Question

Sodium sulfate forms several hydrates. A sample of one of these hydrates is heated until all the water is removed. What is the formula of the original hydrate if it loses 43% of its mass when heated?

Answer 1

Na₂SO₄•(H₂O)₆.

Step-by-step explanation:

The mass that is lost when the sample is heated is water.

Let's assume we have 100 g of the hydrate:

43 grams would be water (H₂O), while the rest (100-43=57) would be sodium sulfate anhydrous (Na₂SO₄).

We convert both those masses to moles, using their respective molar masses:

• H₂O ⇒ 43 g ÷ 18 g/mol = 2.39 mol

• Na₂SO₄ ⇒ 57 g ÷ 142.04 g/mol = 0.40 mol

We can write those results as (Na₂SO₄)₀.₄₀•(H₂O)₂.₃₉. Now we just need to multiply those numbers so that they become integers.

If we multiply both coefficients by 5 we're left with (Na₂SO₄)₂•(H₂O)₁₂.

Simplify and thus the final answer is Na₂SO₄•(H₂O)₆.