The Student Room Group
Uni students - Complete our survey >>
Uni students - Complete our survey >>
Uni students - Complete our survey >>

This discussion is now closed.

Check out other Related discussions

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

Scroll to see replies

Original post by posthumus
Ah, thanks :biggrin: That's reassuring too... I was wondering where the H2O went :confused: I don't even know what it does :tongue:

O2+ 2H2O + 4e- <-----> 4OH-

It this right? :smile:
&
Is it right for me to think this process is reversible?


Apologies I meant left hand side.

Yep that's right.

Have you got the data booklet on your pc?
Original post by James A
You mean benzenediazonium chloride? There's a noticeable difference between the two!

Make sure you don't say phenylammonium chloride in the exam!


Haha oh yeah I didn't even notice that. I got the two steps mixed up haha thanks. :smile:

Also, does anyone know how we determine if NH3 is going to result in deprotonation or ligand exchange?
Hey guys, I just seem to never understand what causes a complex ion to be the way it is!

I was going through one of the past papers (jan2012) and in one of the multiple questions, its asks:

When a solution containing 0.10 mol of chromium(III) chloride, CrCl3.6H2O, is treated with excess silver nitrate solution, .20 mol of silver chloride, AgCl, is immediately precipitated. The formula of the complex ion in the solution is


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



basically what its asking is
CrCl3 + NO3Ag ----> ?????

The answer is C, [CrCl(H2O)5]2+, but I just dont understand why it is so! does anybody care to help?
Original post by yahyazhar
Hey guys, I just seem to never understand what causes a complex ion to be the way it is!

I was going through one of the past papers (jan2012) and in one of the multiple questions, its asks:



basically what its asking is
CrCl3 + NO3Ag ----> ?????

The answer is C, [CrCl(H2O)5]2+, but I just dont understand why it is so! does anybody care to help?


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]Cl3
c) [Cr(H2O)6]Cl2
d) [Cr(H2O)6]Cl

As you can see for c) 1 mole of [Cr(H2O)6]Cl2 will 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:
Original post by James A
Apologies I meant left hand side.

Yep that's right.

Have you got the data booklet on your pc?


Nope ! I have printed out copies here somewhere, but I must get familiar with the ones you actually get in the exam.... as in unit 4, It took me forever to find the entropy or whatever for a particular molecule :redface:
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]Cl3
c) [Cr(H2O)6]Cl2
d) [Cr(H2O)6]Cl

As you can see for c) 1 mole of [Cr(H2O)6]Cl2 will 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:


Oh wow that cleared it up really easily thank you very much!
Reply 986
Avatar for AS01
AS01
12
Original post by James A


Compound X reacts with cold nitrous acid to give a yellow ppt in an alkaline solution. So that means that compound X has a phenylamine group.


Why so? I know you get yellow precipitate when u react phenol with diazonium and amine with diazonium but never knew u get yellow ppt with amine and nitrous acid.
Reply 987
Avatar for AS01
AS01
12
I have a question :smile:
[CoCl4]2- is a tetrahedral ion, [Co(H2O)6]2+, Co(OH)2 (H2O) 4] are octahedral ions. Write equations to show ligand exchange and deprotonation using Cl-, H2O and OH-.
Original post by AS01
Why so? I know you get yellow precipitate when u react phenol with diazonium and amine with diazonium but never knew u get yellow ppt with amine and nitrous acid.


It said 'Compound X reacts with ice-cold nitrous acid to form a compound that gives a yellow ppt with an alkaline solution of phenol.

I made a typo in my initial answer.
(edited 10 years ago)
Reply 989
Avatar for GeorgeL3
GeorgeL3
5
Hey I've just made some revision cards, if anyone could have a look to see if I've missed anything or made any mistakes that would be really helpful. Of course you can use them as well if you want.
(edited 10 years ago)
Chemistry Unit 5 Revision Cards - George Lewis.docx364.1KB
Reply 990
Avatar for AS01
AS01
12
Original post by James A
It said 'Compound X reacts with ice-cold nitrous acid to form a compound that gives a yellow ppt with an alkaline solution of phenol.

I made a typo in my initial answer.


That makes sense thanks!
Does ammonia displace OH- ions and H20 molecules in ligand exchange reactions? Or just water molecules?
Original post by AtomicMan
Does ammonia displace OH- ions and H20 molecules in ligand exchange reactions? Or just water molecules?


It will replace both if there's a lot of excess ammonia present :smile:
Original post by posthumus
It will replace both if there's a lot of excess ammonia present :smile:


Ok, so in a normal (not excess) amount of ammonia, it just displaces water molecules?
Original post by AtomicMan
Ok, so in a normal (not excess) amount of ammonia, it just displaces water molecules?


Well it removes hydrogens from water molecules (usually 2) to form Hydroxy groups... the compound is precipitate :smile:

So say you have aqua Cu2+

[Cu(H2O)6]2+ + 2NH3 -----> [Cu(H2O)4(OH)2] (s) + 2NH4

^ This happens when ammonia isn't excess :smile:
Original post by GeorgeL3
Hey I've just made some revision cards, if anyone could have a look to see if I've missed anything or made any mistakes that would be really helpful. Of course you can use them as well if you want.


These are amazing, George
Reply 996
Avatar for GeorgeL3
GeorgeL3
5
Original post by Mollymod
These are amazing, George

Thanks, I just went through the syllabus with my notes, the book, chemguide and of course TSR making notes on everything.
I actually noticed on one of the cards I put racemic and scalemic the wrong way round and found a couple of other typos, I'll re-upload it in that last post just for completion.
Does anyone know the apparatus we need to be able to draw for this exam? :smile:
Reflux, Distillation.
Original post by GeorgeL3
Thanks, I just went through the syllabus with my notes, the book, chemguide and of course TSR making notes on everything.
I actually noticed on one of the cards I put racemic and scalemic the wrong way round and found a couple of other typos, I'll re-upload it in that last post just for completion.


Yeah, I've got some, but they're not really to everyone's taste.
Very colourful and lots of information on a double page spread which is how I like my notes, all in one place and accessible. But I like the condensed nature of yours, because they're really concise, and its easy to miss bits out of the course if you dont have the notes condensed in a systematic way.

Related discussions

Latest

Trending

Trending

Articles for you