A titration curve for a 25.0 mL sample of a monoprotic weak acid with is generated at…
CHEMISTRY · Multi-part · AP · Chemistry · Acids and Bases · Acids and Bases
Problem
A titration curve for a 25.0 mL sample of a monoprotic weak acid with Ka=1.0×10−5 is generated at 25 °C using 0.100 M NaOH as titrant. The pH at the equivalence point is found experimentally to be 8.8.
Three indicators are available:
• Methyl red (color change range pH 4.4–6.0)
• Bromothymol blue (pH 6.0–7.6)
• Phenolphthalein (pH 8.3–10.0)
(a) Identify which indicator would provide the most accurate endpoint for this titration and justify your choice based on the given pH ranges.
(b) Predict qualitatively whether the acid concentration determined would be overestimated, underestimated, or essentially correct if methyl red were used instead. Explain your reasoning with reference to the relative positions of the indicator endpoint and the equivalence point.