What amount of calcium hydroxide substance will be obtained by the action of excess water

What amount of calcium hydroxide substance will be obtained by the action of excess water on 40 grams of technical calcium carbide containing 5% impurities.

Given:
m tech. (CaC2) = 40 g
ω approx. = 5%

To find:
n (Ca (OH) 2) -?

Decision:
1) Write the reaction equation:
CaC2 + 2H2O => Ca (OH) 2 + C2H2 ↑;
2) Calculate the molar mass of CaC2:
M (CaC2) = Mr (CaC2) = Ar (CaC2) + Ar (CaC2) * 2 = 40 + 12 * 2 = 64 g / mol;
3) Calculate the mass fraction of CaC2:
ω (CaC2) = 100% – ω approx. = 100% – 5% = 95%;
4) Calculate the mass of pure CaC2:
m clean (CaC2) = ω (CaC2) * m tech. (CaC2) / 100% = 95% * 40/100% = 38 g;
5) Calculate the amount of CaC2:
n (CaC2) = m (CaC2) / M (CaC2) = 38/64 = 0.6 mol;
6) Determine the amount of Ca (OH) 2 (taking into account the coefficients in the reaction equation):
n (Ca (OH) 2) = n (CaC2) = 0.6 mol.

Answer: The amount of Ca (OH) 2 substance is 0.6 mol.