Question

will the concentration of solid naoh increase or decrease if the solid is exposed to air for prolonged periods? briefly explain.

Explanation:

Solid NaOH is hygroscopic (absorbs moisture from air) and also reacts with carbon dioxide in air: \(2\text{NaOH}(s) + \text{CO}_2(g)
ightarrow\text{Na}_2\text{CO}_3(s) + \text{H}_2\text{O}(l)\). The original solid NaOH is consumed (converted to \(\text{Na}_2\text{CO}_3\)) and also absorbs water. But for the "concentration" of solid NaOH (though concentration is more for solutions, here considering the purity or amount of NaOH in the solid sample), the amount of pure NaOH decreases as it reacts and absorbs moisture, so the effective "concentration" (purity) of solid NaOH decreases.

Answer:

The concentration (purity) of solid NaOH will decrease. Because solid NaOH is hygroscopic (absorbs water from air) and reacts with atmospheric \(\boldsymbol{\text{CO}_2}\) (\(2\text{NaOH}(s) + \text{CO}_2(g)
ightarrow\text{Na}_2\text{CO}_3(s) + \text{H}_2\text{O}(l)\)), reducing the amount of pure NaOH in the solid sample.