2.1 Acids and bases

• Characteristics of acids and bases in aqueous solution
• Chemical properties of acids
• Chemical properties of bases
• Strong and weak acids and bases; the pH scale
• Uses of acids and bases in day-to-day life

• explain the characteristics of acids and bases in aqueous solutions
• describe the chemical properties of acids and bases
• classify acids and bases into strong and weak using universal indicator
• outline the uses of acids and bases in day-to-day life
• appreciate the uses of acids and bases in day-to-day activities

“What do lemon juice, car batteries and stomach fluid have in common?”

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1. Acids and bases
   40 min · 2 practice tasks · quiz
   What makes something acidic, how they react, and the pH scale.
2. Reactions of acids and bases
   40 min · 2 practice tasks · quiz
   The three standard acid reactions, neutralisation, and where they are used.
3. Acids and bases around us
   40 min · 1 practice tasks · quiz
   Name common acids and bases in Kenyan homes and industry, then ask what they share.
4. Acids produce hydrogen ions
   40 min · 1 practice tasks · quiz
   An acid is a substance that produces hydrogen ions, H+, in aqueous solution.
5. Bases and alkalis
   40 min · 1 practice tasks · quiz
   A base neutralises an acid. An alkali is a soluble base that produces OH- in water.
6. Acids and bases need water
   40 min · 1 practice tasks · quiz
   Acidic and alkaline properties appear in aqueous solution because that is when H+ and OH- are free.
7. Physical properties of acids and bases
   40 min · 1 practice tasks · quiz
   Compare taste, feel, corrosiveness and electrical conductivity - and the safety limits of those tests.
8. Litmus as an indicator
   40 min · 1 practice tasks · quiz
   Litmus turns red in acid and blue in alkali; it sorts three groups, not fourteen pH values.
9. Methyl orange and phenolphthalein
   40 min · 1 practice tasks · quiz
   Two titration indicators: methyl orange (red/yellow) and phenolphthalein (colourless/pink).
10. Universal indicator
    40 min · 1 practice tasks · quiz
    Universal indicator is a mixture of dyes whose colour maps onto the pH scale.
11. Plant indicators in Kenya
    40 min · 1 practice tasks · quiz
    Red cabbage, hibiscus (rosella), tea and beetroot juices act as homemade indicators.
12. Reading the pH scale
    40 min · 1 practice tasks · quiz
    pH 0 to 14: below 7 acidic, 7 neutral, above 7 alkaline, with Kenyan examples placed on the scale.
13. Each pH unit is tenfold
    40 min · 1 practice tasks · quiz
    The pH scale is logarithmic: a drop of one unit means ten times more H+.
14. Measuring pH
    40 min · 1 practice tasks · quiz
    Use indicator paper, universal indicator and a pH meter; know what each can and cannot do.
15. Strong and weak acids
    40 min · 1 practice tasks · quiz
    Strong acids ionise almost fully; weak acids ionise only partly. Universal indicator and conductivity show the difference.
16. Strong and weak alkalis
    40 min · 1 practice tasks · quiz
    NaOH and KOH ionise fully; ammonia produces only some OH-. Limewater is a special case.
17. Strength is not concentration
    40 min · 1 practice tasks · quiz
    Strength describes ionisation of the substance; concentration describes how much is dissolved.
18. Acids with metals
    40 min · 1 practice tasks · quiz
    Acid plus a metal above hydrogen gives a salt and hydrogen gas. Copper, silver and gold do not react.
19. The squeaky pop test
    40 min · 1 practice tasks · quiz
    Collect hydrogen and test with a lighted splint; a squeaky pop confirms H2.
20. Acids with carbonates
    40 min · 1 practice tasks · quiz
    Acid plus carbonate gives a salt, water and carbon dioxide. Chalk, limestone, eggshell and Magadi soda all fizz.
21. The lime water test
    40 min · 1 practice tasks · quiz
    Carbon dioxide turns lime water milky as calcium carbonate precipitates. Excess CO2 then clears the milkiness.
22. Acids with oxides and hydroxides
    40 min · 1 practice tasks · quiz
    Acid plus a base (metal oxide or hydroxide) gives a salt and water. This is the third reaction pattern.
23. Neutralisation as ions
    40 min · 1 practice tasks · quiz
    The essential change is H+ + OH- forming water. The remaining ions are the salt. Heat is released.
24. Naming the salt from the acid
    40 min · 1 practice tasks · quiz
    The acid names the salt: hydrochloric gives chlorides, sulphuric sulphates, nitric nitrates, ethanoic ethanoates.
25. Stomach acid and antacids
    40 min · 1 practice tasks · quiz
    Gastric juice is dilute hydrochloric acid. Antacids are bases that raise pH enough to ease pain.
26. Soil pH and liming in Kenya
    40 min · 1 practice tasks · quiz
    Highland soils can be too acidic for maize. Lime raises pH; tea prefers acid soil. Over-liming is a real error.
27. Magadi soda and everyday industry
    40 min · 1 practice tasks · quiz
    Lake Magadi supplies soda ash (Na2CO3). Acids and bases also run batteries, soap, fertiliser and water treatment.
28. Safety and putting it together
    40 min · 1 practice tasks · quiz
    Handle acids and alkalis with goggles and dilution rules, then review ions, pH, strength and the three reactions.