A mixture contains substances that are mixed together but are not chemically combined. Air is an example of a mixture as it contains a number of different gases including oxygen, carbon dioxide and nitrogen. A solution is a mixture of a solute and a solvent e.g. salt and water. A solute is the substance which is dissolved (salt) and a solvent is a liquid in which a substance dissolves (water).
Homogeneous and Heterogeneous Mixture Homogeneous These mixtures are made up of more than one phase or of different parts and can be separated physically. The different components are visibly distinguishable from one another. Ex: A chocolate chip cookie, a piece of quartz containing a vein of gold. granite, oil and water, and a bowl of raisin bran cereal.
Heterogeneous Have only one phase, or have a uniform appearance throughout, and any portion of the sample has the same properties and composition. Each region of a sample is identical to all other regions of the sample. Ex: salt water and rubbing alcohol, are considered homogeneous because they are in one phase.
Sometimes it is necessary to separate solutions and to do this we have a number of separating techniques including filtration, evaporation, and distillation.
Filtration Is the method used for separating an insoluble solid (a solid that will not dissolve) from a liquid. A tea bag is an everyday example of a filter. It works because it has small holes to let the liquid through but blocks the larger pieces of solid.
Evaporation Is a method of separating a soluble solid from a solvent e.g. salt and water.
Distillation Distillation is a process involving the vaporization of a liquid by boiling it and then condensing the vapor by cooling it. It can be used to purify a liquid (e.g. to obtain pure water from a salt-water solution).