Calculate the mass fraction of barium hydroxide in the solution if 0.05 mol of barium metal was dissolved in 1000 ml water.

The reaction for obtaining barium hydroxide:

Bam + 2H2O = Bam (OH) 2 + H2.

It can be seen from the reaction equation that the amount of moles of barium and reaction products are equal:

n (Ba) = n (Ba (OH) 2) = n (H2) = 0.05 mol.

Let’s calculate the mass of the reaction products:

m (Ba (OH) 2) = n • Mr = 0.05 • 171 = 8.55 g.

m (H2) = 0.05 * 2 = 0.1 g.

Let us find the mass of the solution, taking into account the reaction products:

m (solution) = 1000 + 8.55 – 0.1 = 1008.4 g.

Accordingly, the mass fraction of hydroxide will be equal to:

W (Ba (OH) 2) = m (Ba (OH) 2) / m (solution) • 100% = 8.55 / 1008.4 • 100% = 0.8%.