Question

what is the mass percent of water in cobalt(iii) chloride hexahydrate? provide an answer to two decimal places.

Explanation:

Step1: Find molar mass of components

Cobalt(III) chloride hexahydrate is $\ce{CoCl3·6H2O}$.
Molar mass of $\ce{Co}$: $58.93\ \text{g/mol}$, $\ce{Cl}$: $35.45\ \text{g/mol}$, $\ce{H2O}$: $18.02\ \text{g/mol}$.
Molar mass of $\ce{CoCl3}$: $58.93 + 3\times35.45 = 58.93 + 106.35 = 165.28\ \text{g/mol}$.
Molar mass of $6\ce{H2O}$: $6\times18.02 = 108.12\ \text{g/mol}$.
Molar mass of $\ce{CoCl3·6H2O}$: $165.28 + 108.12 = 273.4\ \text{g/mol}$.

Step2: Calculate mass percent of water

Mass percent formula: $\frac{\text{Mass of water}}{\text{Mass of hydrate}} \times 100\%$.
Substitute values: $\frac{108.12}{273.4} \times 100\% \approx 39.55\%$.

Answer:

$39.55$