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EDEXCEL CHEMISTRY Module 4

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Reply 20

ian_rider

i put no reaction, no reaction and then oxidised into a carboxyllic acid group

Reply 21

Ferchichi

dammit im so dumb, I shoulda just put no reaction for all of them, then I woulda gotta two marks for sure, seeing as I left the others blank
ARGH

Reply 22

calumtm

It was an OK exam, but i thought i did well enought to get A/B.

And the A boundry is 54?!? I thought it was bang on 80% everytime and was expecting to have to get 60 marks for an A.

54/75=72% for an A? Is that right? :p:

Reply 23

fay_102

jammie08

I thought it was good..rather similar to some past papers. Same for unit 5.

how comes you did unit 4 and 5 in January ?

Reply 24

Fatima52

Does anybody here recall a Kp value of 48.02 (no units); or a buffer solution pH of 5.06?

Regarding that question about 'cooling' the equilibrium reaction 'rapidly', would it have been incorrect to say that position of equil. is shifted in the exoth. direction?

Did you also have to mention +2 stability in part d of qst. 1?

And, finally: in calculating the enthalpy of formation, had an answer of approx.-524 Kj mol-1 been achieved?

Reply 25

ReasonToBelieve

-178kjmol-1 for enthalpy of formation...remember 2 enthalps of atm and 2 EA's

Reply 26

rohitkhannak

Fatima52

I've got the same buffer pH (5.06) as you but my Kp was 64 (exact, no units).

My teacher said, after the exam, (she hadn't seen the paper) that the reaction mixture being cooled had something to do with the reaction being endo/exo. I didn't know so I wrote something else :s-smilie:

I mentioned about +2 and +4 stability in Question 1 as Sn4+ is more stable than Sn2+ and Sn2+ is a reducing agent and Pb2+ doesnt react as it is already stable.

I got a -186 kJ mol-1 for the enthalpy of formation. I think you had to double both the enthalpy of atomisation of Hydrogen and the first electron affinity of hydrogen.

Reply 27

rohitkhannak

My answers:

1) Was pretty okay. Most of the stuff I already knew, and it was all in the text book and even in MTG (Make the Grade)

2) I didn't know what it oxidised to so I put no reaction for the first two (X & Y) but I left Z's blank. The reactions on the next page : I don't remeber the first one but the second one was CHI3 and RCOONa. I don't remember the third one either

3) I didn't really know what the rxn mixture was cooled rapidly so i made up something. I got the Kc value by assuming [I2] =

. Kp was 64 (exact), no units.

4) I got -186 Kjmol-1 for the enthalpy of formation. Rest of the question was quite good as I had prepared for those type of questions.

5) I got the conjugate pairs but mucked up the definition of acid - it should've just been something like 'An acid is a proton donor' but I wrote 'A solution where [H+] > [OH-]' :frown:

. I got the concentration of acid as 0.010... but I couldn't really explain why pH was greater than 7. I got the buffer solution's pH as 5.06.

6) I knew the zwitterion structure but I messed up the rxn with OH-. I guessed the acid chloride rxn right but messed up one with alcohol. The chiral center and the two monomer units were fine.

Reply 28

rosemkate

calumtm

i also thought that it was 80% to get an A. Does anyone know for sure what the grade boundaries are? i just need a B and i screwed up on some of teh questions, so i think i'll have to resit :frown:

.

i thought the exam questions were ok but for some reason i couldn't answer them properly, i just hope i did ok. but i didn't do some of the calculations and the organic questions were ones i wasn't expecting so i just made them up in the end :biggrin:

Reply 29

FAT-ema

I think the secondary alcohol is oxidised to give a ketone but has no reaction for the
ester...that's why it reacts to give CHI3......am I the only one to have put that answer?? :s-smilie:

Reply 30

Fatima52

I remember having stated reactions for 2nd and 3rd parts of that question; for the 2nd part, I'd drawn a carb. acid, and for the 3rd, yet another carb. acid (since since the -OH group would have been oxidised?) although, now I think about it-perhaps I should have drawn an ketone instead?

what had you put for the question asking about the equil. concentration? I got a random 0.0026?

And, were any of your assumptions along the lines of: [H30+]=[CH3CH2COO-]; and that [CH3CH2COOH]initial=[" "]equil.?

Reply 31

Fatima52

How many marks was that question about Kp worth? the one whose answer had been 64 (no units)

Reply 32

jammie08

[QUOTE="fay_102"]how comes you did unit 4 and 5 in January ?[/QUOTEI
I'm a resitter, resitting 4 and 5 only.

Reply 33

jammie08

Yea I got 64 (no units) for Kp as well. Can't remember how many marks there were for it. My assumptions were H30+]=[CH3CH2COO-] and that it was at 25 degrees celcius. Can't remember my buffer pH.. the zwitterion with H+ would produce H3N+ in the product and with OH, it would produce a COO- in the product. With the acid, it would produce NH3+Cl- in the product..(sorry if that doesn't make sense!)
No reactions with first two with ammoniacal silver nitrate, there is with the third.
Oh, I remember getting 0.01 concentration for something...
I think it's about 76% to get an A...read it somewhere in a mark scheme or something.. I also think the reaction cooling question is something to do with it being endothermic..wrote something about that in the exam..dunno if it's right or not.

Reply 34

Fatima52

when reacting Pb with warm HCl, what had most people put? i remember getting cl2 gas as one of the products

Reply 35

Fatima52

So nobody remembers getting 48.02 ANYWHERE on their paper?

Reply 36

jammie08

PbO2 + 4HCl ---> PbCl2 + Cl2 + 2H20

Reply 37

jammie08

which question did you get 48.02 from?

Reply 38

Fatima52

The question about showing the amphoteric nature of al203- I think I gave the correct equation in showing it acting as a base, and state symbols- but I got the second equation wrong- how many marks do you think I would have got?