What is the percent by mass of water in Na2SO4 · 10H2O?

• A. 11.26%
• B. 5.59%
• C. 44.08%
• D. 55.92%

Answer: (D)

Verified step by step guidance

1. Identify the chemical formula of the compound: sodium sulfate decahydrate, which is \(\mathrm{Na_2SO_4 \cdot 10H_2O}\).
2. Calculate the molar mass of the anhydrous part, \(\mathrm{Na_2SO_4}\), by summing the atomic masses of 2 sodium (Na), 1 sulfur (S), and 4 oxygen (O) atoms.
3. Calculate the molar mass of the water part, \$10 \mathrm{H_2O}$, by multiplying 10 by the molar mass of one water molecule (2 hydrogens and 1 oxygen).
4. Add the molar masses of \(\mathrm{Na_2SO_4}\) and \$10 \mathrm{H_2O}\( to get the total molar mass of \)\mathrm{Na_2SO_4 \cdot 10H_2O}$.
5. Calculate the percent by mass of water using the formula: \(\% \text{water} = \left( \frac{\text{molar mass of } 10 \mathrm{H_2O}}{\text{total molar mass of } \mathrm{Na_2SO_4 \cdot 10H_2O}} \right) \times 100\).