When a lump of sugar is placed in a cup of tea, the sugar disappears but it remains unchanged. We know that sugar is unchanged when it mixes with the water of the tea because we can still taste it. This is an example of a solution. The sugar has dissolved in the hot water of the tea.
A solution is a homogenous (same through-out) mixture of two or more substances. The composition of a solution can vary within certain limits. Two words that we should consider are solvent and solute. Generally we refer to the substance that is present in the larger quantity as the solvent. The solute is present in smaller amounts. In our example the sugar is the solute and the water is the solvent. The sugar dissolves in the water. In solutions where one substance is a liquid the other substance is a gas or solid, the liquid is usually the solvent.
Types of Solutions
Liquid solutions are made by dissolving solids, liquids or gases in liquids. Sugar in water is an example of a solution of a solid dissolved in a liquid. Salt water is another example of a common type of solution.
Gaseous solutions are made by dissolving a gas in another gas. All gases mix in all proportions to produce a homogenous solution. Air is an example of a gaseous solution, which is a solution of oxygen and many other gases dissolved in nitrogen.
A solid solution is formed when one solid substance is mixed with another solid substance to produce a homogenous mixture. Many alloys are solid solutions. For example brass is a solid solution in which zinc atoms have been mixed into solid crystal of copper atoms.