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

Posted from TSR Mobile

Can we help each other with F335 my future depends on it

for the rate equation i got H+ as zero order and the other two reactants as first order?

So what are we saying for the 5 marker bromine question then? 7? 10?

Yes mate we need to get something going got a fake fb account ready everybody is struggling but nobody wants to help anyone else

Posted from TSR Mobile

My coursework is the only thing saving my arse right now

Calculated at least 30 marks I've lost 💀😭

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


Posted from TSR Mobile

You're correct. They aren't out yet

Posted from TSR Mobile

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

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

That's what I got too!


Posted from TSR Mobile

Is there still a chance of me getting a B on this paper if I completely messed up all of the calculations?


Posted from TSR Mobile

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 – 1^st order, 1^storder, 2^nd 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.