You are Here: Home

# ligand substitution Tweet

Chemistry discussion, revision, exam and homework help.

Announcements Posted on
1. ligand substitution
[cr(h20)3+] and excess ammonia are added together. suggest the equation

i put:
[Cr(H2O)6]3+ + 4NH3 --> [Cr(NH3)4(H2O)2]3+ + 4H2O

but its wrong, the answer is:
[Cr(H2O)6]3+ + 6NH3 --> [Cr(NH3)6]3+ + 6H2O

2. Re: ligand substitution
(Original post by asaaal)
[cr(h20)3+] and excess ammonia are added together. suggest the equation

i put:
[Cr(H2O)6]3+ + 4NH3 --> [Cr(NH3)4(H2O)2]3+ + 4H2O

but its wrong, the answer is:
[Cr(H2O)6]3+ + 6NH3 --> [Cr(NH3)6]3+ + 6H2O

Your answer is right! Are you reading the mark scheme? On the right hand side it should say "allow [Cr(H2O)6]3+ + 4NH3 --> [Cr(NH3)4(H2O)2]3+ + 4H2O "

I remember doing this question and thinking I was wrong however I recall being taught it that way!
3. Re: ligand substitution
(Original post by YB101)
Your answer is right! Are you reading the mark scheme? On the right hand side it should say "allow [Cr(H2O)6]3+ + 4NH3 --> [Cr(NH3)4(H2O)2]3+ + 4H2O "

I remember doing this question and thinking I was wrong however I recall being taught it that way!
oh so it does !
Thank you
4. Re: ligand substitution
I like how they ''allow'' the correct answer

edit: wait, no, I need to go to the opticians Cr isn't Cu
Last edited by EierVonSatan; 25-05-2012 at 12:35.
5. Re: ligand substitution
(Original post by EierVonSatan)
I like how they ''allow'' the correct answer
the mark scheme is so stupid. I hope i get a good examiner marking my paper though
last year for AS i was 1 mark off an A so i got my paper back and he or she had marked my answer '69.2% yield' wrong :|
how can you mark a number wrong :| it takes absolutely no personal opinion and its so objective... theyd missed out 6 marks over all in that one paper :|
6. Re: ligand substitution
(Original post by EierVonSatan)
I like how they ''allow'' the correct answer
I know! I seriously despise both the biology and chemistry mark schemes -.-
7. Re: ligand substitution
(Original post by EierVonSatan)
I like how they ''allow'' the correct answer
In AQA they don't mention anything about the diaqua complex; they only mention the purple hexaammine complex