45 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) is given as 45 g.
- The mass of water (solvent) is given as 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.

\[ \text{Mass of solution} = \text{Mass of solute} + \text{Mass of solvent} \]

\[ \text{Mass of solution} = 45 \, \text{g} + 100 \, \text{g} = 145 \, \text{g} \]

### Step 3: Calculate the Concentration
- The concentration of the solution is calculated using the formula:

\[ \text{Concentration} = \left( \frac{\text{Mass of solute}}{\text{Mass of solution}} \right) \times 100 \]

- Substituting the values we have:

\[ \text{Concentration} = \left( \frac{45 \, \text{g}}{145 \, \text{g}} \right) \times 100 \]

### Step 4: Perform the Calculation
- Now, calculate the concentration:

\[ \text{Concentration} = \left( \frac{45}{145} \right) \times 100 \approx 31.03\% \]

### Final Answer
- The concentration of the sodium chloride solution at 293 K is approximately **31%**.

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