Calculate the mass of Ca reacted with H2O if H2 with a volume of 6.72 liters was formed.

Given:

V (H2) = 6.72 L;

To find:

m (Ca) -?

Decision:

1) We compose the reaction equation according to the condition of the problem:

Ca + 2H2O = Ca (OH) 2 + H2;

2) Find the amount of hydrogen in 6.72 grams of gas:

n (H2) = V: Vm = 6.72 L: 22.4 L / mol = 0.3 mol;

3) We compose logical equality:

if 1 mol of Ca gives 1 mol of H2,

then x mol of Ca will give 0.3 mol of H2,

then x = 0.3 mol.

4) Find the mass of calcium required for the reaction to proceed:

m (Ca) = n * M = 0.3 mol * 40 g / mol = 12 g;

Answer: m (Ca) = 12 grams.