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 bhowland1994)
    No but you will be required to discuss the uses of halogenoalkanes, eg as fire retardants and
    modern refrigerants.
    I thought so thank you !
    Offline

    0
    ReputationRep:
    (Original post by SophieL1996)
    with displacement reactions of halogens with k halides, why can you shake it with an organic solvent? what does it do and why does it happen??
    You shake it with an organic solvent as that brings out more vibrant colours in the top layer of the solution (The organic solvent layer) allowing you to see what halogen is present. Simple as
    Offline

    0
    ReputationRep:
    (Original post by charlieejobson)
    why does magnesium react diffrently with steam? do we need to know why? also does anyone know if we need to know about back titrations?- what are they?
    well we had an M.C.Q qus 13 in 2013 jan, Why Mg reacts with steam cause the fraction of pariticle with energy grater than the activation energy is higher in the reaction with steam,
    thats the thing we might need to knw.

    what to u mean by back titration ?
    like titrating with acid in burette or otherway around Base inside the burette ?
    Offline

    0
    ReputationRep:
    http://www.edexcel.com/migrationdocu...e_20100607.pdf Q19 b ii
    Offline

    0
    ReputationRep:
    (Original post by ramanan)
    well we had an M.C.Q qus 13 in 2013 jan, Why Mg reacts with steam cause the fraction of pariticle with energy grater than the activation energy is higher in the reaction with steam,
    thats the thing we might need to knw.

    what to u mean by back titration ?
    like titrating with acid in burette or otherway around Base inside the burette ?
    Yes, I too want to know what a back titration is .... anyone know ?
    Offline

    0
    ReputationRep:
    There is no part Q19 b) ii .... :s
    Offline

    0
    ReputationRep:
    (Original post by bhowland1994)
    Yes, I too want to know what a back titration is .... anyone know ?
    Back titration
    Back titration is a titration done in reverse; instead of titrating the original sample, a known excess of standard reagent is added to the solution, and the excess is titrated. A back titration is useful if the endpoint of the reverse titration is easier to identify than the endpoint of the normal titration, as with precipitation reactions. Back titrations are also useful if the reaction between the analyte and the titrant is very slow, or when the analyte is in a non-soluble solid.[28


    Offline

    0
    ReputationRep:
    (Original post by bhowland1994)
    There is no part Q19 b) ii .... :s
    oh sorry its supposed to be jan 2010... my bad http://www.freeexampapers.com/index....ry%2FEdexcel#A Level/Chemistry/Edexcel/2010 Jan
    Offline

    0
    ReputationRep:
    (Original post by bhowland1994)
    Yes, I too want to know what a back titration is .... anyone know ?
    iodine-thiosulfate titrations what we do is back titration how sily-me not knowing this the whole time


    http://www.thestudentroom.co.uk/showthread.php?t=983259 look at post one
    Offline

    2
    ReputationRep:
    (Original post by bhowland1994)
    Yes, I too want to know what a back titration is .... anyone know ?
    Example: I want the concentration of this I2 solution. I've got any Na2S2O3 solution, BUT - I don't know the concentration of that either. So what I do is, titrate the Na2S2O3 against something of known concentration to find the concentration of Na2S2O3; and then I titrate the I2 with the sodium thiosulphate, and can get the concentration of the I2. It can be more complicated but this is one example. They won't ask for the definition, just do the problem in front of you when it comes.

    Which experimental set-ups do we need to be able to draw out? Heat under reflux, distil in situ, alcohol dehydration, anything else?
    Offline

    0
    ReputationRep:
    http://www.freeexampapers.com/index....ry%2FEdexcel#A Level/Chemistry/Edexcel/2010 Jan Q19 bii please!
    • Thread Starter
    Offline

    15
    ReputationRep:
    (Original post by SophieL1996)
    http://www.freeexampapers.com/index....ry%2FEdexcel#A Level/Chemistry/Edexcel/2010 Jan Q19 bii please!
    Just copy & paste, or print screen the question
    Offline

    0
    ReputationRep:
    (Original post by SophieL1996)
    oh sorry its supposed to be jan 2010... my bad http://www.freeexampapers.com/index....ry%2FEdexcel#A Level/Chemistry/Edexcel/2010 Jan
    Figured it out MS was a bit crap telling you on that one, Right: Moles of Sodium Thiosulfate = (vol x con) / 1000 -as the volume is in cm^3- this comes out at 1x10^-3 moles We then look at the original equation, the molar ratio of I2 to Sodium thiosulfate is 1:2 so we therefore divide our original answer by two to get 6.3x10^-4
    Offline

    0
    ReputationRep:
    (Original post by posthumus)
    Just copy & paste, or print screen the question
    9 The concentration of iodine in solution can be measured by titration with

    sodium thiosulfate solution.

    I2(aq) + 2S2O3

    2–(aq) 2I(aq) + S4O6

    2–(aq)

    (a) Name a suitable indicator which could be used for this titration.

    (1)

    ................................ ................................ ................................ ................................ ................................ ................................ ................................ ...............

    (b) The amount of sulfur dioxide in the atmosphere can be measured by passing a known

    volume of air through iodine solution. Sulfur dioxide converts iodine to iodide ions.

    SO2(g) + I2(aq) + 2H2O(l) SO4

    2–(aq) + 4H+(aq) + 2I(aq)

    In an experiment, 100 m3 of air were passed through 100 cm3 of iodine,

    concentration 0.0100 mol dm–3. The remaining iodine was titrated with sodium

    thiosulfate solution and reacted with 12.60 cm3 of sodium thiosulfate, concentration

    0.100 mol dm–3.

    (i) How many moles of iodine were present in the solution of the iodine at the start

    of the experiment?

    (1)

    (ii) How many moles of iodine remained in the solution at the end of the

    experiment?

    (2)

    (iii) Calculate the number of moles of iodine which reacted with the sulfur dioxide,

    and hence the number of moles of sulfur dioxide in 100 m3 of air.

    (2)

    17 *N35692A01724* Turn over

    (iv) The European Commission recommend exposure to sulfur dioxide in air should

    be less than 350 micrograms (350 × 10–6 g) per cubic metre.

    Calculate whether the sulfur dioxide in this sample of air was within this limit.

    One mole of sulfur dioxide has mass 64.1 g.

    (2)

    (c) Explain whether the changes below would or would not improve the experimental

    procedure for measuring the concentration of sulfur dioxide in air used in (b).

    (i) The 100 cm3 of iodine was divided into 25 cm3 samples before titration.

    (1)

    ................................ ................................ ................................ ................................ ................................ ................................ ................................ ...............

    ................................ ................................ ................................ ................................ ................................ ................................ ................................ ...............

    (ii) The concentration of sodium thiosulfate used to titrate the iodine was changed

    from 0.100 mol dm–3 to 0.050 mol dm–3.

    (2)

    ................................ ................................ ................................ ................................ ................................ ................................ ................................ ...............

    ................................ ................................ ................................ ................................ ................................ ................................ ................................ ...............

    ................................ ................................ ................................ ................................ ................................ ................................ ................................ ...............

    (iii) 150 m3 of air was passed through the iodine. The solutions used were of the

    same concentrations as in the original experiment.

    (2)

    ................................ ................................ ................................ ................................ ................................ ................................ ................................ ...............

    ................................ ................................ ................................ ................................ ................................ ................................ ................................ ...............

    ................................ ................................ ................................ ................................ ................................ ................................ ................................ ...............

    (Total for Question 19 = 13 marks)
    Offline

    0
    ReputationRep:
    (Original post by bhowland1994)
    Figured it out MS was a bit crap telling you on that one, Right: Moles of Sodium Thiosulfate = (vol x con) / 1000 -as the volume is in cm^3- this comes out at 1x10^-3 moles We then look at the original equation, the molar ratio of I2 to Sodium thiosulfate is 1:2 so we therefore divide our original answer by two to get 6.3x10^-4
    ah thanks how do you do the next part please??
    Offline

    0
    ReputationRep:
    Hello does anyone know what we need to know about drying agents(and which ones)? I can remember there was a question on them once but I don't know which paper. Any help is much appreciated, thank you.
    Offline

    0
    ReputationRep:
    (Original post by Katy1704)
    Hello does anyone know what we need to know about drying agents(and which ones)? I can remember there was a question on them once but I don't know which paper. Any help is much appreciated, thank you.
    anhydrous... mgso4, cacl2, cao
    Offline

    0
    ReputationRep:
    (Original post by SophieL1996)
    anhydrous... mgso4, cacl2, cao
    Thank you
    Offline

    9
    ReputationRep:
    Does anyone have an executive list of apparatus we might be asked to draw?
    Offline

    0
    ReputationRep:
    Guys, I'd really appreciate it if someone could do a list on what apparatus to draw for which experiments? E.G Alcohol to Aldehyde= Distillation.

    That would be a massive help. I get confused about what to draw when collecting bromoalkanes etc etc
 
 
 
  • 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
    Would you like to hibernate through the winter months?
  • 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.