Types of mixtures, and what 'pure' really means

In everyday talk a mixture is anything mixed, and its parts can be mixtures themselves, like the onion and tomato in poha. In science, every component of a mixture must be a pure substance, such as sugar or salt in water.

Table 8.1 sorts mixtures by the states of their components:

At home we separate a mixture to keep the bit we want and throw the rest away. In science we separate mixtures to get pure substances.

You've seen pure on packets of milk, ghee and spices. The word means different things in shops and in science.

In everyday use, pure means unadulterated. Adulteration is the illegal adding of cheaper or poorer-quality stuff to a product, usually to make more of it or cut costs, like a seller watering down milk. It spoils the product and can be harmful to health.

In science, a pure substance has no other substance in it. It is made of only one kind of particle, and it can't be separated into other kinds of matter by any physical process. By that test, even a packet of "pure" village milk is not pure: it's a mixture of water, fats, proteins, sugars and minerals.