Immiscible liquids
are liquids that do not mix uniformly with each other.
Pour water into a container that has oil and the two form separate layers.
To separate them, we use a
separating funnel
.
⚗️
Activity 5.6 — Let us separate
In this Activity, we will separate mustard oil from water using a separating funnel, and see why the two form layers in a particular order.
Materials needed
5 mL of mustard oil, 20 mL of water, a 50 mL separating funnel, a laboratory stand, and a conical flask. A
separating funnel
is a glass funnel with a tap at the bottom, and that tap is called a
stopcock
.
Procedure
1. Pour a mixture of 5 mL mustard oil and 20 mL water into the 50 mL separating funnel.
2. Let it stand undisturbed. What do you observe?
3. Two separate layers form — the yellow mustard oil on top and water below.
4. Open the stopcock slowly and collect the lower layer of water carefully into a container.
5. Close the stopcock when the water is almost fully drained.
6. Collect the next small portion, which may contain both liquids, and discard it.
7. Open the stopcock again and collect the layer of oil separately.
Observation
Two clear layers form — yellow mustard oil above and water below — and each can be drained off separately.
Explanation
Mustard oil is lighter than water. For the same volume, the oil has less mass, which means its
density
is lower. Density means mass divided by volume. The liquid with the higher density, water, sinks to the bottom, and the lighter oil floats on top. When the stopcock is opened, gravity drains the heavier water out first.
Two immiscible liquids form two layers because they do not dissolve in each other and their densities differ — the denser one settles below and the lighter one floats above.
→ The middle portion, where the two liquids meet, is always discarded so that both collected liquids stay pure.
◆ Summary
Oil and water form two layers in a separating funnel
The denser water is drained out first through the stopcock
The mixed middle portion is discarded and the oil collected separately
Pause and Ponder
🤔 Pause and Ponder — Question 7
7. Why do immiscible liquids form two separate layers in a separating funnel?
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Answer
Because they do not dissolve in each other, and their
densities are different
— so the heavier liquid settles below and the lighter one floats above.
Explanation
Immiscible liquids do not mix into each other at all.
When left undisturbed, gravity pulls the denser liquid downwards.
The less dense liquid is pushed up and floats on top.
In the oil and water case, water is denser, so water forms the lower layer and yellow mustard oil the upper one.
No mixing plus a density difference means two clean layers, one above the other.
🤔 What if …
Two immiscible liquids of the
same density
are mixed in a separating funnel — how will the layers form?
View Answer
Hide Answer
No clear upper or lower layer would form at all. Since both have the same density, gravity cannot pull one below the other and neither will float above. The two would still not dissolve chemically, but their drops would float randomly inside each other and make a cloudy mixture — which makes separating them by opening the stopcock impossible.
What about mixtures where one part is a gas?
Gas particles are free to move in all directions, so gases mix easily and uniformly with other gases.
Hence most mixtures of gases are
homogeneous
— for example the mixture of hydrogen and oxygen used as rocket fuel.
But when solid or liquid particles are mixed into a gas, the result is
heterogeneous
.
Mixture
What is suspended in air
Smoke
Solid particles suspended in air
Fog
Tiny liquid water droplets present in air
Dust
Solid particles suspended in air
And what about solid–solid mixtures?
Most solid–solid mixtures are
heterogeneous
.
To separate them we use a property that one solid has and the other does not.
If iron nails get mixed into sawdust, a
magnet
picks the nails out, because iron is magnetic.
Now let us look at another technique for separating solid–solid mixtures.
CA Maninder Singh is a Chartered Accountant with 16+ years of practical experience and 20+ years of teaching experience. At Teachoo, he simplifies Accounts, Tax and GST with step-by-step examples so students can apply concepts confidently in exams and real life.
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