Chem Chapter 16 Quiz Part 1 – Flashcards

The pH range of human blood is 7.36 and 7.42, and is maintained by buffer systems, which resist changes in pH by neutralizing an added acid or base. The buffer system in human blood is that of carbonic acid and the bicarbonate ion

A buffer is a chemical system that resists changes in pH by neutralizing added acid or base. Most buffer systems contain large amounts of a weak acid and its conjugate base or a weak base and its conjugate base. When base is added to the system, the weak acid neutralizes it, generating more of the conjugate base. When acid is added to the system, the base neutralizes the acid, generating more of the conjugate acid. It is in this fashion that a buffer system can maintain a nearly constant pH.

The common ion effect occurs when two substances, such as NaC2H3O2 and HC2H3O2, share a common ion, in this case C2H3O2. The presence of this ion in aqueous solution causes the acid to ionize even less, resulting in a higher pH, in accordance with Le Chatelier's principle

pH = pKa + log ([base]/[acid]). It is useful because it allows for calculation of the pH of a buffer solution from the initial concentrations of the buffer components, as long as the x is small approximation is valid.

When the concentration of the weak acid is equal to the concentration of the conjugate base, the pH is equal to the pKa of the weak acid. When the acid is present in a larger concentration, it becomes more acidic, and vice versa when more of the base is present.

When a strong acid is added to a buffer system, it converts the conjugate base to the weak acid, raising the weak acid's concentration slightly, causing the pH to drop slightly at most. When a strong base is added to a buffer system, it converts the weak acid to its conjugate base, decreasing the concentration of the weak acid, and slightly raising the pH of the system.

The pH of the solution can be determined by substituting the values of the concentrations of the base and acid and the pKa, which it the -log of the acid ionization constant (pH= pKa + log ([base]/[acid])

Factors influencing the effectiveness of a buffer include the relative concentrations of the weak acid and conjugate base and the absolute concentrations of the acid and base. The closer the concentrations of the weak acid and base are to one another, the more effective the buffer, and the higher the absolute concentrations, the more effective the buffer.

The pH should be within one pH unit of the weak acid's pKa, meaning that the concentrations of the acids and bases should not differ by more than a factor of 10.

In an acid base titration, an acid or base of an unknown concentration is reacted with a basic or acidic solution of known concentration. The solution of known concentration is slowly added to the unknown, as the pH of the solution is monitored. When the solution reaches the equivalence point, at which the number of moles of base is equivalent to the number of moles of acid, the titration is completed.

At the equivalence point for the titration of a weak acid with a strong base, all of the weak acid has been converted to its conjugate base, resulting in a weakly basic solution.