unit 8- MIXING SUBSTANCES

MIXTURES : When two or more substances are mixed together but not chemically joined they are called as mixtures.
Mixtures are absolutely everywhere you look. Mixtures form for most things in nature. Rocks, air, or the ocean, they are just about anything you find. They are substances held together by physical forces, not chemical. This statement means that the individual molecules enjoy being near each other, but their fundamental chemical structure does not change when they enter the mixture.
The methods of separation of mixtures depend on the constituents of the mixtures.
The constituents in a mixture can be separated by easy methods like picking, sieving, or winnowing. You can make a mixture of rice, paper, clips and marbles. These can be separated into different piles of rice, paper, clips and marbles. Some mixtures can be separated by evaporation or condensation.

Solutions : Have you ever put sugar in a glass of milk? After you stir, you can no longer see the sugar. The sugar is still there, as you can taste it. A mixture of sugar and milk is called as solution. By evaporation we can separate the different kinds of matter in solution.

Physical changes: Matter undergoes changes. Changes in matter, in which no new substances are formed are called as physical changes. Changes in temperature can make matter look different. Cooling makes liquid water change to ice. The ice has the same particles, the liquid water has. It can be reverted back to water by melting. Here no new substances are formed. So it is a physical change. Chemical changes : Matter undergoes changes. Some changes produce new substances. Such changes are called as chemical changes. When wood burns, it combines with the oxygen in air and forms smoke and ash.          You notice an orange brown coating on things made of iron when they come in contact with moisture. This is called as rust. Rusting is a chemical change.