To a solution containing potassium hydroxide weighing 11.2 g, an aluminum sulfate solution was added until the

To a solution containing potassium hydroxide weighing 11.2 g, an aluminum sulfate solution was added until the alkali fully interacted. Calculate the mass of the substance that precipitated.

Let’s find the amount of KOH substance.

n = m: M.

M (KOH) = 56 g / mol.

n = 11.2 g: 56 g / mol = 0.2 mol.

Let’s find the quantitative ratios of substances.

6KOH + Al2 (SO4) 3 = 2Al (OH) 3 ↓ + 3K2SO4.

For 6 mol of KOH there is 2 mol of Al (OH) 3.

The substances are in quantitative ratios of 3: 1.

The amount of Al (OH) 3 substance is 3 times less than the amount of KOH substance.

n (Al (OH) 3) = 1 / 3n (KOH) = 0.2: 3 = 0.067 mol.

Let us find the mass of Al (OH) 3.

M (Al (OH) 3) = 78 g / mol.

m = n × M.

m = 78 g / mol × 0.067 mol = 5.23 g.

Answer: 5.23 g.