Calcium metal reacts with water to form calcium hydroxide and hydrogen gas. How much hydrogen is formed when 0.50 g of calcium are added to water?

0.025g

Explanation:

Firstly, we need to write a balanced chemical equation.

Ca + 2H2O - -> Ca (OH) 2 + H2

From the chemical equation, we can see that one mole of calcium metal yielded one mole of hydrogen gas.

Now, we need to know the actual number of moles of hydrogen gas given off.

The number of moles is the mass divided by the atomic mass. The atomic mass of calcium is 40g/mol. The number of moles is thus 0.5/40 = 0.0125 mole

Since the mole ratio is 1:1, the number of moles of hydrogen gas produced too is 0.0125 moles.

We now Proceed to get the mass of the hydrogen gas produced. This is the number of moles of hydrogen multiplied by the molar mass of the diatomic hydrogen gas. The molar mass of the diatomic hydrogen gas is 2g/mol.

The amount given off is thus 2 * 0.0125 = 0.025g