OCR Chemistry A F322 Chains, Energy and Resources Wed 23 May 2012

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Reply 1780

otrivine

did you guys get -82 and 18.3 %

Reply 1781

Weasleys_jumper

Original post by Mr S

yes please :biggrin:

Sorry, I only just saw this :frown:

How did you find the exam?

Reply 1782

Jit-Mistry

Original post by CoolDskool

hydrolysis reaction lead to the substitution of I- and the addition of OH
then heated under "reflux" with accidified dichromate indicated that it was either carboxl group or ketone

working backwards it had to be carboxyl acid because the infra-red-spec indicated OH and C=O both present.

this means the alcohol was a primary and the iodobutane was also primary (1-iodobutane as 2-iodobutane would lead to the formation of a ketone cause it is a secondary halogenalkane)

All in all that paper was pretty basic and the grade boundaries will be high

you know there were methyl groups on them all... if D has a methyl nd is made from C... c also had a methyl... B also had a methyl.... C when reacted will conc acid fromed 2-methylpropen.... so...

C was 2-methylpropan-1-l
D was 2-methylpropanoic acid
B was 2-methyl-1-iodopropane

Reply 1783

G-Sci

Original post by Dizzie31

I don't think you get a H radical?

You get HBr and .C2H5
Second step is .C2H5 + Br2 > C2H5Br and a Bromine radical

Reply 1784

kj14

Original post by Dizzie31

ah, could have. forgot about those dammit. I'm quite sure i haven't lost 20 yet :biggrin:

no you didnt cause the question said show how hbr and bromoethane is formed nothing else , still dont understand how it ends up to be 9 marks? :confused:

Reply 1785

Giggy88

Original post by Theafricanlegend

yeah i said can anyone go through not what the answer is

All I remember is the total enthalpy for reactants was lower than the total enthalpy of products. SO when I did reactant - products I got a negative answer which was -162. So I just left it that way.

Reply 1786

biomagic

i thought there were the same moles of gas on each side?

Reply 1787

OwenL

Original post by John Dogg

I put went to the left as there was less moles of gas. so this would decrease the pressure. ?

Yeah I think that was it, just can't remember which way round I put them. Was confident in my answer. Believe it was left with pressure and right with temp as you said :smile:

Reply 1788

otrivine

Original post by Giggy88

All I remember is the total enthalpy for reactants was lower than the total enthalpy of products. SO when I did reactant - products I got a negative answer which was -162. So I just left it that way.

thats what i got :wink:

did you get 18.3% ? and -82 ?

Reply 1789

sals1234

I found the paper so hard :frown:

was really hoping for an A!

Reply 1790

tsr1994

I got a 7 mark question wrong and redid it on additional paper, I did it correctly on the additional paper but I forgot to cross out the wrong answer. The exam moderators took away my papers and bound them together before I could cross anything out. It was at the end when I had to sort all of that out. What can be done, will the examiner mark the right or wrong answer?

Reply 1791

Jakez123

Original post by John Dogg

I put went to the left as there was less moles of gas. so this would decrease the pressure. ?

increase pressure, shifts to left as there was less moles.
increase temp, shift to right as it was endothermic so it shifts to the exo side

Reply 1792

kj14

Original post by otrivine

did you guys get -82 and 18.3 %

Otrivine how could you mess up?? unlucky man , i did some wrong too, but the answer was 92.1% and +82

Reply 1793

zoeeee00

Original post by Dizzie31

I don't think you get a H radical?

Yeah you don't get a H radical, it's just the radicals that are already present. The Hydrogen atom has bonded with the Bromine radical to make HBr in propagation.

Reply 1794

aallaa

increase in temp favours endothermic which was foward reaction so RHS increase in pressure equilibrium moves to side with fewer moles of gas= LHS as this will decrease total pressure

when they say decrease total pressure than it moves to side with greater moles

Reply 1795

Elldaman

I thought for the last question there were two parts of compound C, one was taken aside and reacted to form a compound with a methyl group, and then the other part of compound C was viewed in the IR Spectroscopy, and therefore it had to be butanoic acid? Can anyone see where I have misread the question or went wrong, because it looks like most other people got 2-methyl propanoic acid.

Reply 1796

John Dogg

Original post by kj14

no you didnt cause the question said show how hbr and bromoethane is formed nothing else , still dont understand how it ends up to be 9 marks? :confused:

As far as i can remember 9 marker was on ethene. you get like 5 for the mechanism and then you had to say how u could form three other products. I think thats where the nine marks are from. I put steam hydration of ethen there somewhere.

Reply 1797

aallaa

and for volatility you could say aboout boiling point as volatility increases as boiling point decreases. As the one had biger boiling point hence lower volatility