NCERT Textbook: The Amazing World of Solutes, Solvents, and Solutions | Science Curiosity Class 8 - New NCERT PDF Download

 Page 1


Chapter 9?—?The Amazing World of Solutes, Solvents, and Solutions
134
Curiosity — Textbook of Science for Grade 8
The Amazing World 
of Solutes, Solvents, 
and Solutions 
9
Probe and ponder
 z What do you think is happening in the picture above? 
 z What happens when you add too much sugar to your tea and it 
stops dissolving? How can you solve this problem?
 z Why do sugar and salt dissolve in water but not in oil? Why is 
water considered a good solvent?
 z Why are water bottles usually tall and cylindrical in shape 
instead of spherical?
 Share your questions 
 
  ?
Chapter 9.indd   134 Chapter 9.indd   134 6/28/2025   5:05:29 PM 6/28/2025   5:05:29 PM
Page 2


Chapter 9?—?The Amazing World of Solutes, Solvents, and Solutions
134
Curiosity — Textbook of Science for Grade 8
The Amazing World 
of Solutes, Solvents, 
and Solutions 
9
Probe and ponder
 z What do you think is happening in the picture above? 
 z What happens when you add too much sugar to your tea and it 
stops dissolving? How can you solve this problem?
 z Why do sugar and salt dissolve in water but not in oil? Why is 
water considered a good solvent?
 z Why are water bottles usually tall and cylindrical in shape 
instead of spherical?
 Share your questions 
 
  ?
Chapter 9.indd   134 Chapter 9.indd   134 6/28/2025   5:05:29 PM 6/28/2025   5:05:29 PM
Chapter 9?—?The Amazing World of Solutes, Solvents, and Solutions
135
Fig. 9.3: Magnified schematic picture of a 
solute evenly distributed in a solvent
Solute
Solvent
You must have taken an Oral Rehydration Solution (ORS) at some 
time in your life. ORS is used to treat dehydration by keeping 
your body hydrated. You have learnt to prepare ORS at home in 
Curiosity, Grade 6. You may have wondered why every sip of 
your homemade ORS tastes the same, no matter how much you 
drink. Why does it not taste salty in one sip and sweet in another?  
This is because when you add sugar and salt to water, they 
form a mixture in which the components are evenly distributed 
throughout. 
Can you predict whether this mixture is uniform or 
not (Fig. 9.1)? What happens when chalk powder is mixed 
with water—does it form a uniform mixture? 
When salt and sugar are mixed with water, a uniform 
mixture is formed, whereas when chalk powder or sand, or 
sawdust is mixed with water, the components are not evenly 
distributed. Such mixtures are known as non-uniform 
mixtures (Fig. 9.2a and 9.2b).
Let us explore the science of mixing things together.
9.1 What Are Solute, Solvent, and Solution?
A uniform mixture, such as that of salt or sugar, and water, is 
called a solution. Whenever a solid is 
mixed with a liquid to form a solution, the 
solid component is called the solute, and 
the liquid component is called the solvent. 
The solute dissolves in the solvent to form 
a solution (Fig. 9.3).
Solute + Solvent  Solution
When a solution is formed by mixing 
two liquids, it is not always clear which 
substance is dissolving the other. In such 
cases, the substance present in smaller 
amount is called the solute, while the one 
in larger amount is called the solvent.
We know air is a 
mixture. Would a 
mixture of gases also be 
considered a solution?
Just as water can act as a solvent in liquid solutions, gases can 
also form solution — with air being a common example.
Air is a gaseous solution. Since nitrogen is present in the largest 
amount in the air, it is considered as the solvent, while oxygen, 
argon, carbon dioxide, and other gases are considered as solutes.
Fig. 9.1: Mixture of 
sugar, salt, and water
Fig. 9.2: Mixture of (a) Sand and 
water; (b) Sawdust and water
Chapter 9.indd   135 Chapter 9.indd   135 6/28/2025   5:05:31 PM 6/28/2025   5:05:31 PM
Page 3


Chapter 9?—?The Amazing World of Solutes, Solvents, and Solutions
134
Curiosity — Textbook of Science for Grade 8
The Amazing World 
of Solutes, Solvents, 
and Solutions 
9
Probe and ponder
 z What do you think is happening in the picture above? 
 z What happens when you add too much sugar to your tea and it 
stops dissolving? How can you solve this problem?
 z Why do sugar and salt dissolve in water but not in oil? Why is 
water considered a good solvent?
 z Why are water bottles usually tall and cylindrical in shape 
instead of spherical?
 Share your questions 
 
  ?
Chapter 9.indd   134 Chapter 9.indd   134 6/28/2025   5:05:29 PM 6/28/2025   5:05:29 PM
Chapter 9?—?The Amazing World of Solutes, Solvents, and Solutions
135
Fig. 9.3: Magnified schematic picture of a 
solute evenly distributed in a solvent
Solute
Solvent
You must have taken an Oral Rehydration Solution (ORS) at some 
time in your life. ORS is used to treat dehydration by keeping 
your body hydrated. You have learnt to prepare ORS at home in 
Curiosity, Grade 6. You may have wondered why every sip of 
your homemade ORS tastes the same, no matter how much you 
drink. Why does it not taste salty in one sip and sweet in another?  
This is because when you add sugar and salt to water, they 
form a mixture in which the components are evenly distributed 
throughout. 
Can you predict whether this mixture is uniform or 
not (Fig. 9.1)? What happens when chalk powder is mixed 
with water—does it form a uniform mixture? 
When salt and sugar are mixed with water, a uniform 
mixture is formed, whereas when chalk powder or sand, or 
sawdust is mixed with water, the components are not evenly 
distributed. Such mixtures are known as non-uniform 
mixtures (Fig. 9.2a and 9.2b).
Let us explore the science of mixing things together.
9.1 What Are Solute, Solvent, and Solution?
A uniform mixture, such as that of salt or sugar, and water, is 
called a solution. Whenever a solid is 
mixed with a liquid to form a solution, the 
solid component is called the solute, and 
the liquid component is called the solvent. 
The solute dissolves in the solvent to form 
a solution (Fig. 9.3).
Solute + Solvent  Solution
When a solution is formed by mixing 
two liquids, it is not always clear which 
substance is dissolving the other. In such 
cases, the substance present in smaller 
amount is called the solute, while the one 
in larger amount is called the solvent.
We know air is a 
mixture. Would a 
mixture of gases also be 
considered a solution?
Just as water can act as a solvent in liquid solutions, gases can 
also form solution — with air being a common example.
Air is a gaseous solution. Since nitrogen is present in the largest 
amount in the air, it is considered as the solvent, while oxygen, 
argon, carbon dioxide, and other gases are considered as solutes.
Fig. 9.1: Mixture of 
sugar, salt, and water
Fig. 9.2: Mixture of (a) Sand and 
water; (b) Sawdust and water
Chapter 9.indd   135 Chapter 9.indd   135 6/28/2025   5:05:31 PM 6/28/2025   5:05:31 PM
Chapter 9?—?The Amazing World of Solutes, Solvents, and Solutions
136
Curiosity — Textbook of Science for Grade 8
Ever heard of ...
The Chashni (sugar syrup) of the Indian 
sweet Gulab jamun is made of a large amount 
of sugar (solid) dissolved in a small amount 
of water (liquid). However, the water is still 
considered as the solvent and sugar as  the 
solute (Fig. 9.4)!
Fig. 9.4: Gulab jamuns 
dipped in sugar syrup
9.2  How Much Solute Can a Fixed Amount of 
Solvent Dissolve?
Activity 9.1: Let us investigate
 z Take a clean glass tumbler and fill it 
half with water.
 z Add one spoon of salt into it and stir well 
till it dissolves completely (Fig. 9.5).
 z Gradually add a spoonful of salt into the glass tumbler and 
stir. Observe how many spoons of salt you can add before it 
stops dissolving completely.
 z Record your observations in Table 9.1.
Amount of salt taken  
(teaspoon)
Observation (salt dissolves/salt 
does not dissolve)
One
Two
Three
Four
…
Table 9.1: Dissolution of salt in water
Some discussion points
 z How many spoons of salt were you able to dissolve before 
some of it remained undissolved?
 z What does this indicate about the capacity of water to 
dissolve salt?
What will happen if we 
keep on adding more 
salt in a given amount 
of water?
Chapter 9.indd   136 Chapter 9.indd   136 6/28/2025   5:05:38 PM 6/28/2025   5:05:38 PM
Page 4


Chapter 9?—?The Amazing World of Solutes, Solvents, and Solutions
134
Curiosity — Textbook of Science for Grade 8
The Amazing World 
of Solutes, Solvents, 
and Solutions 
9
Probe and ponder
 z What do you think is happening in the picture above? 
 z What happens when you add too much sugar to your tea and it 
stops dissolving? How can you solve this problem?
 z Why do sugar and salt dissolve in water but not in oil? Why is 
water considered a good solvent?
 z Why are water bottles usually tall and cylindrical in shape 
instead of spherical?
 Share your questions 
 
  ?
Chapter 9.indd   134 Chapter 9.indd   134 6/28/2025   5:05:29 PM 6/28/2025   5:05:29 PM
Chapter 9?—?The Amazing World of Solutes, Solvents, and Solutions
135
Fig. 9.3: Magnified schematic picture of a 
solute evenly distributed in a solvent
Solute
Solvent
You must have taken an Oral Rehydration Solution (ORS) at some 
time in your life. ORS is used to treat dehydration by keeping 
your body hydrated. You have learnt to prepare ORS at home in 
Curiosity, Grade 6. You may have wondered why every sip of 
your homemade ORS tastes the same, no matter how much you 
drink. Why does it not taste salty in one sip and sweet in another?  
This is because when you add sugar and salt to water, they 
form a mixture in which the components are evenly distributed 
throughout. 
Can you predict whether this mixture is uniform or 
not (Fig. 9.1)? What happens when chalk powder is mixed 
with water—does it form a uniform mixture? 
When salt and sugar are mixed with water, a uniform 
mixture is formed, whereas when chalk powder or sand, or 
sawdust is mixed with water, the components are not evenly 
distributed. Such mixtures are known as non-uniform 
mixtures (Fig. 9.2a and 9.2b).
Let us explore the science of mixing things together.
9.1 What Are Solute, Solvent, and Solution?
A uniform mixture, such as that of salt or sugar, and water, is 
called a solution. Whenever a solid is 
mixed with a liquid to form a solution, the 
solid component is called the solute, and 
the liquid component is called the solvent. 
The solute dissolves in the solvent to form 
a solution (Fig. 9.3).
Solute + Solvent  Solution
When a solution is formed by mixing 
two liquids, it is not always clear which 
substance is dissolving the other. In such 
cases, the substance present in smaller 
amount is called the solute, while the one 
in larger amount is called the solvent.
We know air is a 
mixture. Would a 
mixture of gases also be 
considered a solution?
Just as water can act as a solvent in liquid solutions, gases can 
also form solution — with air being a common example.
Air is a gaseous solution. Since nitrogen is present in the largest 
amount in the air, it is considered as the solvent, while oxygen, 
argon, carbon dioxide, and other gases are considered as solutes.
Fig. 9.1: Mixture of 
sugar, salt, and water
Fig. 9.2: Mixture of (a) Sand and 
water; (b) Sawdust and water
Chapter 9.indd   135 Chapter 9.indd   135 6/28/2025   5:05:31 PM 6/28/2025   5:05:31 PM
Chapter 9?—?The Amazing World of Solutes, Solvents, and Solutions
136
Curiosity — Textbook of Science for Grade 8
Ever heard of ...
The Chashni (sugar syrup) of the Indian 
sweet Gulab jamun is made of a large amount 
of sugar (solid) dissolved in a small amount 
of water (liquid). However, the water is still 
considered as the solvent and sugar as  the 
solute (Fig. 9.4)!
Fig. 9.4: Gulab jamuns 
dipped in sugar syrup
9.2  How Much Solute Can a Fixed Amount of 
Solvent Dissolve?
Activity 9.1: Let us investigate
 z Take a clean glass tumbler and fill it 
half with water.
 z Add one spoon of salt into it and stir well 
till it dissolves completely (Fig. 9.5).
 z Gradually add a spoonful of salt into the glass tumbler and 
stir. Observe how many spoons of salt you can add before it 
stops dissolving completely.
 z Record your observations in Table 9.1.
Amount of salt taken  
(teaspoon)
Observation (salt dissolves/salt 
does not dissolve)
One
Two
Three
Four
…
Table 9.1: Dissolution of salt in water
Some discussion points
 z How many spoons of salt were you able to dissolve before 
some of it remained undissolved?
 z What does this indicate about the capacity of water to 
dissolve salt?
What will happen if we 
keep on adding more 
salt in a given amount 
of water?
Chapter 9.indd   136 Chapter 9.indd   136 6/28/2025   5:05:38 PM 6/28/2025   5:05:38 PM
Chapter 9?—?The Amazing World of Solutes, Solvents, and Solutions
137
You might have observed that, initially, the salt completely 
dissolves in the water, forming a solution. After adding a few 
more spoons of salt, a stage comes when the added salt does not 
dissolve completely and the undissolved salt settles at the bottom. 
This indicates that the water can no longer dissolve any more salt 
because it has reached its limit. The solution in which more solute 
can be dissolved at a given temperature, is called an unsaturated 
solution (Fig. 9.5). However, when the solute stops dissolving and 
begins to settle at the bottom, the solution is called a saturated 
solution at that particular temperature (Fig. 9.6).
The amount of solute present in a fixed quantity of solution 
(or solvent) is termed as its concentration. Depending upon the 
amount of solute present in a fixed quantity of solution, it can be 
called a dilute solution (less amount of solute) or a concentrated 
solution (more amount of solute). Dilute and concentrated are  
relative terms. 
So, one can say in Activity 9.1, the solution obtained by 
dissolving one spoon of salt is dilute as compared to that obtained 
by dissolving two or more spoons of salt. 
Can you now reflect?— which solution is more concentrated; 
2 spoons of salt in 100 mL of water or 4 spoons of salt in 50 mL 
of water?
From Activity 9.1, we can say that the maximum amount of 
solute that dissolves in a fixed quantity of the solvent is called its 
solubility. 
Does temperature affect the solubility of a solute?
Let us find out!
9.2.1 How does temperature affect the solubility of a 
solute?
Activity 9.2: Let us experiment  
(Demonstration activity)
 z Take about 50 mL of water in a glass beaker and measure its 
temperature using a laboratory thermometer, say 20 °C.
 z Add a spoonful of baking soda (sodium hydrogen carbonate) 
to the water and stir until it dissolves. 
Continue adding small amounts of baking 
soda while stirring, till some solid baking 
soda is left undissolved at the bottom of 
the beaker.
Safety first
Be careful while using the 
heating device.
Fig. 9.5: Unsaturated 
solution
Fig. 9.6: Saturated 
solution
Solution
Undissolved 
salt
Chapter 9.indd   137 Chapter 9.indd   137 6/28/2025   5:05:40 PM 6/28/2025   5:05:40 PM
Page 5


Chapter 9?—?The Amazing World of Solutes, Solvents, and Solutions
134
Curiosity — Textbook of Science for Grade 8
The Amazing World 
of Solutes, Solvents, 
and Solutions 
9
Probe and ponder
 z What do you think is happening in the picture above? 
 z What happens when you add too much sugar to your tea and it 
stops dissolving? How can you solve this problem?
 z Why do sugar and salt dissolve in water but not in oil? Why is 
water considered a good solvent?
 z Why are water bottles usually tall and cylindrical in shape 
instead of spherical?
 Share your questions 
 
  ?
Chapter 9.indd   134 Chapter 9.indd   134 6/28/2025   5:05:29 PM 6/28/2025   5:05:29 PM
Chapter 9?—?The Amazing World of Solutes, Solvents, and Solutions
135
Fig. 9.3: Magnified schematic picture of a 
solute evenly distributed in a solvent
Solute
Solvent
You must have taken an Oral Rehydration Solution (ORS) at some 
time in your life. ORS is used to treat dehydration by keeping 
your body hydrated. You have learnt to prepare ORS at home in 
Curiosity, Grade 6. You may have wondered why every sip of 
your homemade ORS tastes the same, no matter how much you 
drink. Why does it not taste salty in one sip and sweet in another?  
This is because when you add sugar and salt to water, they 
form a mixture in which the components are evenly distributed 
throughout. 
Can you predict whether this mixture is uniform or 
not (Fig. 9.1)? What happens when chalk powder is mixed 
with water—does it form a uniform mixture? 
When salt and sugar are mixed with water, a uniform 
mixture is formed, whereas when chalk powder or sand, or 
sawdust is mixed with water, the components are not evenly 
distributed. Such mixtures are known as non-uniform 
mixtures (Fig. 9.2a and 9.2b).
Let us explore the science of mixing things together.
9.1 What Are Solute, Solvent, and Solution?
A uniform mixture, such as that of salt or sugar, and water, is 
called a solution. Whenever a solid is 
mixed with a liquid to form a solution, the 
solid component is called the solute, and 
the liquid component is called the solvent. 
The solute dissolves in the solvent to form 
a solution (Fig. 9.3).
Solute + Solvent  Solution
When a solution is formed by mixing 
two liquids, it is not always clear which 
substance is dissolving the other. In such 
cases, the substance present in smaller 
amount is called the solute, while the one 
in larger amount is called the solvent.
We know air is a 
mixture. Would a 
mixture of gases also be 
considered a solution?
Just as water can act as a solvent in liquid solutions, gases can 
also form solution — with air being a common example.
Air is a gaseous solution. Since nitrogen is present in the largest 
amount in the air, it is considered as the solvent, while oxygen, 
argon, carbon dioxide, and other gases are considered as solutes.
Fig. 9.1: Mixture of 
sugar, salt, and water
Fig. 9.2: Mixture of (a) Sand and 
water; (b) Sawdust and water
Chapter 9.indd   135 Chapter 9.indd   135 6/28/2025   5:05:31 PM 6/28/2025   5:05:31 PM
Chapter 9?—?The Amazing World of Solutes, Solvents, and Solutions
136
Curiosity — Textbook of Science for Grade 8
Ever heard of ...
The Chashni (sugar syrup) of the Indian 
sweet Gulab jamun is made of a large amount 
of sugar (solid) dissolved in a small amount 
of water (liquid). However, the water is still 
considered as the solvent and sugar as  the 
solute (Fig. 9.4)!
Fig. 9.4: Gulab jamuns 
dipped in sugar syrup
9.2  How Much Solute Can a Fixed Amount of 
Solvent Dissolve?
Activity 9.1: Let us investigate
 z Take a clean glass tumbler and fill it 
half with water.
 z Add one spoon of salt into it and stir well 
till it dissolves completely (Fig. 9.5).
 z Gradually add a spoonful of salt into the glass tumbler and 
stir. Observe how many spoons of salt you can add before it 
stops dissolving completely.
 z Record your observations in Table 9.1.
Amount of salt taken  
(teaspoon)
Observation (salt dissolves/salt 
does not dissolve)
One
Two
Three
Four
…
Table 9.1: Dissolution of salt in water
Some discussion points
 z How many spoons of salt were you able to dissolve before 
some of it remained undissolved?
 z What does this indicate about the capacity of water to 
dissolve salt?
What will happen if we 
keep on adding more 
salt in a given amount 
of water?
Chapter 9.indd   136 Chapter 9.indd   136 6/28/2025   5:05:38 PM 6/28/2025   5:05:38 PM
Chapter 9?—?The Amazing World of Solutes, Solvents, and Solutions
137
You might have observed that, initially, the salt completely 
dissolves in the water, forming a solution. After adding a few 
more spoons of salt, a stage comes when the added salt does not 
dissolve completely and the undissolved salt settles at the bottom. 
This indicates that the water can no longer dissolve any more salt 
because it has reached its limit. The solution in which more solute 
can be dissolved at a given temperature, is called an unsaturated 
solution (Fig. 9.5). However, when the solute stops dissolving and 
begins to settle at the bottom, the solution is called a saturated 
solution at that particular temperature (Fig. 9.6).
The amount of solute present in a fixed quantity of solution 
(or solvent) is termed as its concentration. Depending upon the 
amount of solute present in a fixed quantity of solution, it can be 
called a dilute solution (less amount of solute) or a concentrated 
solution (more amount of solute). Dilute and concentrated are  
relative terms. 
So, one can say in Activity 9.1, the solution obtained by 
dissolving one spoon of salt is dilute as compared to that obtained 
by dissolving two or more spoons of salt. 
Can you now reflect?— which solution is more concentrated; 
2 spoons of salt in 100 mL of water or 4 spoons of salt in 50 mL 
of water?
From Activity 9.1, we can say that the maximum amount of 
solute that dissolves in a fixed quantity of the solvent is called its 
solubility. 
Does temperature affect the solubility of a solute?
Let us find out!
9.2.1 How does temperature affect the solubility of a 
solute?
Activity 9.2: Let us experiment  
(Demonstration activity)
 z Take about 50 mL of water in a glass beaker and measure its 
temperature using a laboratory thermometer, say 20 °C.
 z Add a spoonful of baking soda (sodium hydrogen carbonate) 
to the water and stir until it dissolves. 
Continue adding small amounts of baking 
soda while stirring, till some solid baking 
soda is left undissolved at the bottom of 
the beaker.
Safety first
Be careful while using the 
heating device.
Fig. 9.5: Unsaturated 
solution
Fig. 9.6: Saturated 
solution
Solution
Undissolved 
salt
Chapter 9.indd   137 Chapter 9.indd   137 6/28/2025   5:05:40 PM 6/28/2025   5:05:40 PM
Chapter 9?—?The Amazing World of Solutes, Solvents, and Solutions
138
Curiosity — Textbook of Science for Grade 8
 z Now, heat the contents to 50 °C while 
stirring (Fig. 9.7). 
 z What happens to the undissolved baking 
soda? 
 z You will observe that it has dissolved.
 z Continue adding more baking soda while 
stirring at this temperature until some 
solid baking soda remains undissolved.
 z Again, heat the contents further to 70 °C 
while continuing to stir. What do you 
observe?
 z The undissolved baking soda dissolves.
 z What do you infer from this experiment? 
Water at 70 °C dissolves more baking soda 
than water at 50 °C. The amount of baking 
soda dissolved in water at 20 °C is even lesser. 
It has been found that for most of 
the substances, the solubility increases with an increase in 
temperature. We can also say that a saturated solution at a 
particular temperature behaves as an unsaturated solution if the 
temperature is increased.
Our scientific heritage
Water has primarily been used as a solvent for the preparation of 
medicinal formulations in Ayurveda, Siddha, and other traditional 
systems of medicine in India. Additionally, drug formulations have 
been prepared using hydro-alcoholic extracts of the herbs. The 
Indian systems of medicine have also referred to the use of oils, 
ghee, milk, and other substances as solvents for drug formulations, 
to help achieve the therapeutic benefits of the drug. 
Be a scientist 
What inspired Asima Chatterjee to work on medicinal plants?
Asima Chatterjee is renowned for her work in 
developing anti-epileptic and anti-malarial drugs. She 
used solvents and solutions extensively to extract and 
isolate important compounds from medicinal plants. 
She earned a Doctorate of Science, becoming the 
second Indian woman to do so after Janaki Ammal. She 
became the first woman to receive the Shanti Swarup 
Bhatnagar Award in the field of chemical science and 
was also honoured with the Padma Bhushan. 
Laboratory stand
Laboratory 
thermometer
Glass rod
Beaker
Water 
containing 
baking soda
Wire gauze
Tripod stand
Spirit lamp
Fig. 9.7: Dissolution of baking soda in water
Chapter 9.indd   138 Chapter 9.indd   138 6/28/2025   5:05:50 PM 6/28/2025   5:05:50 PM