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# OCR Chemistry B (Salters) F334/F335 Exam Thread 2016 (14th/22nd June) Watch

1. I said organic polymer for coating the cell. Is that allowed too?
2. (Original post by kosvengali)
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Can we help each other with F335 my future depends on it
Yes mate we need to get something going got a fake fb account ready everybody is struggling but nobody wants to help anyone else

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3. For that volatile question and the effect it has on the rate of the reaction, i swear im the only one who put it has no effect - my thinking was because it never told us which chemicals are actually volatile, i assumed only the products would be volatile as it was Br2 and water, whereas the reactants were ions. So loss of products would have no effect on the rate of reaction as the reaction would have already occurred and the rate is determined using the initial concentration of reactants rather than products. Confusing i know
4. (Original post by Tralph123)
for the rate equation i got H+ as zero order and the other two reactants as first order?
That's what I got too!

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5. (Original post by marcus.dyer11)
So what are we saying for the 5 marker bromine question then? 7? 10?
I got 7. In the last question it said KBro3 was in excess so you needed to use Br-. Conc of Br- was 0.167 mol dm-3 therefore the number of moles in the solution of 0.0167 since there was 100cm3. Br- and Br2 were in a 5:3 ratio. So moles of Br2 would be 0.0167 ÷ 5 x 3 = 0.01002 moles and the previous question said this made a 200cm3 sample. The 5 marker then said 83cm3 reacted with 10g of the alkene so the number of moles of Br2 used was 0.01002 ÷ 200 x 83 = 0.0041583 moles. Mass would therefore equal 159.8 (Mr of Br2) x 0.0041583 = 0.66. This is the answer for 10g of the alkene and bromine number asks for 100g so you times this answer by 10 to get 6.6g and rounded up to the nearest whole number is 7.
6. Is there still a chance of me getting a B on this paper if I completely messed up all of the calculations?

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7. For the standard electrode potential question, it was +1.8 V, not -0.26 as it said the sign was the same as for the half-cell with iron. Hence they both had to be positive meaning that as for iron it was +0.77, to get +1.03, it had to be +1.8 for the other one
8. (Original post by Zuzuvela)
Yes mate we need to get something going got a fake fb account ready everybody is struggling but nobody wants to help anyone else

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LOL, that level of security, fair enough tho

I'll set it up tomorrow as I haven't 'friended' everyone yet but there is a decent amount of people so it should be effective 👍

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9. Don't know if someone's asked this already but people are saying ocr released the grade boundaries today. If so, where can I find them? How can they release grade boundaries before they even know how people did? Surely a certain number of people have to get certain grades and that's how they usually work out grade boundaries? I'm so confused wtf they can't do this to me

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10. (Original post by Marli-Ruth)
My coursework is the only thing saving my arse right now

Calculated at least 30 marks I've lost 💀😭
Lmao same

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11. (Original post by brown_eyes)
Don't know if someone's asked this already but people are saying ocr released the grade boundaries today. If so, where can I find them? How can they release grade boundaries before they even know how people did? Surely a certain number of people have to get certain grades and that's how they usually work out grade boundaries? I'm so confused wtf they can't do this to me

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You're correct. They aren't out yet

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12. (Original post by lyricalvibe)
You're correct. They aren't out yet

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Ah thank you

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13. any tips for calculation questions in chemistry please? I'm okay at them, but not amazing - if they throw something new I might not be able to get all marks... so any tip?

I really think we should help each other, just ask random questions because it's so easy to obtain simple method marks in exams.

THANKS
14. (Original post by WittyGonStein)
For the standard electrode potential question, it was +1.8 V, not -0.26 as it said the sign was the same as for the half-cell with iron. Hence they both had to be positive meaning that as for iron it was +0.77, to get +1.03, it had to be +1.8 for the other one
That's exactly what I did, but then I had a hunch I saw the same value somewhere before and it was the same value (-0.26V) on last year's F334 paper too with the same half reaction
15. Anyone has the unofficial mark scheme? Was it one mark for the standard electrode potential question?
16. (Original post by WittyGonStein)
For the standard electrode potential question, it was +1.8 V, not -0.26 as it said the sign was the same as for the half-cell with iron. Hence they both had to be positive meaning that as for iron it was +0.77, to get +1.03, it had to be +1.8 for the other one
that was my reasoning too... hope were right!
17. (Original post by mikejordan97)
That's exactly what I did, but then I had a hunch I saw the same value somewhere before and it was the same value (-0.26V) on last year's F334 paper too with the same half reaction
So it was -0.26V right?
18. (Original post by Elle_w)
That's what I got too!

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H+ was second order the other two were first order

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19. (Original post by Elle_w)
Is there still a chance of me getting a B on this paper if I completely messed up all of the calculations?

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Of course there is! Judging the rest of the paper went well you could drop a minimum of 25 marks and still get an A, the calculation questions were worth a total of 9
20. (Original post by Lozzie97)
1.

Secondary structure– folding of the amino acid chain (alpha helix and beta pleated sheets) Tertiary structure – further folding of the secondarystructure

Describe activesite and it's function – specific shape, where the substrate binds

Partial hydrolysisof trypsin – broke the right handside amide bond only

Benefits of trypsin> bromate (v) catalyst – cheaper?Not toxic?

5 marker on ESC,EP, rate orders and substrates stuff – first order then zero order, E + Sreaction is rate determining step at beginning, then enzymes become saturatedso the EP to E + P becomes the rate determining step

Rate of reaction at70 degrees – hydrogen bonds broken, enzyme denatures, active site changes shape

2.

Electrodes / tank,which solution? – Fe was +ve(tank 1?)

Coating steel? – e.g. paint, to prevent the water andoxygen causing rusting, to prevent the contents reacting with the steel

Why was there amembrane – allow the flow of electrons

Iron forming redbrown precipitate - Fe2+ and OH-and Fe3+ and OH- reacted in precipitation reactions to form Fe(OH)2 (greenprecipitate) and Fe(OH)3 (orange precipitate) and that these were then oxidised(from oxygen in the air) to form Fe2O3.xH2O which is a red-brown precipitate

3.

Bromine number – 390

Prove excess– calculated how many moles of KBrO3- would react with the Br- present and saidhow that value is less than the actual number of moles of KBrO3- present

Bromine number [5] – 7

Why was there E/Zisomerism? – restricted rotation around double bond, two different groupson each carbon in double bond

Draw isomers– ZZ, EZ, EE

Transition metalheterogeneous catalysis – reactants are adsorbed onto the surface, the metaluses the 3d and 4s electrons to form weak bonds to the reactants, bonds in thereactants weaken and break, bonds in products form, products diffuse away fromthe surface

Following BrO3-reaction – colorimetry, Br2 iscoloured, rest colourless, colour changes as reaction progresses

Rate equation – 1st order, 1storder, 2nd order

Temperatureaffecting reaction rate? – would loss of the reactants cause rate ofreaction to decrease as the concentrations of the reactants are now lower

4.

Draw polyester -

What condensationpolymer is this? – polyester

Why did Carothersgo ahead with polyamides? – polyesters do id-id and pd-pd, polyamidesform hydrogen bonds too, hydrogen bonds stronger than others, more energyneeded to separate chains so polyamides are strongerCold-Drawing – stretching thefibre to form a neck which is highly crystallised, chains are closer togetherso intermolecular bonds are stronger

5.

Functional groups present - ketone, ether, phenol

Oxidising aldehyde to carboxylic acid – acidifiedpotassium dichromate

IR spectrum – apocylsin

Mass spectrum -

Recrystallisation –dissolve in minimum amount of hot water, cool to allow to recrystallize, vacuumfiltrate to remove soluble impurities, wash with cold water and dry in adesiccator

Nucleophillicaddition -I've added what I remember, feel free to change if it's wrong.
I think I agree with most of those answers. The only thing that I remember doing differently is I put aldehyde for the functional groups in Vanillin or whatever rather than ketone.

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