The molar mass of HCl (hydrogen chloride; same formula used when referring to hydrochloric acid in solution) is the mass of 1 mole of HCl molecules, expressed in grams per mole (g/mol). It is found by adding the atomic masses of all atoms in the chemical formula.
Goal. Calculate the molar mass of HCl using periodic-table atomic masses.
Step 1: Identify atoms and their counts in HCl
The formula HCl contains 1 hydrogen atom and 1 chlorine atom per molecule.
Step 2: Use atomic masses from the periodic table
| Element | Symbol | Atoms in HCl | Atomic mass (g/mol) | Contribution (g/mol) |
|---|---|---|---|---|
| Hydrogen | H | 1 | 1.008 | 1 × 1.008 = 1.008 |
| Chlorine | Cl | 1 | 35.45 | 1 × 35.45 = 35.45 |
Step 3: Add contributions to obtain the molar mass
The molar mass is the sum of the element contributions:
\[ M(\mathrm{HCl}) = (1 \times 1.008) + (1 \times 35.45) = 36.458\ \text{g/mol} \]
Using typical rounding for atomic masses, the molar mass is reported as: \[ M(\mathrm{HCl}) \approx 36.46\ \text{g/mol} \]
Answer. The molar mass of HCl is 36.46 g/mol.
Visualization: mass contributions of H and Cl in HCl
Common follow-up: converting grams of HCl to moles
Once the molar mass is known, mass-to-moles conversion uses: \[ n = \frac{m}{M} \] For example, a mass \(m\) of HCl corresponds to \(n = \dfrac{m}{36.46}\) moles (with \(m\) in grams).