Answer:
When KOH is added to a buffer solution prepared by adding NaH2PO4 to a solution of H3PO4, the following reactions occur:
H3PO4 + KOH → K3PO4 + H2O
NaH2PO4 + KOH → Na2HPO4 + H2O
In the first reaction, the KOH reacts with the H3PO4 to form K3PO4 and water. This reaction consumes some of the H3PO4 in the buffer solution and decreases the concentration of H+ ions. This results in a shift in the equilibrium towards the dissociation of more H3PO4 to replace the lost H+ ions.
In the second reaction, the KOH reacts with the NaH2PO4 to form Na2HPO4 and water. This reaction consumes some of the NaH2PO4 in the buffer solution and increases the concentration of HPO42- ions. This results in a shift in the equilibrium towards the formation of more H2PO4- ions to replace the lost HPO42- ions.
Overall, the addition of KOH to the buffer solution will cause a shift in the equilibrium of the buffer system, resulting in a change in the pH of the solution. The specific change in pH will depend on the initial concentrations of the buffer components and the amount of KOH added. If the buffer capacity is exceeded, the solution may no longer act as a buffer and the pH will change more dramatically.