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Edexcel Chemistry A2 Unit 5 ~ Wednesday 19th June 2013 (Now Closed)

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Reply 1220

idknow

can anyone help me with my question?

Reply 1221

Chem2013entry

what do you guys think about using unit 6b past papers as revision for unit 4 and 5 papers? unit 6b is the international alternative offered by edexcel for internally assessed practicals. attached the specification for the unit alongside a paper and a mark scheme. The rest of the papers/schemes can be found on the edexcel website. It seems worth it, especially for the organic synthesis part in unit 5.

Unit 6B specification on p7, http://www.edexcel.com/migrationdocuments/GCE%20New%20GCE/International-spec-Chemistry.pdf .

typical question paper and mark scheme http://www.edexcel.com/migrationdocuments/QP%20GCE%20Curriculum%202000/January%202011%20-%20QP/6CH08_01_que_20110119.pdf

http://www.edexcel.com/migrationdocuments/QP%20GCE%20Curriculum%202000/January%202011%20-%20MS/6CH08_01_rms_20110309.pdf

Reply 1222

Dolphino

Original post by idknow

have a quick question,

in the edexcel chemistry book they say that hydrogen reduces dichromate into chromium 2+ but looking at the electrode potentials hydrogen cant reduce it, im guessing it is the zinc that reduces the dichromate is that right and if not any help would be great

In response to a question above:

Amino Acids in their solid form are zwitterions which is why they are solid

and im not sure about the ethanoic acid but assuming its because the reaction doesnt go to completion.

Hi there I've just worked out that it is feasible. You have to first reduce the dichromate to chromium3 with the hydrogen. The E should work out to be +1.33V. Next you reduce the chromium 3 to chromium 2, again with hydrogen. The electrode potential for this reaction is negative, -0.41V. However we need to combine the two together as we are going from the dichromate to the chromium2 (so add the two E values). The total value would thus be positive and feasible!

Hope that helps
(apologies in advance if iam wrong!!)

Reply 1223

Dolphino

So overall, combining both equations together it'd be:

Cr2O7 (2-)+ 6H (+) + 4H2 ----> 2Cr (3+) + 7 H2O

E cell= +0.92 V

Reply 1224

Amila888

hey.. can u explain to me what happens to the solubility of aldehydes and ketones in water, when the length of chain increases?

Reply 1225

username644227

may be a dumb question but...

why would you choose aq ammonia to separate Fe(OH)3 from the mixture of Fe(OH)3 and Cu(OH)3?
i guessed the answer from the multiple choice and luckily i got it right
but i need to understand why

any help please?

EDIT: this is from jan 12
also q14 why would Br2 react with sodium carbonate?
should it only react with acids?

(edited 10 years ago)

Reply 1226

Dolphino

Original post by StellaRawr11

Hey there,
Fe(OH)3 is insoluble in excess ammonia whereas Cu(OH)2 dissolves in exs ammonia. Therefore you would be left with a ppt of Fe(OH)3 which you can easily separate from the solution.

To be honest for the bromine thing I kinda of guessed it- I assumed that the Br2 would react with the water to give HBr which is acidic so Na2CO3 would neutralise it. But I'm not too sure ...

Reply 1227

Dolphino

Original post by Amila888

hey.. can u explain to me what happens to the solubility of aldehydes and ketones in water, when the length of chain increases?

Solubility decreases as the hydrocarbon chain length increases

Reply 1228

username644227

ok another question i think that it needs to be clarified before we all get confused (or only i will get confused) xD

if we see these types or representation of electrode potential equations, how will we know which direction does it go?
is it from right to left always? what about the second one?

equ/Eo
Co2+(aq) | Co(s) -0.28

[H3PO4(aq) + 2H+(aq)], [H3PO3(aq) + H2O(l)] | Pt 0.28

Reply 1229

JRP95

Original post by StellaRawr11

In our actual spec exams I've never seen electrode potentials written like that at all...

Reply 1230

AtomicMan

Original post by StellaRawr11

All electrode potentials are written in as reductions, so the Co2+ is gaining electrons, to form Cobalt solid.

Original post by JRP95

In our actual spec exams I've never seen electrode potentials written like that at all...

Theyre written like that in the data booklet.

Reply 1231

ayeswary

hey guys. how do we draw the displayed formula when ethanoyl chloride reacts with 2 amino butan-2-ol? :confused:

Reply 1232

posthumus

Original post by ayeswary

hey guys. how do we draw the displayed formula when ethanoyl chloride reacts with 2 amino butan-2-ol? :confused:

Hopefully this will help you out...

I believe there should be HCl product also

EDIT: didn't see the fact that it was amino :tongue:

But I guess the group would just stay there... elimination will occur between H in the hydroxy group & chlorine

(edited 10 years ago)

Reply 1233

paddyroddy

Original post by ayeswary

hey guys. how do we draw the displayed formula when ethanoyl chloride reacts with 2 amino butan-2-ol? :confused:

2CH₃COCl + CH₃CH₂CH(NH₂)CH₂OH

Ethanoyl chloride reacts with both NH₂ & OH!

---> CH₃CH₂CH(HNOCCH₃)CH₂OOCCH₃ + 2HCl

(edited 10 years ago)

Reply 1234

AS01

Original post by StellaRawr11

it is from left to right :smile:

Reply 1235

username644227

Thanks AS01 :biggrin:

ok another qs that may come up x]

how many hydrogen environments should benzene have?
if it has substituents like OH or CH3, then what how many H environments does it have?

Thanks :biggrin:

Reply 1236

posthumus

Original post by StellaRawr11

Thanks AS01 :biggrin:

ok another qs that may come up x]

how many hydrogen environments should benzene have?
if it has substituents like OH or CH3, then what how many H environments does it have?

Thanks :biggrin:

Depends on how many groups there are and in what positions they are in?

Phenol and methyl-benzene would have 4 different hydrogen environments

If there's more groups, then there would be way more than that, especially if it is not longer symmetrical

Reply 1237

Dolphino

Original post by posthumus

Where did u get 4 from? I thought it was only three?

Reply 1238

posthumus

Original post by Dolphino

Where did u get 4 from? I thought it was only three?

Did you include that methyl or OH group have 1 hydrogen environment?

Reply 1239

Dolphino

Yeah I did. Basically you know around the methyl group, I thought that the two adjacent hydrogen atoms would be in the same environment since benzene is symmetrical. That environment plus the hydrogenl environment plus the hydrogen environment in methyl group makes three...