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

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http://www.docbrown.info/page07/transition03V.htm

Look at the table for vanadium 2+/3+, it's -0.26 exactly so I am fairly certain that those saying -0.26 in the exam were correct

I see. Thanks. Question was worded awfully in that case and the sooner somebody gets hold of the paper the sooner I can put my case forward

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*sigh*

Original post by Zuzuvela

It's +1.80V they swapped the chromium for vanadium. They said the potential difference was +1.03V, and that the new electrode(vanadium) had the same sign as the opposing electrode (iron, +0.77)
Potential difference is most positive minus least positive .
So least positive plus potential difference is most positive
(+0.77 + +1.03 = 1.80V)

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Idk if it was just an ambiguous question but the electrode potential of the V3+/V2+ half-cell is definitely -0.26. I looked it up. So unless I have the wrong half-cell it must be right, surely?

Reply 563

phagocyte1998

Sorry for posting that again, didn't realise it had already been resolved!

Reply 564

Zuzuvela

Original post by phagocyte1998

Sorry for posting that again, didn't realise it had already been resolved!

No worries.

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Reply 565

phagocyte1998

Original post by Zuzuvela

No worries.

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I felt that there were a lot of ambiguous and poorly worded questions on that paper. In many cases I had two ideas and didn't know which one to choose.

Reply 566

_MAT_

Original post by Zuzuvela

I see. Thanks. Question was worded awfully in that case and the sooner somebody gets hold of the paper the sooner I can put my case forward

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This is true, with any luck, they'll accept your answer anyway as they sometimes do with confusing questions

Reply 567

_MAT_

Original post by phagocyte1998

I felt that there were a lot of ambiguous and poorly worded questions on that paper. In many cases I had two ideas and didn't know which one to choose.

I agree, the membrane question in particular I had two answers and decided to go with the 'simpler'

Reply 568

phagocyte1998

Original post by _MAT_

I agree, the membrane question in particular I had two answers and decided to go with the 'simpler'

I did the same. I was also not sure whether to draw zwitterions for the products of hydrolysis and I wasn't sure whether at 70 degrees the enzyme would be completely denatured (and so not function at all) or whether some enzyme would still catalyse the reaction. In the end I said that there would be a horizontal straight line on the graph of substrate conc vs rate because all of the active sites would be lost...

Reply 569

_MAT_

Original post by phagocyte1998

I assumed there'd be a tiny amount so I did a little curve and then a straight line

Reply 570

_MAT_

Original post by _MAT_

I assumed there'd be a tiny amount so I did a little curve and then a straight line

Most graphs of enzyme activity have no activity at about 65 however I have found one which does so I would assume they'd accept both

Reply 571

phagocyte1998

Original post by _MAT_

I assumed there'd be a tiny amount so I did a little curve and then a straight line

Hopefully they'll credit both. I don't see how we're meant to know the temperature at which all the enzyme is denatured anyway...

What did you put for the question about the volatile liquids?

Reply 572

Marli-Ruth

Original post by _MAT_

I assumed there'd be a tiny amount so I did a little curve and then a straight line

Wait where we supposed to draw something???😳😳😳😳

Reply 573

phagocyte1998

Original post by Marli-Ruth

Wait where we supposed to draw something???😳😳😳😳

I think the question asked you to describe and explain the shape of the graph - I didn't draw anything but they probably credit drawings as well as descriptions.

Reply 574

Marli-Ruth

Original post by phagocyte1998

I think the question asked you to describe and explain the shape of the graph - I didn't draw anything but they probably credit drawings as well as descriptions.

You just saved me from a breakdown <3

Reply 575

Zuzuvela

Original post by phagocyte1998

Hopefully they'll credit both. I don't see how we're meant to know the temperature at which all the enzyme is denatured anyway...

What did you put for the question about the volatile liquids?

That was tricky bromine is volatile and so is water. Its another unclear question. If water wasnt volatile our clothes wouldn't dry at room temperature, and we would never have messed around in year 7 wasting 3 days at a time making salt crystals

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Reply 576

Marli-Ruth

Original post by Zuzuvela

Exactly! I said water :frown:

is it wrong?

Reply 577

_MAT_

Original post by Marli-Ruth

Wait where we supposed to draw something???😳😳😳😳

No but I did anyway

Reply 578

_MAT_

Original post by phagocyte1998

Hopefully they'll credit both. I don't see how we're meant to know the temperature at which all the enzyme is denatured anyway...

What did you put for the question about the volatile liquids?

If they are all equally volatile, they'll all evaporate at the same rate so concentrations will remain constant

If one is more volatile than the others, the concentration will change so rate will change

If source of H+ ions is more volatile, it'll have more of an effect on the rate