AS Chemistry Question MCQ

[kratos009]

Hey guys
I got one Chemistry multi-choice question where i don't understand how they got the answer,

1.Aluminium chloride catalyses certain reactions by forming carbocations (carbonium ions) with
chloroalkanes as shown.
RCl + Al Cl3 ? R+ + AlCl4-


Which property makes this reaction possible?
A AlCl3 exists as the dimer Al2Cl6 in the vapour.
B AlCl3 is a covalent molecule.
C The aluminium atom in Al Cl3 has an incomplete octet of electrons.
D The chlorine atom in RCl has a vacant p orbital.


The answer was C. Could someone explain to me why the AlCl3 has an incomplete octet, because doesn't the aluminium ion give away its three electrons to the Cholride ions?

[123]

Hey this is explained in that Chem MCQ helps book...i think its in pg. 18 (left bottom) : Q18
Heres that book if u don;t hav 1: http://www.megaupload.com/?d=7CBYEBYX

[kratos009]

Thanks a lot 123,  i understand it now.
If you have Chem exam tomorrow, GOOD LUCK.

Oh i just got one more question,

1.How does ammonia behave when its aqueous solution is used to dissolve silver chloride, AgCl ?

A as a base
B as a ligand with the Ag+ ion
C as a ligand with the Cl– ion
D as a reducing agent

the answer was B. I was wondering how does ammonia bind with the positive Ag+ ion, i thought it would bind with the negatively charged chloride ion as an ammonium chloride?thanks

[ghl23]

if i've not mistaken, when ammonia is added to silver chloride.. it reacts with silver to form a soluble complex Ag(NH3)2+ and also liberating Cl- ions

AgCl(s) + 2NH3(aq) ? Ag[(NH3)2]+(aq) + Cl?(aq)

[top_dog77]

thanks for the upload

[ghl23]

and to answer your question.. it forms the amine group(NH2-) which then reacts with the silver ions

[kratos009]

Oh right i get it, thanks a lot.

[123]

Thanks a lot 123,  i understand it now.
If you have Chem exam tomorrow, GOOD LUCK.

Oh i just got one more question,

1.How does ammonia behave when its aqueous solution is used to dissolve silver chloride, AgCl ?

A as a base
B as a ligand with the Ag+ ion
C as a ligand with the Cl– ion
D as a reducing agent

the answer was B. I was wondering how does ammonia bind with the positive Ag+ ion, i thought it would bind with the negatively charged chloride ion as an ammonium chloride?thanks

Even i thought it binds with -ve charged chloride ion as an ammonium chloride  
But it turns out that when the ppt. of AgCl dissolves in NH3 (aq) the silver ion forms a complex ion (
This line is there in the CIE txtbook (pg. 240). Dunno if ur doing A2 levels but the detail involve complex ions & solubility product (A2 level stuff!!). This site explains it well: http://www.chemguide.co.uk/inorganic/group7/testing.html#top
Man the CIE txtbook is really confusing!! Some stuff is not explained and they ask that stuff  in a AS level paper1!!