Use Figure 19.9 to find an indicator for these titrations: (a) 0.25 M C6 H5 COOH (see Appendix C

step 1 To determine which indicator will work best for the following two titrations, we need to solve f

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

Use Figure 19.9 to find an indicator for these titrations:
(a) $0.25 \mathrm{M} \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COOH}$ (see Appendix C) with $0.25 \mathrm{M} \mathrm{KOH}$
(b) $0.50 \mathrm{M} \mathrm{NH}_{4} \mathrm{Cl}$ (see Appendix C) with $0.50 \mathrm{M} \mathrm{NaOH}$

Key Concepts

pH Transition Range

The pH transition range of an indicator refers to the narrow interval over which the indicator changes color. For a titration to be accurately monitored, the indicator’s transition range should overlap the steep section of the titration curve near the equivalence point. This ensures that even a slight deviation in pH produces a noticeable color change, allowing for precise detection of the endpoint.

Indicator Selection

Indicator selection involves choosing a suitable chemical that undergoes a distinct color change at a pH near the expected equivalence point of the titration. Because the color change must be sharp and occur close to the equivalence point to ensure an accurate determination, the indicator’s transition range is carefully matched to the anticipated pH change during the titration process.

Equivalence Point

The equivalence point in a titration is the stage at which the quantity of titrant added is chemically equivalent to the amount of analyte present in the sample. The pH at the equivalence point depends on the strengths of the acid and base involved—if a weak acid is titrated with a strong base, the resulting equivalence point will be above pH 7, since the conjugate base will react slightly with water to generate additional OH? ions.

Acid?Base Titration

Acid–base titration is an analytical procedure where a solution of known concentration (the titrant) is gradually added to a solution of unknown concentration until the reaction reaches completion. In such titrations, the point at which the amount of titrant added exactly neutralizes the analyte is called the equivalence point. This process is fundamental for determining concentrations and understanding reaction stoichiometry in acid–base systems.

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