Ed excel Chemistry A2 12th June, Wednesday

Original post by AS01

Yes it is and if u use dioic u will have two H+ donated. So u have to times H+ conc by two which would not be right coz that acid is weak so it dissociates only slightly hence we would be overestimating the pH

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Seems about right! :^_^:

Reply 222

OP

Original post by MrProff

Seems about right! :^_^:

Did u get first order and Ea as 38kJmol-1?

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Reply 223

Original post by AS01

Did u get first order and Ea as 38kJmol-1?

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on the last question?

Reply 224

OP

Original post by MrProff

on the last question?

Yeah

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Reply 225

Original post by AS01

Yeah

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I got around 414000 Jmol-1 so yeah 41.4KJ but its all down to gradient so seems right

Reply 226

OP

Original post by MrProff

I got around 414000 Jmol-1 so yeah 41.4KJ but its all down to gradient so seems right

Cool! Btw that dioic acid was asking us to compare with salt right? Rather than ethanoic acid

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Reply 227

Well that was a strange exam, the entropy questions were nice and the pH stuff was alright. Not too sure I liked all the mechanism stuff though.

Reply 228

OP

Original post by HarryMWilliams

Well that was a strange exam, the entropy questions were nice and the pH stuff was alright. Not too sure I liked all the mechanism stuff though.

Ikr! That paper was weird!

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Reply 229

Original post by AS01

Ikr! That paper was weird!

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Frankly, I would have prefered to have done the Jan 2013 paper again. :s-smilie:

What "method" did people put for the Section C question about measuring the concentration of iodine and why was the S₂O₈^2- in excess?

Reply 230

OP

Original post by HarryMWilliams

Frankly, I would have prefered to have done the Jan 2013 paper again. :s-smilie:

What "method" did people put for the Section C question about measuring the concentration of iodine and why was the S₂O₈^2- in excess?

Same! Colorimetry and it's coz it reacts with iodine and gives better result coz it makes sure that if iodine which is present in more amount than the conc of thiosulphate then the solution changes color straight away. I didnt write this lol I asked my teacher and she said that's what is thiosulphate for

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Reply 231

Original post by AS01

Same! Colorimetry and it's coz it reacts with iodine and gives better result coz it makes sure that if iodine which is present in more amount than the conc of thiosulphate then the solution changes color straight away. I didnt write this lol I asked my teacher and she said that's what is thiosulphate for

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Ah, I thought about colorimetry and then just went with a running titration (stupidly) after I thought the first example was a colorimtry experiment.

I said it had a much high concentration/volume so it was in excess and didn't act as a limiting factor during the experiment. :s-smilie:

Reply 232

OP

Original post by HarryMWilliams

Ah, I thought about colorimetry and then just went with a running titration (stupidly) after I thought the first example was a colorimtry experiment.

I said it had a much high concentration/volume so it was in excess and didn't act as a limiting factor during the experiment. :s-smilie:

It was iodine clock reaction
Yeah I thought the same I even put it donates S2O3 2- ion but then later I was like no! That doesnt make sense! And wrote something about precise colour and all but I wrote it reacts with IODIDE ion!!!!!

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Reply 233

Original post by AS01

Cool! Btw that dioic acid was asking us to compare with salt right? Rather than ethanoic acid

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Im not sure, pretty sure it was though!

Original post by HarryMWilliams

Frankly, I would have prefered to have done the Jan 2013 paper again. :s-smilie:

What "method" did people put for the Section C question about measuring the concentration of iodine and why was the S₂O₈^2- in excess?

I put colorimetry because it said without sampling, so that means you couldn't do a titration right?

Reply 234

blackraven

15

has anyone done an unofficial mark scheme?

Reply 235

Original post by MrProff

Im not sure, pretty sure it was though!

I put colorimetry because it said without sampling, so that means you couldn't do a titration right?

Yeah, I should have stuck with my initial reaction in all honesty.

http://www.thestudentroom.co.uk/newreply.php?do=newreply&p=43131557

If I can get a copy of the paper then we can try. :smile:

Reply 236

posthumus

20

Could the grade boundaries for a B possibly be below 60/90 ? :colondollar:

Reply 237

randyaloul

The second mcq, the one that asked why 2 methyl propanoic acid had lower entropy, was it a? Because it had lower bp?

Also, I wrote units for activation energy as J :s will I lose marks because I didn't write j/mol?

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Reply 238

posthumus

20

Original post by randyaloul

The second mcq, the one that asked why 2 methyl propanoic acid had lower entropy, was it a? Because it had lower bp?

Also, I wrote units for activation energy as J :s will I lose marks because I didn't write j/mol?

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I think it was more ways of distributing energy or whatever. Because that's what entropy is all about... the most disorder or in other words the most ways of distributing energy

Sorry, I think you would... they did specifically ask for units. I really screwed that one up I think I got 500 something...

Reply 239

OP