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OCR Chemistry A Exam Thread (Breadth - May 27 2016 and Depth - June 10 2016) watch

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    Wait guys I've just gotten even more confused about the UV process.

    By the way do we need to know how the catalyst works eg. the adsorption bit? There's a tiny bit of it in our textbook. Also have you guys bothered learning definitions?
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    Why is the boiling point for silicon high? Due to the breaking of covalent bonds? And what's the difference between graphite and graphene?
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    (Original post by asinghj)
    Ok fair enough but for AS we only need to know about the M+ peak due to carbon 13 hence what I said. Also don't think we need to be able to identify a halo alkane from mass spectrometry
    Think it's more A2 but I think the worst they could ask is for the M+2 as you get M+4 etc and have to normally identify type of dihaloalkane, or suggest, due to the isotopic ratio

    But doubt they would ask a question like that and as far as I'm aware they haven't in past papers
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    (Original post by Cherx)
    Why is the boiling point for silicon high? Due to the breaking of covalent bonds? And what's the difference between graphite and graphene?
    Yeah it forms a giant covalent lattice and covalent bonds are much stronger than London forces

    Graphite is an allotrope of carbon with parallel layers of hexagonal carbon atoms with weak London forces

    Graphene is similar just a single layer

    Both have delocalised electrons, conduct electricity etc
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    (Original post by Cherx)
    Wait guys I've just gotten even more confused about the UV process.

    By the way do we need to know how the catalyst works eg. the adsorption bit? There's a tiny bit of it in our textbook. Also have you guys bothered learning definitions?
    I assume you have the Oxford textbook so there's a bit on ozone I think somewhere

    Not in particular but the old spec used to ask about catalytic converters a lot so I've kinda learnt the process passively

    I think it's firstly adsorped (weakly bonded) to the catalyst, this causes a chemical reaction and weakens the chemical bonds and lowers the activation energy then the products are desorbed

    Not 100% sure on that
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    (Original post by Jitesh)
    Yeah it forms a giant covalent lattice and covalent bonds are much stronger than London forces

    Graphite is an allotrope of carbon with parallel layers of hexagonal carbon atoms with weak London forces

    Graphene is similar just a single layer

    Both have delocalised electrons, conduct electricity etc
    Ah ok so both are trigonal planar including graphite.

    (Original post by Jitesh)
    I assume you have the Oxford textbook so there's a bit on ozone I think somewhere

    Not in particular but the old spec used to ask about catalytic converters a lot so I've kinda learnt the process passively

    I think it's firstly adsorped (weakly bonded) to the catalyst, this causes a chemical reaction and weakens the chemical bonds and lowers the activation energy then the products are desorbed

    Not 100% sure on that
    Yeah it's the second propogations step which I don't understand. How comes it reacts with 0? Where does that come from.

    Ah ok so I found it. HETEROGENEOUS (make sure you spell it right they can deduct marks lol) has a different physical state from the reactant. Reactant molecules adsorbed onto the surface of the catalyst. Products of the reaction leave the surface of the catalyst by desorption.
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    (Original post by Cherx)
    Ah ok so both are trigonal planar including graphite.



    Yeah it's the second propogations step which I don't understand. How comes it reacts with 0? Where does that come from.
    Naturally uv radiation from th sun breaks down ozone and oxygen through homolytic fission
    Normally the formation of ozone has been equal to the depletion of ozone (equilibrium) but CFCs have screwed things up

    We can think of ozone being formed and depleted as O2 + O (equilibrium sign) O3

    And O2 -> 2O breaking via homolytic fission due to presence of UV light.. Not sure why we don't show the radical dot but we got told not to.. As far as I'm aware it is just a radical
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    (Original post by adeninesbff)
    Thanks! Welp, my brain is mush now trying to remember it all
    Hey, I made a mistake with my previous reply for question 2. The correct ionic equation is:
    Cl2(g) + 2OH-(aq) ---> Cl-(aq) + ClO-(aq) + H2O(l)
    I use a piece of paper and realised I made a mistake sorry about that.
    In my defence it was 7 AM and I had just woken up
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    (Original post by Jitesh)
    Think it's more A2 but I think the worst they could ask is for the M+2 as you get M+4 etc and have to normally identify type of dihaloalkane, or suggest, due to the isotopic ratio

    But doubt they would ask a question like that and as far as I'm aware they haven't in past papers
    Well the spec only mentions knowledge of the M+1 peak..
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    (Original post by asinghj)
    Well the spec only mentions knowledge of the M+1 peak..
    In the spec for biology a it only mentioned G1, S G2, M and C for the cell cycle and G0 came up...
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    (Original post by Cherx)
    Wait guys I've just gotten even more confused about the UV process.

    By the way do we need to know how the catalyst works eg. the adsorption bit? There's a tiny bit of it in our textbook. Also have you guys bothered learning definitions?
    I know the definitions of enthalpy changes and homologous series and isomerism but my teacher said the examiner won't ask for definitions, instead it will be about applying your knowledge.

    Looking at the spec it says "explanation of the role of a catalyst. Details of processes are not required"
    So I don't think we need to learn about adsorption but we need to know the difference between homogeneous and heterogeneous catalysts
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    (Original post by Cherx)
    Why is the boiling point for silicon high? Due to the breaking of covalent bonds? And what's the difference between graphite and graphene?

    Silicon is a giant covalent structure, like carbon! So yes. And Graphite is layers of hexagonally arrange carbon atoms, bonded covalently, each layer is bonded together by London forces, graphene is a single layer! Also, in graphite and graphene, only 3/4 of the carbon atoms are bonded and so there is delocalised electrons, therefore they can conduct electricity! (In diamond, all four of the C atoms are bonded so can't conduct)
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    (Original post by Jitesh)
    I assume you have the Oxford textbook so there's a bit on ozone I think somewhere

    Not in particular but the old spec used to ask about catalytic converters a lot so I've kinda learnt the process passively

    I think it's firstly adsorped (weakly bonded) to the catalyst, this causes a chemical reaction and weakens the chemical bonds and lowers the activation energy then the products are desorbed

    Not 100% sure on that
    That's right, as KnockHardy notes mention it, heterogeneous = HARD (heterogeneous, adsorption, reaction, desorption)
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    (Original post by Jitesh)
    In the spec for biology a it only mentioned G1, S G2, M and C for the cell cycle and G0 came up...
    Yeah fair enough, and chi squared also came up on that paper. Let's hope the chemists at OCR stay in the AS spec
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    (Original post by asinghj)
    Yeah fair enough, and chi squared also came up on that paper. Let's hope the chemists at OCR stay in the AS spec
    Chi was on the required calculations bit but I thought it was referring to the full a level course so kind skipped it lol

    Yeah hopefully, breadth was a nice paper (compared to biology)
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    (Original post by Bahcaci)
    No, that is wrong. For the overall equation you have: O3 + O --> 2O2

    You cant have that equation you said, check your book(s), trust me.
    Thats the equation it says in my textbook.
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    Can someone please explain Electronegativity and Periodicity
    Also, the formation of Pi bonds?
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    (Original post by Jitesh)
    Chi was on the required calculations bit but I thought it was referring to the full a level course so kind skipped it lol

    Yeah hopefully, breadth was a nice paper (compared to biology)
    In the main part of spec, chi squared is somewhere in module 5 (A2 stuff). Them stupid idiots at OCR
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    (Original post by 4nonymous)
    Can someone please explain Electronegativity and Periodicity
    Also, the formation of Pi bonds?
    Electronegativity is the attraction of a atom to get the shared pair of electrons, for which you need to know how it changes (increases going up and increases going from left to right)

    Periodicity is the repeating trends across each period of the periodic table (you need to know first ionisation energy increases across a period, the trend in melting and boiling point and atomic radius)

    Formation of pi bonds I have no clue so help?
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    Hey guys,
    If you have a list of a bunch of reactions with the catalysts, ect please could you send it to me? It would be greatly appreciated. Thanks in advance!
 
 
 
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