Acids, Bases and Salts- Quick Revision Notes Class 10

This quick revision notes on Acids, Bases and Salts Class 10 Science includes indicators, properties of acids and bases, pH scale, salts, baking soda, washing soda, bleaching powder, POP and daily life applications of pH.

Acids, Bases and Salts is chapter 2 of class 10 Science of RBSE and one of the most important chapters for board exams.

Here you will find quick revision notes in easy language for fast learning and last-minute revision.

  What are acids?

The substances that produce H⁺ ions in aqueous solution.

Examples: HCl, H₂SO₄, HNO₃ , CH₃COOH

What are Bases?

The substances that produce OH^- in aqueous solution.

Examples – NaOH, KOH , Ca(OH)₂

What are alkalis?

The bases that are soluble in water are known as alkalis.

Examples- – NaOH, KOH, NH₄OH

What are salts?

 The compounds formed by the neutralization reaction between an acid and a base.

Examples- NaCl, KCl, NH₄Cl

What are indicators?

An indicator is a substance what show the nature of a solution (acid or base) by changing its colour or smell.

Types of indicators

(i)    Natural indicators

(ii) Synthetic indicators 

(iii) Olfactory indicators

(i)    Natural indicators- These are obtained from natural sources. Examples – litmus, turmeric, red cabbage, china rose etc

(ii)    Synthetic indicators – These are chemical compounds. Examples – Methyl orange, phenolphthalein.

(iii)   Olfactory indicators- Substances whose smell changes in acidic or basic medium. Examples – onion, vanilla essence, clove oil.

Chemical Properties of Acids

(i)    Reaction with metals – Acid reacts with metal to produce salt and hydrogen gas.

Acid   + Metal →Slat + Hydrogen

HCl + Zn  → ZnSO₄   + H₂↑

(ii)      Reaction with metal carbonates – Salt, carbon dioxide and water are produced.

 Metal carbonates + Acids → salts + CO₂   + Water

   

Na₂CO₃  + 2HCl →2NaCl  + CO₂   + H₂O

CO₂ turns lime water milky due to formation of calcium carbonate.

(iii)    Reaction with Metal hydrogen carbonates - Salt, carbon dioxide and water are produced.

     

NaHCO₃  + HCl → NaCl  + CO₂   + H₂O

(iv)   Reaction with metallic oxide – Salt and water are formed. Metallic oxides are basic in nature.

          

Metal oxide + Acid→ Salt + water

       

CuO + HCl  → CuCl₂ + H₂O

Chemical Properties of Bases

(i)       Reaction with acids – Salt and water are formed. The reaction is called neutralization reaction.

  

Base Acid → Salt +  Water

 

NaOH   + HCl → NaCl  +H₂O

(ii)      Reaction with metals – Salt and hydrogen gas are formed.

   

Zn + NaOH  Na₂ZnO₂  + H₂

Solution of Acids and Bases conduct Electricity

Acids and bases conduct electricity only in aqueous solution because they produce ions when dissolved in water.

When acids are dissolved in water, they produce hydrogen ions.

HCl + H₂O →H₃O⁺   + Cl^-

(Hydrogen ions remain as hydronium ions  in water)

When bases are dissolved in water, they produce hydroxyl ions.

NaOH + H₂O → Na⁺_(aq)  +OH^-_(aq)

These free ions conduct electricity.

 

Strength of Acids and Bases

Strength of acids and bases depends on the concentration of H⁺ and OH^- ions which is measured using the pH scale.

What is pH?

pH is the measure of the concentration of hydrogen ions in a solution.

pH scale range is from 0 to 14.

 

pH	Nature
0-          6	Acidic
7	Neutral
8-14	Basic

 

Lower pH show the more concentration of hydrogen ions.

Higher pH shows the more concentration of hydroxyl ions.

Importance of pH in Everyday Life

i.    Human body – Human body pH range is 7.0- 7.8

ii.   Acid rain – When pH of rain water becomes lower then 5.6, it is called acid rain. It damages plants, soil and pollute water bodies.

iii. Digestive system- Stomach produces hydrochloric acid which helps in digestion. Excess acid is produced during indigestion. Milk of magnesia (Mg(OH)₂) is a mild base which is used as antacid.

iv.Tooth decay – pH of mouth becomes lower than 5.5 causes tooth decay. Toothpaste neutralize acid in the mouth.

v.   Bee sting – Bee sting release acid that causes irritation. Baking soda gives relief.

Salts and their Nature

Salts are formed by the reaction of acid and base. Their nature depends on the strength of acids and bases.

Acid and base	Nature of salt
Strong acid + strong base	Neutral
Strong acid + weak base	Acidic
Weak acid + strong base	Basic

Chemical from Common Salt (NaCl)

(i)       Sodium hydroxide

Chemical formula – NaOH

Preparation – Chlor alkali process

Reaction – 2NaCl + 2H₂O →2NaOH + H₂

(ii)   Bleaching powder

 Chemical formula – Ca(OCl)₂

Preparation – Chlorine is passed on dry calcium hydroxide.

Reaction -  2Ca(OH)₂ + 2Cl₂ →Ca(OCl)₂ +CaCl₂ + 2H₂O

Uses – In water purification, bleaching clothes, disinfectant, oxidizing agent

(iii)   Baking soda

Formula – NaHCO₃

Preparation Method

NaCl + H₂O +CO₂ + NH₃ →NH₄Cl + NaHCO₃

Heating of baking soda

2NaHCO₃→ Na₂CO₃ + H₂O + CO₂

Uses – It is used in baking, as antacid, fire extinguisher

(iv)   Washing Soda

  Formula – Na₂CO₃.10H₂O

Preparation method – Sodium carbonate is obtained by heating of baking soda. Washing soda is obtained by crystallization of sodium carbonate.

  Na₂CO₃.10H₂O → Na₂CO₃ + 10H₂O 

Uses – In glass industry, soap industry, cleaning agent, softening of hard water,

(v)       Plaster of Paris (POP)

Formula – CaSO₄.1/2H₂O

Preparation method

By heating gypsum (CaSO₄.2H₂O)

 

Uses – Plaster on fractured bone, making toys and idols, moulds and casting.

 

Water of Crystallization

The fixed number of water molecules present in one formula unit of a salt is called water of crystallization.

Examples

CuSO₄.5H₂O

Na₂CO₃.10H₂O

CaSO₄.2H₂O

Key Revision Points

i.    Acids produce H⁺ ions.

ii.   Bases produce OH^- ions.

iii. pH is the measure of strength of acids and bases.

iv.  pH affects life, health, soil and environment

v.     NaCl is the raw material in making baking soda, washing soda, sodium hydroxide.

Acids, Bases ands Salts Short Questions with Answers

Q1. What is an acid?

Answer – An acid is a substance that produces H⁺ ions in aqueous solution.

Q2. What is a base?

Answer –  A base is a substance that produces OH^- in aqueous solution.

Q3. What is an alkali?

Answer – A base that is soluble in water is called an alkali.

Q4. What is a slat?

Answer – A salt is formed by the neutralization reaction between an acid and a base.

Q5. Name two natural indicators.

Answer – Litmus and turmeric

Q6. Name two synthetic indicators.

Answer – Methyl oranges and phenolphthalein

Q7. What is an olfactory indicator?

Answer – An indicator that shows change by smell with an acid or base.

Q8. Which gas is evolved when an acid reacts with a metal?

Answer – Hydrogen gas

Q9. Which gas is evolved when an acid reacts with metal carbonate?

Answer – Carbon dioxide

Q10. What is a neutralization reaction?

Answer – When an acid and base reacts to form a salt and water and neutralize each other.

Q11.What is pH scale?

Answer – The scale used to measure acidity or basicity of a solution. Its range is from 0 to 14.

Q12. What is the pH of a neutral solution?

Answer – 7

Q13. What is an antacid?

Answer – A basic substance used to neutralize excess acid in the stomach.

Q14.What is water of crystallization?

Answer – The fixed number of water molecules present in a salt is called water of crystallization.

Q15. What is the full form POP?

Answer – Plaster of Paris