Consider the titration of a 25.0-mL sample of 0.115 M RbOH with 0.100 M HCl. Determine each quantity. a. the initial pH b. the volume of added acid required to reach the equivalence point c. the pH at 5.0 mL of added acid d. the pH at the equivalence point e. the pH after adding 5.0 mL of acid beyond the equivalence point

Acid-base titration is a quantitative analytical method used to determine the concentration of an acid or a base in a solution. It involves adding a titrant (a solution of known concentration) to a solution of the substance being analyzed, known as the analyte, until the chemical reaction between the two is complete. This point of completion is known as the equivalence point.

In our example, the titration involves the reaction between RbOH, a strong base, and HCl, a strong acid. The process monitors the change in pH as the HCl is added to the RbOH solution. When the titrant is added, it reacts with the analyte to form water and a salt, and the change in the pH is recorded to determine when the equivalence point is reached.

Calculating the initial pH of a strong base, finding the volume of acid required to reach the equivalence point, and determining the pH at various stages of the titration, are key aspects of this process. These calculations rely on stoichiometric relationships between the acid and base, the concept of pH, and an understanding of the properties of strong acids and bases, which dissociate completely in water.

The pH at the equivalence point of a titration between a strong acid and a strong base is a fundamental concept in acid-base chemistry. This pH signifies a neutral solution because at the equivalence point, equal amounts of the acid and base have reacted to form water and a neutral salt.

In the example provided, we reach the equivalence point when the amount of HCl added is stoichiometrically equivalent to the amount of RbOH present in the solution. Since both RbOH and HCl are strong (meaning they completely dissociate in water), the resulting salt, RbCl, has no acidic or basic properties and the solution is pure water, leading to a neutral pH of 7.

Under the assumption that the reaction between the strong base and the strong acid is going to completion, no additional calculations are needed to determine the pH at the equivalence point. However, for weak acids or bases, the pH at the equivalence point can be acidic, basic, or neutral depending on the relative strengths of the acids and bases involved.

Determining the initial pH of a strong base like RbOH involves understanding how it reacts in water. Strong bases dissociate completely in aqueous solutions to form hydroxide ions (OH⁻). The concentration of these hydroxide ions directly influences the pH of the solution.

To calculate the initial pH, one must take the negative logarithm of the hydroxide ion concentration to find the pOH, and then subtract this value from 14 (since pH + pOH = 14 in aqueous solutions at 25°C). In the exercise given, the initial concentration of RbOH is equal to the initial concentration of OH⁻ because RbOH is a strong base that dissociates completely. Hence, the initial pOH is calculated from the concentration of RbOH, and consequently, the initial pH is found to be basic due to the presence of hydroxide ions.