NCERT Textbook: Nature of Matter: Elements, Compounds, and Mixtures | Science Curiosity Class 8 - New NCERT PDF Download

 Page 1


116
Curiosity — Textbook of Science for Grade 8
 
 z Which of the entities in the picture above consist of matter, and 
which of them do not?
 z How can elements be combined to form a compound? 
 z How could the discovery of a compound that absorbs carbon 
dioxide from the air contribute to solving environmental 
challenges?
 z Share your questions  
  ?
8
Nature of Matter?: 
Elements, Compounds, 
and Mixtures 
Probe and ponder
Chapter 8.indd   116 Chapter 8.indd   116 6/28/2025   2:51:17 PM 6/28/2025   2:51:17 PM
Page 2


116
Curiosity — Textbook of Science for Grade 8
 
 z Which of the entities in the picture above consist of matter, and 
which of them do not?
 z How can elements be combined to form a compound? 
 z How could the discovery of a compound that absorbs carbon 
dioxide from the air contribute to solving environmental 
challenges?
 z Share your questions  
  ?
8
Nature of Matter?: 
Elements, Compounds, 
and Mixtures 
Probe and ponder
Chapter 8.indd   116 Chapter 8.indd   116 6/28/2025   2:51:17 PM 6/28/2025   2:51:17 PM
Chapter 8?—?Nature of Matter: Elements, Compounds, and Mixtures
117
Have you ever wondered what the world around you is made 
of? Look around! The staircase you use, the air you breathe, the 
water in your bottle, the food in your lunch box, the clothes and 
shoes you wear, the book you read, the trees outside, the ball you 
play with and even the stick you carry — all of these are examples 
of matter, which you have learnt in earlier grades. 
You have also learnt that all these things are made up of tiny 
particles. Most of the things around us are not made of just one 
substance; rather they are made up of two or more substances 
mixed together. Let us now understand how different substances 
come together to form mixtures.
8.1 What Are Mixtures?
Have you ever wondered what makes 
your poha (Fig. 8.1) so delicious or how 
to make the perfect sprout salad? While 
these dishes may seem very different, they 
share something in common—they are 
both made by mixing several ingredients. 
We observe the mixing of substances in 
everyday life. Sugar dissolved in water 
is also a mixture, and so are soups and 
lemonade. 
When two or more substances are 
mixed, where each substance retains 
its properties, it is called a mixture. 
The individual substances that make up 
a mixture are called its components. 
The components of a mixture do not 
react chemically with each other. In some 
mixtures, the components — like green 
gram, chickpeas, onion, and tomato 
in a sprout salad (Fig. 8.2), are easy to 
see. Such mixtures, where the different 
components are generally visible with the naked eye or with a 
magnifying device, are non-uniform in nature. Can you identify 
a few more examples of non-uniform mixtures around you?
On the other hand, some mixtures have components that 
cannot be seen separately even with the help of a microscope. 
For example, sugar and water particles cannot be seen separately 
in their mixture. Such types of mixtures, where the components 
are evenly distributed and cannot be distinguished, are uniform 
in nature (Fig. 8.3). Can you list a few uniform mixtures?
Fig. 8.1: Poha
Fig. 8.2: Sprout salad
Fig. 8.3: Uniform mixture  
of sugar and water
Chapter 8.indd   117 Chapter 8.indd   117 6/28/2025   2:51:20 PM 6/28/2025   2:51:20 PM
Page 3


116
Curiosity — Textbook of Science for Grade 8
 
 z Which of the entities in the picture above consist of matter, and 
which of them do not?
 z How can elements be combined to form a compound? 
 z How could the discovery of a compound that absorbs carbon 
dioxide from the air contribute to solving environmental 
challenges?
 z Share your questions  
  ?
8
Nature of Matter?: 
Elements, Compounds, 
and Mixtures 
Probe and ponder
Chapter 8.indd   116 Chapter 8.indd   116 6/28/2025   2:51:17 PM 6/28/2025   2:51:17 PM
Chapter 8?—?Nature of Matter: Elements, Compounds, and Mixtures
117
Have you ever wondered what the world around you is made 
of? Look around! The staircase you use, the air you breathe, the 
water in your bottle, the food in your lunch box, the clothes and 
shoes you wear, the book you read, the trees outside, the ball you 
play with and even the stick you carry — all of these are examples 
of matter, which you have learnt in earlier grades. 
You have also learnt that all these things are made up of tiny 
particles. Most of the things around us are not made of just one 
substance; rather they are made up of two or more substances 
mixed together. Let us now understand how different substances 
come together to form mixtures.
8.1 What Are Mixtures?
Have you ever wondered what makes 
your poha (Fig. 8.1) so delicious or how 
to make the perfect sprout salad? While 
these dishes may seem very different, they 
share something in common—they are 
both made by mixing several ingredients. 
We observe the mixing of substances in 
everyday life. Sugar dissolved in water 
is also a mixture, and so are soups and 
lemonade. 
When two or more substances are 
mixed, where each substance retains 
its properties, it is called a mixture. 
The individual substances that make up 
a mixture are called its components. 
The components of a mixture do not 
react chemically with each other. In some 
mixtures, the components — like green 
gram, chickpeas, onion, and tomato 
in a sprout salad (Fig. 8.2), are easy to 
see. Such mixtures, where the different 
components are generally visible with the naked eye or with a 
magnifying device, are non-uniform in nature. Can you identify 
a few more examples of non-uniform mixtures around you?
On the other hand, some mixtures have components that 
cannot be seen separately even with the help of a microscope. 
For example, sugar and water particles cannot be seen separately 
in their mixture. Such types of mixtures, where the components 
are evenly distributed and cannot be distinguished, are uniform 
in nature (Fig. 8.3). Can you list a few uniform mixtures?
Fig. 8.1: Poha
Fig. 8.2: Sprout salad
Fig. 8.3: Uniform mixture  
of sugar and water
Chapter 8.indd   117 Chapter 8.indd   117 6/28/2025   2:51:20 PM 6/28/2025   2:51:20 PM
118
Curiosity — Textbook of Science for Grade 8
Mishraloha was the name given to the mixture of two or more metals 
that had properties distinct from its constituent metals. Ancient 
Indian texts, such as the Charaka Samhita, Susruta Samhita, Rasaratna 
Samucchaya, Rasa Jala Nidhi, etc., mention the use of alloys for 
medicinal purposes. For example, Bronze, also known as Kamsya, is 
an alloy made up of Copper (Tamra, 4 parts) and Tin (Vanga, 1 part), 
was used to improve digestion and boost immunity.
Our scientific heritage
8.1.1 Is air a mixture?
In Curiosity, Grade 6, you learnt about air and its composition in 
the chapter ‘Nature’s Treasures’. Is air a mixture? What kind of 
mixture is it? 
You have learnt that air is a uniform mixture of mainly 
nitrogen, oxygen, argon, carbon dioxide, and water vapour. Out of 
these, oxygen is required by most of the living beings to stay alive. 
It also helps in combustion. Nitrogen, which constitutes about 78% 
of the air, does not take part in combustion. We also learnt that air 
has water vapour in it. When warm air touches a cool surface, the 
water vapour turns into liquid water, forming tiny droplets. Recall 
the experiment where you tested the presence of carbon dioxide 
in the air that we exhale. Let us confirm the presence of carbon 
dioxide in the air.
Activity 8.1: Let us experiment
 z Take a glass tumbler and fill it half with water.
 z Add a small amount of calcium oxide 
(quick lime) slowly to it.
 z What do you observe?
 z Calcium oxide reacts vigorously with 
water to form calcium hydroxide and releases heat. 
Safety first
Perform this step carefully.
A step further
Do you know that stainless steel is also a mixture? 
Stainless steel contains iron, nickel, chromium, 
and a small amount of carbon. They are mixed 
so uniformly that the entire mixture appears 
the same throughout and one cannot see the 
individual substances. Such mixtures are known 
as alloys. Brass, a mixture of copper and zinc, 
and bronze, a mixture of copper and tin, are 
some other examples of alloys (Fig. 8.4).
Fig. 8.4: Utensils made of 
stainless steel, brass, and bronze
Chapter 8.indd   118 Chapter 8.indd   118 6/28/2025   2:51:32 PM 6/28/2025   2:51:32 PM
Page 4


116
Curiosity — Textbook of Science for Grade 8
 
 z Which of the entities in the picture above consist of matter, and 
which of them do not?
 z How can elements be combined to form a compound? 
 z How could the discovery of a compound that absorbs carbon 
dioxide from the air contribute to solving environmental 
challenges?
 z Share your questions  
  ?
8
Nature of Matter?: 
Elements, Compounds, 
and Mixtures 
Probe and ponder
Chapter 8.indd   116 Chapter 8.indd   116 6/28/2025   2:51:17 PM 6/28/2025   2:51:17 PM
Chapter 8?—?Nature of Matter: Elements, Compounds, and Mixtures
117
Have you ever wondered what the world around you is made 
of? Look around! The staircase you use, the air you breathe, the 
water in your bottle, the food in your lunch box, the clothes and 
shoes you wear, the book you read, the trees outside, the ball you 
play with and even the stick you carry — all of these are examples 
of matter, which you have learnt in earlier grades. 
You have also learnt that all these things are made up of tiny 
particles. Most of the things around us are not made of just one 
substance; rather they are made up of two or more substances 
mixed together. Let us now understand how different substances 
come together to form mixtures.
8.1 What Are Mixtures?
Have you ever wondered what makes 
your poha (Fig. 8.1) so delicious or how 
to make the perfect sprout salad? While 
these dishes may seem very different, they 
share something in common—they are 
both made by mixing several ingredients. 
We observe the mixing of substances in 
everyday life. Sugar dissolved in water 
is also a mixture, and so are soups and 
lemonade. 
When two or more substances are 
mixed, where each substance retains 
its properties, it is called a mixture. 
The individual substances that make up 
a mixture are called its components. 
The components of a mixture do not 
react chemically with each other. In some 
mixtures, the components — like green 
gram, chickpeas, onion, and tomato 
in a sprout salad (Fig. 8.2), are easy to 
see. Such mixtures, where the different 
components are generally visible with the naked eye or with a 
magnifying device, are non-uniform in nature. Can you identify 
a few more examples of non-uniform mixtures around you?
On the other hand, some mixtures have components that 
cannot be seen separately even with the help of a microscope. 
For example, sugar and water particles cannot be seen separately 
in their mixture. Such types of mixtures, where the components 
are evenly distributed and cannot be distinguished, are uniform 
in nature (Fig. 8.3). Can you list a few uniform mixtures?
Fig. 8.1: Poha
Fig. 8.2: Sprout salad
Fig. 8.3: Uniform mixture  
of sugar and water
Chapter 8.indd   117 Chapter 8.indd   117 6/28/2025   2:51:20 PM 6/28/2025   2:51:20 PM
118
Curiosity — Textbook of Science for Grade 8
Mishraloha was the name given to the mixture of two or more metals 
that had properties distinct from its constituent metals. Ancient 
Indian texts, such as the Charaka Samhita, Susruta Samhita, Rasaratna 
Samucchaya, Rasa Jala Nidhi, etc., mention the use of alloys for 
medicinal purposes. For example, Bronze, also known as Kamsya, is 
an alloy made up of Copper (Tamra, 4 parts) and Tin (Vanga, 1 part), 
was used to improve digestion and boost immunity.
Our scientific heritage
8.1.1 Is air a mixture?
In Curiosity, Grade 6, you learnt about air and its composition in 
the chapter ‘Nature’s Treasures’. Is air a mixture? What kind of 
mixture is it? 
You have learnt that air is a uniform mixture of mainly 
nitrogen, oxygen, argon, carbon dioxide, and water vapour. Out of 
these, oxygen is required by most of the living beings to stay alive. 
It also helps in combustion. Nitrogen, which constitutes about 78% 
of the air, does not take part in combustion. We also learnt that air 
has water vapour in it. When warm air touches a cool surface, the 
water vapour turns into liquid water, forming tiny droplets. Recall 
the experiment where you tested the presence of carbon dioxide 
in the air that we exhale. Let us confirm the presence of carbon 
dioxide in the air.
Activity 8.1: Let us experiment
 z Take a glass tumbler and fill it half with water.
 z Add a small amount of calcium oxide 
(quick lime) slowly to it.
 z What do you observe?
 z Calcium oxide reacts vigorously with 
water to form calcium hydroxide and releases heat. 
Safety first
Perform this step carefully.
A step further
Do you know that stainless steel is also a mixture? 
Stainless steel contains iron, nickel, chromium, 
and a small amount of carbon. They are mixed 
so uniformly that the entire mixture appears 
the same throughout and one cannot see the 
individual substances. Such mixtures are known 
as alloys. Brass, a mixture of copper and zinc, 
and bronze, a mixture of copper and tin, are 
some other examples of alloys (Fig. 8.4).
Fig. 8.4: Utensils made of 
stainless steel, brass, and bronze
Chapter 8.indd   118 Chapter 8.indd   118 6/28/2025   2:51:32 PM 6/28/2025   2:51:32 PM
Chapter 8?—?Nature of Matter: Elements, Compounds, and Mixtures
119
 z Stir continuously to make a solution of calcium 
hydroxide. This solution is called lime water.
 z Filter it and observe its colour.
 z Leave this colourless solution in a petri dish for a few 
hours (Fig. 8.5a).
 z Keep stirring the solution at regular intervals.
 z What do you observe (Fig. 8.5b)? 
 z Does it turn milky? 
Can you explain why the solution has turned milky?
You know that lime water turns milky when carbon 
dioxide reacts with calcium hydroxide to form calcium 
carbonate (insoluble tiny white particles) and water 
(Fig. 8.5). Since lime water turns milky when exposed to 
air, this activity demonstrates the presence of carbon 
dioxide in the air. 
Calcium hydroxide + Carbon dioxide  Calcium carbonate + Water
Apart from gases, have you ever observed anything 
else present in the air? Have you ever noticed tiny shining 
particles moving in a beam of sunlight entering a dark room 
through a small opening? What are these particles? 
Activity 8.2: Let us explore
 z Take a black sheet of paper. Ensure that it is free from 
any visible dust particles.
 z Place the black sheet of paper undisturbed near an open 
window (Fig. 8.6a), or in the garden, for a few hours.
 z What do you observe?
You may notice tiny particles settled on its surface. You 
may use a magnifying glass to examine the particles more 
closely (Fig. 8.6b).
This shows that dust particles are suspended in the air. 
They are not an integral part of the air and are considered 
pollutants. The nature and the number of dust particles in 
the air may vary from time to time and from place to place.
A step further
The major pollutants present in the air are particulate matter 
(dust, soot) and gases like carbon monoxide, ozone, nitrogen 
dioxide, and sulfur dioxide. The air quality index (AQI) is a 
tool used to describe the air quality.
Lime 
water 
turns 
milky
Lime 
water
Petri 
dish 
Petri 
dish 
(a)
(b)
Fig. 8.5: Lime water turns milky 
in the presence of carbon dioxide
(b)
Fig. 8.6: Black sheet of paper 
(a) with no dust particles; 
(b) with dust particles
(a)
Chapter 8.indd   119 Chapter 8.indd   119 6/28/2025   2:51:37 PM 6/28/2025   2:51:37 PM
Page 5


116
Curiosity — Textbook of Science for Grade 8
 
 z Which of the entities in the picture above consist of matter, and 
which of them do not?
 z How can elements be combined to form a compound? 
 z How could the discovery of a compound that absorbs carbon 
dioxide from the air contribute to solving environmental 
challenges?
 z Share your questions  
  ?
8
Nature of Matter?: 
Elements, Compounds, 
and Mixtures 
Probe and ponder
Chapter 8.indd   116 Chapter 8.indd   116 6/28/2025   2:51:17 PM 6/28/2025   2:51:17 PM
Chapter 8?—?Nature of Matter: Elements, Compounds, and Mixtures
117
Have you ever wondered what the world around you is made 
of? Look around! The staircase you use, the air you breathe, the 
water in your bottle, the food in your lunch box, the clothes and 
shoes you wear, the book you read, the trees outside, the ball you 
play with and even the stick you carry — all of these are examples 
of matter, which you have learnt in earlier grades. 
You have also learnt that all these things are made up of tiny 
particles. Most of the things around us are not made of just one 
substance; rather they are made up of two or more substances 
mixed together. Let us now understand how different substances 
come together to form mixtures.
8.1 What Are Mixtures?
Have you ever wondered what makes 
your poha (Fig. 8.1) so delicious or how 
to make the perfect sprout salad? While 
these dishes may seem very different, they 
share something in common—they are 
both made by mixing several ingredients. 
We observe the mixing of substances in 
everyday life. Sugar dissolved in water 
is also a mixture, and so are soups and 
lemonade. 
When two or more substances are 
mixed, where each substance retains 
its properties, it is called a mixture. 
The individual substances that make up 
a mixture are called its components. 
The components of a mixture do not 
react chemically with each other. In some 
mixtures, the components — like green 
gram, chickpeas, onion, and tomato 
in a sprout salad (Fig. 8.2), are easy to 
see. Such mixtures, where the different 
components are generally visible with the naked eye or with a 
magnifying device, are non-uniform in nature. Can you identify 
a few more examples of non-uniform mixtures around you?
On the other hand, some mixtures have components that 
cannot be seen separately even with the help of a microscope. 
For example, sugar and water particles cannot be seen separately 
in their mixture. Such types of mixtures, where the components 
are evenly distributed and cannot be distinguished, are uniform 
in nature (Fig. 8.3). Can you list a few uniform mixtures?
Fig. 8.1: Poha
Fig. 8.2: Sprout salad
Fig. 8.3: Uniform mixture  
of sugar and water
Chapter 8.indd   117 Chapter 8.indd   117 6/28/2025   2:51:20 PM 6/28/2025   2:51:20 PM
118
Curiosity — Textbook of Science for Grade 8
Mishraloha was the name given to the mixture of two or more metals 
that had properties distinct from its constituent metals. Ancient 
Indian texts, such as the Charaka Samhita, Susruta Samhita, Rasaratna 
Samucchaya, Rasa Jala Nidhi, etc., mention the use of alloys for 
medicinal purposes. For example, Bronze, also known as Kamsya, is 
an alloy made up of Copper (Tamra, 4 parts) and Tin (Vanga, 1 part), 
was used to improve digestion and boost immunity.
Our scientific heritage
8.1.1 Is air a mixture?
In Curiosity, Grade 6, you learnt about air and its composition in 
the chapter ‘Nature’s Treasures’. Is air a mixture? What kind of 
mixture is it? 
You have learnt that air is a uniform mixture of mainly 
nitrogen, oxygen, argon, carbon dioxide, and water vapour. Out of 
these, oxygen is required by most of the living beings to stay alive. 
It also helps in combustion. Nitrogen, which constitutes about 78% 
of the air, does not take part in combustion. We also learnt that air 
has water vapour in it. When warm air touches a cool surface, the 
water vapour turns into liquid water, forming tiny droplets. Recall 
the experiment where you tested the presence of carbon dioxide 
in the air that we exhale. Let us confirm the presence of carbon 
dioxide in the air.
Activity 8.1: Let us experiment
 z Take a glass tumbler and fill it half with water.
 z Add a small amount of calcium oxide 
(quick lime) slowly to it.
 z What do you observe?
 z Calcium oxide reacts vigorously with 
water to form calcium hydroxide and releases heat. 
Safety first
Perform this step carefully.
A step further
Do you know that stainless steel is also a mixture? 
Stainless steel contains iron, nickel, chromium, 
and a small amount of carbon. They are mixed 
so uniformly that the entire mixture appears 
the same throughout and one cannot see the 
individual substances. Such mixtures are known 
as alloys. Brass, a mixture of copper and zinc, 
and bronze, a mixture of copper and tin, are 
some other examples of alloys (Fig. 8.4).
Fig. 8.4: Utensils made of 
stainless steel, brass, and bronze
Chapter 8.indd   118 Chapter 8.indd   118 6/28/2025   2:51:32 PM 6/28/2025   2:51:32 PM
Chapter 8?—?Nature of Matter: Elements, Compounds, and Mixtures
119
 z Stir continuously to make a solution of calcium 
hydroxide. This solution is called lime water.
 z Filter it and observe its colour.
 z Leave this colourless solution in a petri dish for a few 
hours (Fig. 8.5a).
 z Keep stirring the solution at regular intervals.
 z What do you observe (Fig. 8.5b)? 
 z Does it turn milky? 
Can you explain why the solution has turned milky?
You know that lime water turns milky when carbon 
dioxide reacts with calcium hydroxide to form calcium 
carbonate (insoluble tiny white particles) and water 
(Fig. 8.5). Since lime water turns milky when exposed to 
air, this activity demonstrates the presence of carbon 
dioxide in the air. 
Calcium hydroxide + Carbon dioxide  Calcium carbonate + Water
Apart from gases, have you ever observed anything 
else present in the air? Have you ever noticed tiny shining 
particles moving in a beam of sunlight entering a dark room 
through a small opening? What are these particles? 
Activity 8.2: Let us explore
 z Take a black sheet of paper. Ensure that it is free from 
any visible dust particles.
 z Place the black sheet of paper undisturbed near an open 
window (Fig. 8.6a), or in the garden, for a few hours.
 z What do you observe?
You may notice tiny particles settled on its surface. You 
may use a magnifying glass to examine the particles more 
closely (Fig. 8.6b).
This shows that dust particles are suspended in the air. 
They are not an integral part of the air and are considered 
pollutants. The nature and the number of dust particles in 
the air may vary from time to time and from place to place.
A step further
The major pollutants present in the air are particulate matter 
(dust, soot) and gases like carbon monoxide, ozone, nitrogen 
dioxide, and sulfur dioxide. The air quality index (AQI) is a 
tool used to describe the air quality.
Lime 
water 
turns 
milky
Lime 
water
Petri 
dish 
Petri 
dish 
(a)
(b)
Fig. 8.5: Lime water turns milky 
in the presence of carbon dioxide
(b)
Fig. 8.6: Black sheet of paper 
(a) with no dust particles; 
(b) with dust particles
(a)
Chapter 8.indd   119 Chapter 8.indd   119 6/28/2025   2:51:37 PM 6/28/2025   2:51:37 PM
120
Curiosity — Textbook of Science for Grade 8
8.1.2 Types of mixtures
You know that the term ‘mixture’ in common usage refers to the 
mixing of two or more components. The components of a mixture 
may themselves be mixtures, as in poha and sprout salad, or 
pure substances like sugar or common salt dissolved in water. 
However, in science, all the components of a mixture must be 
pure substances only.
Mixtures could be of several types depending on the physical 
state of their components. Some mixtures with their examples are 
shown in Table 8.1. Complete the third column—
S.No. Mixture-type Examples
Uniform or  
non-uniform
1. Gas and gas Air Uniform
2. Gas and liquid Aerated water (soda water)
Oxygen dissolved in water
…………………
…………………
3. Solid and gas Carbon particles in air …………………
4. Liquid and 
liquid
Acetic acid in water (vinegar)  
Oil and water
…………………
…………………
5. Solid and liquid Sand and water 
Seawater
…………………
…………………
6. Solid and solid Baking powder (baking soda and 
tartaric acid)  
Alloys
…………………
 
…………………
Table 8.1: Different types of mixtures
You learnt in earlier grades about the separation of mixtures. It 
is done to separate the components of a mixture. The examples 
discussed were from everyday life, where separation is done 
to obtain the component of interest and other components are 
discarded. However, in science, the purpose of separating a 
mixture is to obtain pure substances.
8.2 What Are Pure Substances?
Have you ever noticed the word ‘pure’ written on the packs of 
some consumables, such as milk, ghee, and spices (Fig. 8.7)? The 
word ‘pure’ has slightly different meanings in common usage 
and in science.
In common usage, ‘pure’ means unadulterated products. 
Adulteration is an illegal process of adding substances which 
are cheaper, or of a poor quality, to a product. This is usually 
done to increase the quantity or reduce the manufacturing cost. 
However, it deteriorates the quality of the product. It can also 
make the product hazardous to health. 
 Fig. 8.7: Some 
consumable items
Chapter 8.indd   120 Chapter 8.indd   120 6/28/2025   2:51:38 PM 6/28/2025   2:51:38 PM