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NSWChemistryQuick questions
Module 5: Equilibrium and Acid Reactions
Quick questions on Acid-base titrations and indicators explained: HSC Chemistry Module 5
11short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What is titration basics?Show answer
A titration is a volumetric analysis in which a solution of known concentration (the titrant, usually in the burette) is added gradually to a solution of unknown concentration (the analyte, usually in a conical flask) until the reaction is complete.
What is calculation pattern?Show answer
For an acid-base titration with 1:1 stoichiometry:
What is comparing titration curves?Show answer
The shape of a titration curve depends on the strengths of the acid and base involved. The table below traces pH against the fraction of titrant added (acid being titrated with base), making the differences explicit.
What is why each curve has the equivalence pH it does?Show answer
Strong acid / strong base (HCl + NaOH). Equivalence pH 7 because the salt (NaCl) does not hydrolyse. The transition is very steep, so several indicators work.
What is indicator selection rule?Show answer
Choose an indicator whose colour change range straddles the equivalence pH. If the equivalence pH is 8.7 (weak acid / strong base), phenolphthalein (8.3-10.0) brackets it; methyl orange (3.1-4.4) would change far too early.
What is weak acid / weak base?Show answer
No sharp transition. No indicator gives a reliable end point. Not used quantitatively in HSC.
What is step 5: Indicator?Show answer
This is a strong acid / strong base titration. The equivalence pH is 7, and the steep transition allows several indicators. Bromothymol blue (pH 6.0 to 7.6) is the most precise choice because its range straddles pH 7.
What is confusing equivalence and end point?Show answer
Equivalence is stoichiometric; end point is indicator-dependent. Always say which one you mean.
What is forgetting the stoichiometric ratio for diprotic species?Show answer
$H_2SO_4 + 2NaOH$ means moles of NaOH equals 2 times moles of acid.
What is reporting too many sig figs?Show answer
Burette readings give 3 to 4 sig figs typically. Match your answer.
What is rinsing the conical flask with the analyte solution?Show answer
Rinse only with distilled water. Rinsing with the analyte changes the moles of analyte present.