MIXTURES AND SOLUTIONS
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.
Mixtures can be categorized as heterogeneous or homogeneous. Heterogeneous mixtures do not appear to be the same throughout. Concrete, conglomerate rock, as well as oil and vinegar are all heterogeneous mixtures. The particles are large enough to be seen and can be separated from the mixture.
Homogeneous mixtures are very well mixed. A salt solution is a homogeneous mixture. In a solution, one substance is dissolved in another. The particles in a solution are atoms, ions, or molecules. The particles are obviously too small to be seen and will not separate out on standing, but can be separated by the process of evaporation.
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.