Answer
$[Na^+] = [OH^-] \approx 0.2786M$
Work Step by Step
1. Find the total number of $NaOH$ moles in the final solution:
* Nº of moles = Concentration * volume (Dont forget to convert volume to Liter)
$0.042 \times 0.170 + 0.0376 \times 0.4$
$0.00714 + 0.01504$
$0.02218$ moles.
2. Find the total volume in the final solution:
42 + 37.6 = 79.6 ml = 0.0796 L
3. Now, we can calculate the concentration of NaOH in the final solution:
$C = \frac{n(mol)}{V(L)}$
$C = \frac{0.02218}{0.0796}$
$C \approx 0.2786M (NaOH)$
4. Because NaOH is a strong base:
$[NaOH] = [Na^+] = [OH^-] \approx 0.2786M$
