This question is about weak acids.
Table 1 shows the pH ranges of some acid-base indicators.
| Indicator | pH range |
|---|---|
| Bromophenol blue | 3.0 – 4.6 |
| Methyl red | 4.4 – 6.2 |
| Thymol blue | 8.0 – 9.6 |
Identify the indicator from Table 1 that is most suitable for use in a titration between propanoic acid and potassium hydroxide.
Give the expression for the acid dissociation constant (KaK_{\text{a}}Ka) for propanoic acid (C2H5COOH\text{C}_2\text{H}_5\text{COOH}C2H5COOH).
Calculate the pH of a 0.0850 mol dm−30.0850\text{ mol dm}^{-3}0.0850 mol dm−3 propanoic acid solution. Give your answer to 2 decimal places. For propanoic acid, pKa=4.87\text{p}K_{\text{a}} = 4.87pKa=4.87.
For propanoic acid, Ka=1.35×10−5 mol dm−3K_{\text{a}} = 1.35 \times 10^{-5}\text{ mol dm}^{-3}Ka=1.35×10−5 mol dm−3.
20.0 cm320.0\text{ cm}^320.0 cm3 of 0.150 mol dm−30.150\text{ mol dm}^{-3}0.150 mol dm−3 potassium hydroxide solution are added to 35.0 cm335.0\text{ cm}^335.0 cm3 of 0.150 mol dm−30.150\text{ mol dm}^{-3}0.150 mol dm−3 propanoic acid solution to form a buffer solution.
Calculate the pH of the solution formed. Give your answer to 2 decimal places.
A student plans to titrate propanoic acid solution with a solution of methylamine. Explain why this titration could not be done successfully using an indicator.
