2014 Chemistry Exam Solutions

[2NE1]

Guys i'm really confused about question 6 mc answer. I thought it was a weak acid added to a weak base, because the PH levels out at 2..and doesn't decrease even after you add excess acid. If it was HCL wouldn't it decrease to around 1?

Omg same too, I thought it was weak acid and weak base, because theres no clear equivalence point. Then I looked at the solutions and saw that it started pH11, probably a strong base then?
But then I just googled and a weak base has pH between 7-11 :/ So I don't know but I picked C

[skybluemaniac]

Omg same too, I thought it was weak acid and weak base, because theres no clear equivalence point. Then I looked at the solutions and saw that it started pH11, probably a strong base then?
But then I just googled and a weak base has pH between 7-11 :/ So I don't know but I picked C

No it's definitely a weak base. the Ph is around 10.3 if you look at the question again. If it was a strong acid the line should continue to decrease..

[Lizzy7]

But some parts specifically asked for side chains.....

Yeah that's right, they wouldn't have specified "amino acid side chains" if they only wanted the names of the amino acids themselves. So the answer would be the "amino acid side chains"

[thushan]

I think this is a little nitpicky and between you and me, I think when the writers wrote the questions they wouldn't have picked up on the fact students would notice the difference (I don't think they put that 'amino acid side chain' deliberately).

Personally, I'd pay both naming the amino acids and writing the side chains themselves.

[Robert123]

Guys i'm really confused about question 6 mc answer. I thought it was a weak acid added to a weak base, because the PH levels out at 2..and doesn't decrease even after you add excess acid. If it was HCL wouldn't it decrease to around 1?

The key thing is is that its "volume added" not "moles added". Now what does that mean, well if the concentration of HCL is 0.01 M, then, no matter how much volume you add, the pH will not go below 2.

[2NE1]

The key thing is is that its "volume added" not "moles added". Now what does that mean, well if the concentration of HCL is 0.01 M, then, no matter how much volume you add, the pH will not go below 2.

wait so what do you think the answer is

[ras]

With the 6 MC, if you look at the approximate end point of the titration, the pH is below 7, at approx 5, and this implies a strong acid and a weak base, I think.

[2NE1]

With the 6 MC, if you look at the approximate end point of the titration, the pH is below 7, at approx 5, and this implies a strong acid and a weak base, I think.

yeah thats what I think too, there is definitely an end point present, not like a weak base, weak acid titration where you can't really see it

[xmishle]

Does anyone know if a little bit of red pen is picked up by the scanner?

[Brunette15]

Could you say KOH was a catalyst, speeds up the reactions for Question 10.
I know it is an electrolyte, I don't even know why I didn't write that in the first place but I couldn't be bothered explaining the exchange of OH- between the anode and cathode. I'll probs lose a mark for saying its a catalyst LOLL but nothing in the question suggests it can't be.

I think I said something about it being a catalyst last minute too...I was running out of time and it was the only thing I was able to come up with lol

[swagsxcboi]

I think I said something about it being a catalyst last minute too...I was running out of time and it was the only thing I was able to come up with lol

I doubt catalyst will be accepted

[Mieow]

I wonder how many people fell into the trap in the MC chromatography question where the origin was actually at 2cm rather than 0cm.

Also I'm getting kinda nervous I'm not gonna get the full mark for some worded questions, because when I compare what I wrote to thushan's, mine sounded significantly much more general and idk if i used enough chemical metalanguage to earn the full mark 

[thushan]

With the 6 MC, if you look at the approximate end point of the titration, the pH is below 7, at approx 5, and this implies a strong acid and a weak base, I think.

Definitely strong acid-weak base titration.

pH at equivalence point is 5 and there's a pretty decently sharp endpoint. Weak acid-weak base basically have no sharp endpoint; it's practically a near-horizontal line (yes horizontal, not vertical) near the equivalence point.

[swagsxcboi]

I wonder how many people fell into the trap in the MC chromatography question where the solvent front was actually at 2cm rather than 0cm.

omg I know right!! I was about to then checked again. So many cheeky MCs. another one was the first question which asked for reverse reaction. cheeky cheeky

[speedy]

Could you say KOH was a catalyst, speeds up the reactions for Question 10.
I know it is an electrolyte, I don't even know why I didn't write that in the first place but I couldn't be bothered explaining the exchange of OH- between the anode and cathode. I'll probs lose a mark for saying its a catalyst LOLL but nothing in the question suggests it can't be.

LOL -> exact same answer and thought process as me aha