What is the molarity of a solution containing 4g of NaOH in 500 mL of solution?

Question

Accepted Answer

To determine the molarity of the solution, we need to calculate the number of moles of NaOH and then divide by the volume of the solution in liters.

1. **Calculate the number of moles of NaOH:**
   - The molar mass of NaOH (sodium hydroxide) is approximately 40 g/mol.
   - Given mass of NaOH = 4 g.
   - Number of moles = mass / molar mass = 4 g / 40 g/mol = 0.1 mol.

2. **Convert the volume of the solution from milliliters to liters:**
   - Given volume = 500 mL.
   - To convert milliliters to liters, divide by 1000.
   - Volume in liters = 500 mL / 1000 = 0.5 L.

3. **Calculate the molarity of the solution:**
   - Molarity (M) = moles of solute / liters of solution.
   - Molarity = 0.1 mol / 0.5 L = 0.2 M.

Therefore, the molarity of the solution is 0.2 M, which corresponds to Option 2.

**Explanation for why other options are incorrect:**

- **Option 1 (0.1 M):** This option is incorrect because it assumes either a different number of moles or a different volume. Given the calculations, 0.1 mol of NaOH in 0.5 L results in a molarity of 0.2 M, not 0.1 M.

- **Option 3 (0.3 M):** This option is incorrect because it overestimates the concentration. For the given amount of NaOH and volume, the molarity is 0.2 M, not 0.3 M.

- **Option 4 (0.4 M):** This option is incorrect because it significantly overestimates the concentration. The calculations clearly show that the molarity is 0.2 M, not 0.4 M.

In conclusion, based on the calculations and logical reasoning, Option 2 is the correct answer, as it accurately reflects the molarity of the solution given the provided data.