40 g of sodium chloride is dissolved in 100 g of water at 293 K. Find its concentration at this temperature.

Explanation

To find the concentration of sodium chloride (NaCl) dissolved in water, we can follow these steps:

### Step 1: Identify the mass of solute and solvent
- The mass of sodium chloride (solute) = 40 g
- The mass of water (solvent) = 100 g

### Step 2: Calculate the mass of the solution
The mass of the solution is the sum of the mass of the solute and the mass of the solvent.
\[ \text{Mass of solution} = \text{Mass of solute} + \text{Mass of solvent} = 40 \, \text{g} + 100 \, \text{g} = 140 \, \text{g} \]

### Step 3: Calculate the concentration
Concentration can be calculated using the formula:
\[ \text{Concentration} = \left( \frac{\text{Mass of solute}}{\text{Mass of solution}} \right) \times 100 \]
Substituting the values we have:
\[ \text{Concentration} = \left( \frac{40 \, \text{g}}{140 \, \text{g}} \right) \times 100 \]
\[ \text{Concentration} = \left( 0.2857 \right) \times 100 \approx 28.57\% \]

### Final Answer
The concentration of sodium chloride in the solution is approximately **28.57%**.

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