Question

What is difference in the meaning of a pure substance to a common man and a chemist?

Answer 1

Answer:

A chemist calls pure substance to the form of matter which contain all same units (the units may be atoms as in elements, or molecules as in compounds, or formula units as in ionic substaces).

There it should be noted that in a pure form all the units must be same.

For example .:

water is a pure substance because it contain only *H2O* molecules,

similarly gold, silver, copper, iron etc are also pure substances because each contain only one type of atoms,

also Sodium chloride or table salt which contain only the same formula units *NaCl* is a pure substance.

Now those substances which contain different molecules in different proportions, they are called as impure substances.

For example: milk, ghee, wood, soil/clay, cement, steel, glass, (i.e. all those substances which are a sort of mixtures of different compounds)

Common MAN .:

While to a common man the pure substances are all those thing which are 100% in their natural form.

For example,

he consider the milk in which there is no impurity as pure substance, similarly if the water is completely colourless, odourless, and tasteless then for him it is pure.