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Edexcel A2 Chemistry Exams -6CH04 (14th June) and 6CH05 (22nd June) Discussion Thread watch

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    (Original post by tootfruity)
    3 can dissociate into NH3 and HCl, and then the HCl can dissociate further to produce H+ ions and Cl- ions which are strongly acidic?
    I'm not sure if NH4Cl to NH3 + HCl counts as dissociating....does it?

    I thought dissociating meant to make H+ or OH- ions straight away then if possible make more eg. H+ from the same compound... now I'm confused.
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    https://c838cff4741acb48ae1ed62e5992...0Chemistry.pdf

    Q19)b)v) i dont get how its hazardous due to being in powder form?

    (v) Icing sugar can be hazardous when it is being finely powdered in a factory. Explain why sucrose is stable at room temperature, in spite of your answer topart (iii), but its manufacture is hazardous.

    MS: (hazardous because small particles/ powder have/ has)larger surface area and react faster
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    Can someone explain the advantages and disadvantages of biofuels and biodiesel
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    (Original post by maria17xo)
    I am really stuck on this one marker question, i have tried but can't seem to get the right answer. can someone please explain it. it is question 3d on multiple choice. Thanks

    http://qualifications.pearson.com/co...e_20130612.pdf
    This question really got me too haha. If you work out the moles of the acid and alkali, you'll find that the acid is in excess. When you subtract the moles of alkali from the moles of acid to see how many moles of acid you have left over, you'll find that it is the same as the moles of ethanoate ions formed. Thus, [HA] = [A-], which means that Ka = [H+] (think about the expression for Ka and you'll see why this is the case). So, to find [H+], you just use your value for Ka!
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    can anyone give a links to Jan 16 U4 paper? MS+QP?
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    (Original post by ihaspotato)
    I'm not sure if NH4Cl to NH3 + HCl counts as dissociating....does it?

    I thought dissociating meant to make H+ or OH- ions straight away then if possible make more eg. H+ from the same compound... now I'm confused.
    Hmm maybe you're right I don't know :/ I would say that the question is probably elimination:
    We know ammonia is a weak base so it will have the highest pH (most alkaline) and then carboxylic acids are weakly acidic so that leaves NH4Cl so be left as the most acidic?!
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    (Original post by imnoteinstein)
    https://c838cff4741acb48ae1ed62e5992...0Chemistry.pdf

    Q19)b)v) i dont get how its hazardous due to being in powder form?

    (v) Icing sugar can be hazardous when it is being finely powdered in a factory. Explain why sucrose is stable at room temperature, in spite of your answer topart (iii), but its manufacture is hazardous.

    MS: (hazardous because small particles/ powder have/ has)larger surface area and react faster
    Do you not get what the mark scheme is saying? In case you don't, larger surface area = increase in collision frequency hence increase in rate of reaction.
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    (Original post by TeaAndTextbooks)
    Does anyone know where I can find Jan 16 IAL Chem4? Thanks

    Posted from TSR Mobile
    Incase you didn't find it yet! I know it's too late lol
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  1. File Type: pdf January 2016 (IAL) QP - Unit 4 Edexcel Chemistry.pdf (516.0 KB, 56 views)
  2. File Type: pdf January 2016 (IAL) MS - Unit 4 Edexcel Chemistry.pdf (336.5 KB, 49 views)
  3. File Type: pdf WCH04_01_pef_20160303.pdf (97.6 KB, 57 views)
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    (Original post by n2697)
    Attachment 549061and this one! Thanks in advance
    Step 1: Work out moles of HCl.

    Step 2: Work out concentration of [H+] (which will be equal to [HCl] since HCl dissociates fully, being a strong acid) once added to the solution using the formula concentration = moles * 1000 / volume.

    Step 3: -log([H+]) = pH
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    (Original post by Don Pedro K.)
    Do you not get what the mark scheme is saying? In case you don't, larger surface area = increase in collision frequency hence increase in rate of reaction.

    okay im probably being dumb af: I get that the rate increases bc large surface area. Whats the hazard though? Why is that dangerous?
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    (Original post by n2697)
    Attachment 549059help d:
    3:1 molar ratio so concentration will be in a 3:1 molar ratio since they are all in the same volume.

    Thus:
    Ka = [H+][CH3COO-] / [CH3COOH]

    Rearranging...

    [H+] = Ka * [CH3COOH] / [CH3COO-]

    [H+] = (1.7x10-5)(3)/(1) =====> [H+] = 5.1x10-5 moldm-3.

    Therefore, pH = -log(5.1x10-5) = 4.29.... = 4.3 to 1 decimal place
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    (Original post by imnoteinstein)
    okay im probably being dumb af: I get that the rate increases bc large surface area. Whats the hazard though? Why is that dangerous?
    Haha no dw I think I would have had to have done the previous parts, because that probably gives a clue.Not sure sorry :s
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    (Original post by maria17xo)
    I am really stuck on this one marker question, i have tried but can't seem to get the right answer. can someone please explain it. it is question 3d on multiple choice. Thanks

    http://qualifications.pearson.com/co...e_20130612.pdf
    This a buffer question (as theres a weak acid involved) so you have to work out how much salt if form from the neutralisation and then work out the left over amount of ethanoic acid, use these values in the Ka equation for buffers and the answer is D
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    Could someone please explain why there are different answers to similar questions?
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    how many peaks are there in a low resolution nmr spectrum for pentanal
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    Somebody tell me why it's not B?

    Funky_Giraffe samb1234
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    (Original post by imnoteinstein)
    okay im probably being dumb af: I get that the rate increases bc large surface area. Whats the hazard though? Why is that dangerous?
    The question is talking about the combustion of sucrose, its dangerous because finely powdered sugar (sucrose) can ignite because of the increased rate of reaction. Having the sugar ignite into flames is pretty dangerous
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    (Original post by sonam_28)
    how many peaks are there in a low resolution nmr spectrum for pentanal
    5 peaks
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    (Original post by Don Pedro K.)
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    Somebody tell me why it's not B?

    Funky_Giraffe samb1234
    Did you include water in you Kc calculation? At equilibrium you get 3 mol of water and 3 mol of the ester.
    There would be 1 mol of acid and 3 mol of ethanol. So Kc would be 3^2/3=3
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    (Original post by Don Pedro K.)
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    Somebody tell me why it's not B?

    Funky_Giraffe samb1234
    the answer is C, because you use mole rations to calculate the amount of reactants used up.
    so for Kc you get 9/3, (3*3/1*3/)
 
 
 
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