The molecular mass of sodium chloride obtained by using a colligative property is

Options

A. 58.5 g/mol
B. 29.25 g/mol
C. 117 g/mol
D. 85 g/mol

Answer

To find the molecular mass of sodium chloride (NaCl) using colligative properties, we will follow these steps:

### Step 1: Calculate the Molecular Mass of NaCl
The molecular mass of sodium chloride can be calculated using the atomic masses of sodium (Na) and chlorine (Cl).

- Atomic mass of Na = 23 g/mol
- Atomic mass of Cl = 35.5 g/mol

**Calculation:**
\[ \text{Molecular mass of NaCl} = \text{Atomic mass of Na} + \text{Atomic mass of Cl} = 23 + 35.5 = 58.5 \text{ g/mol} \]

### Step 2: Determine the Van't Hoff Factor (i)
The Van't Hoff factor (i) is defined as the ratio of the number of particles in solution after dissociation to the number of formula units initially dissolved.

For NaCl, it dissociates into two ions:
- NaCl → Na\(^+\) + Cl\(^-\)

Thus, if we start with 1 mole of NaCl, it will produce 2 moles of particles (1 mole of Na\(^+\) and 1 mole of Cl\(^-\)).

**Calculation:**
\[ i = \frac{n_f}{n_i} = \frac{2}{1} = 2 \]

### Step 3: Calculate the Observed Molecular Mass
The observed molecular mass (M) can be calculated using the formula:
\[ M = \frac{\text{Calculated Molecular Mass}}{i} \]

Substituting the values we have:
\[ M = \frac{58.5 \text{ g/mol}}{2} = 29.25 \text{ g/mol} \]

### Conclusion
The molecular mass of sodium chloride obtained using a colligative property is **29.25 g/mol**.