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Topic ladders · Chemistry

Acids, Bases & Salts

One topic, four rungs: from Classes 1–3 to Classes 11–12. Start at your own stage, or climb from the bottom. Every rung follows the same six steps: Notice, Guess, Try, Observe, Explain, Ask another question.

Print the family table: all four rungs side by side on one sheet, so everyone at home can find their own rung.

Choose your class stage

Rung 1 · Classes 1–3

Sour and Soapy (Early Experience)

Before you start: safety and help

For the grown-up who helps.

  • Safety: No tasting, even of food liquids: in experiments we never taste. Use only the liquids listed; never cleaners, bleach or anything from an unlabelled bottle. Keep vinegar and lemon away from eyes; if any gets in, rinse with plenty of clean water. Wash hands afterwards.

What you need

  • Small cups of: lemon juice, vinegar, soap solution, sugar solution, water (prepared by a grown-up and labelled)
  • No tasting: we use eyes, nose (from a distance) and fingers only

Child steps

  1. Notice. Think about foods you have eaten. Which ones tasted sour? (lemon, tamarind, curd, amla) Which things at home feel slippery? (soap)
  2. Guess. Which of these liquids might be sour? Which might feel slippery?
  3. Try. Look at each liquid. Wave the air above the cup towards your nose to smell it. Rub a drop of soap water between your fingers.
  4. Observe. Group the liquids by how they look, smell or feel.
  5. Explain. Describe the differences you noticed.
  6. Ask another question. Where else do we find sour or soapy things at home?
For teachers
  • Learning aims: Explore everyday substances that will later be linked to acids and bases.
  • Key vocabulary: sour, slippery, smell, liquid, different.
  • Review: Children describe one difference they observed.

Rung 2 · Classes 4–7

Testing with Indicators

Before you start: safety and help

For the grown-up or teacher who helps. Students: read it too, so you know the rules.

  • Safety: Making red cabbage indicator: chop a few cabbage leaves, cover with hot water, leave 15 minutes, and strain. You do the chopping and the hot water.
  • Turmeric paper: rub turmeric paste on white paper and let it dry.
  • Safety: Test only the liquids listed. Never test bathroom or kitchen cleaners, bleach, drain or toilet cleaner. No tasting. Keep liquids away from eyes. Turmeric stains.

What you need

  • Red cabbage indicator (made by a grown-up) or turmeric paper
  • Lemon juice, vinegar, soap solution, baking soda solution, water
  • Small clear containers, a spoon or dropper

Student steps

  1. Notice. Some substances can change colour when mixed with certain liquids.
  2. Guess. Which of your liquids will change the colour of the indicator?
  3. Try. Add a few drops of each liquid to a little indicator and record the colour.
  4. Observe. Group the liquids by the colour they produced.
  5. Explain. One group is acidic and another is basic. Water stays the same colour as the indicator: it is neutral.
  6. Ask another question. What happens to the colour if you slowly add baking soda solution to a cup of indicator with vinegar in it?
For teachers
  • Learning aims: Use a natural indicator to classify everyday substances as acidic, neutral or basic.
  • Key vocabulary: indicator, acid, base, neutral, colour change.
  • Expected colours: red cabbage turns pink or red with acids (lemon, vinegar), stays purple with water, and turns blue-green with bases (baking soda, soap). Turmeric stays yellow with acids and water and turns reddish-brown with bases.
  • Step 6: the colour moves from pink back through purple towards green as the base cancels the acid. The final colour depends on how much of each was added.
  • Review: Students classify three substances and show the indicator colours.

Rung 3 · Classes 8–10

Neutralisation and Salt Formation

Before you start: safety and help

For the grown-up or teacher who helps. Students: read it too, so you know the rules.

  • Must be done in a school laboratory under a teacher's supervision and the school's safety rules, with goggles on throughout. Not a home activity. Even though the product is "salt", it is never tasted.

What you need

  • School laboratory only: dilute hydrochloric acid and dilute sodium hydroxide (school laboratory strength), universal indicator or phenolphthalein, dropper or burette, thermometer, evaporating dish, safety goggles

Student steps

  1. Notice. Acids and bases can cancel each other out.
  2. Guess. What happens when an acid and a base are mixed in the right amounts?
  3. Try. With your teacher, add the alkali to the acid a little at a time until the indicator shows neutral. Then the teacher evaporates part of the solution to obtain salt crystals.
  4. Observe. Record temperature change, indicator colour, and appearance of the salt.
  5. Explain. Write a word equation (hydrochloric acid + sodium hydroxide → sodium chloride + water) and explain neutralisation.
  6. Ask another question. Where is neutralisation used in daily life (antacid tablets for stomach acid, lime added to acidic soil, toothpaste)?
For teachers
  • Learning aims: Understand neutralisation; produce and identify a salt.
  • Key vocabulary: neutralisation, salt, indicator, acid, alkali, exothermic.
  • Note: Neutralisation gives off heat, so the temperature rises a little. The old advice to put baking soda on bee stings and vinegar on wasp stings has little evidence behind it; it is better not to teach it as fact.
  • Review: Students describe the process and one everyday application.

Rung 4 · Classes 11–12

Quantitative Acid–Base Investigation

Before you start: safety and help

For the grown-up or teacher who helps. Students: read it too, so you know the rules.

  • Safety: School laboratory with a teacher; goggles on; use a pipette filler, never mouth pipetting.

What you need

  • School laboratory only: standard apparatus for titration (burette, pipette, conical flask, indicator, standard solution) or a pH meter, safety goggles

Student steps

  1. Notice. The concentration of acids and bases can be determined precisely.
  2. Guess / Hypothesise. Choose a quantitative question (concentration of acetic acid in vinegar, a pH curve, etc.).
  3. Try. Carry out a titration or pH investigation following proper procedures; repeat until titres agree within 0.1 cm³.
  4. Observe. Record titres or pH data carefully and process them.
  5. Explain. Calculate concentrations, plot curves if relevant, and discuss accuracy.
  6. Ask another question. How are acid–base titrations used in industry or environmental monitoring?
For teachers
  • Learning aims: Perform quantitative acid–base analysis; evaluate experimental accuracy.
  • Check: household vinegar is usually about 4–5% acetic acid; compare with the bottle's label.
  • Review: Students present results, calculations and evaluation.

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