A solution is prepared by adding 10 g of NaCl to 18 g of water. Calculate mole fraction of NaCl. (Molar mass of NaCl = 58.5 g).

Answer

To calculate the mole fraction of NaCl in the solution, we will follow these steps:

### Step 1: Identify the given data
- Mass of NaCl = 10 g
- Mass of water = 18 g
- Molar mass of NaCl = 58.5 g/mol

### Step 2: Calculate the moles of NaCl
Using the formula for moles:
\[ \text{Moles of NaCl} = \frac{\text{mass of NaCl}}{\text{molar mass of NaCl}} \]
Substituting the values:
\[ \text{Moles of NaCl} = \frac{10 \, \text{g}}{58.5 \, \text{g/mol}} \approx 0.171 \, \text{moles} \]

### Step 3: Calculate the moles of water
The molar mass of water (H₂O) is 18 g/mol. Using the same formula:
\[ \text{Moles of water} = \frac{\text{mass of water}}{\text{molar mass of water}} \]
Substituting the values:
\[ \text{Moles of water} = \frac{18 \, \text{g}}{18 \, \text{g/mol}} = 1 \, \text{mole} \]

### Step 4: Calculate the total moles in the solution
\[ \text{Total moles} = \text{Moles of NaCl} + \text{Moles of water} \]
Substituting the values:
\[ \text{Total moles} = 0.171 \, \text{moles} + 1 \, \text{mole} = 1.171 \, \text{moles} \]

### Step 5: Calculate the mole fraction of NaCl
The mole fraction (X) of NaCl is given by:
\[ X_{\text{NaCl}} = \frac{\text{Moles of NaCl}}{\text{Total moles}} \]
Substituting the values:
\[ X_{\text{NaCl}} = \frac{0.171 \, \text{moles}}{1.171 \, \text{moles}} \approx 0.146 \]

### Final Answer
The mole fraction of NaCl in the solution is approximately **0.146**.

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