Titration
4 marks · NormalThe steps below are used in a titration experiment to find the volume of sulfuric acid needed to neutralise 25.0 cm³ of potassium hydroxide solution.
State how the potassium hydroxide solution should be measured and transferred to the flask.
Name a suitable indicator for this titration, and state the expected colour change at the endpoint.
Explain why it is important to read the burette at eye level.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) Use a pipette (with pipette filler) to measure and transfer to a conical flask.
(b) Phenolphthalein; colourless to pale pink.
(c) To avoid parallax error / ensure accurate volume reading.
Also accept: correct alternative indicators and colour changes
Common mistakes: incorrect indicator colour changes
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Mentions pipette (with filler) used to transfer to conical flask.
B2 (b) · 1 mark · Names phenolphthalein (or methyl orange if justified).
B3 (b) · 1 mark · Gives correct colour change at endpoint: colourless to pale pink (or yellow to orange for methyl orange).
B4 (c) · 1 mark · Explains reading burette at eye level avoids parallax error.
Worked solution
a) Use a pipette with filler to measure 25.0 cm³ potassium hydroxide and transfer to a conical flask.
b) Use phenolphthalein as indicator; it changes from colourless (acidic) to pale pink (alkaline) at the endpoint.
c) Reading at eye level prevents parallax error, giving an accurate burette reading.