What is the volume of acetylene obtained from 40 g of calcium carbide containing 20% impurities?

The reaction for the synthesis of acetylene from calcium carbide is described by the following chemical reaction equation:
CaC2 + 2H2O = C2H2 + Ca (OH) 2;
From 1 mole of calcium carbide, 1 mole of acetylene is synthesized.
Let’s calculate the available chemical amount of silicon carbide substance.
M CaC2 = 40 + 12 x 2 = 64 grams / mol;
N CaC2 = 40 x 0.8 / 64 = 0.5 mol;
The same amount of acetylene will be synthesized.
Let’s calculate its volume by multiplying the amount of the substance and the volume of 1 mole of the gaseous substance.
V C2H2 = 0.5 x 22.4 = 11.2 liters;