Ever wondered why lemons make your tongue tingle while soap feels slippery?
💡 In Simple Words: Acids are sour substances that give up hydrogen ions, bases are bitter and feel soapy because they release hydroxide ions, and when they meet they cancel each other out to make water and a salt. This is the heart of many everyday reactions.
What are Acids, Bases and Salts?
In everyday language, an acid is something that tastes sour and can corrode metal. In chemistry, it’s any substance that can donate a hydrogen ion (H+) to another molecule. A base feels slippery and tastes bitter; chemically it’s a substance that can accept a hydrogen ion or give away a hydroxide ion (OH-). When an acid and a base combine, they form a salt and water – a process called neutralisation.
Acids – simple definition and everyday examples
Think of an acid as a “hydrogen‑donor”. Common acids you see around are:
- Citric acid in oranges
- Acetic acid in vinegar
- Hydrochloric acid in your stomach
All of them release H+ when dissolved in water.
Properties of Acids
- Sour taste – like lemon juice.
- Turns blue litmus red – litmus is a paper that changes colour.
- Conducts electricity because the released H+ ions move in the solution.
- Reacts with metals to give hydrogen gas.
Bases – simple definition and everyday examples
A base is a “hydrogen‑acceptor” or a “hydroxide‑giver”. Everyday bases include:
- Sodium hydroxide in drain cleaners
- Ammonia solution used for cleaning windows
- Baking soda (sodium bicarbonate) in cooking
Properties of Bases
- Bitterness – think of unsweetened cocoa.
- Turns red litmus blue.
- Feels slippery because OH- ions neutralise skin oils.
- Conducts electricity due to free OH- ions.
Salts – how they form and why they matter
A salt is any ionic compound that results when the positive part of an acid (its cation) pairs with the negative part of a base (its anion). Table salt (NaCl) is the classic example, but there are thousands of others used in fertilizers, medicines, and food preservatives.
Acid‑Base Reactions (Neutralisation)
When an acid meets a base, the H+ from the acid and the OH- from the base join to make water (H₂O). The leftovers – the remaining ions – combine to give a salt. A typical equation looks like:
HCl (acid) + NaOH (base) → NaCl (salt) + H₂O (water)
This reaction is the basis of many lab experiments and industrial processes, such as making fertilizers.
Comparing Acids, Bases and Salts
| Feature | Acid | Base | Salt |
|---|---|---|---|
| Key ion in water | H+ | OH- | None (neutral) |
| pH range | 0‑6 (lower = stronger) | 8‑14 (higher = stronger) | ≈7 (neutral) |
| Taste | Sour | Bitter | Usually tasteless |
| Litmus test | Blue → Red | Red → Blue | No change |
| Common example | Vinegar (acetic acid) | Soap (sodium hydroxide) | Table salt (sodium chloride) |
Key points to remember for ICSE exams
- Know the difference between a strong acid (completely dissociates, e.g., HCl) and a weak acid (partially dissociates, e.g., acetic acid).
- Remember the pH scale – 7 is neutral, below 7 is acidic, above 7 is basic.
- Be able to write balanced neutralisation equations and identify the salt formed.
- Understand how to test for acids and bases using litmus paper, phenolphthalein, and universal indicator.
- Recall everyday sources of acids and bases – they help you answer application‑type questions.
📝 Likely Exam Questions
1. Write the balanced equation for the reaction between hydrochloric acid and calcium hydroxide. Name the salt formed.
Answer: 2HCl + Ca(OH)₂ → CaCl₂ + 2H₂O. The salt is calcium chloride.
2. Explain why a solution of sodium carbonate is basic.
Answer: Sodium carbonate (Na₂CO₃) dissociates to give CO₃²⁻ ions, which react with water to produce OH⁻ ions, raising the pH and making the solution basic.
3. A student adds a few drops of phenolphthalein to an unknown solution and it turns pink. What does this indicate?
Answer: Phenolphthalein turns pink in basic solutions, so the unknown solution is a base.
4. Differentiate between a strong acid and a weak acid with examples.
Answer: A strong acid completely ionises in water (e.g., HCl), producing many H⁺ ions. A weak acid only partially ionises (e.g., acetic acid), so fewer H⁺ ions are released.
5. Describe one industrial use of neutralisation reactions.
Answer: Neutralisation is used to treat acidic industrial waste water by adding lime (Ca(OH)₂) to raise the pH and precipitate harmful metals as salts, making the water safe to discharge.