Solution facts for kids
In chemistry, a solution is a homogeneous mixture of two or more substances. The substances that are dissolved are called solutes. The substance the solutes are dissolved in is called the solvent. An example is a solid like salt or sugar (which are crystalline solids), dissolved in a liquid (like water). Gases can dissolve in liquids. An example is carbon dioxide or oxygen in water. Liquids may dissolve in other liquids and gases in other gases.
The amount of solute added to the solvent determines the concentration of the solution. The solution with the large amount of solute is called a concentrated solution; the solution with less solute is called a dilute solution.
Examples of solid solutions are alloys and some minerals. For example, brass is an alloy of copper and zinc.
The term "aqueous solution" is used when one of the solvents is water.
Contents
Types
Homogeneous means that the components of the mixture form a single phase. Heterogeneous means that the components of the mixture are of different phase.
Gaseous mixtures
If the solvent is a gas, only gases (non-condensable) or vapors (condensable) are dissolved under a given set of conditions. An example of a gaseous solution is air (oxygen and other gases dissolved in nitrogen).
Liquid solutions
Liquids dissolve gases, other liquids, and solids. An example of a dissolved gas is oxygen in water, which allows fish to breathe under water. An examples of a dissolved liquid is ethanol in water, as found in alcoholic beverages. An example of a dissolved solid is sugar water, which contains dissolved sucrose.
Solid solutions
If the solvent is a solid, then gases, liquids, and solids can be dissolved.
- Gas in solids:
- Liquid in solid:
- Solid in solid:
Solubility
The ability of one compound to dissolve in another compound is called solubility. When a liquid can completely dissolve in another liquid the two liquids are miscible. Two substances that can never mix to form a solution are said to be immiscible.
Usually, the greater the temperature of the solvent, the more of a given solid solute it can dissolve. However, most gases and some compounds exhibit solubilities that decrease with increased temperature. Such behavior is a result of an exothermic enthalpy of solution. Some surfactants exhibit this behaviour. The solubility of liquids in liquids is generally less temperature-sensitive than that of solids or gases.
Properties
The physical properties of compounds such as melting point and boiling point change when other compounds are added. There are several ways to quantify the amount of one compound dissolved in the other compounds collectively called concentration. Examples include molarity, volume fraction, and mole fraction.
The properties of ideal solutions can be calculated by the linear combination of the properties of its components. If both solute and solvent exist in equal quantities (such as in a 50% ethanol, 50% water solution), the concepts of "solute" and "solvent" become less relevant, but the substance that is more often used as a solvent is normally designated as the solvent (in this example, water).
Liquid solution characteristics
In principle, all types of liquids can behave as solvents: liquid noble gases, molten metals, molten salts, molten covalent networks, and molecular liquids. In the practice of chemistry and biochemistry, most solvents are molecular liquids. They can be classified into polar and non-polar, according to whether their molecules possess a permanent electric dipole moment. Another distinction is whether their molecules can form hydrogen bonds (protic and aprotic solvents). Water, the most commonly used solvent, is both polar and sustains hydrogen bonds.
Salts dissolve in polar solvents, forming positive and negative ions that are attracted to the negative and positive ends of the solvent molecule, respectively. If the solvent is water, hydration occurs when the charged solute ions become surrounded by water molecules. A standard example is aqueous saltwater. Such solutions are called electrolytes. Whenever salt dissolves in water ion association has to be taken into account.
Polar solutes dissolve in polar solvents, forming polar bonds or hydrogen bonds. As an example, all alcoholic beverages are aqueous solutions of ethanol. On the other hand, non-polar solutes dissolve better in non-polar solvents. Examples are hydrocarbons such as oil and grease that easily mix, while being incompatible with water.
An example of the immiscibility of oil and water is a leak of petroleum from a damaged tanker, that does not dissolve in the ocean water but rather floats on the surface.
Related pages
See also
In Spanish: Solución para niños
- Molar solution
- Percentage solution (disambiguation)
- Solubility equilibrium
- Total dissolved solids is a common term in a range of disciplines, and can have different meanings depending on the analytical method used. In water quality, it refers to the amount of residue remaining after the evaporation of water from a sample.
- Upper critical solution temperature
- Lower critical solution temperature
- Coil–globule transition
