Titration Method: Past Paper Questions
Apparatus · Procedure · Indicator Selection · Calculations · Salt Preparation
Examiner's Opening Note
Titration questions on Paper 6 are the most predictable — and the most mark-losing. Students who lose marks here almost always do so on three classic traps: (1) not specifying apparatus precision, (2) forgetting to repeat without indicator, and (3) vague endpoint descriptions. This paper trains you to eliminate all three.
Apparatus
Name the piece of apparatus used to accurately measure exactly 25.0 cm³ of alkali before transferring it to the conical flask.
Name the apparatus used to add acid drop-by-drop to the alkali during a titration, and state the precision it should be read to.
A student uses a burette reading of 0.00 cm³ (initial) and 24.65 cm³ (final). Calculate the titre volume and state whether this is concordant with a second titre of 24.70 cm³.
Describe how you would set up and read a burette correctly to minimise parallax error.
Why is a conical flask (Erlenmeyer flask) preferred over a beaker during a titration?
Procedure
Describe the full titration procedure from the point where 25.0 cm³ of sodium hydroxide solution has been transferred to the conical flask. Include what you observe at the endpoint.
A student wants to make pure, dry sodium chloride crystals. Explain why the titration method (excess acid/alkali method) is used rather than the excess solid method, and describe the steps after the rough titration to obtain a pure salt.
State TWO safety precautions a student must take when using concentrated hydrochloric acid in a titration.
A student rinsed her conical flask with distilled water before adding the alkali from the pipette. Her teacher said this was correct. Explain why rinsing the conical flask with distilled water does NOT affect the titration result.
Explain why a student should perform a rough titration before recording accurate results.
The Indicator Trap
A student uses phenolphthalein indicator during a titration to find the exact volume of hydrochloric acid needed to neutralise sodium hydroxide. She then wants to make pure sodium chloride. Explain why she must repeat the titration WITHOUT the indicator to obtain a pure salt sample.
Methyl orange indicator is yellow in alkali and red in acid. A student is titrating hydrochloric acid into sodium hydroxide. State the colour change at the endpoint and explain, at the molecular level, why the indicator changes colour.
A student titrates 25.0 cm³ of 0.100 mol/dm³ NaOH with HCl and obtains concordant titres of 24.80 cm³ and 24.75 cm³. Calculate the mean titre and then calculate the concentration of the HCl solution. Show all working.
Universal indicator is NOT suitable for titrations. Give TWO reasons why.
Design a full titration experiment to determine the concentration of an unknown ethanoic acid (CH₃COOH) solution using 0.200 mol/dm³ sodium hydroxide solution. Your answer must include: apparatus, indicator choice with justification, procedure steps, and how you would calculate the concentration.
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🏆 The Three Marks You Must Never Lose
Always say: 'repeat without indicator to avoid contaminating the salt crystals'
Concordant means within 0.10 cm³ — state the difference, not just 'yes'
At endpoint: state the specific colour change (yellow → orange, NOT 'changes colour')
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