9.75 g of potassium, containing 20% impurities, entered into a reaction with water.

9.75 g of potassium, containing 20% impurities, entered into a reaction with water. Calculate the mass of alkali in the resulting solution.

Let’s write the reaction equation:

2K + 2H2O = 2KOH + H2 ↑

Let’s find the mass fraction of potassium in a potassium sample:

w (K) = 100 – w (impurities) = 100 – 20 = 80.

Find the mass of potassium in the potassium sample:

m (K) = m (K) sample * w (K) / 100 = 9.75 * 80/100 = 7.8 (g).

Let’s find the amount of potassium substance:

v (K) = m (K) / M (K) = 7.8 / 39 = 0.2 (mol).

According to the reaction equation, 2 mol of KOH is formed per 2 mol of K, therefore:

v (KOH) = v (K) = 0.2 (mol).

Thus, the mass of potassium hydroxide alkali in the resulting solution is:

m (KOH) = v (KOH) * M (KOH) = 0.2 * 56 = 11.2 (g).

Answer: 11.2 g.