Two separate titrations are carried out at using KOH as the titrant

CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases

Problem

Two separate titrations are carried out at

25\,^{\circ}\text{C}

using

0.100\,\text{M}

KOH as the titrant. • Titration 1:

25.0\,\text{mL}

0.100\,\text{M}

weak acid A (

K_a = 1.0 \times 10^{-5}

) • Titration 2:

25.0\,\text{mL}

0.100\,\text{M}

weak acid B (

K_a = 3.0 \times 10^{-8}

) (a) For each titration, calculate the

pH

of the solution at the equivalence point. (b) Using your calculated

pH

values, determine which of the two acids would require an indicator with the higher

pH

transition range for accurate end-point detection. Justify your choice. (c) The laboratory has the indicators phenolphthalein (transition range

(\approx pH\,8.2\text{--}10.0)

) and bromothymol blue (transition range

(\approx pH\,6.0\text{--}7.6)

). Identify which indicator, if any, is suitable for each titration and explain your reasoning in terms of indicator color change relative to the equivalence-point

pH

Related theory

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