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๐ฌ Think about it
Keep adding sugar to your tea and one day it just won't dissolve any more — it piles up at the bottom. Water can only hold so much, like a sponge that can soak up only so much water. Let's find that limit.
What happens when we keep adding salt to water?
- At first the salt dissolves completely.
- After a few spoons, the salt stops dissolving.
- The extra salt settles at the bottom.
- This shows water has reached its limit.
Example:
Too much sugar in tea stops dissolving and gathers at the bottom of the cup.
In this Activity, we will keep adding salt to water to find how much it can dissolve.
Materials needed
A clean glass tumbler, water, salt, a spoon.
Procedure
1. Take a clean glass tumbler and fill it half with water.
2. Add one spoon of salt and stir well till it dissolves completely.
3. Gradually add a spoonful of salt and stir each time.
4. Observe how many spoons dissolve before salt stops dissolving.
5. Record your observations in Table 9.1.
2. Add one spoon of salt and stir well till it dissolves completely.
3. Gradually add a spoonful of salt and stir each time.
4. Observe how many spoons dissolve before salt stops dissolving.
5. Record your observations in Table 9.1.
Table 9.1 — Dissolution of salt in water
| Amount of salt taken (teaspoon) | Observation (salt dissolves / salt does not dissolve) |
|---|---|
| One | Salt dissolves |
| Two | Salt dissolves |
| Three | Salt dissolves |
| Four | Salt does not dissolve (settles at bottom) |
Observation
A few spoons of salt dissolve fully, but after a point the added salt does not dissolve and settles at the bottom.
Explanation
Water can dissolve only a limited amount of salt at a given temperature. Once it reaches that limit, no more salt dissolves. This shows that a fixed amount of solvent has a fixed dissolving capacity.
โ Summary
- Salt added spoon-wise
- First dissolves fully
- Then settles down
- Water has a limit
What are saturated and unsaturated solutions?
- An unsaturated solution can still dissolve more solute.
- This is at a given temperature.
- A saturated solution cannot dissolve any more solute.
- Extra solute then settles at the bottom.
Unsaturated solution
Saturated solution
Can dissolve more solute.
Cannot dissolve more solute.
No solute settles at the bottom.
Extra solute settles at the bottom.
At a given temperature.
At that particular temperature.
What do concentration, dilute, and concentrated mean?
- Concentration is the amount of solute in a fixed quantity of solution.
- A dilute solution has less solute.
- A concentrated solution has more solute.
- Dilute and concentrated are relative terms.
Example:
One spoon of salt in water is dilute compared to four spoons in the same water, which is concentrated.
What is solubility?
- Solubility is the maximum amount of solute that dissolves.
- It is measured in a fixed quantity of solvent.
- It is taken at a particular temperature.
Example:
The most salt that 100 mL of water can dissolve at a given temperature is its solubility.
๐ Our scientific heritage
- Ningel village in Manipur still makes salt the traditional way.
- Salty water is drawn from wells lined with old tree trunks.
- The salt solution is boiled until the water evaporates.
- The salt crystals are shaped into round "salt cakes".
Important Points
- A fixed amount of solvent dissolves only a limited amount of solute.
- Saturated = no more dissolves; unsaturated = more can dissolve.
- Solubility is the maximum solute a fixed solvent dissolves at a temperature.
โ Test Yourself
-
What is a saturated solution?
View Answer
A solution that cannot dissolve any more solute at that temperature; extra solute settles at the bottom. -
What is an unsaturated solution?
View Answer
A solution that can still dissolve more solute at a given temperature. -
Which is more concentrated: 1 spoon or 4 spoons of salt in the same water?
View Answer
Four spoons. More solute in the same amount of water means a more concentrated solution. -
What is solubility?
View Answer
The maximum amount of solute that can dissolve in a fixed quantity of solvent at a particular temperature. -
Are dilute and concentrated fixed or relative terms?
View Answer
They are relative — a solution is dilute or concentrated only compared with another.
Important Definitions
- Saturated solution — a solution that cannot dissolve any more solute at that temperature.
- Unsaturated solution — a solution that can dissolve more solute at a given temperature.
- Concentration — the amount of solute present in a fixed quantity of solution or solvent.
- Dilute solution — a solution with a small amount of solute.
- Concentrated solution — a solution with a large amount of solute.
- Solubility — the maximum amount of solute that dissolves in a fixed quantity of solvent at a particular temperature.
๐ NCERT Question 2 — Fill in the blanks
Complete the blanks about displacement, solubility, density, and a saturated glucose solution.
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๐ NCERT Question 5 — Which one of the
Which statement about saturated and unsaturated solutions is most appropriate, and why are the others wrong?
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