Covering Lessons 1 to 5: titrations, gravimetric analysis, qualitative ion testing, UV-Vis and AAS, and chromatography. Use this checkpoint to see whether you can move between techniques and choose the right evidence for the right analytical problem.
Which statement best distinguishes the endpoint from the equivalence point in a titration?
Which process sequence correctly describes gravimetric analysis?
Which reagent is used to test for chloride ion in qualitative analysis?
Which statement about AAS is correct?
What is the correct formula for Rf in TLC?
Why is phenolphthalein more suitable than methyl orange for a weak acid-strong base titration?
If a precipitate is weighed before it is fully dry, what is the most likely effect?
A solution gives a pale blue precipitate with NaOH(aq) and a blue-green flame test. Which ion is most strongly supported?
What does a smaller extra peak on an HPLC chromatogram most strongly suggest?
Which statement best distinguishes qualitative from quantitative analysis?
Explain how a back titration can be used to determine the amount of active base in an antacid tablet. 3 marks
A chemist obtains a white precipitate with AgNO3(aq) and writes the molecular equation AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq). Write the net ionic equation and explain why it is preferred when discussing qualitative tests. 4 marks
Evaluate why HPLC is generally more suitable than TLC alone for pharmaceutical purity testing. In your answer, refer to sensitivity, retention time, and impurity detection. 4 marks
1. B — endpoint is the observed indicator change; equivalence point is the stoichiometric point.
2. D — gravimetric analysis follows dissolve → precipitate → filter → dry → weigh.
3. A — AgNO3(aq) is used to test for chloride ion.
4. C — AAS measures absorption by ground-state atoms after atomisation.
5. B — Rf is compound distance divided by solvent-front distance.
6. D — phenolphthalein better matches the higher-pH equivalence region.
7. A — incomplete drying leaves water, making measured mass too high.
8. C — pale blue precipitate plus blue-green flame strongly supports Cu2+.
9. B — an additional peak suggests an impurity or extra component.
10. C — qualitative asks what is present; quantitative asks how much is present.
Q11 (3 marks): A known excess of acid is added to the crushed antacid tablet so the active base reacts completely. The acid left over is then titrated with a standard base solution. The moles of excess acid are calculated from the second titration and subtracted from the initial moles of acid added. This gives the moles of acid that reacted with the antacid, which can then be converted to the amount of active base using stoichiometry.
Q12 (4 marks): The net ionic equation is Ag+(aq) + Cl-(aq) → AgCl(s). It is preferred because it removes spectator ions such as Na+(aq) and NO3-(aq), leaving only the species that actually undergo chemical change. In qualitative analysis, this makes the test logic clearer by showing exactly which ions are responsible for the observed precipitate.
Q13 (4 marks): HPLC is generally more suitable than TLC alone for pharmaceutical purity testing because it is more sensitive and can detect smaller impurity levels. Retention time provides stronger instrumental evidence for component identity when compared with a standard under the same conditions. HPLC also produces peak patterns that reveal minor impurities more clearly than a simple TLC plate. TLC is useful as a fast screening tool, but HPLC gives more reliable and detailed evidence for high-stakes purity decisions.
Tick when you've finished the review and checked your answers.