Chemistry unit 6 June 2016

Announcements Posted on
    Offline

    3
    ReputationRep:
    (Original post by samb1234)
    The mistake you made was the - sign. If you are doing it that way, i.e. reduced species -oxidised species, you do NOT change the sign of the ecell values, i.e. in this case you would have X--0.14
    But why we don't change it, as in what they have put, it is the value for the reduction of Sn and it's oxidation should be the opposite of the equation with a change to the sign ?

    Posted from TSR Mobile
    Offline

    2
    ReputationRep:
    (Original post by PlayerBB)
    But why we don't change it, as in what they have put, it is the value for the reduction of Sn and it's oxidation should be the opposite of the equation with a change to the sign ?

    Posted from TSR Mobile
    There are different ways of approaching it. Either you flip the sign and treat it as a normal sum and add the two numbers together (my personal preference) or you can remember the formula Ecell = Ereduction -Eoxidation (which is doing exactly the same thing, Eoxidation is the reduction potential for the oxidised species so by subtracting it you are flipping the sign, just as you would if you did the first method)
    Offline

    3
    ReputationRep:
    (Original post by samb1234)
    There are different ways of approaching it. Either you flip the sign and treat it as a normal sum and add the two numbers together (my personal preference) or you can remember the formula Ecell = Ereduction -Eoxidation (which is doing exactly the same thing, Eoxidation is the reduction potential for the oxidised species so by subtracting it you are flipping the sign, just as you would if you did the first method)
    Ahh, sorry for asking, but if the question gave us that the reaction is feasible, and gave us one of the potentials, do we also do this or directly, go by Ecell= Ered - Eoxi ?

    Posted from TSR Mobile
    Offline

    2
    ReputationRep:
    (Original post by PlayerBB)
    Ahh, sorry for asking, but if the question gave us that the reaction is feasible, and gave us one of the potentials, do we also do this or directly, go by Ecell= Ered - Eoxi ?

    Posted from TSR Mobile
    It's the same process, the only difference with feasibility questions is you have to do what it tells you to do. Normally you would say the more negative one is the one which would be oxidised, but for feasibility you have to assume it happens as it tells you in the question and do the maths as if they are right and then comment after if it is feasible
    Offline

    3
    ReputationRep:
    (Original post by samb1234)
    It's the same process, the only difference with feasibility questions is you have to do what it tells you to do. Normally you would say the more negative one is the one which would be oxidised, but for feasibility you have to assume it happens as it tells you in the question and do the maths as if they are right and then comment after if it is feasible
    Ahhh, thank you SO MUCH!!!

    Posted from TSR Mobile
    Offline

    3
    (Original post by Adorable98)
    http://qualifications.pearson.com/co...e_20110119.pdf

    Q2(ii)

    The answer is:
    The concentration of iodine is proportional to the titre

    Why's that?
    Anyone ??
    Offline

    3
    ReputationRep:
    (Original post by Adorable98)
    Anyone ??
    \displaystyle \mathrm{C_{S_{2}O_{3}^{2-}}V_{S_{2}O_{3}^{2-}}=C_{I_{2}}V_{I_{2}}} \iff \mathrm{V_{S_{2}O_{3}^{2-}}= \frac{C_{I_{2}}V_{I_{2}}}{C_{S_{  2}O_{3}^{2-}}}} \Rightarrow \mathrm{V_{s} \propto C_{I_{2}} }

    This is what I wrote on my mock.

    Has anyone done the NMR question on June 2013? It was one of those questions you'd really appreciate so long it didn't come in your exam.
    Offline

    3
    (Original post by Ayman!)
    \displaystyle \mathrm{C_{S_{2}O_{3}^{2-}}V_{S_{2}O_{3}^{2-}}=C_{I_{2}}V_{I_{2}}} \iff \mathrm{V_{S_{2}O_{3}^{2-}}= \frac{C_{I_{2}}V_{I_{2}}}{C_{S_{  2}O_{3}^{2-}}}} \Rightarrow \mathrm{V_{s} \propto C_{I_{2}} }

    This is what I wrote on my mock.

    Has anyone done the NMR question on June 2013? It was one of those questions you'd really appreciate so long it didn't come in your exam.
    So is that a formula I should know?
    Offline

    1
    ReputationRep:
    (Original post by Ayman!)
    \displaystyle \mathrm{C_{S_{2}O_{3}^{2-}}V_{S_{2}O_{3}^{2-}}=C_{I_{2}}V_{I_{2}}} \iff \mathrm{V_{S_{2}O_{3}^{2-}}= \frac{C_{I_{2}}V_{I_{2}}}{C_{S_{  2}O_{3}^{2-}}}} \Rightarrow \mathrm{V_{s} \propto C_{I_{2}} }

    This is what I wrote on my mock.

    Has anyone done the NMR question on June 2013? It was one of those questions you'd really appreciate so long it didn't come in your exam.
    That NMR question was honestly one of the more difficult ones, I couldn't even understand the spectrum
    Offline

    3
    ReputationRep:
    (Original post by demotivated)
    That NMR question was honestly one of the more difficult ones, I couldn't even understand the spectrum
    Heck yeah. IAL May 15 and Jan 16 also have decent ones but not nearly as difficult.

    (Original post by Adorable98)
    So is that a formula I should know?
    I think so. I'm not sure how to show that they're proportional otherwise. We learnt the C1V1 = C2V2 formula in GCSEs so it kinda just stuck.
    Offline

    1
    ReputationRep:
    Can anyone help me with an NMR question in Jan 2014 IAL https://52e1064b4dc7f9fd87a96faa7f7e...0Chemistry.pdf

    Question 3 (h)

    The answer for the displayed formula is

    But I don't understand how to figure out that the methyl group is attached to a carbon from the spectrum? I would just draw 4 carbons in a straight chain
    Offline

    2
    ReputationRep:
    (Original post by demotivated)
    Can anyone help me with an NMR question in Jan 2014 IAL https://52e1064b4dc7f9fd87a96faa7f7e...0Chemistry.pdf

    Question 3 (h)

    The answer for the displayed formula is

    But I don't understand how to figure out that the methyl group is attached to a carbon from the spectrum? I would just draw 4 carbons in a straight chain
    Check the spectrum. It shows that there are four different proton environments so based on the analysis of that spectrum, we can deduce a structure for the compound. If you see the spectrum, one of the environments shows around 8 small peaks and those number of peaks are actually telling us that the neighbouring carbon has 7 hydrogen around it which splits into 8(with reference to the n+1 rule).
    Offline

    2
    ReputationRep:
    I hope I'm correct lol I suck in this topic
    Offline

    2
    ReputationRep:
    (Original post by Ayman!)
    Heck yeah. IAL May 15 and Jan 16 also have decent ones but not nearly as difficult.



    I think so. I'm not sure how to show that they're proportional otherwise. We learnt the C1V1 = C2V2 formula in GCSEs so it kinda just stuck.

    Ayman, how are the moles of Iodine and Sodium Thiosulfate equal? Like did you assume this that they are equal?
    Offline

    1
    ReputationRep:
    (Original post by sabahshahed294)
    Check the spectrum. It shows that there are four different proton environments so based on the analysis of that spectrum, we can deduce a structure for the compound. If you see the spectrum, one of the environments shows around 8 small peaks and those number of peaks are actually telling us that the neighbouring carbon has 7 hydrogen around it which splits into 8(with reference to the n+1 rule).
    I think they are 9 peaks, but even then I don't see any carbon in the structure which has 8 hydrogen atoms attached to the carbons adjacent? It's also really inconvinient how we don't get the data booklet
    Offline

    2
    ReputationRep:
    Um, actually we should be provided with the data booklet because read what's written in page no 1.
    Offline

    2
    ReputationRep:
    http://qualifications.pearson.com/co...et_Issue_2.pdf
    Offline

    3
    (Original post by Ayman!)
    Heck yeah. IAL May 15 and Jan 16 also have decent ones but not nearly as difficult.



    I think so. I'm not sure how to show that they're proportional otherwise. We learnt the C1V1 = C2V2 formula in GCSEs so it kinda just stuck.
    I see, thank you!
    Offline

    3
    ReputationRep:
    (Original post by Ayman!)
    Has anyone done the NMR question on June 2013? It was one of those questions you'd really appreciate so long it didn't come in your exam.
    Yeah, It was tough lol but tbh I found the question about electrode potentials in IAL January 2015 much harder..........If I have done this paper(Jan 2015), I would come out subbing from that question
    Offline

    3
    ReputationRep:
    (Original post by Adorable98)
    Anyone ??
    Also, in addition to what Ayman have wrote, Here as the volume of thiosulphate ions increase. then the concentration of Iodine increases as well that's because the concentration of iodine is directly proportional to the volume of thiosulphate ions

    Which means, the more Sodium thiosulphate is added from the burette then it means there's more of the Iodine in the flask so the higher the concentration of Iodine
 
 
 
Write a reply… Reply
Submit reply

Register

Thanks for posting! You just need to create an account in order to submit the post
  1. this can't be left blank
    that username has been taken, please choose another Forgotten your password?
  2. this can't be left blank
    this email is already registered. Forgotten your password?
  3. this can't be left blank

    6 characters or longer with both numbers and letters is safer

  4. this can't be left empty
    your full birthday is required
  1. Oops, you need to agree to our Ts&Cs to register
  2. Slide to join now Processing…

Updated: October 15, 2016
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

Today on TSR
Poll
How are you feeling about doing A-levels?
Useful resources
Study resources

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.