Chemical Properties of Acids and Bases
Senior 2 · Chemistry
Chemical Properties of Acids and Bases
Lesson 4 of 4
20 min
You meet acids and bases every day: in the vinegar on your food, the soap in your hand, the battery in a moto and the lime on a farmer's field. The same properties that make them useful, above all their ability to react and to neutralise, also make them dangerous. A careless splash of sodium hydroxide can blind a person for life. Knowing both sides makes you a safer and better chemist.
| Acid | Uses |
|---|---|
| Sulfuric acid, H2SO4 | electrolyte in car and motorcycle batteries; making fertilisers such as ammonium sulfate; making detergents and paints |
| Hydrochloric acid, HCl | cleaning rust and scale from steel before it is coated; in your stomach, helping to digest food and kill germs |
| Nitric acid, HNO3 | making ammonium nitrate fertiliser; making explosives for mining and quarrying |
| Ethanoic acid, CH3COOH (vinegar) | flavouring and preserving food (pickling) |
| Citric acid and ascorbic acid (vitamin C) | in fruit; added to drinks and foods; vitamin C is essential in the diet |
| Carbonic acid, H2CO3 | gives fizzy drinks their sharp taste |
| Base | Uses |
|---|---|
| Sodium hydroxide, NaOH (caustic soda) | making soap from oils and fats; drain cleaners; making paper; refining vegetable oils |
| Calcium hydroxide, Ca(OH)2 (slaked lime), and calcium oxide | neutralising acidic soils and lakes; treating drinking water and factory waste; mortar, plaster and whitewash |
| Magnesium hydroxide, Mg(OH)2, and aluminium hydroxide, Al(OH)3 | antacids for indigestion |
| Ammonia solution, NH3(aq) | household cleaners (glass and surfaces); making fertilisers |
| Sodium hydrogencarbonate, NaHCO3 | baking powder; antacids; some fire extinguishers |
If an acid or alkali touches your skin or eyes, rinse at once with plenty of cool running water for at least 15 minutes. Remove contaminated clothing, and get medical help, especially for the eyes. Do not try to "neutralise" a splash on the body with another chemical: the neutralisation itself releases heat and wastes precious seconds.
A factory must neutralise 98 kg of sulfuric acid in its waste water with slaked lime. What mass of calcium hydroxide is needed? (H = 1, O = 16, S = 32, Ca = 40)
Tip
For every "use" answer, name the property
Examiners reward the reason: "lime is used on acidic soil because it is a base that neutralises acids", or "sodium hydroxide is used to make soap because it reacts with fats and oils". For dangers, give the hazard and the precaution together: "corrosive, so wear goggles and gloves".
Give one use each of sulfuric acid, sodium hydroxide and magnesium hydroxide.
Solution: Sulfuric acid: electrolyte in car batteries (or making fertilisers). Sodium hydroxide: making soap (or drain cleaner). Magnesium hydroxide: an antacid for indigestion.
A soil has a pH of 4.5. Which should the farmer add: ammonium sulfate, lime or vinegar? Explain.
Solution: Lime. The soil is too acidic; lime is a base that neutralises the acid and raises the pH. Ammonium sulfate and vinegar would make the soil even more acidic.
Why should bleach never be mixed with an acidic toilet cleaner?
Solution: The mixture releases poisonous chlorine gas.
Sodium hydroxide solution splashes onto a student's arm. What should be done?
Solution: Rinse the arm immediately under plenty of cool running water for at least 15 minutes, remove any contaminated clothing, and tell the teacher so that medical help can be obtained if needed.
What mass of calcium hydroxide neutralises 49 kg of sulfuric acid? (H = 1, O = 16, S = 32, Ca = 40)
Solution: 49 kg ÷ 98 g/mol = 500 mol of H2SO4. The ratio is 1 : 1, so 500 mol of Ca(OH)2 is needed: 500 × 74 = 37 000 g = 37 kg.
Summary
Sources and credits
This lesson adapts CC BY-SA material and is shared under CC BY-SA 4.0.
