Acids, Bases and Salts

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• Questions
• Summary

1. Acid is a substance which furnishes H⁺ ions or H₃O⁺ ions when dissolved in water.
2. Acids have one or more replaceable hydrogen atoms.
3. Acids are classified into two types namely organic acids and inorganic acids.
   1. Organic acids:- Acids present in plants and animals (living beings) are organic acids eg. HCOOH, CH₃COOH (Weak acids).
   2. Inorganic acids:- Acids from rocks and minerals are inorganic acids or mineral acids eg. HCl, HNO₃, H₂SO₄ (Strong acids).

The base is a substance which releases hydroxide ions when dissolved in water.

1. Strong bases:- These are bases which ionise completely in aqueous solution eg.NaOH, KOH.
2. Weak bases:- These are bases which ionise partially in aqueous solution eg. NH₄OH, Ca(OH₂)

 

Indicators - Indicators are substances which indicate the acidic or basic nature of the substance/solution by their colour change.

Types of Indicators:

1. Natural indicators
2. Synthetic indicators
3. Olfactory indicators

A universal indicator is a special kind of indicator which is used to measure the strength of acidity or alkalinity. It is prepared by several organic indicators of different of different colours. It is found in green blue solution or in the form of yellow litmus paper.

The colour of some acid-base indicators in the acidic and basic medium are given below.

Neutralisation Reaction

When an acid and base react with each other they neutralize each other and given salt and water

Acid + Base → Salt + Water

Since in the reaction between acid and base both neutralize each other, hence it is also known as neutralization reaction.

Example:
Sodium sulphate and water are formed when a sulphuric acid reacts with sodium hydroxide (a base).

H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O

In similar way, when nitric acid reacts with sodium hydroxide, sodium nitrate and water are formed.

HNO₃ + NaOH → NaNO₃ + H₂O

The reaction of the acid with metal

Acids give hydrogen gas along with respective salt when they react with a metal.
Metal + Acid → Salt + Hydrogen

Example:

Hydrogen gas and zinc chloride are formed when hydrochloric acid reacts with zinc metal.
Zn + 2HCl → ZnCl₂ + H₂

Hydrogen gas and sodium chloride are formed when hydrochloric acid reacts with sodium metal.
2Na + 2HCl → 2NaCl + H₂

The reaction of metal with a base

When alkali (base) reacts with metal, it produces salt and hydrogen gas.

Alkali + Metal → Salt + Hydrogen

Example:

Sodium aluminate and hydrogen gas are formed when sodium hydroxide reacts with aluminium metal.
2NaOH + 2Al + 2H₂O → 2NaAlO₂ + 2H₂

Sodium hydroxide gives hydrogen gas and sodium zincate when reacts with zinc metal.
2NaOH + Zn → Na₂ZnO₂ + H₂

The reaction of acids with metal carbonate:

Acids give carbon dioxide gas and respective salts along with water when they react with metal carbonates.

Metal carbonate + Acid → Salt + Carbon dioxide + Water

Examples:

Sulphuric acid gives calcium sulphate, carbon dioxide gas, calcium sulphate and water when it reacts with calcium carbonate.

CaCO₃ + H₂SO4 → CaSO₄ + CO₂ + H₂O

Reaction of acid with hydrogen carbonates (Bicarbonates)

When an acid reacts with hydrogen carbonates, it gives carbon dioxide gas, respective salt and water.

Acid + Metal hydrogen carbonate → Salt + Carbon dioxide + Water

Examples:

Hydrochloric acid gives carbon dioxide, sodium chloride and water when it reacts with sodium bicarbonate.

NaHCO₃ + HCl → NaCl + CO₂ + H₂O

The reaction of Base with metal hydrogen carbonates/Metal Carbonate

No reaction will occur when base reacts with hydrogen carbonates/Metal Carbonate.

Base + Hydrogen Carbonates/Metal Carbonate →  No reaction

Reaction of acid with metal oxides:

Metal oxides are basic in nature. Thus, when an acid reacts with a metal oxide both neutralize each other. In this reaction, respective salt and water are formed.

Acid + Metal → Oxide Salt + Water

Calcium is a metal, thus calcium oxide is a metallic oxide which is basic in nature. When
an acid; such as hydrochloric acid; reacts with calcium oxide, neutralization reaction takes
place and calcium chloride; along with water; is formed.

2HCl + CaO → CaCl₂ + H₂O

Similarly, when a sulphuric acid reacts with zinc oxide, zinc sulphate and water are formed.

H₂SO₄ + ZnO → ZnCl₂ + H₂O

Base reacts with Non-metallic oxide and produces salt and water.

Ca(OH)2(s) + CO2(g) → CaCO₃(s) + H₂O(g)