Question

An element combines with oxygen to form an oxide. The oxide dissolves in water. This aqueous solution changes blue litmus to red. Write:

The nature of the aqueous solution (alkaline or acidic)

Answer 1

• Nature of aqueous solutions

An aqueous solution comprises water in form of a solvent. An aqueous solution can be acidic as well as basic. The nature depends on the number of hydroxide ions and hydrogen ions that are present in the aqueous solution.

• Example of oxide

An example of oxide is Carbon dioxide $\left({\mathrm{CO}}_2\right)$ and its formation reaction is given below:

$$\begin{gathered} \mathrm{C}\left(\mathrm{s}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)\to {\mathrm{CO}}_2\left(\mathrm{g}\right) \\ \mathrm{Carbon}\mathrm{Oxygen}\mathrm{Carbon} \\ \mathrm{dioxide} \end{gathered}$$

The reaction of Carbon dioxide $\left({\mathrm{CO}}_2\right)$ with Water $\left({\mathrm{H}}_2\mathrm{O}\right)$ is given as:

$$\begin{gathered} {\mathrm{CO}}_2\left(\mathrm{g}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to {\mathrm{H}}_2{\mathrm{CO}}_3\left(\mathrm{aq}\right) \\ \mathrm{Carbon}\mathrm{Water}\mathrm{Carbonic} \\ \mathrm{dioxide}\mathrm{Acid} \end{gathered}$$

• Change in colour of the litmus paper

When an element combines with Oxygen $\left({\mathrm{O}}_2\right)$, then it forms an Oxide $\left({\mathrm{O}}^{2-}\right)$. This Oxide in water changes blue litmus to red. Litmus paper is majorly used for testing whether an aqueous solution is acidic, basic, or alkaline in nature. When the solution changes from blue to red, then the solution is acidic and if the colour changes from red to blue, then the solution is basic.

Thus, the nature of the aqueous solution is acidic.