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Question
Analysis shows that nickel oxide has the formula Ni0.98O1.00. What fractions of nickel exist as Ni2+ and Ni3+ ions?
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Solution
The formula Ni0.98O1.00 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%
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