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
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.