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

Reply 1680

Qwob

1

Original post by orange94

ImageUploadedByStudent Room1371561322.970061.jpg

Do we need to know Al complex? HELP HELP HELP!

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No.

Reply 1681

posthumus

20

Original post by flower123456

Can someone help me answer question 4 please. It's from the jan 2012 paper.

If Iodide (I-) is being turned into iodine then it must be getting oxidized therefore hydrogen peroxide is an oxidizing agent

Iodine to Iodide is the opposite... therefore thiosulfate is a reducing agent

Reply 1682

flower123456

1

Original post by posthumus

If Iodide (I-) is being turned into iodine then it must be getting oxidized therefore hydrogen peroxide is an oxidizing agent

Iodine to Iodide is the opposite... therefore thiosulfate is a reducing agent

Thank you! Seems so simple now :smile:

Reply 1683

johnny-marr

Can someone outline the process of steam distillation for me? And why is it better than normal distillation?

Reply 1684

Qwob

1

Original post by flower123456

Can someone help me answer question 4 please. It's from the jan 2012 paper.

H2O2 is liberating Iodine from KI. KI is an ionic compound so it must contain I-, which is then turned into molecular I2. This oxidation, as there's a loss of electrons. So H2O2 is oxidising agent.

The thiosulfate equation is:

2 S₂O₃²⁻ + I₂ → S₄O₆²⁻ + 2 I⁻

Here Iodine is being reduced as it gains electrons. So thiosulfate is reducing agent.

Answer is B.

Reply 1685

flower123456

1

Original post by Qwob

H2O2 is liberating Iodine from KI. KI is an ionic compound so it must contain I-, which is then turned into molecular I2. This oxidation, as there's a loss of electrons. So H2O2 is oxidising agent.

The thiosulfate equation is:

2 S₂O₃²⁻ + I₂ → S₄O₆²⁻ + 2 I⁻

Here Iodine is being reduced as it gains electrons. So thiosulfate is reducing agent.

Answer is B.

Thank you that's a really good explanation. :smile:

Reply 1686

orange94

Original post by bubblegummer

Why is scantium a d-block element but not a transition metal?

Lol is this really a question. Pretty standard stuff.

First if all you have to understand what the definition of a transition metal is

A transition metal is one which forms one or more stable ions which have incompletely filled d orbitals.

Sc as an ion is sc3+ which has an empty d- orbital!

You must remember that it had the electronic configuration [Ar] 3d1 4s2

When it loses its 3electrons it's left with [Ar]

Get it now ?? Looool

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Reply 1687

randyaloul

Original post by Polish master

Does anyone know which is correct out of these two when it comes to the coupling stage in azo dye production ?

1. Diazonium salt + Phenol -------> dye + HCl (this one is from the textbook)
2. Diazonium salt + Phenol + NaOH ---------> dye + NaCl + H20 (this one is from the GCP)

Both books have been prone to errors for unit 5 and I'm not sure which one to go for.

Definitely first as far as I know. And it's "Alcoholic" phenol.

Reply 1688

JRP95

2

Original post by orange94

Lol is this really a question. Pretty standard stuff.

Get it now ?? Looool

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Now that wasn't very nice...

Reply 1689

randyaloul

What do we need to know about Combinatorial chemistry? Something tells me there's going to be a gigantic question tomorrow where we have to explain the processes related and such. My 2 textbooks explain it very vaguely, and so I don't have a very good idea about it. Sooo, what do we need to know about it?

Reply 1690

luckypants

Can someone explain what solvent extraction is used for? Thanks.

Reply 1691

JRP95

2

Original post by johnny-marr

Can someone outline the process of steam distillation for me? And why is it better than normal distillation?

You just heat water and pass the steam into whatever you were originally going to distill, the advantage is that, if what you were originally going to distill decomposes at High temperatures, the steam will lower its boiling temp so it will distill without decomposing and give you a higher yield.

Reply 1692

JRP95

2

Original post by doodledee1

on the jan 2013 paper there are a couple of multi choice questions I am confused about, firstly question 2c (i thought was C, correct answer B) and also question 11 (I thought was B, correct answer D). Could someone please explain them , thanks!

For 2c remember that standard electrode potential of chromium means only 1 mole of it, so you use half of 396 (as that would be for cr2)

For 11 I think the amide group is the c=o next to the n-h bond, that entire structure kind of forms an n substituted amide. There is no ketone group as a ketone is a C=O with the carbon attached to 2 other carbon atoms which is not present in the molecule.

Reply 1693

F1's Finest

21

Original post by 994

June 2012, Question 9a

How many main peaks on the nmr of caffeine

The answer's 4, but I thought the Hs on the CH3 are all the same because they're all bonded to carbons, which are all bonded to nitrogens, which are themselves all bonded to only carbons?

The three -CH3 groups are in their own environment.

If you look to the carbon on the far right hand side, you'll see it has only 3 visible bonds attached to it, which means that it must contain a hydrogen atom (which wasn't drawn in the picture to confuse you!)

Reply 1694

Hellz_Bellz!

2

I keep getting As in the past papers I'm doing... but the real thing is always so much harder than the past ones :cry2:

By the way, do we need to know all the reactions from AS? Like how to convert alkenes to halogenoalkanes and all that crap?

Reply 1695

F1's Finest

21

Original post by Hellz_Bellz!

I keep getting As in the past papers I'm doing... but the real thing is always so much harder than the past ones :cry2:

By the way, do we need to know all the reactions from AS? Like how to convert alkenes to halogenoalkanes and all that crap?

Yep, learn all of that, it's a synoptic paper after all :colone:

Reply 1696

TheMJCG

1

Hello everyone :smile:

are you guys learning preparation of chromium (II) ethanoate?

Reply 1697

F1's Finest

21

Original post by 994

I get the H on its own. So even though they all have this in common

the Hs circled are still different environments?

Yeah, all in their own environments. So three seperate CH3 environments. + the one on the far right as you were saying.

Reply 1698

AtomicMan

13

Original post by Hellz_Bellz!

I keep getting As in the past papers I'm doing... but the real thing is always so much harder than the past ones :cry2:

By the way, do we need to know all the reactions from AS? Like how to convert alkenes to halogenoalkanes and all that crap?

Yes

And also, does anyone know whether the dyes are precipitates, or solutions when the products are formed from coupling reaction?

Reply 1699

Bubble734

4

Original post by posthumus

One Cl- will react with the NO3Ag to form AgCl :smile:

A [Cr(OH)6]3-
B [Cr(H2O)6]3+
C [CrCl(H2O)5]2+
D [CrCl2(H2O)4]+

Lets re-write including the Cl- ions:

b) [Cr(H2O)6]Cl₃c) [Cr(H2O)6]Cl₂d) [Cr(H2O)6]Cl

As you can see for c) 1 mole of [Cr(H2O)6]Cl₂will give you 2 moles of AgCl (as it has 2 Cl- ions).

And also b) will give 3 moles, d) will give 1 mole.

Hope that helps :smile:

I'm stuck on this question too but still don't understand- why did you write the Cl outside of the square brackets? Are the Cl ions bonded to the chromium at this point?
Anyone?!
Thanks

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

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