Eclat Institute

For H2 Organic Chemistry QA, a positive result is only the first step.

This carousel shows what common tests prove, where students often overclaim, and how to state the safest conclusion in Paper 4.

H2 Chemistry Practical: Indirect Titration With Calcium Carbonate

Add excess HCl to calcium carbonate, titrate the leftover HCl with NaOH, then use the 1:2 ratio to find CaCO3.

Quick Paper 4 checklist: rough titres, concordant readings, mean titre, anomalies, and how bad readings affect calculations.

A quick practical-revision carousel for starch, reducing sugar, protein, and fats.

Remember the pairings:
1. Iodine solution -> blue-black for starch
2. Benedict's solution + heat -> green, yellow, orange, or brick-red precipitate for reducing sugar
3. Biuret reagent -> lilac, purple, or violet for protein
4. Ethanol emulsion test -> cloudy white emulsion for fats

Save this before practical revision. The marks usually depend on the exact reagent, method, and observation.

Paper 4 isn't a memory test - it's a hands-on test.

Examiners are watching how you handle the apparatus, the data, and the write-up.

Nine habits that separate full-marks from the rest:

1. Don't time one swing. Time twenty swings
2. Read every scale at eye level
3. Linearise before you plot
4. Plot points as crosses, never dots
5. Combine errors the way the formula says
6. Spot the anomaly. Circle it. Don't average it in
7. Let the spreadsheet do the maths (new in 9478)
8. A real conclusion = number + unit + comparison
9. Every plan needs five things on paper

Save it. Send it to your lab partner.

Walk into Paper 4 knowing what the examiner is silently scoring.

Paper 4 isn't about knowing more chemistry — it's about not throwing marks away on technique.

9 habits the examiner is quietly looking for 👇

1) Rinse each piece with what's going into it

2) Titres must agree within 0.10 cm³

3) KMnO₄ → acidify with dil. H₂SO₄ only (never HCl/HNO₃)

4) Add starch only when the I₂/S₂O₃²⁻ flask turns pale yellow

5) Every observation = state + colour + change

6) NaOH vs NH₃ tells cations apart (Al³⁺ / Zn²⁺ / Cu²⁺)

7) Calorimetry: extrapolate back to t = mix to find true ΔT

8) Plot points as crosses, never dots — best-fit line, not dot-to-dot

9) Two readings? Double the error.

Save this. Re-read it before every lab session. Tag a friend who still rinses the burette with deionised water 🧪

Based on MOE 9729 Paper 4 syllabus.