5.85 g of NaCl are dissolved in `500 cm^3` of water. Calculate the formality of the solution.

Answer

To calculate the formality of the NaCl solution, we will follow these steps:

### Step-by-Step Solution:

1. **Identify the mass of NaCl and the volume of the solution:**
- Given mass of NaCl = 5.85 g
- Volume of solution = 500 cm³ (which is equivalent to 500 mL)

2. **Calculate the formula mass of NaCl:**
- The formula mass (molar mass) of NaCl can be calculated as follows:
- Sodium (Na) has an atomic mass of approximately 23 g/mol.
- Chlorine (Cl) has an atomic mass of approximately 35.5 g/mol.
- Therefore, the formula mass of NaCl = 23 g/mol + 35.5 g/mol = 58.5 g/mol.

3. **Calculate the number of formula masses:**
- The number of formula masses (in moles) is calculated using the formula:
\[ \text{Number of formula masses} = \frac{\text{mass of solute (g)}}{\text{formula mass (g/mol)}} \]
- Substituting the values:
\[ \text{Number of formula masses} = \frac{5.85 \text{ g}}{58.5 \text{ g/mol}} \approx 0.1 \text{ moles} \]

4. **Calculate the formality of the solution:**
- Formality is defined as:
\[ \text{Formality} = \frac{\text{Number of formula masses}}{\text{Volume of solution (mL)}} \times 1000 \]
- Substituting the values:
\[ \text{Formality} = \frac{0.1 \text{ moles}}{500 \text{ mL}} \times 1000 \]
- Simplifying this gives:
\[ \text{Formality} = \frac{0.1}{500} \times 1000 = 0.2 \text{ mol/L} \]

### Final Answer:
The formality of the NaCl solution is **0.2**.