Hey there! Sign in to join this conversationNew here? Join for free

Edexcel - Chemistry Unit 2 - 4 June 2013 Watch

  • View Poll Results: Which topic(s) are you finding most difficult?
    Shapes of molecules and ions
    11.66%
    Intermediate bonding and bond polarity
    15.95%
    Intermolecular forces
    9.82%
    Redox
    17.79%
    Group 2 & 7
    40.49%
    Kinetics & Equilibria
    14.11%
    Organic Chemistry - Alcohols and Halogenoalkanes
    39.26%
    Mechanisms
    26.38%
    Green Chemistry
    28.83%

    Offline

    0
    ReputationRep:
    (Original post by posthumus)
    Heat under Reflux apparatus





    At most you'll just need to know this really:

    The liberated iodine reacts with thiosulfate ion

    I2 + 2S2O3^2- ----> 2I- + S4O6^2-

    They give you this stuff anyway usually, it's calculations you should be most concerned with
    That's what I thought but this is the mark scheme:
    Name:  ImageUploadedByStudent Room1370330654.417563.jpg
Views: 133
Size:  132.1 KB


    Posted from TSR Mobile
    Offline

    2
    ReputationRep:
    (Original post by SophieL1996)
    thanks but that's part a I mean the iionic equations. thank you
    Oops! Sorry!

    bi. Well, you know there has to be 2H+ because H2O is formed. In an ionic equation the charges on both sides must balance. Currently you have ClO- + 2H+ --> Cl- + H2O, so the charge on the LHS is +1 but the RHS is -1. So you add 2 electrons to the LHS to get ClO- + 2H+ + 2e- --> Cl- + H2O

    It's the same principle for the iodide. You need 2 iodide ions to make 1 iodine molecule, and you need to add 2 electrons to the RHS to make the charges balance

    2I- --> I2 + 2e-


    ii. You simply check that the number of moles of electrons transferred in each equation is the same (in this case it is, but if it isn't you just multiply one or both equations to get equal moles of electrons) and then add the equations together. You don't need to show the electrons in the final equation.

    ClO- + 2H+ + 2I- --> Cl- + H2O + I2
    • PS Reviewer
    Offline

    20
    ReputationRep:
    PS Reviewer
    (Original post by wanna_get_A*)
    can u send me the jan 13 paper please?


    Posted from TSR Mobile
    Here
    Attached Images
  1. File Type: pdf 6CH02_01_rms_20130307.pdf (226.4 KB, 47 views)
  2. File Type: pdf 6CH02_01_que_20130116.pdf (453.6 KB, 50 views)
    Offline

    0
    ReputationRep:
    (Original post by Matterhorn)
    That's what I thought but this is the mark scheme:
    Name:  ImageUploadedByStudent Room1370330654.417563.jpg
Views: 133
Size:  132.1 KB


    Posted from TSR Mobile


    Because they asked how you would collect gaseous alkenes. Either you collect it over water or in a syringe. Just make sure there's an open end or else pressure will build up. :cool:
    • Thread Starter
    Offline

    14
    ReputationRep:
    (Original post by Matterhorn)
    That's what I thought but this is the mark scheme:
    Name:  ImageUploadedByStudent Room1370330654.417563.jpg
Views: 133
Size:  132.1 KB


    Posted from TSR Mobile
    Geor was right :eek:

    That's nowhere in the book though god damn it ... what year is this question from ???? Hopefully it doesn't come up
    Offline

    0
    ReputationRep:
    (Original post by bhowland1994)
    You heat under reflux
    Mark scheme says ignore any use pumice reflux :s


    Posted from TSR Mobile
    • PS Reviewer
    Offline

    20
    ReputationRep:
    PS Reviewer
    (Original post by SophieL1996)
    hi, how did you do q 21 b i and ii? I don't really understand. thanks
    For the first equation, just add two hydrogens on the left hand side to balance, then balance the charge with electrons. So two electrons on the left.

    For the second equation, you need 2I- on the left hand side and therefore you need two electrons on the right hand side to balance.

    moles of thiosulfate = 24.2*0.05/1000

    Then you look at the mole ratio in the equation they give you in the question. Iodine reacts with thiosulfate in a 1:2 ratio, so divide the answer above by two.
    • Thread Starter
    Offline

    14
    ReputationRep:
    (Original post by airheadbuster)


    Because they asked how you would collect gaseous alkenes. Either you collect it over water or in a syringe. Just make sure there's an open end or else pressure will build up. :cool:
    Even if it's gaseous alkenes the reflux is meant to condense it back into the mixture
    Offline

    0
    ReputationRep:
    (Original post by posthumus)
    Geor was right :eek:

    That's nowhere in the book though god damn it ... what year is this question from ???? Hopefully it doesn't come up
    May 2011


    Posted from TSR Mobile
    Offline

    0
    ReputationRep:
    (Original post by posthumus)
    Geor was right :eek:

    That's nowhere in the book though god damn it ... what year is this question from ???? Hopefully it doesn't come up
    May 2011 17 f)ii) :cool:
    Offline

    0
    ReputationRep:
    (Original post by James A)
    For the first equation, just add two hydrogens on the left hand side to balance, then balance the charge with electrons. So two electrons on the left.

    For the second equation, you need 2I- on the left hand side and therefore you need two electrons on the right hand side to balance.

    moles of thiosulfate = 24.2*0.05/1000

    Then you look at the mole ratio in the equation they give you in the question. Iodine reacts with thiosulfate in a 1:2 ratio, so divide the answer above by two.
    ok thanks
    Offline

    0
    ReputationRep:
    (Original post by Linked)
    do i have to remember the actual equations - including state symbols?
    Just remember the reaction of H2SO4 and the strongest reducing agent KI

    So the first reaction is the reduction of H2SO4...

    KI + H2SO4 -------> HI + KHSO4 (really simple one)

    Now HI can reduce H2SO4 as well

    2HI + H2SO4 --------> I2 + SO2 + 2H20

    Finally as HI is such a strong reducing agent it can reduce again

    6HI + SO2 ------> 3I2 + H2S +2H20



    Now all you need to remeber is that KI and KCl only do the first step and KBr does the first and second step
    Offline

    0
    ReputationRep:
    (Original post by posthumus)
    Even if it's gaseous alkenes the reflux is meant to condense it back into the mixture
    I don't think butene can condense under normal laboratory conditions.
    Offline

    0
    ReputationRep:
    (Original post by posthumus)
    Even if it's gaseous alkenes the reflux is meant to condense it back into the mixture
    I guess just don't use reflux when you need to collect gaseous mixtures :/


    Posted from TSR Mobile
    Offline

    0
    ReputationRep:
    Can someone please jot down the names then of alll the equipment set ups we need to know and an example of what reaction they are used for, so distillation, heating under reflux and this new one regarding the collection of gaseous mixtures .....
    • Thread Starter
    Offline

    14
    ReputationRep:
    (Original post by airheadbuster)
    I don't think butene can condense under normal laboratory conditions.
    (Original post by Matterhorn)
    I guess just don't use reflux when you need to collect gaseous mixtures :/

    Posted from TSR Mobile
    I guess alkenes have a very low boiling temperature, which makes sense !

    So does anyone have an image of what the apparatus should look like ? I know geor posted one yesterday

    Also is Beryllium the only one which has BeO layer, hence it can't react with water ? If not, then why is it so unreactive
    Offline

    1
    ReputationRep:
    this exam is my *****
    Offline

    0
    ReputationRep:
    Guys in the Jan 2012 MS it says Water can form 2 Hydrogen bonds per molecule, but some guys on here seem to think it's four?
    Offline

    0
    ReputationRep:
    if i draw a horizontal test tube to collect the gaseous alkenes with the ceramic fibre and everything, do i still need to draw an opening to not build pressure up? if so, where do i put it?
    • Thread Starter
    Offline

    14
    ReputationRep:
    (Original post by GCSE-help)
    Guys in the Jan 2012 MS it says Water can form 2 Hydrogen bonds per molecule, but some guys on here seem to think it's four?
    Yup stick to two !!! It's four in solid form (crystals).
 
 
 
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • Poll
    What's your favourite Christmas sweets?
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

    Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

    Quick reply
    Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.