Question

Why shouldn't alkalies like NaOH and KOH be left exposed to air?

Answer 1

Hygroscopic:

Hygroscopic is the ability to absorb water from the surrounding environment.

Examples of hygroscopic substances:

Zinc chloride, ⁣$\left({\mathrm{ZnCl}}_2\right)$ Calcium chloride, ⁣$\left({\mathrm{CaCl}}_2\right)$ Sodium chloride, ⁣$\left(\mathrm{NaCl}\right)$.

Alkalies like sodium hydroxide (NaOH) and (KOH) shouldn't be left exposed to air because these are hygroscopic in nature and absorb moisture from the atmosphere, due to which they ultimately dissolve.

Reaction involves:

$$\begin{gathered} 4\mathrm{NaOH}\left(\mathrm{l}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)\stackrel{}{\to }\underset{\mathrm{Sodium}\mathrm{Peroxide}}{2{\mathrm{Na}}_2{\mathrm{O}}_2\left(\mathrm{l}\right)}+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right) \\ 2\mathrm{KOH}\left(\mathrm{l}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)\stackrel{}{\to }\underset{\mathrm{Potassium}\mathrm{Peroxide}}{{\mathrm{K}}_2{\mathrm{O}}_2\left(\mathrm{l}\right)}+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right) \end{gathered}$$