We interact with acids, bases, and salts every day — in food, cleaning agents, and even the environment. But what makes them chemically unique?
What are Acids?
Acids are substances that:
- Taste sour (like lemon, vinegar)
- Turn blue litmus paper red
- Release H⁺ ions (protons) in water
- Have a pH less than 7
Examples:
- Hydrochloric acid (HCl)
- Sulphuric acid (H₂SO₄)
- Citric acid (from citrus fruits)
Strong acids: Fully dissociate in water (e.g., HCl)
Weak acids: Partially dissociate (e.g., CH₃COOH)
What Are Bases (Alkalis)?
Bases are substances that:
- Taste bitter, feel slippery
- Turn red litmus paper blue
- Release OH⁻ ions (hydroxide) in water
- Have a pH greater than 7
Alkalis are water-soluble bases.
Examples:
- Sodium hydroxide (NaOH)
- Ammonium hydroxide (NH₄OH)
- Calcium hydroxide (Ca(OH)₂)
Strong bases: Fully dissociate (e.g., NaOH)
Weak bases: Partially dissociate (e.g., NH₃)
What Are Salts?
Salts are formed when an acid reacts with a base (neutralisation) or when a metal reacts with an acid.
General formula:
Acid + Base → Salt + Water
Examples:
- HCl + NaOH → NaCl + H₂O (common salt)
- H₂SO₄ + Ca(OH)₂ → CaSO₄ + 2H₂O
- Acid-Base Indicators
These substances change color depending on the pH:
- Litmus paper: blue → red (acid), red → blue (base)
- Methyl orange: red (acid), yellow (base)
- Phenolphthalein: colourless (acid), pink (base
7 Most Frequently Asked Questions on Acids, Bases, and Salts.
1) What exactly defines an acid or a base?
- Arrhenius definition:
Acid → produces H⁺ in water
Base → produces OH⁻ in water - Brønsted-Lowry definition:
Acid → proton donor
Base → proton acceptor - Lewis definition:
Acid → electron pair acceptor
Base → electron pair donor
2. ) What is the difference between strong/weak and concentrated/dilute acids or bases?
- Strong acid/base: Fully ionizes in water (e.g., HCl, NaOH)
- Weak acid/base: Partially ionizes (e.g., CH₃COOH, NH₃)
- Concentrated: Large amount of acid/base per volume
- Dilute: Small amount of acid/base per volume
3. What is an amphoteric substance?
Amphoteric substances can act both as acids and bases.
Examples:
- Water (H₂O)
- Aluminium hydroxide (Al(OH)₃)
- Zinc oxide (ZnO)
4.) How are salts formed and what types are there?
- Salts are formed from acid-base neutralisation or acid-metal reactions.
Acid + metal → salt + H₂; Acid + carbonate → salt + CO₂ + H₂O.
There are several types:
- Normal salts come from complete neutralisation between an acid and a base, like sodium chloride (NaCl) formed from HCl and NaOH.
- Acid salts result from partial neutralisation and still contain replaceable hydrogen, like sodium bisulphate (NaHSO₄).
- Basic salts arise when there’s an excess of base or a metal hydroxide, like zinc hydroxide chloride (Zn(OH)Cl).
- Double salts are combinations of two different salts crystallised together, such as alum (potassium aluminium sulphate).
Salts can also form when acids react with metals or carbonates, releasing hydrogen gas or carbon dioxide.
5.) What is pH, and how is it calculated?
- pH = –log[H⁺]
- pOH = –log[OH⁻]
- pH + pOH = 14
6.) What are common acid-base indicators and how do they work?
Acid-base indicators are substances that change colour depending on the pH of the solution.
For example:
- Litmus turns red in acidic solutions and blue in basic solutions.
- Methyl orange turns red in acids and yellow in bases.
- Phenolphthalein is colourless in acids but turns pink in bases.
- Choose indicator based on acid-base strength.
7.) Where are acids, bases, and salts used in real life?
Acids, bases, and salts have many important uses in everyday life, industry, and the environment.
For instance:
- In industry, sulphuric acid is used to make fertilisers, and sodium hydroxide is used in soap and paper production.
- At home, vinegar acts as an acid, while bleach contains alkalis, and table salt (sodium chloride) is a common salt used in cooking.
- In the environment, acid rain caused by sulphur dioxide and nitrogen oxides lowers soil and water pH, harming ecosystems; neutralisation methods are often used to treat such problems.
- In biology, the body uses buffers (mixtures of acids and bases) to keep blood pH stable, and hydrochloric acid in the stomach helps digestion.
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