2.2 Acids, Bases and Indicators

• Introduction to acids and bases
• Identification of acids and bases using litmus paper
• Preparation of acid-base indicators from plant extracts
• Classification of commonly used substances as acids or bases using plant-extract indicators
• Physical properties of acids and bases
• Uses of acids, bases and indicators in real life

• identify acids and bases using a litmus paper
• prepare an acid-base indicator from plant extracts
• describe the physical properties of acids and bases
• outline applications of acids, bases and indicators in real life
• appreciate the uses of acids and bases in real life

“Why are acids and bases important?”

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1. Why acids and bases matter
   40 min · 1 practice tasks · quiz
   Acids and bases are already in the kitchen, the body and the farm. This sub-strand teaches how to tell them apart and use them safely.
2. What acids are
   40 min · 1 practice tasks · quiz
   An acid is a substance that turns blue litmus red. In food it often tastes sour. Concentrated acids are corrosive.
3. What bases are
   40 min · 1 practice tasks · quiz
   A base turns red litmus blue. Dilute bases often feel soapy. Ash, soap, lime and toothpaste are everyday bases. Alkalis dissolve in water.
4. Acids in the Kenyan kitchen
   40 min · 1 practice tasks · quiz
   Lemon, vinegar, sour fruit, sour milk and some drinks are acids you already cook with. They flavour and preserve. They are still not lab reagents to taste from a bottle.
5. Bases: ash, soap and lime
   40 min · 1 practice tasks · quiz
   Soap, jiko ash, toothpaste and lime are the working bases. They clean, treat soil and can irritate skin if strong.
6. How to use litmus paper
   40 min · 1 practice tasks · quiz
   Litmus is an indicator. Blue paper goes red in acid. Red paper goes blue in a base. Use a drop; do not soak the booklet.
7. Identifying acids with litmus
   40 min · 1 practice tasks · quiz
   Test household solutions with blue litmus. Lemon, vinegar and other sour kitchen liquids should turn it red. Record in a table.
8. Identifying bases with litmus
   40 min · 1 practice tasks · quiz
   Soap, ash water, toothpaste and detergent should turn red litmus blue. Same table skills as the acid hunt.
9. Neither acid nor base
   40 min · 1 practice tasks · quiz
   Some solutions leave both litmus papers unchanged. Water and sugar water are the Grade 7 examples. They are still mixtures; they are not "nothing".
10. Plant indicators
    40 min · 1 practice tasks · quiz
    Coloured plant juices can act as indicators. Prefer cabbage, hibiscus or beetroot. Use flowers sparingly to protect plants.
11. Preparing a plant indicator
    40 min · 1 practice tasks · quiz
    Chop, extract with a little water, filter, label. Share roles. Do not taste. Dispose of pulp in a solid-waste bin.
12. Classifying with a plant indicator
    40 min · 1 practice tasks · quiz
    Use your extract on household solutions. Compare with litmus. Creativity is reading a new colour key you made yourselves.
13. Universal indicator and pH
    40 min · 1 practice tasks · quiz
    pH is a number: below 7 acidic, 7 near neutral, above 7 basic. Universal indicator shows colours on a chart. No titration.
14. Physical properties of acids
    40 min · 1 practice tasks · quiz
    Acids: sour in food, corrosive when concentrated, turn blue litmus red, often watery solutions. Do not taste lab acids.
15. Physical properties of bases
    40 min · 1 practice tasks · quiz
    Bases: soapy or slippery when dilute, bitter in food ideas, turn red litmus blue, corrosive when concentrated.
16. Investigating properties together
    40 min · 1 practice tasks · quiz
    A shared investigation: compare an acid and a base on appearance, litmus, plant indicator, and feel or food-sour where safe. Present a group table.
17. Acids fizz with baking soda
    40 min · 1 practice tasks · quiz
    Many acids fizz with baking soda (a carbonate). Observe bubbles. This is not a titration and not a home drain-cleaner experiment.
18. Uses of acids
    40 min · 1 practice tasks · quiz
    Food flavour and pickles, vitamin C, stomach digestion, some cleaners, car batteries. Search one Kenyan use. Do not sip industrial acids.
19. Uses of bases
    40 min · 1 practice tasks · quiz
    Soap, toothpaste, ash, antacids and agricultural lime. Bases clean, treat soil and can soothe extra stomach acid. Strong ones still burn.
20. Indicators and antacids
    40 min · 1 practice tasks · quiz
    Indicators report acid or base so people can test soil, water and products. Antacids reduce extra stomach acid. Not a titration; not a clinic replacement.
21. Soil acidity and lime
    40 min · 1 practice tasks · quiz
    Some Kenyan soils are too acidic for good crops. Agricultural lime is a base that reduces that acidity. Test, then lime. Link to Agriculture.
22. Waste, safety and appreciation
    40 min · 1 practice tasks · quiz
    Dispose of waste as instructed, spare the plants, respect peers' roles. Appreciation is using acids, bases and indicators wisely in Kenyan life.