Titration curves and indicatorsEdexcel A-Level Chemistry: Mind map

Exam questions on Titration curves and indicators

1. A student titrates 25.0 cm³ of 0.100 mol dm⁻³ hydrochloric acid with 0.100 mol dm⁻³ sodium hydroxide solution from a burette, recording the pH with a calibrated meter at 298 K, where $K_w$ = 1.00 × 10⁻¹⁴ mol² dm⁻⁶.
   Describe the change in pH on adding alkali close to the equivalence point and explain why it happens.2 marks
2. A student titrates 25.0 cm³ of 0.100 mol dm⁻³ ethanoic acid (pKₐ = 4.76) with 0.100 mol dm⁻³ sodium hydroxide solution at 298 K. The pH at the equivalence point is about 8.7. The indicators available are methyl orange (colour change over pH 3.2–4.4), bromothymol blue (pH 6.0–7.6) and phenolphthalein (pH 8.2–10.0).
   Explain why methyl orange is not suitable for this titration.2 marks
3. A student titrates 25.0 cm³ of 0.100 mol dm⁻³ of an unknown weak monobasic acid, HX, with 0.100 mol dm⁻³ sodium hydroxide solution, using a pH meter. After adding 12.5 cm³ of sodium hydroxide solution the pH is 3.80, and the equivalence point is reached after 25.0 cm³.
   Determine $K_a$ for the acid HX. Explain your method.3 marks