Q38 / 180 · JIPMER 2016 · Chemistry

If oxide ions are arranged in hcp and the aluminium ions occupy two thirds of octahedral voids. What will be the formula of the compound?

  • A
    $\mathrm{AlO}_3$
  • Correct answer
    B
    $\mathrm{Al}_2 \mathrm{O}_3$
  • C
    $\left(\mathrm{Al}_2 \mathrm{O}_3\right)_2$
  • D
    $\mathrm{Al}_3 \mathrm{O}_4$

Solution

In hcp arrangement of oxide ion. Number of octabedral (oh) voids for each oxide ion $=1$ Number of tetrahedral $(\mathrm{Td}$ ) voids for each oxide ion $=2$ $\mathrm{Al}^{3+}$ occupies only $2 / 3$ of octahedral voids. Thus, number of $\mathrm{Al}^{3+}$ for each oxide ion $=2 / 3$ $\Rightarrow$ Ratio of oxide ion : Aluminium ion $\Rightarrow 3: 2$ Thus, formula is $\mathrm{Al}_2 \mathrm{O}_3$.

Hence, the correct answer is option: 'B'.

Relevant Questions