A weak base-strong acid is a type of chemical system where a weak base (a substance that partially accepts protons) reacts with a strong acid (a substance that completely donates protons). This interaction is particularly important in the context of acid-base titrations, where the reactions and pH changes are closely studied.
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In a weak base-strong acid system, the strong acid completely ionizes, while the weak base only partially ionizes, resulting in a solution with a low pH.
The pH of a weak base-strong acid solution can be calculated using the formula: pH = pKa - log([HA]/[A-]), where [HA] is the concentration of the weak base and [A-] is the concentration of the conjugate base.
The titration of a weak base with a strong acid results in a sigmoidal titration curve, with a sharp endpoint at the equivalence point.
The buffer capacity of a weak base-strong acid system is highest near the equivalence point, where the concentration of the conjugate base and weak base are equal.
Weak base-strong acid systems are commonly encountered in biological systems, such as the regulation of blood pH by the carbonic acid-bicarbonate buffer system.
Review Questions
Explain the characteristics of a weak base-strong acid system and how it differs from a strong base-strong acid system.
In a weak base-strong acid system, the strong acid completely ionizes, while the weak base only partially ionizes, resulting in a solution with a low pH. This is in contrast to a strong base-strong acid system, where both the base and acid fully ionize, leading to a neutral pH at the equivalence point. The titration curve of a weak base-strong acid system is sigmoidal, with a sharp endpoint at the equivalence point, while a strong base-strong acid system has a linear titration curve.
Describe how the pH of a weak base-strong acid solution can be calculated and explain the factors that influence the pH.
The pH of a weak base-strong acid solution can be calculated using the formula: pH = pKa - log([HA]/[A-]), where [HA] is the concentration of the weak base and [A-] is the concentration of the conjugate base. The pH of the solution is influenced by the strength of the weak base, as indicated by its pKa value, as well as the relative concentrations of the weak base and its conjugate base. A higher pKa value or a higher concentration of the weak base will result in a higher pH, while a lower pKa or a higher concentration of the conjugate base will lead to a lower pH.
Discuss the significance of weak base-strong acid systems in biological processes and explain how the buffer capacity of these systems is maximized at the equivalence point.
Weak base-strong acid systems are important in biological systems, such as the regulation of blood pH by the carbonic acid-bicarbonate buffer system. In these systems, the weak base and its conjugate base work together to maintain a relatively stable pH, even in the face of changes in the concentration of protons. The buffer capacity of a weak base-strong acid system is maximized at the equivalence point, where the concentration of the conjugate base and weak base are equal. This is because the system is most resistant to changes in pH when the concentrations of the weak base and its conjugate are similar, allowing the buffer to effectively neutralize added acids or bases.
Related terms
Weak Base: A weak base is a substance that only partially accepts protons in an aqueous solution, resulting in an incomplete ionization.
Strong Acid: A strong acid is a substance that completely donates protons in an aqueous solution, resulting in a high concentration of hydrogen ions.
Acid-Base Titration: An acid-base titration is a laboratory technique used to determine the unknown concentration of an acid or base by neutralizing it with a known concentration of a standard solution.