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biochris
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#1
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#1
So.. how did you guys find the exam?
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dlyslexlicth
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i found it pretty good, some questions were tricky though like the sodium lactate one; using the titration curve to suss out the ph for sodium lactate
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leafy9
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(Original post by biochris)
So.. how did you guys find the exam?
Quite good.

Perhaps too easy?

Now I'm just worried about high grade boundaries.
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biochris
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(Original post by dlyslexlicth)
i found it pretty good, some questions were tricky though like the sodium lactate one; using the titration curve to suss out the ph for sodium lactate
I assumed that the pH of sodium lactate sol was the same as the pH at equivalence point... what about you?
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deathbychem
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Does anyone remember what we had to do in the last question?
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deathbychem
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#6
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In which we had to do something about the buffer solution with the help of ionic equations?
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leafy9
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The last question was a bronsted-Lowry acid/base question. I think I might have got the 2 the wrong way round...
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deathbychem
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does anyone remember the how to do the last question?
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deathbychem
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#9
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Can we please discuss the paper mcqs if anyone remembers?

Yeah how did you guys do the congugate base and acid question?
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begining
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(Original post by leafy9)
Quite good.

Perhaps too easy?

Now I'm just worried about high grade boundaries.

Same here, Think the grade boundaries r going to be very high.
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biochris
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(Original post by deathbychem)
does anyone remember the how to do the last question?
pKa of lactic acid is smaller than that of ethanoic acid, so lactic acid is a stronger acid and acts as a proton donor
so.. CH3CH(OH)COOH + CH3COOH ---> CH3CH(OH)COO- + CH3COOH2+
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begining
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Does anyone know the link to Unit 5 paper. really having alot of trouble. Or can we discuss it here?
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deathbychem
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Okay and how did you manage with the graph?
and that NMR spectroscopy question?

ALSO how did you make that skeletal diagram in the 1st question?
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deathbychem
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Hey @Biochris

remember we had to tell how the buffer is made with the help of ionic equations. I think that was the 2nd last question.. no? How did you answer that?
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biochris
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(Original post by begining)
Does anyone know the link to Unit 5 paper. really having alot of trouble. Or can we discuss it here?
There is not any thread for IAL Chemistry Unit 5... we could discuss it here but since the thread is not very active I would recommend you to visit this thread http://www.thestudentroom.co.uk/show....php?t=2630539 which is about both CH04 and CH05...
Or you can start you are own thread..
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deathbychem
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(Original post by biochris)
pKa of lactic acid is smaller than that of ethanoic acid, so lactic acid is a stronger acid and acts as a proton donor
so.. CH3CH(OH)COOH + CH3COOH ---> CH3CH(OH)COO- + CH3COOH2+

Okaay phew i got this right.
Thannkyou :')
Um please discuss this paper. I want to see how much marks will i get
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biochris
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(Original post by deathbychem)
Hey @Biochris

remember we had to tell how the buffer is made with the help of ionic equations. I think that was the 2nd last question.. no? How did you answer that?
"First mark:
(buffer contains) reservoir of HA and A—
OR
(buffer contains) large concentrations of
[HA] and [A-]
OR
both equations:
HA ⇌ A— + H+ and NaA Na+ + A—
(1)
Second mark:
(Addition of alkali/base)
HA + OH– → A– + H2O
OR
description/equations to show that H+ reacts
with OH— (to form H2O) and more acid
dissociates (to replace H+)
(1)
Third mark:
(Addition of acid)
A– + H+ → HA
OR
A– reacting with H+ in any context described in
words (e.g. by reference to weak acid
equilibrium)
(1)
Fourth mark:
the ratio of [A–]÷[HA] hardly changes / the ratio
of [HA]÷ [A–] hardly changes
OR
[A–] nor [HA] changes significantly (1)"
This is from the Jan 2010 mark scheme
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deathbychem
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omg. killme.
are you getting an A?
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biochris
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#19
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Which was the right answer in the first MCQ?
I put D (quench with NaHCO3 and titrate with standard sodium thiosulfate solution) but A (measure pH with pH meter) seemed right, too...
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deathbychem
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#20
(Original post by biochris)
"First mark:
(buffer contains) reservoir of HA and A—
OR
(buffer contains) large concentrations of
[HA] and [A-]
OR
both equations:
HA ⇌ A— + H+ and NaA Na+ + A—
(1)
Second mark:
(Addition of alkali/base)
HA + OH– → A– + H2O
OR
description/equations to show that H+ reacts
with OH— (to form H2O) and more acid
dissociates (to replace H+)
(1)
Third mark:
(Addition of acid)
A– + H+ → HA
OR
A– reacting with H+ in any context described in
words (e.g. by reference to weak acid
equilibrium)
(1)
Fourth mark:
the ratio of [A–]÷[HA] hardly changes / the ratio
of [HA]÷ [A–] hardly changes
OR
[A–] nor [HA] changes significantly (1)"
This is from the Jan 2010 mark scheme


do we have to answer this EXACTLY THIS WAY?
and these same equations?
can you explain or elaborate on the 3rd mark, i dont get that.
Plus didnt you make references from the sodium lactate thingy?
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