Final answer:
Hydroxide ions from dissolved NaOH can react with hydronium ions to form water, but an excess of OH- remains, contributing to the solution's basicity. The Na+ ion is a spectator and does not participate in the reaction. The equation OH- + H₂O → H₂O + OH- just shows that hydroxide ions exist freely in the solution.
Step-by-step explanation:
When sodium hydroxide (NaOH) is dissolved in water, it dissociates into sodium ions (Na+) and hydroxide ions (OH-). The hydroxide ions can react with hydrogen ions (H+) in the solution, which includes hydronium ions (H₃O+), to form water molecules.
This reaction is described by the equation H+ (aq) + OH- (aq) → H₂O. Nonetheless, not all hydroxide ions will necessarily react with hydronium ions; there will be an excess of OH- ions if NaOH is added to pure water, as NaOH is a strong base and will dissociate completely. This excess of OH- ions is what gives the solution its basic properties.
Regarding the OH- ions reacting with water itself, it is not a reaction that modifies the number of OH- ions or H₂O molecules because the equation OH- + H₂O → H₂O + OH- essentially states that hydroxide exists freely in the solution without changing the composition of water.
The fluoride ion (F-) in contrast, is capable of reacting with water, accepting a proton in a process known as salt hydrolysis, which can make the solution slightly basic. When NaOH is dissolved in water, the Na+ ion doesn't participate in the acid-base reactions, which is why it's often referred to as a spectator ion.