Question

Question: Write the chemical formula and give the name of the anhydride corresponding to each of the following acids or bases and identify it as an acid or base anhydride

$$\begin{gathered} {\mathbf{\text{(a)H}}}_{\mathbf{\text{3}}}{\mathbf{\text{AsO}}}_{\mathbf{\text{4}}} \\ {\mathbf{\text{(b)H}}}_{\mathbf{\text{2}}}{\mathbf{\text{MoO}}}_{\mathbf{\text{4}}} \\ \mathbf{\text{(c)RbOH}} \\ {\mathbf{\text{(d)H}}}_{\mathbf{\text{2}}}{\mathbf{\text{SO}}}_{\mathbf{\text{3}}} \end{gathered}$$

Short answer

$$\begin{gathered} {\text{(a) As}}_{\text{2}}{\text{O}}_{\text{3}}\to \text{Basic Anhydride} \\ {\text{(b) MoO}}_3\to \text{Basic Anhydride} \\ {\text{(c) Rb}}_{\text{2}}\text{O}\to \text{Basic Anhydride} \\ {\text{(d) SO}}_2\to \text{Acidic Anhydride} \end{gathered}$$

Step-by-step solution

Understanding the concept of acid and base anhydride 

By withdrawing water from an oxoacid until only the oxide remains, an acid anhydride is formed and a base anhydride is formed when water is removed from metallic hydroxides.

$$\begin{gathered} \mathbf{Oxoacid}\mathbf{-}\mathbf{water}\mathbf{=}\mathbf{acidanhydride} \\ \mathbf{Metalichydroxide}\mathbf{-}\mathbf{water}\mathbf{=}\mathbf{baseanhydide} \end{gathered}$$

Applying the concept

(a) Magnesium oxide (${\text{As}}_{\text{2}}{\text{O}}_{\text{3}}$) is basic anhydride as it is derived from the metallic hydroxide ${\text{H}}_{\text{3}}{\text{AsO}}_{\text{4}}$.

(b) Dichloride monoxide ${\text{MoO}}_3$ is the basic anhydride as it is derived from the metallic hydroxide ${\text{H}}_{\text{2}}{\text{MoO}}_{\text{4}}$.

(c) Sulphur trioxide ${\text{Rb}}_{\text{2}}\text{O}$ is the basic anhydride as it is derived from the metallic hydroxide $\text{RbOH}$.

(d) Cesium oxide ${\text{SO}}_2$is the basic anhydride as is it derived from the metallic hydroxide of ${\text{H}}_{\text{2}}{\text{SO}}_{\text{3}}$ .