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💬 Think about it
Pour mustard oil into water and they refuse to mix — the oil floats on top. Since they form clear layers, we can drain them apart. How? With a separating funnel. Let us try.
What are immiscible liquids?
Immiscible liquids
Im-
Not
miscible
Able to mix
↓
Immiscible
= they do
not
mix. Two layers form, the lighter on top. A separating funnel splits them.
How do two liquids behave when mixed?
Two liquids
Mix or stay apart
1. Miscible
They mix fully
Example:
Acetone and water
Vinegar and water
2. Immiscible
They form two layers
Example:
Oil and water
Mustard oil and water
- They are liquids that do not mix together.
- They form separate layers, like oil and water.
- They are examples of heterogeneous mixtures.
Example:
Mustard oil floats as the upper layer and water stays below.
In this Activity, we will use a separating funnel to separate mustard oil from water.
Procedure
1. Pour a mixture of 5 mL mustard oil and 20 mL water into a 50 mL separating funnel.
2. Let it stand undisturbed. You see two separate layers form (Fig. 5.16). The yellow mustard oil is on top and water below, because oil is lighter.
3. Open the stopcock slowly to collect the lower water layer carefully into a container.
4. Close the stopcock when the water is almost fully drained.
5. Collect and discard the small middle portion that may contain both liquids.
6. Collect the oil layer separately by opening the stopcock again.
2. Let it stand undisturbed. You see two separate layers form (Fig. 5.16). The yellow mustard oil is on top and water below, because oil is lighter.
3. Open the stopcock slowly to collect the lower water layer carefully into a container.
4. Close the stopcock when the water is almost fully drained.
5. Collect and discard the small middle portion that may contain both liquids.
6. Collect the oil layer separately by opening the stopcock again.
◆ Summary
- Pour oil and water in a funnel.
- Let layers form.
- Drain the lower water layer.
- Collect the oil separately.
Can a gas be part of a heterogeneous mixture?
Gas mixtures that are homogeneous
Gas mixtures that are heterogeneous
Gas particles move freely in all directions
A solid or a liquid is suspended in the gas
So they mix easily and uniformly with other gases
The suspended particles do not mix uniformly
Hydrogen and oxygen — used as a rocket fuel
Smoke (solid particles in air), fog (water droplets in air), dust in the air
Most
mixtures of gases are homogeneous
Here a gas is one of the components of a heterogeneous mixture
- Most gas-gas mixtures are homogeneous, since gases mix evenly.
- But some mixtures with a gas are heterogeneous.
- Smoke (solids in air), fog (liquid droplets in air) and dust are heterogeneous.
Example:
A hydrogen-oxygen mixture (rocket fuel) is homogeneous, but smoke is heterogeneous.
Important Points
- Immiscible liquids do not mix and form separate layers.
- A separating funnel separates them by their different densities.
- Smoke, fog and dust are heterogeneous mixtures with a gas.
❓ Test Yourself
-
What apparatus separates two immiscible liquids?
View Answer
A separating funnel. -
Why does mustard oil sit on top of water?
View Answer
Oil is lighter (less dense) than water. -
Give one heterogeneous mixture that contains a gas.
View Answer
Smoke, fog or dust in air.
Important Definitions
- Immiscible liquids — liquids that do not mix and form separate layers.
- Separating funnel — apparatus that separates immiscible liquids by their different densities.
📋 NCERT Question 5 — The label on a cooking
The label on a cooking oil pack says one litre (910 g). If this oil is mixed with water, will it form a separate layer? If so, which substance will be on top? How will you separate the two layers? Also, draw the diagram of the apparatus used.
View Answer →
❔ What if …
- … two immiscible liquids of the same density are mixed in a separating funnel?
- How will the layers form?
