The addition of HCl to the buffer solution shifts to reactants i.e. the equilibrium of the reaction to the left towards the reactants, resulting in an increase in the concentration of NH3 and a decrease in the concentration of NH4+. This leads to an increase in the pH of the solution, making it more basic.
If HCl (hydrochloric acid) is added to the buffer solution, it will cause the equilibrium of the reaction to shift to the left towards the reactants.
In the given reaction, NH3(aq) + H2O(l) ⇌ NH4+(aq) + OH-(aq), the NH3 acts as a weak base, while NH4+ acts as its conjugate acid. The addition of HCl, a strong acid, introduces additional H+ ions into the solution.
The H+ ions from HCl will react with the OH- ions from the dissociation of water to form H2O. This reaction consumes OH- ions, resulting in a decrease in their concentration. As a result, according to Le Chatelier's principle, the equilibrium will shift to the left in order to restore the balance of reactants and products.
This shift to the left will favor the formation of NH3 and H2O, causing the concentration of NH3 to increase and the concentration of NH4+ to decrease. Consequently, the pH of the solution will increase, becoming more basic.