Calculate the mass of potassium reacted with 125 g of water.

Let’s write the reaction equation:
2K + 2H2O = 2KOH + H2 ↑.
It can be seen from the reaction equation that the amounts of the substance are equal:
ν (H2O) = ν (K).
Knowing that ν (in-va) = m (in-va) / M (in-va) = V (in-va) / Vm (in-va), we get:
m (H2O) / M (H2O) = m (K) / M (K).
Let’s define the molar masses:
M (H2O) = 1 * 2 + 16 = 18 g / mol.
M (K) = 39.1 g / mol.
Let’s determine the mass of potassium that can react with water:
m (K) = m (H2O) * M (K) / M (H2O).
Substitute the numerical values:
m (K) = m (H2O) * M (K) / M (H2O) = 125 * 39.1 / 18 = 271.5 g.
Answer: the mass of potassium reacted is 271.5 g.