Question

A sample of MgCO3•3H20 (magnesium carbonate trihydrate) is heated until 40.37 grams of water are released. How many grams did the original hydrate weigh?

Answer 1

80061 Chemistry, Other

A sample of $\mathrm{MgCO_3\cdot 3H_2O}$ (magnesium carbonate trihydrate) is heated until $40.37\mathrm{g}$ of water are released. How many grams did the original hydrate weigh?

Answer:

When a hydrate salt is heated water is released and anhydrous salt is formed. The balanced chemical equation for the reaction is

$$\mathrm{MgCO_3 \cdot 3H_2O} \rightarrow \mathrm{MgCO_3 + 3H_2O}$$

M $(\mathrm{MgCO_3 \cdot 3H_2O}) = 138~\mathrm{g/mol}$

M $(\mathrm{H_2O}) = 18~\mathrm{g/mol}$

From the balanced chemical equation: $3\mathrm{H}_2\mathrm{O}$ is released from $1\mathrm{MgCO_3 \cdot 3H_2O}$.

$3 \times 18\mathrm{g}$ of $\mathrm{H_2O}$ is released from $138\mathrm{g}$ of $\mathrm{MgCO_3 \cdot 3H_2O}$.

$40.37\mathrm{g}$ of $\mathrm{H_2O}$ is released from $138\times 40.37 / (3\times 18) = 103.168\mathrm{g}$ of $\mathrm{MgCO_3\cdot 3H_2O}$

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