What mass of calcium reacts with water if 7.4 grams of calcium hydroxide is formed as a result of the reaction?

1.Calculate the amount of calcium hydroxide substance by the formula:
n = m: M, where M is molar mass.
M (Ca (OH) 2) = 40 + 2 × (16 + 1) = 40 + 34 = 74 g / mol.
n = 7.4: 74 g / mol = 0.1 mol.
2. Let’s compose the reaction equation:
Ca + 2H2O = Ca (OH) 2 + H2.
According to the reaction equation, there is 1 mole of calcium per 1 mole of calcium hydroxide, that is, the substances are in quantitative ratios of 1: 1, which means their amount of substance will be the same.
n (Ca) = n (Ca (OH) 2) = 0.1 mol.
3.Calculate the mass of calcium by the formula: m = n M,
M (Ca) = 40 g / mol.
m = 40 g / mol × 0.1 mol = 4 g.
Answer: m = 4 g.