T over 1000 x number of moles and it was endothermic coz the temp was going down! What did you guys put for how hybridisation in methane helps determine its shape?? I put sp3 constitutes 4 sigma bonds which give rise to bond angle of 109.5 and a tetrahedral shape. And what was AlCl3 and Al2O3, one of them conducts I said AlCl3 is covalent and it is held together by covalent bonds so carries no ions and thus cannot conduct where Al2O3 is held together by ionic bonds and it is an ionic lattice structure and in molten possesses ions which are free to move about but the Al2O3 becomes decomposed in the process.
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    (Original post by seventyfourable)
    I got the same values for the pH I rounded to 11.5 too. For the indicator I put the pKa value is in between the range of the pH values therefore in the range of pH valus given, the H+ ion concentration is large enough to drive the forward/backward reaction allowing a colour change. However, at other values it is not. Well at least that is what I remember putting. Do you remember what you got for the q=mcdeltaT bit?
    I cant remember exactly but the key thing is that 100cm3 = 100g i think and the c is the specific heat capacity of water if i remembered correctly... temperature would just be diff. The energy is for a specific amount of mole i think... then convert it to energy KJ/one mol. I put a positive sign because I think its endothermic as temperature dropped
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    argh.. i guessed croh3 is a strong base and hence the solution is neutral = = do u think i would get a mark for at least getting the concept right and identifying that the acid is a strong acid
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    (Original post by arthurhoe123)
    Well, for the Pka and ph relationship. I am pretty sure is that... well heres what i did. I wrote that assume Hln is the indicator. It is a weak acid then Hln dissociate into H+ and ln- ions in equilibrium and they exist in two colours A and B. Because they are two distinct different colours, the colour change would occur when Ln- = Hln which would bring ph=pka and that would be the range whereby the first colour change would occur.
    I wrote something of the sort, but I remember saying something about the half equivalence point as well I said the pKa and pH equal when another and the half equivalence point when the two HIN and IN- are present in roughly equal amounts so H+ = Ka, so that is when the indicator is most effective, something along those lines!
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    (Original post by arthurhoe123)
    Paper 1 was quite easy i thought. Except for 2 question i was unsure. for q 1 i got D which was 6.6x10^23 as there are 11 atoms in there. everyone seem to got ^22 so i am not sure.

    And there is one question on wavelength and frequency what did everyone get? i got infrared and infrared
    Apparently D is correct...ffs, I fell for their trap and put 6.02 x 10^22 :/ I thought I had that one right!
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    For the salt hydrolysis (Q6) i think I thought because Cr is a complex ion it was ligand formation because H20 forms a ligand with it which leads to excess H+ ions ... not sure though but I saw a similar question in one of the past papers but with Fe instead so I am guessing it is the same
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    (Original post by seventyfourable)
    For the salt hydrolysis (Q6) i think I thought because Cr is a complex ion it was ligand formation because H20 forms a ligand with it which leads to excess H+ ions ... not sure though but I saw a similar question in one of the past papers but with Fe instead so I am guessing it is the same
    Yeah ur right as well, leaving excess H+ ions in solution therefore acidic (I wrote that too, just incase they dont accept the combination of strong acid weak base argument)..I think both answers r correct! It was only 2 marks anyway one for identifying and one for giving a reason! Umm what did you put for the CH3COONH4?
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    (Original post by MAMDS1993)
    Yeah ur right as well, leaving excess H+ ions in solution therefore acidic (I wrote that too, just incase they dont accept the combination of strong acid weak base argument)..I think both answers r correct! It was only 2 marks anyway one for identifying and one for giving a reason! Umm what did you put for the CH3COONH4?
    hey sry im butting in but i thought it would be neutral since it's a weak acid weak base combination hope it's right
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    (Original post by aeyurttaser13)
    hey sry im butting in but i thought it would be neutral since it's a weak acid weak base combination hope it's right
    yep I put the same thing I'm pretty sure that ones right
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    yesss exactly! CH3COOH and NH4OH !
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    (Original post by seventyfourable)
    yep I put the same thing I'm pretty sure that ones right
    haha im glad.. i think i lost marks in the carbon 14 question, and a couple more.. fingers crossed for a 7 in paper 2

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Updated: May 23, 2012
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