Titration curves and indicatorsEdexcel A-Level Chemistry: Flashcards
What these 13 flashcards ask
- pH at the equivalence point for a strong acid with a strong base
- Approximate vertical section for HCl with NaOH
- Why is the equivalence point of ethanoic acid with NaOH above pH 7?
- Suitable indicator for a weak acid with a strong base
- Suitable indicator for a strong acid with a weak base
- What happens to the curve for a weak acid with a weak base?
- Rule for choosing an indicator
- What is buffer action on a titration curve?
- Which point on a weak acid–strong base curve gives pKₐ?
- Why is the pH at half-equivalence equal to pKₐ?
- ΔH neutralisation of a strong acid with a strong base
- Why is ΔH neutralisation of a weak acid less exothermic?
- Formula to find the energy transferred in a calorimetry experiment
Exam questions on Titration curves and indicators
- 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 = 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
- 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
- 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 for the acid HX. Explain your method.3 marks
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).