The percent composition by mass of a compound is the percent by mass of each element in the compound. To determine the percent composition by mass of HCl (hydrochloric acid), we need to know the molar masses of hydrogen (H) and chlorine (Cl).
The molar mass of hydrogen (H) is approximately 1.01 g/mol, and the molar mass of chlorine (Cl) is approximately 35.45 g/mol. The molar mass of HCl is the sum of these two masses:
Molar mass of HCl = 1.01 g/mol (H) + 35.45 g/mol (Cl) = 36.46 g/mol
Now, we can calculate the percent composition by mass of each element in HCl:
Percent composition of H = (Mass of H / Molar mass of HCl) × 100
Percent composition of H = (1.01 g/mol / 36.46 g/mol) × 100 ≈ 2.77%
Percent composition of Cl = (Mass of Cl / Molar mass of HCl) × 100
Percent composition of Cl = (35.45 g/mol / 36.46 g/mol) × 100 ≈ 97.23%
Therefore, the percent composition by mass of HCl is approximately 2.77% hydrogen and 97.23% chlorine.