Question

The equivalent weight of aluminum in Al₂O₃ is:

Answer 1

Equivalent weight: is the mass of one equivalent, that is the mass of a given substance that will combine with or displace a fixed quantity of another substance.

Step 1: Calculating the valency of Aluminium

Let the oxidation state of Aluminium = x

Oxidation state of oxygen = -2

Now,

$$\begin{gathered} 2\left(x\right)+3(-2)=0 \\ 2x=6 \\ x=3 \end{gathered}$$

Step 2: Calculating the equivalent mass of Aluminium

Molecular mass of Aluminium $=27\mathrm{g}{\mathrm{mol}}^{-1}$

Valency = Oxidation state = 3

Formula for equivalent weight,

$$\begin{gathered} \mathrm{Equivalent}\mathrm{weight}=\frac{\mathrm{Molecular}\mathrm{mass}}{\mathrm{Valency}} \\ \mathrm{Equivalent}\mathrm{weight}=\frac{27\mathrm{g}{\mathrm{mol}}^{-1}}{3}=9\mathrm{g}{\mathrm{mol}}^{-1} \end{gathered}$$

Hence, the equivalent weight of Aluminium is $9\mathrm{g}{\mathrm{mol}}^{-1}$.