Grade 10 general science Matter and Chemical Reactions – Acids, Bases and Salts Notes

1. Distinguish between acids and bases using the universal indicator and a pH chart.
2. Explain the role of acids and bases in biological and chemical processes.
3. Identify products of chemical reactions of acids and bases.
4. Classify salts according to their behaviour when exposed to air.
5. Outline applications of salts in real-life situations.
6. Promote proper and safe use of salts in day-to-day life.

Key terms (simple definitions)

• Acid: A substance that tastes sour, turns blue litmus red and gives H+ ions in water (e.g. vinegar, lemon).
• Base (alkali): A substance that tastes bitter, feels slippery, turns red litmus blue and gives OH– ions in water (e.g. soap, soda solution).
• Salt: An ionic compound formed when an acid reacts with a base or when acid reacts with a metal or carbonate (e.g. sodium chloride).
• pH: A number (0–14) that tells how acidic or basic a solution is. 7 = neutral (pure water); below 7 = acidic; above 7 = basic.
• Universal indicator: A mixture of dyes that shows different colours for different pH values (handy for testing many substances).

pH chart (visual)

How to tell acids and bases using universal indicator

1. Dip universal indicator paper into the solution or add a few drops of liquid indicator. Observe the colour change.
2. Compare the colour to the pH chart (as above) to read the pH number.
3. If pH < 7: substance is acidic. If pH > 7: substance is basic (alkaline). If pH = 7: neutral.

Roles of acids and bases in biological and chemical processes

• Biological:
  • Stomach acid (HCl) helps digest proteins and kills some microbes.
  • Enzymes work best at particular pH values — blood pH ~7.4 is tightly controlled in the body.
  • Soil pH affects plant growth; farmers add lime (a base) to acidic soils to improve crops.
• Chemical and everyday:
  • Cleaning: many cleaners are basic (soaps) or acidic (vinegar) to dissolve dirt, grease or limescale.
  • Manufacturing: acids/bases are used in making fertilisers, dyes, and in chemical synthesis.
  • Water treatment: alum (a salt) helps settle impurities; acids may be used to control pH.

Products of reactions involving acids and bases (simple reactions)

Classification of salts by behaviour when exposed to air

Applications of salts in daily life (Kenyan examples)

• Cooking & food preservation: sodium chloride (table salt) — seasoning, preserving fish and meat; iodized salt helps prevent iodine deficiency (goitre).
• Agriculture: fertilisers (salts of nitrogen, phosphorus, potassium) help crop growth — used carefully to avoid soil damage.
• Water treatment: alum (a salt) used by households and waterworks to clarify water.
• Health & medicine: Epsom salt (magnesium sulfate) used in baths; sodium bicarbonate (baking soda) used as an antacid in small safe amounts.
• Household uses: salt for cleaning, removing stains, unblocking drains with proper methods, and in soap manufacture.
• Industry and construction: salts used in plaster, ceramics and leather tanning.

Promoting proper and safe use of salts

• Use iodized table salt at home to prevent iodine deficiency (Kenyan public health guidance supports iodized salt).
• Limit salt intake to reduce risk of high blood pressure — avoid excess consumption of salty foods.
• Store salts in airtight, labelled containers to keep them dry and safe from contamination.
• Do not taste unknown chemicals — only taste food-grade salt. Wear gloves when handling strong salts or industrial chemicals.
• Use fertilisers as recommended: excess salts can harm soil and plants and contaminate water sources.
• Dispose of chemical salts safely — follow local guidance (avoid pouring industrial salts down drains).

Suggested learning experiences (classroom & home activities)

1. Make a pH chart using universal indicator paper or red cabbage extract. Test common household solutions (lemon, vinegar, soap, water) and record pH.
2. Carry out a safe neutralization: mix measured vinegar (acetic acid) with measured baking soda solution and observe pH change and CO₂ release. Record the final product (salt: sodium acetate) — explain concept in words.
3. Reaction of acid with carbonate: drop vinegar on a small piece of chalk (calcium carbonate) in a watch glass; collect and test produced gas with limewater (if available) to show CO₂.
4. Observe the behaviour of small samples of different salts left in open dishes for several days and record changes (use safe, labelled samples: table salt, washing soda, calcium chloride if available).
5. Group research and presentation: local uses of salts in Kenyan households (food, agriculture, water treatment) and discussion on safe practices.
6. Role-play: a community health message promoting iodized salt and limiting salt intake.

Short summary for revision

Acids give H+ in water and turn indicator red; bases give OH– in water and turn indicator blue. pH scale (0–14) shows acidity/basicity. Neutralization between an acid and a base produces a salt and water. Salts differ in how they react to air (deliquescent, hygroscopic, efflorescent, stable). Salts are important in cooking, agriculture, water treatment and health — but must be used and stored safely.

Assessment questions (short)

1. Give the pH ranges for strong acids, weak acids, neutral and strong bases.
2. What products form when hydrochloric acid reacts with sodium hydroxide? Write a simple equation.
3. Name one deliquescent salt and one efflorescent salt and describe what they do in air.
4. Explain one biological role of acids in the human body.
5. Mention two safe everyday practices for handling salts at home.