AQA CHEM5 A2 Chemistry - 19th June 2013

Hey, sorry for bothering you again but what's the product formed when excess ammonia reacts with aluminium and what's it's colour? Thanks

In xs of ammonia i swear its green soln? we did a test for it because the text book was wrong....?

Hi there! No bother- I like helping people- it helps me revise too

Again: CGP is ambiguous here because it simply states 'No Change', but in actual fact:

[Al(H₂O)₆]³⁺ as a solution by itself is colourless.

adding dil. NH_3(aq) we get Al(H₂O)(OH)_3(s) which is a white precipitate

adding XS NH_3(aq) we get [Al(H₂0)₂(OH)₄]^-_(aq) which is slightly soluble and therefore forms a colourless solution if fully dissolved in water.


Hope this helps!

I think so because the ionisation enthalpy is: the enthalpy change when one mole of electrons are removed from one mole of gaseous atoms.

So they have to be gaseous thus enthalpy of atomisation has to occur first

[CoCl₄]^2- is blue
[CuCl₄]^2- is yellow

Those are the only two we need to know

ohh yeah, the definition in the textbook says something about water molecules, and the markscheme says do not allow any mention of water molecules..FFS. made me distrustful of all the other standard definitions :/

as for the chlorine complexes, ive learnt [CoCl4]2- as blue solution
[CuCl4]2- as yellow green solution. and they match up to mark scheme answers.

sorry I didn't make myself clear, I meant for the element that would undergoing electron affinity. Does it make a difference if the all the enthalpy of atomisation first for both elements and then the ionisation energy and then the electron affinity. I'm not entirely sure if I'm making myself clear..

Just reverse your knowledge of the colour of the compounds so if it says its yellow then you know its the CrO4^2- ? is this what you mean

I thought that this was only for XS OH-?? I've got it written down that XS NH3 has no effect on Al ??

Hydration - Enthalpy change when one mole of gaseous molecules or ion is dissolved in sufficient water to produce an infinitely dilute solution.

Solution - Enthalpy change when one mole of a compound is dissolved in sufficient solute to produce a solution in which the ions are far enough apart so as not to react.

From memory that's what it said in the text book i got them from but mark schemes seem to vary on it if anybody has any more concise definitions that would be good haha

for the solution 1 dont you have to mention the formation of aqueous ions?

Hey I am a little confused on lattice enthalpies. In AQA book in chapter 12 it says when there is covalent characters in the ionic bond it increases the lattice formation enthalpy. But then in chapter 13 it says Aluminum oxide has a lower melting point because of the extra covalent bonds it has. I am so confused

hey guys. When drawing complexes out, do we used a double headed arrow to represent the co-ordinate bond? In the Jan 13 mark scheme, the diagrams just had a normal line, no double headed arrow.

I know that double headed arrows represent co-ordinate bond, and straight line represents covalent bond

Would have thought double head - says in the book that ligands form coordinate bonds with the transition metal ion