What is the molarity of Na+ ions in the solution formed by mixing 42.0 mL of 0.180 M NaOH and 37.6 mL of 0.410 M NaOH, assuming the volumes are additive?

• A. 0.280 M
• B. 0.250 M
• C. 0.295 M
• D. 0.320 M

Answer: (A)

Verified step by step guidance

1. First, calculate the number of moles of NaOH in each solution separately. Use the formula: \( \text{moles} = \text{molarity} \times \text{volume in liters} \). For the first solution: \( \text{moles of NaOH} = 0.180 \, \text{M} \times 0.0420 \, \text{L} \). For the second solution: \( \text{moles of NaOH} = 0.410 \, \text{M} \times 0.0376 \, \text{L} \).
2. Add the moles of NaOH from both solutions to find the total moles of NaOH in the mixed solution. Since NaOH dissociates completely in water, the moles of NaOH will be equal to the moles of \( \text{Na}^+ \) ions.
3. Calculate the total volume of the mixed solution by adding the volumes of the two solutions: \( \text{total volume} = 42.0 \, \text{mL} + 37.6 \, \text{mL} \). Convert this total volume into liters by dividing by 1000.
4. Determine the molarity of \( \text{Na}^+ \) ions in the mixed solution using the formula: \( \text{molarity} = \frac{\text{total moles of Na}^+}{\text{total volume in liters}} \).
5. Review the calculations to ensure accuracy and compare the calculated molarity with the given options to identify the correct answer.