Grade 7 Integrated Science MIXTURES, ELEMENTS AND COMPOUNDS – Acids,bases and indicators Notes
Integrated Science — MIXTURES, ELEMENTS AND COMPOUNDS
Subtopic: Acids, Bases and Indicators (Age 12, Kenya)
- What acids and bases are (simple idea).
- Examples from everyday life in Kenya.
- How indicators show whether a substance is acid or base.
- Simple safe experiments you can do at home or in class.
1. What are acids and bases?
- Acids are substances that taste sour and can turn blue litmus paper red. Examples: lemon juice, vinegar (used in cooking), some soft drinks.
- Bases (alkalis) are substances that feel slippery (like soap) and can turn red litmus paper blue. Examples: soap solution, washing soda, baking soda solution.
2. pH idea (simple)
pH tells us how acidic or basic a substance is.
3. Indicators — how we test acids or bases
An indicator is a substance that changes colour in acid or in base.
- Litmus paper: Blue litmus turns red with acid. Red litmus turns blue with base.
- Phenolphthalein: Colourless in acid, pink in base (used in labs).
- Universal indicator: Gives many colours to estimate pH (like the scale above).
- Natural indicator — red cabbage juice: Cheap and easy. It turns pink/red with acids, purple near neutral, and green/blue with bases.
4. Everyday examples (Kenyan context)
- Acids: Lemon (citric acid), vinegar used in cooking and cleaning, soft drinks (carbonic and citric acids).
- Bases: Soap water used to wash clothes, baking soda (used in baking), some household cleaners (use with care).
- Neutral: Pure water is neutral (pH 7).
5. Simple safe experiments
- Chop a small red/purple cabbage leaf.
- Boil in about 1 cup (250 ml) of water for 10 minutes. Let cool and strain; the purple water is your indicator.
- Put small spoonfuls of the indicator into separate cups. Add a little lemon juice to one cup and a little soap solution or baking soda solution to another.
- Watch the colour change: acid → pink/red, neutral → purple, base → green/blue.
- Put 1 teaspoon of baking soda (sodium bicarbonate) in a small cup.
- Add a little vinegar (about 2–3 teaspoons). Watch the fizz. This is carbon dioxide gas being made.
- Explain: Acid (vinegar) + base (baking soda) → fizz (CO2) + water + salt (neutralisation).
6. Key words
Acid, Base (or Alkali), Indicator, Neutral, pH, Neutralisation.
7. Quick summary
Acids taste sour and turn blue litmus red. Bases feel slippery and turn red litmus blue. Indicators (like litmus or red cabbage juice) change colour to show acids or bases. Everyday items at home are often acids (lemon, vinegar) or bases (soap, baking soda).
8. Try these questions
- Name two acids and two bases you can find at home.
- What colour would blue litmus paper turn if put in lemon juice?
- Describe a safe way to make an indicator using a plant.
- What gas do you see when baking soda reacts with vinegar?
Prepared for Integrated Science — MIXTURES, ELEMENTS AND COMPOUNDS. Use these notes in class or at home for revision. Good luck and enjoy learning!