How to calculate the fraction of elements with diffrent oxidation states within a compound?

[hitmankratos]

Hi

 

There is a chemistry problem that I'm really not able to do. It's basically the reaction of Lanthanum with Hydrogen to produce the nonstochiometric compound LaH2.90 . So, if we know that the compound contains Hˉ, La⁺² and La⁺³ (yeah its a little 3 there), how can we know the fraction of La⁺² and La⁺³ present in the compound?

 

I know that the answer will be 10.9% La+2 and 90%La+3....but I have NO IDEA on how to get that...

I'm not asking for HOW to do it completely, but just clues that can guide me into finding the answer...

 

Thanks in advance,

[cypress]

Each La⁺³ is grouped with 3H and each La⁺² with 2 of course. If you were to define fraction of La⁺³ as X what is the fraction of La⁺² in terms of X?

 

Then if you were to multiply the fractions of each with the number of corresponding hydrogens what would that equate to?

[hitmankratos]

I just don't get it for some reason...

Basically, the equation is : LaH2 + LaH3 --> LaH2.90

 

I'm just comparing the hydrogens...so 2.9 = H3(x) + H2(y)....this equation cannot be solved as i don't have a second equation....

 

Any other clues?

Edited October 4, 2010 by hitmankratos