Question

A ribbon of silvery-white element when heated in a flame burns with a dazzling white light and leaves a white powder. The white powder when dissolved in water turns red litmus blue. Answer the following:

Is the solution of white powder acidic or alkaline?

Answer 1

1. A ribbon of the silvery-white element is magnesium and the white powder obtained while burning is magnesium oxide.
2. The reaction can be written as:

$$\begin{gathered} 2\mathrm{Mg}\left(\mathrm{s}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)\to 2\mathrm{MgO}\left(\mathrm{s}\right) \\ \mathrm{Magnesium}\mathrm{Oxygen}\mathrm{Magnesium} \\ \mathrm{Oxide} \end{gathered}$$

3. When we dissolve the white powder in the water, we will get magnesium hydroxide.

$$\begin{gathered} \mathrm{MgO}\left(\mathrm{s}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to \mathrm{Mg}{\left(\mathrm{OH}\right)}_2\left(\mathrm{s}\right) \\ \mathrm{Magnesium}\mathrm{Water}\mathrm{Magnesium} \\ \mathrm{oxide}\mathrm{hydroxide} \end{gathered}$$

4. Magnesium hydroxide is alkaline because ${\mathrm{OH}}^{-}$ ions are present.

5. Hence, we can say that solution of white powder is alkaline.