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

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a few questions:
what was the electrode potential of V3+?
what was put over steel to protect it?
Which electrode was the tank 1 on which was tank 2?
What was the need of the thing in the middle of the 2 tanks?

-0.26
Platinum?
+ve one was the one with the more +ve standard electrode potential
Membrane, stops the half cells from mixing, also could probably say acts as a
'salt bridge' allowing the circuit to be completed

(These were just my answers)

Reply 301

Taz35

Original post by Zuzuvela

Grade boundaries should be around 56 for an A. That's not unreasonable considering the paper Look at how many of the questions had not come up before in any way shape or form. First time I've seen cold drawing, First time I've seen 10marks worth of maths in one question (bromine number). First time recrystallisation has ever been 3 marks. First time heterogeneous catalysis has been asked. First time that we have been asked to show something is in excess.First time that I've seen a 5 mark question on rusting iron and been given 3 lines to put it on. It's an absolute disgrace of a paper and some action will have to be taken if the grade boundaries do not reflect it's difficulty. OCR if you are reading this then its not to say go and make F335 easy to make up for your questions. Make it like you do every year, so that those who work hard get what they deserve.

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THIS OMG!!! you deserve an A* for just writing this. I couldn't have put it better

Reply 302

Zuzuvela

Original post by Daniel9998

but there were two amide links so it split into 3 molecules

Partial hydrolysis by an enzyme. So it was specific to only one bond which they stated. That's borderline not on the spec to be honest

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Reply 303

_MAT_

Original post by Daniel9998

but there were two amide links so it split into 3 molecules

Yeah but it said that it was a partial hydrolysis and only one amide link broke I think

Reply 304

Zuzuvela

Am I the only one who struggled for space in a lot of the questions. The 5 marker on iron, the rate equation etc

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Reply 305

_MAT_

Original post by popo12twenty

Iron was in tank 1 because it was a positive electrode

That's what I got

Reply 306

jordan_chung18

Original post by IBerrr

Why was it partial hydrolysis? I don't remember reading that?!?! I drew 3 molecules and also I'm 90% sure the question was 3 marks

it said the enzymes break only the amide bond where C=O comes from lysine or whatever the amino acid was

Reply 307

Zuzuvela

Original post by _MAT_

Yeah but it said that it was a partial hydrolysis and only one amide link broke I think

Yes only one broke they told us which one. It truly was a bad exam. That should have been 3 marks that question for recognising it.

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Reply 308

chloewilliamsss

Original post by AlbertoMerckx

Yeh!

Which solution was solution A and which was solution B? like which one has which ions in

Reply 309

Jane-98

For the hydrolysis of the polyamide did you for the left hand side monomer need to make both the nh2 groups into nh3+ or just one as the oh carboxylic acid coup would lose an oxygen to give a o- so overall = no charge

Reply 310

_MAT_

Original post by chloewilliamsss

Which solution was solution A and which was solution B? like which one has which ions in

A was iron, B was the other one I believe

Reply 311

rosschatburn

Original post by kidlikethat

I got 10 too!!?

I also got 10!

I worked out the concentration of the Bromine to be 0.075mol/dm3 from the previous question and equation and then used this to find the number of moles of bromine that was used up (from the volume that was added) for 10g of the hexene, from this found the mass. And then multiple by 10 to get it for 100g

Reply 312

username1254695

For the question asking to draw the structure of the E/Z isomers was it supposed to be drawn as skeletal or full structural?

Reply 313

Daniel9998

Original post by chloewilliamsss

Which solution was solution A and which was solution B? like which one has which ions in

I put solution A in the left tank I think

Reply 314

Lauren2812

For the rusting one I put how Fe2+ and OH- and Fe3+ and OH- reacted in precipitation reactions to form Fe(OH)2 (green precipitate) 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. Not sure if any of this is right or not. There were not enough lines for this one!!

For the bromine number one I got 390 and 7.

For the rate equation I got first order, first order, second order.

For the E/Z isomerism, how did you label them as E and Z? I just wrote E or Z next to the double bonds in each of the three molecules but I'm not sure if that is okay.

For the hydrolysis of the peptide I hydrolysed the right peptide bond but not the left one. What did people put for the advantages of trypsin over borate?

It was annoying how the recrystallisation one was only worth 3 marks!!

Also, I thought the mechanism with CN- was a two step mechanism?!

The functional groups in the molecule were phenol, ether and aldehyde. The reaction reagent was acidified potassium dichromate. The IR spectrum was of the second molecule.

Iron half cell was the positive electrode. Electrodes were made of platinum. I think the membrane may have been to allow electrons to flow. V electrode potential was -0.26V (or something similar).

Trying to remember more of the questions but can't.

(edited 7 years ago)

Reply 315

Animabella

Paper was okay apart from question 3 was a *****! Can anyone else tell me about the E/Z isomers? How many were there, I put 4? Also the Bromine 5 marker? Does anyone have the answer???

Reply 316

Zuzuvela

Original post by babymonkey1996

What did everyone put for the first 5 marker on enzymes and substrates?

Never come up before. It was vague so I talked about orders with respect to enzyme and substrate. Basically first order and after the plateau zero order. Both involved in rds as both in rate equation rds was the first step as it was reversible?

Not 100% sure then again nobody is

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Reply 317

AlbertoMerckx

how did everyone go about the question where it said one molecule of that acid reacted with two molecules of the other substance. I drew the amide bonds but left the other functional groups unreacted. was it trying to get us to do a repeating unit?

Reply 318

KINGYusuf

Anyone get 195g for the first Bromine Q?

Also who else ran out of time

Reply 319

HecTic_H

1.
Secondary structure -
Tertiary structure -

Describe active site and it's function -

Partial hydrolysis of trypsin -

Benefits of trypsin > bromate (v) catalyst -

5 marker on ESC, EP, rate orders and substrates stuff -

Rate of reaction at 70 degrees -

2.

Electrodes / tank, which solution? -

Coating steel? -

Why was there a membrane -
Salt bridge

Iron forming red brown precipitate

3.
Bromine number

Prove excess

Bromine number [5] -

Why was there E/Z isomerism?

Draw isomers

Transition metal heterogeneous catalysis -

Following BrO3- reaction -

Rate equation -

Temperature affecting reaction rate?

4.

Draw polyester -

What condensation polymer is this?-
Polyester

Why did Carothers go ahead with polyamides?

5.

Oxidising aldehyde to carboxylic acid -
Acidified dichromate

IR spectrum -
Apocylsin

Mass spectrum -

Recrystallisation -

Nucleophillic substitution -

Can we get going at filling that, I might have missed a few questions and only answered the ones for certain.