Citric acid, which is present in citrus fruits, is a triprotic acid (Table 16.3). (a) Calculate the pH of a 0.040 M solution of citric acid. (b) Did you have to make any approximations or assumptions in completing your calculations? (c) Is the concentration of citrate ion 1C6H5O7 3-2 equal to, less than, or greater than the H+ ion concentration?

Triprotic acids, like citric acid, can donate three protons (H+) per molecule in solution. This characteristic affects their dissociation constants (Ka1, Ka2, Ka3), which determine the extent of ionization at different pH levels. Understanding the stepwise dissociation is crucial for calculating pH and concentrations of ions in solution.

pH is a measure of the hydrogen ion concentration in a solution, calculated using the formula pH = -log[H+]. For weak acids, such as citric acid, the pH can be determined using the acid dissociation constants and the initial concentration of the acid. This often involves approximations, especially when the acid is not fully dissociated.

In a solution of a weak acid, the concentrations of the acid, its conjugate base, and hydrogen ions reach an equilibrium. For citric acid, the concentration of the citrate ion (C6H5O7^3-) will depend on the degree of dissociation and the pH. Understanding the relationship between these concentrations is essential for answering questions about their relative amounts.