Page 103 - Innovator's Science-8

3. Solid and gas Carbon par cles in air ______________

4. Liquid and liquid Ace c acid in water (vinegar) ______________
Oil and water ______________

5. Solid and liquid Sand and water Seawater ______________
6. Solid and solid Baking powder (baking soda ______________
tartaric acid) and Alloys ______________

In earlier classes, you learned how mixtures can be separated to get the

part we need, like picking out stones from rice or filtering tea. These
examples are from daily life, where we keep the useful part and throw away
the rest. But in science, separating mixtures is done for a different reason.
Scientists separate mixtures to get pure substances—materials that are not

mixed with anything else. This helps them study the properties of each
substance more clearly and use them in experiments or making new
products.

WHAT ARE PURE SUBSTANCES?

The word "pure" on packs of things like milk, ghee, and spices means

something different in everyday life and in science. In daily life, "pure"
usually means the product is unadulterated, which means it has no harmful
or cheaper substances mixed in. Adulteration is the illegal and unsafe
process of adding low-quality or cheap substances to a product to increase
quantity or reduce making costs. This makes the product less good and can

even be dangerous to health. For example, water might be added to milk,
or starch might be mixed in with spices. These additions spoil the quality
and can harm people if consumed. So, when a product is called pure, it
means it does not have any such unwanted or harmful additions and is safe

and genuine to use.
In science, however, a pure substance is the one that has no other
substance present in it. For a scientist, even these products that look pure

can be considered impure if they are made of more than one substance.

A pure substance is a kind of matter that cannot be separated into other
kinds of matter by any physical process. When a scientist says that
something is pure, it means that the substance consists of the same type of
particles.

WHAT ARE THE TYPES OF PURE SUBSTANCES?
When water is cooled, it changes from liquid to solid, forming ice. When it is
heated, it changes from liquid to vapor or steam. This shows that water can

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Science-8