Oxidation numbers of A, B and C are +2, +5 and -2 respectively. What could be the possible formula?

a) #A_2(BC_2)_2#
b) #A_3(BC_4)_2#
c) #A_2(BC_3)_2#
d) #A_3(B_2C)_2#

1 Answer
anor277
Dec 28, 2017

This is a good question....

We propose to make a neutral salt.....and thus the ionic charges MUST sum to neutrality, to ZERO....

Explanation:

And so we gots #A^(2+)#, #B^(5+)#, and #C^(2-)#, as the parent ions.....their combinations must form a neutral salt....

And we must go thru the formulae sequentially....

#a.# #A_2(BC)_2-=(A^(2+))_2(B^(5+)C^(2-))_2#...the charge on this species is #+10# so this is not a contender....

#b.# #A_3(BC_4)_2-=(A^(2+))_3(B^(5+)C_4^(2-))_2#...the charge on this species is #0# so this is a contender....

#c.# #A_2(BC_3)_2-=(A^(2+))_2(B^(5+)C_3^(2-))_2#...the charge on this species is #+2# so this is NOT a contender....

#d.# #A_3(B_2C)_2-=(A^(2+))_3(B_2^(5+)C^(2-))_2#...the charge on this species is #+22# so this is NOT a contender...

Remember, all I am doing is assessing positive versus negative charge...this is an exercise in arithmetic and book-keeping not chemistry.....AND don't trust my arithmetic. Satisfy yourself that what I have written is kosher.

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