Question

Nickel oxide has the formula $NiO_{0.98} O_{1.00}$ What fractions of nickel exist as $Ni^{2+}$ and $Ni^{3+}$ ion?

• A. $Ni^{2+} = 64\%$ and $Ni^{3+} = 36\%$
• B. $Ni^{2+} = 96\%$ and $Ni^{3+} = 4\%$
• C. $Ni^{2+} = 25\%$ and $Ni^{3+} = 75\%$
• D. $Ni^{2+} = 33\%$ and $Ni^{3+} = 67\%$

Answer 1

Answer: (B)

$98\, Ni$ atoms are associated with $100$ O-atoms
Out of $98 \,Ni$ atoms, suppose Ni present as $Ni^{2+}=x$
Then Ni present as $Ni^{3+}=98-x$
Total charge on $x \,Ni^{2+}$ and $(98-x)Ni^{3+}$ + should be equal to charge on $100\,O^{2-}$ ions
Hence, $x \times 2 +(98-x)\times 3 =100 \times 2$
or $2x+294-3x =200$
or $x=94$
$\therefore $ Fraction of $Ni$ present as $Ni^{2+} = \frac{94}{98}\times 100 = 96\%$
Fraction of $Ni$ present as $Ni^{3+} = \frac{4}{98}\times 100 = 4\%$