Question

Spinel is an important class of oxides consisting of two types of metal ions with the oxide ions arranged in CCP pattern. The normal spinel has one-eighth of the tetrahedral holes occupied by one type of metal ion and half of the octahedral hole occupied by another type of metal ion. Such a spinel is formed by $Z{n}^{2+}$, $A{l}^{3+}$ and $O^{2-}$ with $Z{n}^{2+}$ in the tetrahedral holes. The formula of the spinel is:

• A. $ZnA{l}_2{O}_4$
• B. $Z{n}_{2}A{l}_3{O}_4$
• C. $ZnA{l}_3{O}_4$
• D. none of the above

Answer 1

The correct option is A $ZnA{l}_2{O}_4$

Since the oxide ions are present at CCP sites,

Number of oxide ions per unit cell $=4$

Number of one of the metal ion $=\frac{1}{8}\times 8=1$

Number of second metal ion $=\frac{1}{2}\times 4=2$

Now, to balance the negative charge of $O^{2-}$ ions$=4\times (-2)=-8$

Number of $A{l}^{3+}$ ions will be $2$ and number of $Z{n}^{2+}$ ions will be $1.$

Therefore, the formula of the spinel is $ZnA{l}_2{O}_4$.