Final answer:
When equal moles of a weak acid (HClO2) and a strong base (RbOH) are mixed, the solution becomes basic because the strong base completely dissociates, providing sufficient OH- ions to neutralize the partially dissociated weak acid.
Step-by-step explanation:
When combining an equal number of moles of a weak acid such as HClO2 (chlorous acid) with a strong base like RbOH (rubidium hydroxide), the resulting solution's pH depends on the compounds' dissociation behavior in water. HClO2, being a weak acid, does not dissociate completely, meaning not all of its molecules will donate H+ ions to form hydronium ions (H3O+). Conversely, RbOH is a strong base and will dissociate completely, providing an equal molarity of OH- (hydroxide ions) to the solution. The dissociated hydroxide ions will react with the hydronium ions from the dissociation of HClO2 forming water molecules:
H3O+ + OH- → 2H2O
Since the amount of moles of the base matches the moles of the acid and the base is strong (fully dissociates), it will neutralize the effects of the weak acid. As a result, the solution will generally be basic, as the undissociated HClO2 does not supply enough H3O+ to counter the amount of OH- furnished by the complete dissociation of the RbOH.