Acids, Bases, and Salts Class 10 Notes

Acids, bases, and salts form the core of Chapter 2 in CBSE Class 10 Science. A clear understanding of these topics is crucial for exam success. These notes offer a detailed summary of their properties, chemical reactions, practical uses, important definitions, and key equations. Scroll down to download the PDF for easy revision.

Subject	Science (Chemistry)
Class	10
Board	CBSE & State Boards
Chapter No.	2
Chapter Name	Acids, Bases, and Salts
Type	Notes pdf
Session	2025-26

Acids	Bases
1. Sour in taste.	1. Bitter in taste.
2. Change the color of the blue litmus to red.	2. Change the color of the red litmus to blue.

Acid-Base Indicators:

Natural Indicators: Litmus, turmeric, red cabbage leaves, turmeric, colored petals of some flowers such as Hydrangea, Petunia, and Geranium.
Synthetic Indicators: Methyl orange, phenolphthalein, etc.

Note: A stain of curry on a white cloth becomes reddish-brown when soap, which is basic in nature, is scrubbed on it.

Chemical Properties of Acids and Bases

1.Acids and Bases in the Laboratory

Indicators changing color

Red litmus solution	Blue litmus solution	Phenolphthalein solution	Methylorgane solution
Acid - No change Base - Blue	Acid - Red Base - No change	Acid - Colorless Base - Pink	Acid - Red Base - Yellow

Olfactory Indicators: There are some substances whose odour changes in acidic or basic media. These are called olfactory indicators. For example vanilla, onion, and clove.

2. How do Acids and Bases react with Metals?

i. Reaction of Acids with Metals:

The metal displaces hydrogen atoms from the acids as hydrogen gas and forms a compound called salt.

Acid + Metal → Salt + Hydrogen gas

Reaction of zinc granules with dilute sulphuric acid and testing hydrogen by burning — *The reaction of zinc granules with dilute sulphuric acid and testing hydrogen by burning*

Reaction: Zn + H2SO4 → ZnSO4 + H2↑

ii. Reactions of Bases with Metals:

2NaOH (aq) + Zn (s) → Na2ZnO2 (s) (Sodium zincate) + H2 (g)

3. How do Metal Carbonates and Metal Hydrogencarbonates React with Acids?

All metal carbonates and hydrogen carbonates react with acids to give corresponding salt, carbon dioxide, and water.

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

Na2CO3 (s) + 2HCl (aq) → 2NaCl (aq) + H2O (l) + CO2 (g)
NaHCO3 (s) + HCl (aq) → NaCl (aq) + H2O (l) + CO2 (g)

On passing the carbon dioxide gas evolved through lime water:

Ca(OH)2 (aq) (lime water) + CO2 (g) → CaCO3 (s) (white precipitate) + H2O (l)

On passing excess carbon dioxide the following reaction takes place:

CaCO3 (s) + H2O (l) + CO2 (g) → Ca(HCO3)2 (aq) (soluble in water)

Limestone, chalk, and marble are different forms of calcium carbonate.

4. How do Acids and Bases React with each other?

Neutralization Reaction: An acid and a base react with each other to give salt and water. This reaction is known as the Neutralization reaction.

Base + Acid → Salt + Water

NaOH (aq) + HCl (aq) → NaCl (aq) + H2O (l)

5. Reaction of Metallic Oxides with Acids

Metal oxide + Acid → Salt + Water

CuO + HCl → CuCl2 (blue-green) + H2O

Metallic oxides are basic oxides.

6. Reaction of a Non-metallic Oxide with Base

Non-Metal oxide + Base → Salt + Water

CO2 + Ca(OH)2 → CaCO3 + H2O

Non-Metallic oxides are acidic oxides.

What do All Acids and Bases have in Common?

Acids contain H+ ions as cations and anions such as Cl– in HCl, NO3– in HNO3, SO42– in H2SO4, and CH3COO– in CH3COOH. Since the cation present in acids is H+ this suggests that acids produce hydrogen ions, H+ (aq), in solution, which are responsible for their acidic properties.

What Happens to an Acid in a Water Solution?

acids bases and salts class 10 notes pdf — *Preparation of HCl gas*

NaCl + H2SO4 → Na2SO4 + HCl

The HCl gas evolved in the above experiment turns moist blue litmus red, but has no effect on dry litmus paper.

This experiment suggests that hydrogen ions in HCl are produced in the presence of water. The separation of H+ ions from HCl molecules cannot occur in the absence of water.

HCl + H2O → H3O+ + Cl–

Hydrogen ions cannot exist alone, but they exist after combining with water molecules. Thus hydrogen ions must always be shown as H+ (aq) or hydronium ions (H3O+).

H+ + H2O → H3O+

What Happens to a Base in a Water Solution?

NaOH(s) + H2O → Na+ (aq) + OH– (aq)

Bases generate hydroxide (OH– ) ions in water. Bases that are soluble in water are called alkalis.

All bases do not dissolve in water. An alkali is a base that dissolves in water.

The acid must always be added slowly to water with constant stirring because:

The process of dissolving an acid or a base in water is a highly exothermic one.
If water is added to concentrated sulphuric acid, the heat generated may cause the mixture to splash out and cause burns.
The glass container may also break due to excessive local heating.

Dilution: Mixing an acid or base with water results in a decrease in the concentration of ions (H3O+/OH– ) per unit volume. Such a process is called dilution.

How Strong Are Acid or Base Solutions?

We can judge the strength of an acid or a base by making use of a universal indicator, which is a mixture of several indicators. The universal indicator shows different colors at different concentrations of hydrogen ions in a solution.

pH Scale

A scale for measuring hydrogen ion concentration in a solution, called pH scale has been developed.
The p in pH stands for ‘potenz’ in German, meaning power.
On the pH scale, we can measure pH generally from 0 (very acidic) to 14 (very alkaline).
pH should be thought of simply as a number that indicates the acidic or basic nature of a solution.
The higher the hydronium ion concentration, the lower the pH value.

The pH of a neutral solution is 7.
Values less than 7 on the pH scale represent an acidic solution.
As the pH value increases from 7 to 14, it represents an increase in OH– ion concentration in the solution, that is, an increase in the strength of the alkali.
Generally, paper impregnated with the universal indicator is used for measuring pH.

acid base and salt class 10 notes — *Variation of pH with the change in concentration of H+ (aq) and OH– (aq) ions*

pH of some common substances shown on a pH paper (colours are only a rough guide)

Importance of pH in everyday life

Are plants and animals pH sensitive?

Our body works within the pH range of 7.0 to 7.8.
When pH of rainwater is less than 5.6, it is called acid rain.
When acid rain flows into the rivers, it lowers the pH of the river water. The survival of aquatic life in such rivers becomes difficult.

pH in our digestive system

It is very interesting to note that our stomach produces hydrochloric acid. It helps in the digestion of food without harming the stomach.
During indigestion, the stomach produces too much acid and this causes pain and irritation. To get rid of this pain, people use bases called antacids.
These antacids neutralize the excess acid. Magnesium hydroxide (Milk of magnesia), a mild base, is often used for this purpose.

pH change as the cause of tooth decay

Tooth decay starts when the pH of the mouth is lower than 5.5.
Tooth enamel, made up of calcium hydroxyapatite (a crystalline form of calcium phosphate) is the hardest substance in the body.
Bacteria present in the mouth produce acids by degradation of sugar and food particles remaining in the mouth after eating.
The best way to prevent this is to clean the mouth after eating food.
Using toothpaste, which is generally basic, for cleaning the teeth can neutralize the excess acid and prevent tooth decay.

Self-defense by animals and plants through chemical warfare

Bee-sting leaves an acid that causes pain and irritation. The use of a mild base like baking soda on the stung area gives relief. Stinging hair of nettle leaves injects methanoic acid causing burning pain.

More About Salts

pH of Salts

Salts of a strong acid and a strong base are neutral with a pH value of 7.
Salts of a strong acid and weak base are acidic with a pH value of less than 7.
Those of a strong base and weak acid are basic in nature with a pH value of more than 7.

Chemicals From Commal Salt

The salt formed by the combination of hydrochloric acid and sodium hydroxide solution is called sodium chloride (NaCl)/Common Salt.

The common salt thus obtained is an important raw material for various materials of daily use, such as sodium hydroxide, baking soda, washing soda, bleaching powder, and many more.

1.Sodium Hydroxide

When electricity is passed through an aqueous solution of sodium chloride (called brine), it decomposes to form sodium hydroxide. The process is called the chlor-alkali process because of the products formed– chlor for chlorine and alkali for sodium hydroxide.
2NaCl (aq) + 2H2O (l) → 2NaOH (aq) + Cl2 (g) + H2 (g)
Chlorine gas is given off at the anode, and hydrogen gas at the cathode. Sodium hydroxide solution is formed near the cathode.

*Important products from the chlor-alkali process*

Bleaching Powder

Chlorine gas is used for the manufacture of bleaching powder.
Bleaching powder is produced by the action of chlorine on dry slaked lime [Ca(OH)2].
Bleaching powder is represented as CaOCl2, though the actual composition is quite complex.
Ca(OH)2 + Cl2 → CaOCl2 + H2O

Bleaching powder is used –

for bleaching cotton and linen in the textile industry, for bleaching wood pulp in paper factories, and for bleaching washed clothes in laundry;
as an oxidizing agent in many chemical industries; and
to make drinking water free from germs.

Baking Soda

The chemical name of the compound is sodium hydrogen carbonate (NaHCO3).
It is produced using sodium chloride as one of the raw materials.
NaCl + H2O + CO2 + NH3 → NH4Cl + NaHCO3
It is a mild non-corrosive basic salt.
The following reaction takes place when it is heated during cooking
2NaHCO3 → Na2CO3 + H2O+CO2

Uses of Baking Soda

For making baking powder, which is a mixture of baking soda (sodium hydrogen carbonate) and a mild edible acid such as tartaric acid.
Carbon dioxide produced during the heating of baking powder can cause bread or cake to rise making them soft and spongy.
Sodium hydrogen carbonate is also an ingredient in antacids. Being alkaline, it neutralizes excess acid in the stomach and provides relief.
It is also used in soda-acid fire extinguishers.

Washing Soda

It is Na2CO3.10H2O.

Uses of washing soda

Sodium carbonate (washing soda) is used in the glass, soap, and paper industries.
It is used in the manufacture of sodium compounds such as borax.
Sodium carbonate can be used as a cleaning agent for domestic purposes.
It is used for removing the permanent hardness of the water.

Water of Crystallization

The water of crystallization is the fixed number of water molecules present in one formula unit of salt. Five water molecules are present in one formula unit of copper sulphate. The chemical formula for hydrated copper sulphate is CuSO4.5H2O.

Plaster of Paris

On heating gypsum (CaSO4.2H2O) at 373 K, it loses water molecules and becomes calcium sulphate hemihydrate (CaSO4.1/2H2O). This is called Plaster of Paris.

Uses of Plaster of Paris

The substance is used by doctors as plaster for supporting fractured bones in the right position.
Plaster of Paris is used for making toys, materials for decoration, and making surfaces smooth.

🧪 NCERT Solutions – Class 10 Science Chapter 2: Acids, Bases and Salts

📘 In-text Questions (Page-wise Solutions)

🔹 Page 18

Q1. You have been provided with three test tubes. One of them contains distilled water and the other two contain an acidic and a basic solution respectively. If you are given only red litmus paper, how will you identify the contents of each test tube?
✅ Answer:
Dip the red litmus paper into each test tube:

Acidic solution: No change (red remains red)
Basic solution: Turns blue
Distilled water: No change (neutral)

🔹 Page 22

Q1. Why should curd and sour substances not be kept in brass or copper vessels?
✅ Answer:
Curd and sour substances contain acids that react with brass or copper to form toxic compounds, which are harmful to health.

Q2. Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example. How will you test for the presence of this gas?
✅ Answer:
Hydrogen gas is released.
Example:
$\text{Zn} + \text{H}_2\text{SO}_4 → \text{ZnSO}_4 + \text{H}_2 ↑$
Test: Bring a burning matchstick near the gas. It burns with a pop sound, confirming hydrogen.

🔹 Page 25

Q1. Why do HCl, HNO₃, etc., show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not?
✅ Answer:
HCl and HNO₃ ionize in water to produce H⁺ ions, showing acidic behavior. Alcohol and glucose do not ionize to produce H⁺ ions, hence are not acidic.

Q2. Why does dry HCl gas not change the colour of dry litmus paper?
✅ Answer:
Dry HCl gas does not ionize to produce H⁺ ions without water. Hence, it does not show acidic behavior and doesn't affect dry litmus.

📙 NCERT Exercise Questions (Back of Chapter)

🔹 Q1. A solution turns red litmus blue, its pH is likely to be –

a) 1
b) 4
c) 5
d) 10
✅ Answer: (d) 10

🔹 Q2. A solution reacts with crushed egg-shells to give a gas that turns lime-water milky. The solution contains –

a) NaCl
b) HCl
c) LiOH
d) KCl
✅ Answer: (b) HCl

🔹 Q3. 10 mL of a solution of NaOH is found to be completely neutralized by 8 mL of a given solution of HCl. If we take 20 mL of the same solution of NaOH, the amount of HCl required to neutralize it will be –

✅ Answer: 16 mL

🔹 Q4. Which one of the following types of medicines is used for treating indigestion?

a) Antibiotic
b) Analgesic
c) Antacid
d) Antiseptic
✅ Answer: (c) Antacid

🔹 Q5. Write word equations and then balanced equations for the reactions taking place when –

a) Dilute sulphuric acid reacts with zinc granules
✅ Word: Sulphuric acid + Zinc → Zinc sulphate + Hydrogen
✅ Balanced:
$\text{Zn} + \text{H}_2\text{SO}_4 → \text{ZnSO}_4 + \text{H}_2 ↑$

b) Dilute hydrochloric acid reacts with magnesium ribbon
✅ Balanced:
$\text{Mg} + 2\text{HCl} → \text{MgCl}_2 + \text{H}_2 ↑$

c) Dilute sulphuric acid reacts with aluminium powder
✅ Balanced:
$2\text{Al} + 3\text{H}_2\text{SO}_4 → \text{Al}_2(\text{SO}_4)_3 + 3\text{H}_2 ↑$

d) Dilute hydrochloric acid reacts with iron filings
✅ Balanced:
$\text{Fe} + 2\text{HCl} → \text{FeCl}_2 + \text{H}_2 ↑$

🔹 Q6. Compounds such as alcohols and glucose also contain hydrogen but are not categorized as acids. Describe an activity to prove it.

✅ Answer:
Activity: Connect a circuit with glucose/alcohol solution and bulb. No conductivity = no ionization = no H⁺ ions ⇒ not acids.

🔹 Q7. Why does distilled water not conduct electricity, whereas rainwater does?

✅ Answer:
Distilled water is pure and lacks ions. Rainwater contains dissolved acidic gases like CO₂, forming ions that conduct electricity.

🔹 Q8. Why do acids not show acidic behavior in the absence of water?

✅ Answer:
Acids ionize in water to release H⁺ ions, responsible for acidic behavior. Without water, ionization doesn't occur.

🔍 CBSE Board Exam Questions (Previous Years + Sample Papers)

🔹 1-Mark Questions

What is the nature of aqueous solutions of sodium carbonate and ammonium chloride?
(CBSE 2020)
📝 Answer:

Sodium carbonate: Basic
Ammonium chloride: Acidic

Name the acid present in ant sting and give its chemical formula.
(CBSE 2019)
📝 Answer:

Methanoic acid (Formic acid), HCOOH

Which gas is evolved when an acid reacts with a metal carbonate? How can it be tested?
(CBSE 2022)
📝 Answer:

Carbon dioxide; tested by passing it through lime water which turns milky.

🔹 2-Mark Questions

Write the chemical equation for the reaction of zinc with hydrochloric acid. What happens when a burning candle is brought near the gas evolved?
(CBSE 2018)
📝 Answer:

The gas burns with a pop sound indicating hydrogen.

Why does dry HCl gas not change the colour of dry litmus paper?
(CBSE 2020)
📝 Answer:
Dry HCl does not ionize without water, so it doesn’t produce H⁺ ions to change litmus color.

🔹 3-Mark Questions

Write any three chemical properties of acids.
(CBSE 2019)
📝 Answer:

React with metals to produce hydrogen
React with metal carbonates to produce CO₂
Turn blue litmus red

A student adds dilute HCl to Zn granules and collects the evolved gas. Name the gas. How will you test its presence? Write the balanced chemical equation.
(CBSE 2023)
📝 Answer:
Gas: Hydrogen
Test: Burns with a pop sound
Equation:

🔹 4-Mark Questions (Assertion & Reason Based)

Assertion (A): A solution of NaOH turns red litmus blue.
Reason (R): NaOH is a strong base.
(CBSE Sample Paper 2024)
📝 Answer:
Both A and R are true, and R is the correct explanation of A.
Assertion (A): Dry ammonia gas turns red litmus blue.
Reason (R): Dry ammonia is basic in nature.
📝 Answer:
A is false, R is true. Dry ammonia does not change litmus color as it needs moisture to form NH₄OH.

🔹 5-Mark Questions

Explain the chemical reaction that takes place during the preparation of washing soda from baking soda. Also mention two uses of washing soda.
(CBSE 2022)
📝 Answer:

Uses:

Softening hard water
Used in glass and paper industries

What is a neutralization reaction? Explain with a suitable example. Give one application of this reaction in daily life.
(CBSE 2018)
📝 Answer:
When acid and base react to form salt and water.

Example:

Application: Antacids neutralize excess stomach acid.

📌 Map of Frequently Asked Topics

Topic	Frequency	Common Question Types
Acids & Bases – Indicators	High	1M, 2M
Metal Reactions with Acids	High	2M, 3M
Reactions of Acid with Carbonates	Medium	2M, 3M
pH Scale	High	Assertion/Reason, 3M
Salts (Washing/Baking Soda)	Medium	3M, 5M

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