Edexcel A2 Chemistry 6ch04/05 JUNE 2015

Reply 1200

hsheahan

2

Catalyst in transesterification?

Reply 1201

Callum_Stewart

1

Original post by Connor_1949

At complete neutralisation, lots of CH3CH2COO- is produced.
This is a weak base which can react with water

CH3CH2COO- + H2O --> CH3CH2COOH + OH-

It's weird but basically the conjugate base adds OH- to the solution increasing the pH.

^ This.

Reply 1202

madmenace

8

wth was that??!!! how am I supposed to know why there are two outliers??
!!!

I wrote because temperature increased :s-smilie:

unless I smash unit 5 (which will never happen) bye bye to my A grade...

couldn't even finish without rushing part C.... didn't even do the empirical formula properly!!!!

how where u suppoed to use AHf values?

anyone?

Reply 1203

Callum_Stewart

1

Original post by madmenace

wth was that??!!! how am I supposed to know why there are two outliers??
!!!

I wrote because temperature increased :s-smilie:

unless I smash unit 5 (which will never happen) bye bye to my A grade...

couldn't even finish without rushing part C.... didn't even do the empirical formula properly!!!!

how where u suppoed to use AHf values?

anyone?

Yeah, because its an exothermic reaction, at higher conc. it releases a lot of heat, which increases the rate of the reaction, thus the two points are high than they should have been.

Reply 1204

Nautic4l

12

Was the pH not 10.88 for the excess NaOH one?

Reply 1205

madmenace

8

Original post by Wahid1

The only respectable section was section C

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hey how did u use the AH f values to get a value for Ah surrounding???

and was your entropy change really positive?

Reply 1206

AnishaJayne

2

Didn't know how to draw the biodiesel, and screwed up the order of X. I got 0..306 tonnes which isn't right but I had no clue how to even attempt this, I got 3.1 but then it can't be more than 2.5 if only 79% yield right? 😰 hard paper but doable I guess, very time pressured didn't get to over look questions much

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Reply 1207

frozo123

12

Original post by Nautic4l

Was the pH not 10.88 for the excess NaOH one?

12.0 brah

Reply 1208

Stillreading

14

Original post by _bindra

I hope so, check old markschemes they usually give a mark for mentioning something that sounds like LeChateliers principle. As for the neutral bit, the question didnt ask anything about neutrality but I included it anyway. It only asked about its pH.

Ah thanks, that's made me feel more calm! Cheers, hope you get the mark you want :smile:

Reply 1209

Wahid1

7

Original post by madmenace

hey how did u use the AH f values to get a value for Ah surrounding???

and was your entropy change really positive?

-311 KJ for enthalpy.

That's a huge ****ing energy change

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Reply 1210

_bindra

4

Original post by Callum_Stewart

Yeah, because its an exothermic reaction, at higher conc. it releases a lot of heat, which increases the rate of the reaction, thus the two points are high than they should have been.

Ohhh it seems so obvious now! Three easy marks lost :frown:

Reply 1211

Mufinator

1

it was sodium hydroxide for the transesterification, but then crossed it out for some brain dead reason so now im not getting marked

Reply 1212

Wahid1

7

The only positive from this exam is everyone found the paper difficult...

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Reply 1213

Callum_Stewart

1

Original post by AnishaJayne

Didn't know how to draw the biodiesel, and screwed up the order of X. I got 0..306 tonnes which isn't right but I had no clue how to even attempt this, I got 3.1 but then it can't be more than 2.5 if only 79% yield right? 😰 hard paper but doable I guess, very time pressured didn't get to over look questions much

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The aspirin molecule is a larger molecule than the salicylic acid, because you're adding stuff like CO2 and acyl groups, so it actually CAN be heavier, you just can't get more moles of it.