The combination of two or more substances can either result to the formation of Compounds or Mixtures. While Chemical Compounds are formed by two or more elements held together by chemical bonds, Mixtures on the other hand are a combination of different substances which could be elements or compounds that can be separated by Mechanical or Physical Methods. Separation of Compounds on the other hand is by chemical reactions.
Examples of common Compounds are Common Salt (Sodium Chloride - NaCl), Water (H2O), and Table Sugar (Sucrose - C12H22O11). Both Sodium Chloride and Sucrose can dissolve in Water to form a Solution. A salt-water Solution or Sugar-water solution can be separated different physical means that can either recover both both the compounds in the mixture, or just one of the compounds. For example, a mixture of salt and water can be heated to dryness to recover the salt while the water is allowed to evaporate and escape into the Atmosphere. Distillation on the other hand, can be used to recover both the Water and the salt.
Types of Mixtures
There are different kinds of Mixtures that falls within two types of Mixtures. The components of the mixtures could be substances in the three different States of Matter: Solid, Liquid and Gaseous. But it is whether they combine Uniformly or not that determines what type of mixture they could give birth to. This brings us to two types of Mixtures: Homogeneous Mixtures and Heterogeneous Mixtures.
Homogeneous mixtures are uniform Mixtures. That is the components are evenly mixed so that you can obtain the same quantitative composition from random samples. For example, we can say that air contains Nitrogen, 78.08 %. Oxygen, 20.95%. Carbon (IV) Oxide, 0.03% because it is a homogeneous mixture of gases. Solutions are also great examples of homogeneous mixtures. Here, the concept of Solvents and Solutes comes into play. The Solvent is the substance that dissolves the other components. It is the Carrier. The Solvent in a Salt Solution is the water that dissolves the Salt (Solute).
If you dissolve sugar in a bowl of water to form a sugar solution and pour the solution into five different cups the percentage of sugar in the solution in each cup will be the same. This is also true for sea water. Sea water taken from the middle of the sea will contain the same dissolved components combined in the same proportion with that taken from the Beach.
Heterogeneous Mixtures are Mixtures that are not uniform. Suspensions and Colloids are two Examples of heterogeneous mixtures.
Suspensions are mixtures whose constituents are initially suspended and eventually settles down. Raw Starch or Pap can be mixed with water to form a cloudy mixture. But you would soon come back after some time to find that the starch has become a thick mass at the bottom of the container with a clear layer of water at the top. Dust in air is an example that forms a Solid-gas Mixture.
While suspensions are heterogeneous mixtures that must eventually settle, Colloids forms heterogeneous mixtures that will not settle. Colloids brings in the concept of dispersion of the three states of matter. Here, Solid could disperse in gas as in smoke, gas dispersed in liquid as in soapy foams, Liquid dispersed in solid as in Gels like Toothpaste, and solid dispersed in liquid as in Dough.