Acid-base titrations and choice of indicator — practice questions

Question 1 · difficulty L1 · recall

What marks the end point of an acid-base titration when a suitable indicator is used?

• A. Formation of a metal precipitate in every titration
• B. Complete evaporation of the solution
• C. A persistent colour change near equivalence
• D. A sudden increase in the mass of the burette

Question 2 · difficulty L2 · understanding

Which indicator is generally suitable for titrating a weak acid with a strong base?

• A. Potassium permanganate because it is self-indicating
• B. Methyl orange only because the equivalence point is acidic
• C. Starch because iodine is produced
• D. Phenolphthalein

Question 3 · difficulty L3 · application

A burette is rinsed only with distilled water and then filled with the titrant without conditioning it. What error is most likely?

• A. Residual water dilutes the titrant
• B. The titrant becomes more concentrated than its stock solution
• C. The analyte is completely neutralised before titration begins
• D. The indicator changes into a primary standard

Question 4 · difficulty L4 · analysis

A student adds 20 mL of distilled water to the conical flask after pipetting a fixed amount of acid into it. How does this affect the titre in an ideal titration?

• A. The titre doubles because the acid volume doubled
• B. Essentially unchanged; acid moles are unchanged
• C. The titre becomes zero because the acid is diluted
• D. The required base volume decreases in exact proportion to dilution

Question 5 · difficulty L5 · analysis

For a strong acid–weak base titration, why is methyl orange usually preferred over phenolphthalein?

• A. It forms a precipitate exactly at neutral pH
• B. It reacts stoichiometrically with the acid as a second titrant
• C. Its transition range matches the acidic equivalence region
• D. Its colour change requires a strongly basic solution