Use Figure 19.9 to find an indicator for these titrations: (a) 0.5 M(CH3)2 NH (see Appendix C) w

step 1 To determine which indicator will work best for these titrations, we need to calculate the pH at

Use Figure 19.9 to find an indicator for these titrations:...

Key Concepts

Strong Base-Strong Acid Titration

When a strong base titrates with a strong acid, both reactants completely dissociate in solution, leading to a neutralization reaction that results in an equivalence point typically near pH 7. An indicator used in this titration must exhibit a color change around neutral pH in order to reliably signal the equivalence point.

Weak Base-Strong Acid Titration

In a weak base–strong acid titration, the weak base reacts with the strong acid to form its conjugate acid, which can hydrolyze and lower the pH of the solution at the equivalence point. This results in an acidic equivalence point, necessitating the use of an indicator that changes color in an acidic pH range to accurately detect the endpoint of the titration.

Equivalence Point

The equivalence point in a titration is the stage at which the amount of titrant added completely reacts with the analyte according to the stoichiometry of the reaction. The pH at the equivalence point depends on the nature of the acid and base used. For instance, in titrations involving a weak base and a strong acid, the equivalence point will be on the acidic side due to the hydrolysis of the resulting conjugate acid, whereas titrations involving strong acids and strong bases yield an equivalence point close to neutral pH.

Acid-Base Titration

An acid-base titration is an analytical technique used to determine the concentration of an acid or a base in a solution by neutralizing it with a base or acid of known concentration. This process involves gradually adding the titrant to the analyte until the reaction reaches the equivalence point, where the quantities of acid and base are stoichiometrically balanced.

Indicator Selection

Indicator selection involves choosing a chemical that exhibits a distinct color change near the pH corresponding to the titration’s equivalence point. This color change enables accurate determination of when the equivalence point has been reached. The chosen indicator must have a transition range that brackets the expected pH at the equivalence point to ensure clear observation of the endpoint.

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