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

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Reply 360

_MAT_

Original post by Ferdous Shah

Where is it released? And how long does it normally take for an unofficial mark scheme to come out?

Never usually one for salters since hardly anyone does it

Reply 361

Zuzuvela

I thought the coating would be a non conductor since we were talking about electricity

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Reply 362

username1084917

For the isomers did you get 2? I got 2 and named one E and the other Z ?

Cold drawing: The chains are pulled making them straight and more crystalline so chains are closer together and so stronger IMF so mor energy needed to break them etc...

Reply 363

LewisEdwards1234

Original post by Zuzuvela

It requires 2 moles of bromine

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Did it explicitly say 2 moles?

Reply 364

Lauren2812

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 - aldehyde, 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.

(edited 7 years ago)

Reply 365

IBerrr

Original post by LewisEdwards1234

I go 195g, not sure where people got the 390g from as the mass of the c6h10 was 82 then bromine is 79.9x2 so you do (79.9x2)/ 82 then multiply that by 100

You did the whole thing correct, the only problem you've come across is that the molecule bromine reacted with was hexa-1,6-diene (the -1,6- may have been different) so what that means is 2 bromine molecules react with 1 molecule of hexadiene as there are two double bonds. So you would simply do 195x2 = 390. You will most likely only drop one mark so don't worry.

Reply 366

megancopps

Original post by Amyfrancis97

Is it just me that found this paper ridiculously hard? So frustrating. Anyone else not answer the calculation either?

You are not alone I didn't answer them

Reply 367

Akalanka25

Original post by IBerrr

- at higher temperatures increased value of rate constant/K, so the rate of reaction will change/increase
- as volatiles are lost, concentration of reaction changes/decreases
- change in concentration of reactants will change the rate of reaction

That's what I put anyway, where i just wrote 'change/decrease' I'm pretty sure in the exam I just put 'change'

I said this but is that right though, as the answer seems to impy it can both increase or decrease

Reply 368

username1084917

For the for the functional group I put ether, aldehdye and phenol

Reply 369

notyous

why was it s second order for H+ for the rate equation one?

Reply 370

Bella09

Original post by LewisEdwards1234

I go 195g, not sure where people got the 390g from as the mass of the c6h10 was 82 then bromine is 79.9x2 so you do (79.9x2)/ 82 then multiply that by 100

There were 2 double bonds so 2 bromine molecules were needed. I got 390 but I doubt it's right bc all my answers were dodgy haha

Reply 371

jordan_chung18

Original post by LewisEdwards1234

I go 195g, not sure where people got the 390g from as the mass of the c6h10 was 82 then bromine is 79.9x2 so you do (79.9x2)/ 82 then multiply that by 100

The alkene was a diene so you needed two moles of Br2 to get the moles of Br hence being 390g

Reply 372

Amyfrancis97

Original post by KINGYusuf

Anyone get 195g for the first Bromine Q?

Also who else ran out of time

I ran out of time so bad

Reply 373

George12411

There's a reason no one does salters, especially salters B due to the fact they manage to make absolute ******** papers. Joke of a course tbh how they've managed to make this paper 5x worse than 2015 is beyond me. No wonder everyone does AQA and this course won't exist next year. JOKE

Reply 374

jack.lp.thompson

Original post by Kira Yagami

For the for the functional group I put ether, aldehdye and phenol

That is correct but It said put 2 not 3

Reply 375

_MAT_

Original post by jack.lp.thompson

That is correct but It said put 2 not 3

Could of sworn it said put all

Reply 376

username1254695

Original post by _MAT_

Ahahah if you want to stop dwelling I suggest stop watching this thread :biggrin:

lol true, but whatever happens happens, really wanted to think I got those 4 marks (theres still the chance I didn't though :colondollar:

)

Original post by jack.lp.thompson

That is correct but It said put 2 not 3

I'm sure it didn't specify the number it just asked to put the functional groups present other than benzene

(edited 7 years ago)

Reply 377

Zuzuvela

Original post by jack.lp.thompson

That is correct but It said put 2 not 3

It said put all, apart from benzene. And there was 3

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Reply 378

yoyo.sat

Original post by IBerrr

I dont understand how the bromine number can be 390 or 195 when its meant to be how many grams of bromine in 100 grams of sample, surely it has to be less than 100 grams because its impossible to have 195 g of bromine in 100 g of sample?

Reply 379

IBerrr

Original post by Akalanka25

I said this but is that right though, as the answer seems to impy it can both increase or decrease

Well think about it. If a reactant is removed, this will increase the concentration of the one reactant but also decrease the concentration of the other. If the reactant that increases in concentration was second order then the rate will also increase, however, if the reactant REMOVED was second order, then the rate of reaction will decrease. As we were not told which of the reactants were removed, the mark scheme will most likely require candidates to write 'change' as opposed to 'increase/decrease', although I imagine it will ALLOW 'increase/decrease'