Metallic barium weighing 82.2 g was dissolved in 500 ml water. Determine the mass fraction of barium hydroxide in the solution.

V = m: ρ

1. Let’s find the amount of barium substance by the formula:

n = m: M, M (Ba) = 137 g / mol.

n (Ba) = 82.2: 137 g / mol = 0.6 mol.

2. Let’s compose the reaction equation for the dissolution of barium in water.

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

The amount of barium substance and barium hydroxide are in the ratio of 1: 1.

n (Ba) = n (Ba (OH) 2) = 0.6 mol.

Find the mass of barium hydroxide by the formula: m = n M,

M (Ba (OH) 2) = 137 + 2 (16 + 1) = 171 g / mol.

m = 171 g / mol x 0.6 mol = 102.6 g.

Let’s find the mass of the solution.

The mass of the solution is determined by the formula:

m (solution) = m (substance) + m (water).

V = m: ρ

m (water) = Vρ,

p (water) = 1 g / ml.

m (water) = 500 ml x 1 g / ml = 500 g.

m (solution) = 500 g + 102.6 g = 602.6 g.

Find the mass fraction of barium hydroxide in 602.6 g of solution.

602.6 g – 100%,

102.6 g – x%,

x = (102.6 g x 100%): 602.6 = 17.03%.

Or we will calculate by the formula:

W = m (substance): m (solution) × 100%,

w (Ba (OH) 2) = (102.6 g: 602.6) X 100% = 17.03%.

Answer: w (Ba (OH) 2) = 17.03%.