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EDEXCEL CHEMISTRY 6B - 19th June - 12hrs passed!

so how was it for you guys?

i had ********ng no idea of the first question (energetics). i'll probably get 2/10 on that question.

did anyone do the 2nd question? there was a question asking you which of the reactions "alcohol+carboxylic acid" or "alcohol+acid chloride" gave a greater yield. i wrote alcohol+acid chloride because the ester could acid hydrolise in HCl back to the c.acid and alcohol. is that correct? :s-smilie:

the paper was OK overall, except the first question, which took me completely by surprise as it did not come up in any past paper.

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Reply 1

Tombola

I sort of rambled my way through question 1.

Didn't know the definition of Hess's Law. Didn't know where the 30cm of HCL was meant to come in... I got 43KJ mole for first part and flopped on the 2nd part.

Alternative questions: 3 - THANK YOU!!!!
Question 4.... Slightly more dubious and complicated but at least there's no real calculations.

Did half of question 2... then realised I couldn't do the maths properly and I only had a vague idea of the grignard (That was annoying because the mechanisms are easy)

Reply 2

aminalia89

q1) -43 kj/mol and +101.6 kj /mol
2) ch3ch2mgbr is the grignard
thats all i can remember for now.
EDIT: oh and the mass of sodium propanoate was 1.8g

Reply 3

Tombola

Awww... -.-
I got a positive value :frown:

Figures. It threw me off with Ethene. I used Ethane at first, then realised what it said.

Reply 4

Timba

It's a thermal decomposition.. the value must be positive

My answer was around +50kJmol-1

I dont usually say this but I thought that paper was really easy

Reply 5

aminalia89

if the temperature increases then its exothermic as energy is given to the surroundings so enthalpy should be negative.

Reply 6

Calira

dreamer*girl

did anyone do the 2nd question? there was a question asking you which of the reactions "alcohol+carboxylic acid" or "alcohol+acid chloride" gave a greater yield. i wrote alcohol+acid chloride because the ester could acid hydrolise in HCl back to the c.acid and alcohol. is that correct? :s-smilie:

I put the acid chloride reaction gave the greater yield as an equilibrium is set up in the carboxylic acid reaction.
I did questions 2 and 4... didn't have a clue about the hydrated copper ions or whatever they were... and wouldn't have been able to do the question about why water wouldn't react with the CCl4 (I remember my teacher telling us not to write about stearic hindrance, but I forgot what we were supposed to write)... meh.

Reply 7

Timba

The temperature only increases because you have to put energy into the system for the reaction to occur, therefore it's endothermic.

Reply 8

Tombola

Timba

It's a thermal decomposition.. the value must be positive

My answer was around +50kJmol-1

I dont usually say this but I thought that paper was really easy

It certainly was rather easy. (Assuming revision was done)
Which questions did you attempt?

Reply 9

Tombola

The CCl4 question is from unit 5.

Water has lone pair.
Si contains d-orbitals C doesn't.
Water can't attack the carbon but the silicon.

I put it in waffly terms like that... so I expect that there's a chance I might lose marks from wording.

Reply 10

Timba

2 and 3, really nice questions!

What I did get wrong was the TYPE of reagent that a grignard reagent is. I said electrophile but it's actually a nucleophile :frown:

Reply 11

Creative

meh easy paper.. just revised what didn't come up properly on unit 4 and 5, and voila. Apart from that.. I didn't revise anything from last year but cmon.. question 1 was adding and multiplying :rolleyes:

Reply 12

redmeg

i got -43 and +101.6 for the first question aswell

Reply 13

Tombola

For question 4 - Last section. It talked about the pH when BaCrO4 was created and PbCrO4

What was the answer to these?

I put acidic in the first one... but i wasn't sure whether it's actually neutral buffer, where as the 2nd one is purely acidic.

Reply 14

aminalia89

this thread is pretty quiet...

Reply 15

a pirate life for me

I did q2 and 3,

Question 1 I think I might have gotten the second part right but I didn't have the answer to the first part so I just put in the formulas and used a substituted value that I guess. The explanation part was okay, but again because it was all consequential on my first answer, only the theory was correct and the application of this made-up number that I used. Hopefully get me a few marks for doing that.

Question 2 was ok-ish, but I forgot what ethanol and an ester make (only 1 mark)

But I do remember that the other one gave the greater yield.

Question 3 was my saviour, nice, easy, lots of theory and very little calculations. Maths is my worst subject ever. But there was a calculation I think for Ka that I did I can't remember what question that was, possible 2... That was a bit tricky but got there in the end. Can't remember my exact values but I do remember I first had to work out [H+] then I did something else to get conc and thus n, then finally I used the n = m x FM to get the 1.6 or 1.8 or something.

That's all I remember but it wasn't a bad paper at all, I just wasn't prepared for enthalpy of neut and my ester/grignards chemistry is a bit rusty. Nevermind. At least the practical was spot on =[