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

The volume of the solution is 10 mL, which is equivalent to 0.01 L. Thus, the moles of NaOH can be calculated as follows:

[ \text{Moles of NaOH} = \text{concentration} \times \text{volume} = 10^{-4} \text{ mol/L} \times 0.01 \text{ L} = 10^{-6} \text{ mol} ]

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

[ \text{Total Volume} = 10 \text{ mL} + 990 \text{ mL} = 1000 \text{ mL} = 1.0 ext{ L} ]

The new concentration can be calculated using the moles and the final volume:

[ \text{Concentration of NaOH} = \frac{10^{-6} \text{ mol}}{1.0 ext{ L}} = 10^{-6} ext{ mol/L} ]

Knowing that pOH is calculated as follows:

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

We can find the pH using the relation:

[ \text{pH} + \text{pOH} = 14 ]

Thus,

[ \text{pH} = 14 - 6 = 8 ]

The pH of the diluted solution is closest to 8.