1. When potassium interacts with an excess of water, the following reaction occurs:
2K + 2H2O = 2KOH + H2 ↑;
2.calculate the chemical amount of potassium:
n (K) = m (K): M (K) = 3.9: 39 = 0.1 mol;
3.determine the amount of potassium hydroxide obtained:
n (KOH) = n (K) = 0.1 mol;
4.calculate the mass of the hydroxide:
m (KOH) = n (KOH) * M (KOH);
M (KOH) = 39 + 16 + 1 = 56 g / mol;
m (KOH) = 0.1 * 56 = 5.6 g.
Answer: 5.6 g.
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