Changing the pH of a solution affects the equilibrium position of an acid-base reaction by shifting the equilibrium either towards the reactants or the products, depending on whether the pH is increased or decreased. In the case of the reaction between hydrofluoric acid HF and sodium hydroxide NaOH , the reaction can be represented as follows:HF + NaOH NaF + H2OThis is an acid-base reaction where HF acts as the acid and NaOH acts as the base. When the reaction reaches equilibrium, both the reactants and products are present in the solution.If the pH of the solution is increased i.e., the solution becomes more basic , the concentration of hydroxide ions OH- increases. According to Le Chatelier's principle, the equilibrium will shift to counteract this change. In this case, the equilibrium will shift towards the reactants left to consume the excess hydroxide ions. This results in the formation of more HF and NaOH, and a decrease in the concentration of the products, NaF and H2O.On the other hand, if the pH of the solution is decreased i.e., the solution becomes more acidic , the concentration of hydronium ions H3O+ or hydrogen ions H+ increases. The equilibrium will again shift according to Le Chatelier's principle, this time towards the products right to consume the excess hydrogen ions. This results in the formation of more NaF and H2O, and a decrease in the concentration of the reactants, HF and NaOH.In summary, changing the pH of a solution containing an acid-base reaction between HF and NaOH will affect the equilibrium position by shifting it either towards the reactants or the products, depending on whether the pH is increased or decreased.