* Chemistry * Predictions / discussion / aftermath * (1 thread please)

AnneElizabeth

Thought it was quite challenging to be honest, I definitely didn't do as well as I thought - The questions seemed different? Like there weren't many generic questions that come up every year.
The experiments were ok but it was downhill from there for me.. I was relying on Q4 but I don't think I got full marks.

BrendaN_f

JamJamJamJam wrote: »

I got x = 7 for that part of Q4. I was kinda dilly-dallying around then so it could easily be wrong! That's all I can remember?

yep, got that as well

Exothermic

Q6. (e) I got 205.6 if I remember correctly.

jumpguy

Q1 - Grand out. Got 4.7978% w/v

Q3 - Weird, but once I got into it it was okay. For what-to-do-at-stage-3-to-get-a-maximum-yield I said cool the Benzoic acid and stir it so the NaCl will dissolve.

Q4 - No complaints, grand out.

Q6 - Grand, silly me though, for the nature of crude oil I just said it was a mixture of different hydrocarbons, shoulda probably said they were also polar and non-polar. The rest was fine. Got +200 and something for the heat of formation. Definitely remember it was positive anyway.

Q7 - For the conjugate base of sulphuric acid I said the conjugate base was 2H+ and this itself was an acid according to Arrhenius's acid definition, dunno if that's right. So glad somehow asked last night how to get the H+ ions when given the pH! Laws of logs ftw (I hope they found their antilog button :P ). I got 1.724x10^-3

Q9 - Did as an extra question. For the Kc I had to use the -b formula and it was longish. The Le Chatlier's Principal question was nice.

Q10 - Did (a) and (c). Nothing out of the ordinary really.

Q11 - Did (a) and (b).


Overall, thought it was a fair but challenging paper, caveats in nearly every question. I really hope I got the A1, but if I do it won't be by any substantial margin. :-/

brian93

It was an average paper. All the nice topics came up, but some of the questions were weird.

Q.1 was fine except the original and dilute things confused me!
Q.2 was grand
Q.4 was hard, only managed maybe 4 or 5 right answers
Q.5 was nice. Common chemistry sense!
Q.6 could have been nicer. Normally my best question but bits threw me off
Q.7 was weird. Never came across Arnehius before, and the HA acid was weird, but bar that it was an ok question!
Q.10 was ok. Rates of reaction could have been nicer, but it was doable and part b wasn't really course stuff but was doable too.
Q.11 part a and c were nice.

Tada! Hope to god I get a B...

Pre Judas

Very enjoyable paper. I thought the Blood-Ethanol Q was a nice touch!

DM360

Overall a good paper I think. Went well enough.

Q1. Grand, predicted correctly. Got 4.8% w/v I think

Q2. Very handy. Little bit about prep of ethanoic acid and then some simple questions on eugenol

Q3. New kind of format I suppose. A lot on method but really nothing challenging.

Q4. Was okay. Got x=7, pretty sure that's correct. Didn't get the Cu + Ag equation though. Think I got 8

Q5. Lovely, straight forward just knowing the history and basic knowledge about the atom

Q6. Topical I suppose. 'What is the nature' question was quite vague, just put down all the properties I knew. Ended up with 206.5 for (e). Also wasn't sure whether 'light gasoline' meant refinery gas or petrol so don't think I got full marks.

Q7. Found it quite straightforward until the very last line. Wasn't sure about concentration of sulfuric acid but gave it a go anyway.

Q9. Not the easiest of equilibrium questions by any means but I worked out some sort of value anyway. The Le Chatelier's part was grand though

Q10. a) Nice enough, nothing too troubling. I didn't do my reaction profile on graph paper though, some people in the centre did.

b) Really enjoyed this question. A lot of changing units and keeping tabs on numbers. I got 12.5mg/100ml anyway. Not 100% sure

c) Pretty basic for any Physics student such as myself. A very short question, just threw it in at the very end

macskanadrag

It was a fair paper I thought, with some challenging questions and some nice ones. I was really delighted that we discussed:
- antilog
- what goes to the top and bottom at the ethanoic acid experiment
- even the cathode rays, althought i wasn't sure in answering that but at least i could picture it
THANK YOU GUYS WHO WERE HERE YESTERDAY!

I regret that i did Q6, the fuel one, got roped into it before i realised that i don't actually know a lot about it :-/ Same with the stupid equilibrium calculation, i know i don't know it then why...? (even though i understood it yesterday when somebody calculated it here on the thread) In the end, i decided to look through my questions rather than doing that lovely ethanol-blood Q! That looked interesting

Ah well, fingers crossed i have my B1 and the consequent college place, fingers VERY crossed!

AnneElizabeth

jumpguy wrote: »

Q7 - For the conjugate base of sulphuric acid I said the conjugate base was 2H+ and this itself was an acid according to Arrhenius's acid definition, dunno if that's right. So glad somehow asked last night how to get the H+ ions when given the pH! Laws of logs ftw (I hope they found their antilog button :P ). I got 1.724x10^-3

There's an antilog button?! I didn't have a clue how to do this so I thought I'd show off my knowledge of logs and try and work it out mathematically... It didn't work

Iceuil

I think it was a really really nice paper. Really hope it will compensate my terrible result in biology. The only thing that i didnt like was the mark allocations. They didnt write marks for each question. Especially in Q2, where they just wrote (20) and (30). Section B was extremelly friendly, but section A was a bit tricky, but nice paper overall, really happy with it

ragalag

Anyone know the answer to the equilibrium question...qs 9 (a)?

jumpguy

AnneElizabeth wrote: »

There's an antilog button?! I didn't have a clue how to do this so I thought I'd show off my knowledge of logs and try and work it out mathematically... It didn't work

I don't have it on my calculator anyway, there were people talking about it last night. I had to do it the good old fashioned rules-of-logs way.

aranciata

please please please someone help - how many marks will i lose if i got the denominator wrong in the bleach titration (i had it as 4 when it's 2)

technically, all my answers are wrong (half of the correct answers)... have i lost 20 marks?

Avogadro1

didn't think it was too bad. was different to other years and somewhat tricky in parts but happy with the questions i did, does many people have answers to compare.?

Q1 was happy bleach came up,
got diluted = 0.0322 M/L
original = 0.644 M/L
47.978 g/L
4.8%

Q2 part (a) was ok but unsure about (b)
is clove oil acceptable for the natural product?
and is water the answer to (iii) ?

Q4 more difficult than usual
got x = 7
for (f) i said it went to Cu3+ and Al-, does anybody know what that was.?

Q6 was ok but didnt know part (a)
got +205.6 for (e)

Q7 forgot to write answers on my exam paper but thought it was ok

Q9 (a) got 3.9307 M/L
(b) got exothermic

Q10 was very unusual but i liked it.
for (b) (i) got 6.6 hours
and for (ii) got 112.5/100
but that is something ive never done before so couldnt be very sure about those answers

Q11 was ok, not brilliant.

overall relatively happy. not many in my school do chem but most found it ok, different to other years.

Exothermic

I think I got the equilibrium conc. of Hydrogen to be 0.06 moles at the end after I divided by the 12 litres. I think. I'm not a hundred percent sure though. I didn't scribble down my numerical answers so I could check them after I forgot.

aranciata

Exothermic wrote: »

I think I got the equilibrium conc. of Hydrogen to be 0.06 moles at the end after I divided by the 12 litres. I think. I'm not a hundred percent sure though. I didn't scribble down my numerical answers so I could check them after I forgot.

With an equal number of molecules on both sides did the vessel have to be considered?

BrendaN_f

Avogadro1 wrote: »

Q10 was very unusual but i liked it.
for (b) (i) got 6.6 hours
and for (ii) got 112.5/100
but that is something ive never done before so couldnt be very sure about those answers

got these same answers, hopefully we're both right!

DM360

Avogadro1 wrote: »

Q2 part (a) was ok but unsure about (b)
is clove oil acceptable for the natural product?
and is water the answer to (iii) ?

Q9 (a) got 3.9307 M/L
(b) got exothermic

Q10 was very unusual but i liked it.
for (b) (i) got 6.6 hours
and for (ii) got 112.5/100
.

I said eugenol for natural product and yes there's water, it's an emulsion mixture.

I got 3.9307 for the concentration of the HI gas. I had that as 5-2x where the concentration of Hydrogen gas was x. Found x to be 1.0693 mol/L
I got endothermic for the forward reaction though

And yeah 6.6 hours and then 12.5/100

._.

FML.

soccymonster

The exam was really good! Everything I looked over last night and this morning came up Although I wasnt aiming for and i'm preety sure i didn't get an A1, the exam was really nice! Did 10 out of 11 questions which is really weird for me too

AnneElizabeth

jumpguy wrote: »

I don't have it on my calculator anyway, there were people talking about it last night. I had to do it the good old fashioned rules-of-logs way.

How do you do it out of interest? I used rules of logs too but I got a crazy answer. Didn't know what to do with the minus either.

Alibear

Lovely paper - Very fair.

red_red_wine

The numerical answers I got were:

1 (e) (i) 0.032 moles/L
(II) 0.64 mol/L

(F) (I) 47.68 g/L
(II) 4.768 %

6 (e) 205.6 kJ/mol

9 (a) 0.04456 mol/L [not sure about this one.]

10 (b) (i) 6.6 hrs

(II) 112.5 mg/100ml

Overall, I'm actually really happy with it. Having been petrified yesterday by my teacher telling me it was going to be 'savagely difficult', it was a relief to actually be able to do it!

jumpguy

AnneElizabeth wrote: »

How do you do it out of interest? I used rules of logs too but I got a crazy answer. Didn't know what to do with the minus either.

I can't really remember, but I think the pH of the weak acid was 2.45 or 3.45 or something...

But anyway, assuming it was 2.45

-log[H+] = 2.45
log[H+] = -2.45
10^-2.45 = [H+] (converting logs to indices)
1/10^2.45 = [H+] (converting negative indice to a fraction - a law of indices)

Then you had to half that answer to get the H2SO4 concentration.

Did it last night too: http://www.boards.ie/vbulletin/showpost.php?p=72874928&postcount=177

mpdg

Not too shabby!

Still had problems with that antilogs thing . Thanks for helping anyway!

1. Bleach! Since the paper on the exam paper is so thin, I could see "ClO-" through the paper before the exam began. Was lovely.

Couldn't get: Two reasons why excess KI was used.

2. Gorgeous.

3. Meh. Weird. I did it but it won't be counted as I did ten questions and I screwed up loads.

4. Think I got 7/8 answers right.

5. Hadn't planned on relying on Atomic Theory but this could be 50 our of 50 marker.

6. Was mostly fine, as I like this section of the course, but couldn't get (d) at all

7. Crazy question. Won't be counted I hope!

8. Lovely. Bit unsteady about the bonds breaking/forming thing but I think it was fine.

10. Did all three parts. (a) and (b) were a doddle. I know I got my maths wrong in (b) though. (c) was fine, but I didn't know what a radioisotope was so I spoofed.

11. Did (a) and (b). Everything was great up until the last part of (b) iii. My friend said it had something to do with Hydrogen bonds? Gah.

I am scared/too tired to tot up my marks. The A1 could still be in reach!

aranciata

anyone??? DID WE HAVE TO CONSIDER THE SIZE OF THE VESSEL IN THE EQUILIBRIUM CONSTANT QUESTION?

jumpguy

aranciata wrote: »

anyone??? DID WE HAVE TO CONSIDER THE SIZE OF THE VESSEL IN THE EQUILIBRIUM CONSTANT QUESTION?

No. Well, I hope not anyway, I didn't.

The conventration of hydrogen must be very small as the Kc given to us was very small, hence telling us the position of equilibrium was very much to the left.

aranciata

jumpguy wrote: »

No. Well, I hope not anyway, I didn't.

The conventration of hydrogen must be very small as the Kc given to us was very small, hence telling us the position of equilibrium was very much to the left.

Oh thank lord. Was I right to get the square root of both sides too? Because the top and bottom lines were both squared.. (5-2x)^2 and (x)^2 if i remember

KoolAidRelic

jumpguy wrote: »

No. Well, I hope not anyway, I didn't.

The conventration of hydrogen must be very small as the Kc given to us was very small, hence telling us the position of equilibrium was very much to the left.

Yes we did... The equilibrium constant equation uses concentrations (i.e. mol dm^-3).

Five moles in a twelve litre flask = 5/12 mol dm^-3.

jumpguy

aranciata wrote: »

Oh thank lord. Was I right to get the square root of both sides too? Because the top and bottom lines were both squared.. (5-2x)^2 and (x)^2 if i remember

I was thinking about doing this but instead I decided to square it out and use the -b formula (wasn't feeling brave :P ). It was long and fairly tedious, but I'm sure they'll accept both methods.