Question

how do we test purity of a substance

Answer 1

There are many ways in which we can test the purity of a substance one of them can be to see if the mixture is homogeneous mixture or heterogeneous mixture.
A homogeneous mixture is a mixture in which all molecules are composed of a similar type.
For example if milk consist of molecules say M then the molecular structure will consist of only Molecules.

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Answer 2

The purity of a substance can be checked in many ways .It exactly means that a substance made up of a same chemical nature and consists of a single kind of particles.
In case we cant call milk as pure because it is made up of water ,proteins and fats which are not of a same kind .
According to science a pure substance can only be a element or compound mixed in a fixed proportions by mass and are cannot be separated by physical methods.
Homogeneous and Heterogeneous mixtures are both not a pure substance as they do mot have same kind of molecules or atoms in them.
In this way we can test the purity of a substance.
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