Find the mass of hydrochloric acid in the solution.
The mass fraction of a substance is calculated by the formula:
W = m (substance): m (solution) × 100%,
m (substance) = (m (solution) × W): 100%,
m (substance) = (20 g × 20%): 100% = 4 g.
Let’s find the amount of hydrochloric acid substance by the formula:
n = m: M.
M (HCl) = 36 g / mol.
n = 4 g: 36 g / mol = 0.11 mol.
Let’s compose the reaction equation, find the quantitative ratios of substances.
2Na + 2HCl = 2NaCl + H2 ↑.
According to the reaction equation, 2 mol of hydrochloric acid accounts for 1 mol of hydrogen. Substances are in quantitative ratios of 2: 1.
The amount of hydrogen substance will be 2 times less than the amount of hydrochloric acid substance.
n (H2) = 2n (HCl) = 0.11: 2 = 0.055 mol.
Let’s find the volume of hydrogen.
V = Vn n, where Vn is the molar volume of gas, equal to 22.4 l / mol, and n is the amount of substance.
V = 0.055 mol × 22.4 L / mol = 1.23 L.
Answer: 1.23 liters.