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Playbook

Practical Chemistry

3 q · 0% HARD in 10 years. Lab + food + health applications (food preservation, toothpaste action, curd-keeping methods). Read once, recognise, done — under 20 min total.

questions in the bank
3
tagged HARD
0%
subtopic(s)
1
worked examples
2

When you’ll see it

A food-preservation method, a curd-keeping/dairy method, a toothpaste action, or a lab-method recall.

How this chapter is tested

3 q in 10 years · ZERO HARD. Tiniest playbook in the bank. Lab + food + health applications. Toothpaste prevents decay by neutralising acid (from bacteria fermenting sugar) — modern pastes are basic, with fluoride (F⁻) to strengthen enamel (CaF₂ is harder than hydroxyapatite). Curd-keeping: refrigerate (slow bacterial action) — adding sugar/salt also helps but the primary method is cold. Food preservation: salting (NaCl draws water out via osmosis), sugar (jam), refrigeration, canning, drying, vacuum-sealing, adding preservatives (BHA, BHT, sodium benzoate).

Read once in 15 minutes — the 3 q in 10 years means you'll see 0–1 of these per paper, but they're free marks if you've read them. Don't allocate more than 30 min of prep.

The sub-skills

The rules and habits that decide whether you get a question right.

  • Food-preservation methods

    Physical: refrigeration, freezing, drying, canning, vacuum-sealing, smoking. Chemical: salting (osmosis dehydration), sugaring (osmosis), pickling (acid), preservatives (sodium benzoate, BHA, BHT, sulphur dioxide). Curd → refrigerate.

  • Toothpaste action

    Bacteria ferment sugar → produce acid → demineralise enamel (Ca₅(PO₄)₃OH). Toothpaste neutralises acid (mild base) + fluoride (F⁻) replaces hydroxyl in enamel → fluorapatite (Ca₅(PO₄)₃F) which is harder + more acid-resistant. Brushing also mechanically removes plaque.

2 worked examples from the bank

Real past-year questions illustrating the playbook. Click to reveal options + solution.

Example 1Practical ChemistryEASY
Among the following, which is not the correct method for keeping the curd?

[Q77 · Apr · 2023]

Example 2Practical ChemistryEASY
Toothpaste prevents tooth decay by :

[Q78 · Apr · 2023]

Traps to expect

Distractor shapes specific to this chapter. The page-wide Traps section covers the bank-level patterns.

  • Toothpaste 'cleans by mechanical action only'

    The mechanical action of brushing matters, but toothpaste itself works CHEMICALLY: (a) neutralising acid, (b) fluoride incorporation into enamel. Wrong option treats toothpaste as a pure cleanser.

Drill every practical chemistry question

3 questions from the bank, scoped to the named subtopic.

Drill the 3 questions

Related playbooks

Often paired with this one — drill these next if you found the worked examples above tractable.