Question

A student has 470.0 mL of a 0.1429 M aqueous solution of Na2SO4 to use in an experiment. He accidentally leaves the container uncovered and comes back the next week to find only a solid residue. The mass of the residue is 21.64 g. Determine the chemical formula of this residue.

If the substance is a hydrate, use a period instead of a dot in its formula.

Answer 1

Answer to the Question 86225

A student has 470.0 mL of a 0.1429 M aqueous solution of Na₂SO₄ to use in an experiment. He accidentally leaves the container uncovered and comes back the next week to find only a solid residue. The mass of the residue is 21.64 g. Determine the chemical formula of this residue.

Decision:

unknown substance: Na₂SO₄*x H₂O

$$n(Na_2SO_4 * xH_2O) = C * V$$ $$V = 470.0 \text{ mL} = 0.47 \text{ L}$$ $$n(Na_2SO_4 * xH_2O) = 0.1429 \frac{\text{mol}}{\text{L}} * 0.47 \text{ L} = 0.067163 \text{ mol}$$ $$M(Na_2SO_4 * xH_2O) = \frac{m}{n(Na_2SO_4 * xH_2O)}$$ $$M(Na_2SO_4 * xH_2O) = \frac{21.64 \text{ g}}{0.067163 \text{ mol}} = 322 \text{ g/mol}$$ $$M(Na_2SO_4 * xH_2O) = (142 + 18x) \text{ g/mol}$$ $$(142 + 18x) = 322$$ $$x = 10$$ $$Na_2SO_4 * 10H_2O$$

Answer: Na₂SO₄*10H₂O

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