Question 1

How is a burette read correctly?

Accepted Answer

Keep the liquid surface at eye level and read the burette scale to 0.01 mL. Read the bottom of the meniscus for a colourless solution and the top for dark potassium permanganate. Since burette values increase downwards, a falling liquid level corresponds to an increasing reading.

Question 2

Why are both phenolphthalein and methyl orange suitable for a strong acid-strong base titration?

Accepted Answer

A strong acid-strong base titration has a very steep pH change near equivalence. Phenolphthalein changes over pH 8.2–10.0, while methyl orange changes over pH 3.1–4.4, so each transition falls within that steep region. Phenolphthalein is colourless at pH 7 and becomes pink only after the pH enters its transition range.

Question 3

What colour marks the end point in a KMnO4 titration?

Accepted Answer

The end point is the first permanent pale pink colour produced by a slight excess of MnO4- from the KMnO4 solution. In practice, the colour should persist for about 30 seconds. The solution does not need to become a deep purple colour.

Question 4

Why is oxalic acid titrated with KMnO4 at about 60–70 °C?

Accepted Answer

The permanganate oxidation of oxalic acid is slow initially, especially before enough Mn2+ has formed. Mild heating speeds the reaction, while the first additions are made slowly. The Mn2+ product then autocatalyses the reaction.

Question 5

What is the molar ratio of Fe2+ to MnO4- with Mohr's salt?

Accepted Answer

The ratio is 5:1. Each Fe2+ ion loses one electron as it becomes Fe3+, giving five electrons in total. One MnO4- ion accepts five electrons in acidic medium and becomes Mn2+.

Titration Bench — Burette, Indicators and Redox Endpoints

About this lab

Practice