A solution of sodium hydroxide (NaOH) has a pH of 10 - VCE - SSCE Chemistry - Question 12 - 2005 - Paper 1

The volume of the NaOH solution is 10 mL, which is 0.01 L. The number of moles of NaOH is:

$ext{moles NaOH} = [NaOH] \times \text{volume} = 10^{-4} \text{ M} \times 0.01 ext{ L} = 10^{-6} ext{ moles}$

The total volume after mixing 10 mL of NaOH with 990 mL of water is:

$\text{Total Volume} = 10 ext{ mL} + 990 ext{ mL} = 1000 ext{ mL} = 1 ext{ L}$

After dilution, the concentration of NaOH in the total volume is:

$[NaOH] = \frac{\text{moles of NaOH}}{\text{total volume}} = \frac{10^{-6} \text{ moles}}{1 \text{ L}} = 10^{-6} ext{ M}$

To find the pOH of the diluted solution:

$pOH = -\log[OH⁻] = -\log(10^{-6}) = 6$

Now, to find the pH:

$pH = 14 - pOH = 14 - 6 = 8$

The pH of the diluted solution is closest to 8. Therefore, the correct answer is:

A. 8