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

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1. (Original post by Lozzie97)
I think by sign being the same it meant that iron would still be the positive electrode therefore the electrode potential for iron would be more positive than the electrode potential for vanadium. Therefore the electrode potential would be -0.26 (which is the actual electrode potential for the half equation).
Yes that was my reasoning, I also plugged the numbers back into the E cell equation to check and it seemed to work out ok, the purpose of the electrode was to see if it would work in place of the other electrode so it'd make sense if it was less than the iron one.

2. 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
3. (Original post by _MAT_)

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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4. *sigh*
5. (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?
6. Sorry for posting that again, didn't realise it had already been resolved!
7. (Original post by phagocyte1998)
Sorry for posting that again, didn't realise it had already been resolved!
No worries.

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8. (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.
9. (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
10. (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'
11. (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...
12. (Original post by phagocyte1998)
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...
I assumed there'd be a tiny amount so I did a little curve and then a straight line
13. (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
14. (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?
15. (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???😳😳😳😳
16. (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.
17. (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
18. (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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19. (Original post by Zuzuvela)
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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Exactly! I said water is it wrong?
20. (Original post by Marli-Ruth)
Wait where we supposed to draw something???😳😳😳😳
No but I did anyway

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