A 10 mL sample of 0.010 M HCl is diluted by adding distilled water at constant temperature - VCE - SSCE Chemistry - Question 8 - 2010 - Paper 1

When a 10 mL sample of 0.010 M HCl is diluted, the concentration of H^+ ions will decrease because dilution reduces the number of moles of H^+ in a given volume of solution. Since HCl is a strong acid that fully dissociates in solution, an increase in the concentration of water leads to a decrease in the concentration of H^+.

According to the water dissociation equilibrium at 25°C, the relationship between [H^+] and [OH^-] is given by:
$[H^+][OH^-] = 1.0 imes 10^{-14}$

Therefore, if the concentration of [H^+] decreases, the concentration of [OH^-] must increase to maintain the constant product. Hence, the correct effect of dilution will be a decrease in [H^+] and an increase in [OH^-].

Thus, the answer is B:

• H^+: decrease
• OH^-: increase