Which of the following has the highest percent by mass of chlorine? a. HClO b. HClO2 c. HClO3 d. HClO4 e. All the same
The correct answer and explanation is:
Correct Answer: a. HClO
Explanation:
To determine which compound has the highest percent by mass of chlorine, we must calculate the mass percent of chlorine in each of the given compounds using this formula: Percent by mass of Cl=(Molar mass of ClMolar mass of compound)×100\text{Percent by mass of Cl} = \left( \frac{\text{Molar mass of Cl}}{\text{Molar mass of compound}} \right) \times 100
The atomic masses (approximate):
- H = 1 g/mol
- Cl = 35.5 g/mol
- O = 16 g/mol
Option a: HClO
- Molar mass = 1 (H) + 35.5 (Cl) + 16 (O) = 52.5 g/mol
- Percent Cl = (35.5 / 52.5) × 100 ≈ 67.6%
Option b: HClO₂
- Molar mass = 1 + 35.5 + (2 × 16) = 67.5 g/mol
- Percent Cl = (35.5 / 67.5) × 100 ≈ 52.6%
Option c: HClO₃
- Molar mass = 1 + 35.5 + (3 × 16) = 83.5 g/mol
- Percent Cl = (35.5 / 83.5) × 100 ≈ 42.5%
Option d: HClO₄
- Molar mass = 1 + 35.5 + (4 × 16) = 99.5 g/mol
- Percent Cl = (35.5 / 99.5) × 100 ≈ 35.7%
Option e: All the same
- Incorrect, since we just calculated different percentages.
Conclusion:
As the number of oxygen atoms increases in the series HClO → HClO₄, the total molar mass of the compound increases while the mass of chlorine remains the same (35.5 g/mol). Therefore, the percentage of chlorine by mass decreases with more oxygen atoms.
Thus, HClO has the highest percent by mass of chlorine.