The kcl molar mass is the mass of one mole of potassium chloride formula units. It is obtained by summing the atomic masses of K and Cl from the periodic table.
Result: \(M(\mathrm{KCl}) \approx 74.55\ \text{g/mol}\).
Step 1: Identify the formula and count atoms
Potassium chloride has formula \(\mathrm{KCl}\), which contains:
- \(1\) potassium atom (\(\mathrm{K}\))
- \(1\) chlorine atom (\(\mathrm{Cl}\))
Step 2: Read atomic masses from the periodic table
Using common periodic table values (rounded to two decimal places):
- \(M(\mathrm{K}) \approx 39.10\ \text{g/mol}\)
- \(M(\mathrm{Cl}) \approx 35.45\ \text{g/mol}\)
Step 3: Add contributions to get the KCl molar mass
\[ M(\mathrm{KCl}) = 1\cdot M(\mathrm{K}) + 1\cdot M(\mathrm{Cl}) \]
\[ M(\mathrm{KCl}) = 39.10 + 35.45 = 74.55\ \text{g/mol} \]
| Element | Count in \(\mathrm{KCl}\) | Atomic mass (g/mol) | Contribution (g/mol) |
|---|---|---|---|
| \(\mathrm{K}\) | \(1\) | \(39.10\) | \(1 \cdot 39.10 = 39.10\) |
| \(\mathrm{Cl}\) | \(1\) | \(35.45\) | \(1 \cdot 35.45 = 35.45\) |
| Total | \(74.55\ \text{g/mol}\) | ||
Extra check: mass percent composition (optional but useful)
Percent by mass for each element in \(\mathrm{KCl}\) follows directly from the molar mass:
\[ \%\mathrm{K} = \frac{39.10}{74.55}\cdot 100 \approx 52.46\%, \qquad \%\mathrm{Cl} = \frac{35.45}{74.55}\cdot 100 \approx 47.54\% \]
Using the molar mass for conversions
Once \(M(\mathrm{KCl})\) is known, mass–mole conversions use:
\[ m = n \cdot M \quad \text{and} \quad n = \frac{m}{M} \]
Example: The mass of \(0.250\ \text{mol}\) KCl is
\[ m = 0.250 \cdot 74.55 = 18.64\ \text{g} \]