Question

What is the molarity of a solution that contains 25 grams of sodium chloride in 500 milliliters of water?

Answer 1

To calculate the molarity (M) of a solution, you can use the formula:

\[
\text{Molarity (M)} = \frac{\text{moles of solute}}{\text{liters of solution}}
\]

1. **Calculate the moles of sodium chloride (NaCl)**:
- First, find the molar mass of NaCl. The molar mass of sodium (Na) is approximately 22.99 g/mol, and the molar mass of chlorine (Cl) is approximately 35.45 g/mol.
- So, the molar mass of NaCl is:
\[
\text{Molar mass of NaCl} = 22.99 \, \text{g/mol} + 35.45 \, \text{g/mol} = 58.44 \, \text{g/mol}
\]

- Now, calculate the moles of NaCl present in 25 grams:
\[
\text{Moles of NaCl} = \frac{\text{mass}}{\text{molar mass}} = \frac{25 \, \text{g}}{58.44 \, \text{g/mol}} \approx 0.428 \, \text{moles}
\]

2. **Convert the volume of the solution from milliliters to liters**:
- Since 1 liter = 1000 milliliters, 500 milliliters is:
\[
500 \, \text{mL} = 0.500 \, \text{L}
\]

3. **Calculate the molarity**:
- Now, plug the values into the molarity formula:
\[
\text{Molarity} = \frac{0.428 \, \text{moles}}{0.500 \, \text{L}} = 0.856 \, \text{M}
\]

Thus, the molarity of the solution is approximately **0.856 M**.