A solution is a homogeneous mixture of two or more substances. It is usually made up of a solute and a solvent. Generally, Solute+Solvent = Solution A solute is any substance that is dissolved in a solvent. For example, when granulated sugar dissolves in water to give a clear sugar solution, the sugar is the solute, while water is the solvent. Relative to the solvent, a solute is usually present in small amounts. A solvent is any substance in which a solute dissolves. It is usually the part of the solution that is present in the largest amount. Two liquids are said to be miscible if they form a single phase (homogeneous solution) or dissolve in each other in all proportions. For example, ethanol and water are miscible. If two liquids do not form a single phase (or do not dissolve in each other) in any appreciable amount, they are said to be immiscible. For example, water and oil are immiscible. When mixed, they separate into two distinct layers. Substances that are only slightly soluble in a given solvent are said to be insoluble. An aqueous solution is one in which water is the solvent. A dilute solution is one that contains a small amount of solute compared to the maximum amount the solvent can dissolve at that temperature. A concentrated solution is one that contains a large amount of solute compared to the maximum amount the solvent can dissolve at that temperature. A saturated solution is one that is in equilibrium with undissolved solute at a given temperature and pressure: Solute(solid) ⇌ Solute(dissolved) In other words, it contains the maximum amount of solute that can be dissolved at that particular temperature. An unsaturated solution contains less solute than the maximum amount (saturated solution) possible at the same temperature. A supersaturated solution is a solution that contains more solute than the saturated solution at the same temperature. This type of solution is very unstable. When it is agitated, or a speck of the solute is added to it, the excess solute will begin to crystallize out rapidly from the solution until the concentration becomes equal to that of the saturated solution.
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