Final answer:
The role of NaOH in buffer solutions is to react with the weak acid present in the buffer, forming water and the conjugate base, thus preventing significant pH changes. In concentrated buffer solutions, the addition of NaOH has only a minimal effect on the pH, showcasing the buffer's capacity to stabilize the solution's pH.
Step-by-step explanation:
Role of Sodium Hydroxide in Buffer Systems
The role of sodium hydroxide (NaOH) in buffer systems is fundamental to maintaining a stable pH. For instance, in an acetic acid/sodium acetate (HC2H3O2/NaC2H3O2) buffer, the addition of NaOH leads to an acid-base reaction where the OH- ions from NaOH react with HC2H3O2, producing water (H2O) and acetate ions (C2H3O2-).
This reaction prevents a drastic change in pH, which is the essence of a buffer's function. Similarly, in a phosphate buffer, NaOH converts the weak acid, sodium dihydrogen phosphate (NaH2PO4), into sodium monohydrogen phosphate (Na2HPO4), which is its conjugate base, again mitigating significant pH alterations.
The effectiveness of buffering action is highlighted by the fact that adding small amounts of NaOH to a buffer will result in only a slight change in pH, which contrasts sharply with the same addition made to pure water. The capacity of a buffer, such as a mixture of sodium acetate and acetic acid, depends on its concentration.
At higher concentrations like 0.500 M, the same addition of NaOH yields a very small pH variation, demonstrating the buffer's capacity to neutralize added strong bases and acids.
This buffering action is graphically represented by a curve showing minimal pH change despite the gradual addition of NaOH to a buffer solution, in contrast to the steep change that occurs when NaOH is added to unbuffered solutions.