Lithium hydroxide was obtained by dissolving lithium peroxide in hot water. Determine the mass fraction

| August 7, 2021 | education

Lithium hydroxide was obtained by dissolving lithium peroxide in hot water. Determine the mass fraction of alkali in a solution obtained by dissolving 4.6 g of lithium peroxide in 125 ml of water

Find the amount of lithium peroxide Li2O2.

n = m: M.

M (Li2O2) = 46 g / mol.

n = 4.6 g: 46 g / mol = 0.1 mol.

Let’s compose the reaction equation. Let’s find the quantitative ratios of substances.

2 Li2O2 + 2Н2О = 4 LiOH + O2

According to the reaction equation, there are 4 mol of LiOH for 2 mol of Li2O2.

Substances are in quantitative ratios 2: 4 = 1: 2.

n (LiOH) = 2 n (Li2O2) = 0.1 mol × 2 = 0.2 mol.

Let us find the mass of LiOH.

M (LiOH) = 24 g / mol.

m = n × M.

m = 24 g / mol × 0.2 mol = 4.8 g.

m (solution) = m (H2O) + m (LiOH) – m (O2).

m (H2O) = Vp.

m (H2O) = 125 ml × 1 g / ml = 125 g.

n (O2) = ½ n (Li2O2) = 0.1 mol: 2 = 0.05 mol.

Let’s find the mass of O2.

M (O2) = 32 g / mol.

m = 32 g / mol × 0.05 mol = 1.6 g.

m (solution) = 125 g + 4.8 g – 1.6 g = 128.2 g.

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

w (LiOH) = (4.8 g: 128.2 g) x 100% = 3.74%.

Answer: 3.74%.



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