Page 107 - Science Class 6 Times Publication

Pure and impure substances

The substances which are made of only one kind of atoms or molecules

and have denite composition and properties are called pure
substances. Gold, silver, copper, hydrogen, oxygen, carbon dioxide,
water with no dissolved gases and salts, etc are some examples of
pure substances. The water that we use is usually impure because
it contains dissolved oxygen gas, salts, minerals, etc. Rain water is
considered as the purest natural form of water. In fact, it may not be
pure because it may contain dust particles and dissolved gases due
to air pollution.

The substances which are made up of two or more kinds of molecules

and do not have denite composition and properties are called impure
substances. The mixtures are the impure substances. For example,
air, water from natural sources, jelly, fruit juices, cold drinks, tea,
etc are some impure substances. Milk is also an impure substance
because it is a mixture of fat and water.
We need both pure and impure substances in our daily life. Sometimes
impure substances may spoil our health. For example, dirty air and
water (which are impure) can transmit diseases. But, it doesn’t mean
that impure substances are necessarily harmful for health. We use
many things in the form of mixtures. For example, our foods, milk,
tea, medicines, etc are the mixtures or impure substances.

Mixture

A mixture is formed if we mix two or more substances together. A
mixture is an impure substance.

Activity 10.1

To prepare mixtures of different substances
Materials required: Common salt, sand, cooking oil, water, beakers,
spoon, etc
Procedure

1. Take three clean beakers, ll half of them with clean water
and label them as I, II and III respectively.

Times' Crucial Science and Environment 103 Book 6