Last reviewed: 25 October 2026
Acids and bases are all around us, from the lemon juice in the kitchen to the soap in the bathroom and the fertiliser on the farm. Junior school Integrated Science introduces how to identify them, how to measure their strength and how they react. This guide covers each idea with everyday Kenyan examples and the experiments learners are expected to describe.
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What Acids Are
Acids are substances that taste sour (though you should never taste chemicals in the laboratory), turn blue litmus paper red and have a pH below 7. Strong acids are corrosive. Everyday acids include citric acid in lemons and oranges, ethanoic acid in vinegar, lactic acid in sour milk (mala) and carbonic acid in fizzy drinks. Laboratory acids include hydrochloric, sulphuric and nitric acid, which must be handled with great care.
What Bases Are
Bases are the chemical opposite of acids. Bases that dissolve in water are called alkalis. They usually feel soapy or slippery, turn red litmus paper blue and have a pH above 7. Everyday examples include soap, toothpaste, baking soda, wood ash solution, antacid tablets for indigestion and household cleaners containing ammonia. Laboratory alkalis such as sodium hydroxide are strongly corrosive.
Indicators
An indicator is a substance that changes colour depending on whether it is in an acid or a base.
- Litmus paper: acids turn blue litmus red; bases turn red litmus blue. Neutral substances leave both unchanged.
- Universal indicator: shows a range of colours that match the pH scale, from red for strong acids through green for neutral to purple for strong alkalis.
- Plant extract indicators: coloured flowers and vegetables, such as red cabbage, hibiscus or other brightly coloured petals, can be crushed and soaked in water or alcohol. The coloured extract changes colour in acids and bases.
Making a Plant Indicator
This practical activity is often described in exam questions. Crush coloured petals or red cabbage in a mortar, add a little water or methylated spirit, then filter to get a clear coloured liquid. Add drops to test substances such as lemon juice, soap solution, water and baking soda solution, and record the colour change in a table. Substances that give the same colour belong to the same group.
The pH Scale
The pH scale runs from 0 to 14. A pH of 7 is neutral; pure water is the classic example. Below 7 is acidic, and the lower the number, the stronger the acid. Above 7 is basic or alkaline, and the higher the number, the stronger the base. Lemon juice has a low pH, around 2, while soap solution typically sits around 9 to 10.
Neutralisation
When an acid reacts with a base, they cancel each other out to form a salt and water. This is neutralisation. Everyday uses include:
- Indigestion: antacid tablets neutralise excess stomach acid.
- Insect stings: bee stings are acidic and are sometimes treated with a mild base such as baking soda paste.
- Farming: farmers add lime to acidic soils to raise the pH so crops grow better.
- Teeth: toothpaste is mildly alkaline and helps neutralise acids made by bacteria in the mouth.
Safety With Acids and Bases
Wear eye protection, never taste or smell chemicals directly, add acid to water rather than water to acid, and wash spills on skin immediately with plenty of water. These safety rules are commonly tested alongside the science.
Revision Tips
Make a two-column table: acids on one side, bases on the other, with examples, litmus colour and pH range. Learn three uses of neutralisation with explanations. Then practise questions in the Grade 8 Integrated Science papers and check our mixtures, elements and compounds guide. The exam countdown offers five free questions a day and the What to Revise report shows where to focus. Full papers with answers are in the Monthly Pass (KSh 500 by M-Pesa).