Question

Analysis shows that nickel oxide has the formula Ni_0.98O_1.00. What fractions of nickel exist as Ni²⁺ and Ni³⁺ ions?

Answer 1

The formula Ni_0.98O_1.00 indicates that 98 Ni atoms are associated with 100 O atoms. Suppose,

Number of Ni atoms present as Ni²⁺ = x

∴ Number of Ni atoms present as Ni³⁺ = 98 − x

Since nickel oxide is electrically neutral, the total charge present on x Ni²⁺ ions and (98 − x) Ni³⁺ ions should be equal to the total charge present on 100 O²⁻ ions. Therefore, we have

(x × 2) + (98 − x) × 3 = 100 × 2

or 2x + 294 − 3x = 200

or x = 94

∴ Fraction of Ni present as Ni²⁺ = `94/98 xx 100`

= 95.9

= 96%

and fraction of Ni present as Ni³⁺ = `(98 - 94)/98 xx 100`

= 4.08

= 4%