Looking closely at something we already know a little about.
Mixtures
Two or more things put together, without any new thing being formed.
their Separation
Taking those things back out, one from the other.
What is a mixture?
Mixture
Two or more things
put together in one place
No new thing is formed
each one keeps its own identity
↓
A mixture is formed when two or more substances are mixed
and no new substance is made
When two or more things are mixed and
no new substance
is formed, the result is called a
mixture
.
The words "no new substance" are the important part of this idea.
The things that are mixed
do not lose their identity
.
Salt dissolves in water, but the salt is still salt — that is exactly why we can take it back out.
This one idea is the base of the whole chapter.
Definition
A
mixture
is formed when two or more substances are mixed together in such a way that no new substance is formed, and each substance keeps its own identity.
What are some everyday examples of mixtures?
Mixture
What is mixed
What we see
Salt water
Salt + water
Salt disappears; sea water is the same thing
Sand and water
Sand + water
Sand does not dissolve; it settles down
Oil and water
Cooking oil + water
They never mix; two layers form
Muddy water
Very fine soil + water
Cloudy water after rain
Black sketch pen ink
Several coloured dyes
Looks like one colour, is actually many
These are not laboratory things — all five are found in an ordinary house.
Tea is a mixture too — water, milk, sugar and tea leaves all together.
Air
is a mixture of many gases.
Milk
and
blood
are also mixtures, and both come back later in this chapter.
How do we separate the things in a mixture?
The one rule behind every method
Two substances are mixed
but they are not identical
↓
Find one property where they differ
dissolving, boiling point, density, particle size
↓
Use that difference to pull them apart
Every separation stands on a
difference in one property
.
Two substances differ in some one thing, and we catch hold of that difference.
That property could be — which one dissolves and which does not, what the boiling point is, which is denser, whose particles are bigger, or which one turns straight into vapour on heating.
Important Points
No difference means no separation — this is why we always look for the property first.
The same mixture can sometimes be separated in more than one way.
Which method separates each of those five mixtures?
Mixture
Method
Property used
Salt water
Evaporation (or distillation, if we want the water back too)
Salt has a far higher boiling point than water
Sand and water
Let it settle and pour off the clear water, or filter it
Sand does not dissolve and its particles are big
Oil and water
Separating funnel
They are immiscible and their densities differ
Muddy water
Add a little alum (fitkari), then filter
Particle size — we deliberately make the particles bigger
Black ink
Paper chromatography
Each colour behaves differently with paper and water
Example
In muddy water the mud particles are so fine that they slip through filter paper. Adding
alum
makes them stick together into big clumps, which then settle and can be filtered.
Example
Put a spot of black ink on a paper strip and stand it in water. The colours travel up at different speeds and separate — this is
paper chromatography
.
Mixture = things mixed without losing their identity. Separation = using one difference between them to take them back apart.
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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