Acids, Bases and Salts: The Chemistry That Touches Daily Life

Acids, bases and salts are not just laboratory chemicals.
They are present in food, medicines, cleaning agents, soil, water, and even inside the human body.

This chapter explains:

• What acids, bases, and salts really are
• How they behave chemically
• Why pH matters in everyday life
• How these substances are classified and used

Understanding this chapter properly makes later topics like electrochemistry, environmental chemistry, and biology much easier.

Acids: What They Really Are

An acid is a substance that produces hydrogen ions (H⁺) when dissolved in water.
Acids show their acidic nature only in aqueous solution.

Dry acids do not show acidity.

Examples:

• Hydrochloric acid (HCl)
• Sulphuric acid (H₂SO₄)
• Nitric acid (HNO₃)

Properties of Acids

Acids have certain common properties:

• They have a sour taste
• They turn blue litmus red
• They conduct electricity in aqueous solution
• They are generally corrosive

Acids react because of the presence of H⁺ ions.

Chemical Properties of Acids

Reaction with Metals

Acids react with metals to produce salt and hydrogen gas.

Example:

Zn + 2HCl → ZnCl₂ + H₂

Only metals above hydrogen in the reactivity series react with acids.

Reaction with Metal Carbonates and Bicarbonates

Acids react with carbonates to form:

• Salt
• Water
• Carbon dioxide
  Example:

Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂

Reaction of Acids with Bases (Neutralisation Reaction)

Acids react with bases to form salt and water.
This type of reaction is called neutralisation.

Example:

HCl + NaOH → NaCl + H₂O

Explanation:

Hydrochloric acid reacts with sodium hydroxide to form sodium chloride (salt) and water.

The acidic nature of the acid and the basic nature of the base are both neutralised.

Another Example

H₂SO₄ + Ca(OH)₂ → CaSO₄ + 2H₂O

Explanation:

Sulphuric acid reacts with calcium hydroxide to form calcium sulphate and water.

Classification and Industrial Uses of Acids

Strong Acids

They ionise completely in water.

Examples: HCl, H₂SO₄, HNO₃

Uses:

• Fertiliser industry
• Batteries
• Chemical manufacturing

Weak Acids

They ionise partially.
Examples: Acetic acid, Carbonic acid
Uses:

• Food preservation
• Vinegar
• Soft drinks

Bases: The Opposite Nature

A base is a substance that produces hydroxide ions (OH⁻) in aqueous solution.
Examples:

• Sodium hydroxide (NaOH)
• Calcium hydroxide [Ca(OH)₂]

Properties of Bases

• Bitter taste
• Soapy feel
• Turn red litmus blue
• Conduct electricity in solution

Chemical Properties of Bases

Reaction of Bases with Acids (Neutralisation Reaction)

Bases react with acids to form salt and water.

This reaction is called neutralisation.

Example:

NaOH + HCl → NaCl + H₂O

Explanation:

Sodium hydroxide (a base) neutralises hydrochloric acid to form sodium chloride and water.

Reaction of Bases with Non-Metal Oxides

Non-metal oxides like carbon dioxide are acidic in nature.

Bases react with these acidic oxides to form salt and water.

Example:

Ca(OH)₂ + CO₂ → CaCO₃ + H₂O

Explanation:
Calcium hydroxide reacts with carbon dioxide to form calcium carbonate and water.
This reaction is used in the limewater test for CO₂.

Reaction of Bases with Metals

Some strong bases like sodium hydroxide react with amphoteric metals such as zinc and aluminium to produce hydrogen gas.

Example with zinc:

Zn + 2NaOH → Na₂ZnO₂ + H₂

Example with aluminium:

2Al + 2NaOH + 2H₂O → 2NaAlO₂ + 3H₂

Explanation:

Zinc and aluminium react with strong bases to form sodium zincate or sodium aluminate and hydrogen gas.

Basicity of an Acid and Acidity of a Base

Basicity of an Acid

Basicity of an acid = number of replaceable H⁺ ions per molecule.
Examples:

• HCl → Basicity = 1
• H₂SO₄ → Basicity = 2

Acidity of a Base

Acidity of a base = number of OH⁻ ions produced per molecule.

Examples:

• NaOH → Acidity = 1
• Ca(OH)₂ → Acidity = 2

pH Scale: Measuring Acidity and Basicity

The pH scale measures the concentration of H⁺ ions.

• pH < 7 → Acidic
• pH = 7 → Neutral
• pH > 7 → Basic

Lower pH means stronger acid.

Higher pH means stronger base.

Importance of pH in Everyday Life

pH of Soil

Incorrect pH affects crop yield.

pH of Blood

Human blood has pH around 7.4.
Even slight change can be harmful.

pH of Tooth Decay

Acids produced by bacteria lower mouth pH below 5.5 and cause tooth decay.

pH of Water Bodies

Acid rain lowers pH of lakes and rivers, harming aquatic life.

Salts: Neutral Compounds

A salt is formed when an acid reacts with a base.

Salts may be:

• Neutral
• Acidic
• Basic

depending on the nature of acid and base used.

Classification of Salts – Part I

Neutral Salts

Formed from strong acid + strong base.

Example: NaCl

Acidic Salts

Formed from strong acid + weak base.

Example: NH₄Cl

Basic Salts

Formed from weak acid + strong base.

Example: Na₂CO₃

Classification of Salts – Part II

Common Salts and Uses

• Washing soda (Na₂CO₃·10H₂O) → cleaning, glass industry
• Baking soda (NaHCO₃) → baking, fire extinguishers
• Plaster of Paris (CaSO₄·½H₂O) → casts, moulds

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ACIDS, BASES AND SALTS – FAQs