Solution


Solution
Making a saline water solution by dissolving table salt (NaCl) in water. The salt is the solute and the water the solvent.

In chemistry, a solution is a homogeneous mixture composed of only one phase. In such a mixture, a solute is dissolved in another substance, known as a solvent. The solvent does the dissolving.

Contents

Types of solutions

Homogeneous means that the components of the mixture form a single phase. The properties of the mixture (concentration, temperature, density, etc) can be uniformly distributed through the volume but only in absence of diffusion phenomena or after their completion. Usually, the substance present in the greatest amount is considered the solvent. Solvents can be gases, liquids, or solids. One or more components present in the solution other than the solvent are called solutes. The solution has the same physical state as the solvent.

Gas

If the solvent is a gas, only gases are dissolved under any given set of conditions. An example of a gaseous solution is air (oxygen and other gases dissolved in nitrogen). Since interactions between molecules play almost no role, dilute gases form rather trivial solutions. In part of the literature, they are not even classified as solutions, but addressed as mixtures.

Liquid

If the solvent is a liquid, then gases, liquids, and solids can be dissolved. Examples are:

  • Gas in liquid:
    • Oxygen in water.
    • Carbon dioxide in water is a less simple example, because the solution is accompanied by a chemical reaction (formation of ions). Note also that the visible bubbles in carbonated water are not the dissolved gas, but only an effervescence of carbon dioxide that has come out of solution; the dissolved gas itself is not visible since it is dissolved on a molecular level.
  • Liquid in liquid:
    • The mixing of two or more substances of the same chemistry but different concentrations to form a constant.(Homogenization of solutions)
    • Alcoholic beverages are basically solutions of ethanol in water.
  • Solid in liquid:

Counterexamples are provided by liquid mixtures that are not homogeneous: colloids, suspensions, emulsions are not considered solutions.

Body fluids are examples for complex liquid solutions, containing many different solutes. They are electrolytes since they contain solute ions (e.g. potassium and sodium). Furthermore, they contain solute molecules like sugar and urea. Oxygen and carbon dioxide are also essential components of blood chemistry, where significant changes in their concentrations can be a sign of illness or injury.

Solid

If the solvent is a solid, then gases, liquids, and solids can be dissolved.

Solubility

The ability of one compound to dissolve in another compound is called solubility. When a liquid is able to completely dissolve in another liquid the two liquids are miscible. Two substances that can never mix to form a solution are called immiscible.

All solutions have a positive entropy of mixing. The interactions between different molecules or ions may be energetically favored or not. If interactions are unfavorable, then the free energy decreases with increasing solute concentration. At some point the energy loss outweighs the entropy gain, and no more solute particles can be dissolved; the solution is said to be saturated. However, the point at which a solution can become saturated can change significantly with different environmental factors, such as temperature, pressure, and contamination. For some solute-solvent combinations a supersaturated solution can be prepared by raising the solubility (for example by increasing the temperature) to dissolve more solute, and then lowering it (for example by cooling).

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. Together they are called colligative properties. There are several ways to quantify the amount of one compound dissolved in the other compounds collectively called concentration. Examples include molarity, mole fraction, and parts per million (PPM).

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 solutions

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 are able to form hydrogen bonds (protic and aprotic solvents). Water, the most commonly used solvent, is both polar and sustains hydrogen bonds.

Water is a good solvent because the molecules are polar and capable of forming hydrogen bonds(1).

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.

For non-ionic solutes, the general rule is: like dissolves like.

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 with each other, while being incompatible with water.

An example for 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.

Solution preparation from constituent ingredients

It is common practice in laboratories to make a solution directly from its constituent ingredients. There are three cases in practical calculation:

  • Case 1: amount of solvent volume is given.
  • Case 2: amount of solute mass is given.
  • Case 3: amount of final solution volume is given.


In the following equations, A is solvent, B is solute, and C is concentration. Solute volume contribution is considered through ideal solution model.

  • Case 1: amount (ml) of solvent volume VA is given. Solute mass mB = C VA dA /(100-C/dB)
  • Case 2: amount of solute mass mB is given. Solvent volume VA = mB (100/C-1/ dB )
  • Case 3: amount (ml) of final solution volume Vt is given. Solute mass mB = C Vt /100; Solvent volume VA=(100/C-1/ dB) mB
  • Case 2: solute mass is known, VA = mB 100/C
  • Case 3: total solution volume is know, same equation as case 1. VA=Vt; mB = C VA /100


Example: Make 2 g/100ml of NaCl solution with 1 L water Water (properties). The density of resulting solution is considered to be equal to that of water, statement holding especially for dilute solutions, so the density information is not required.
mB = C VA =( 2 / 100 ) x 1000 =20 g

See also

References

IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version:  (2006–) "solution".


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  • solution — [ sɔlysjɔ̃ ] n. f. • déb. XIIIe; soluciun « explication » 1119; lat. solutio, de solvere I ♦ 1 ♦ Opération mentale qui, en substituant une pluralité analysable à un ensemble complexe d éléments entremêlés, parvient à surmonter une difficulté, à… …   Encyclopédie Universelle

  • Solution — So*lu tion (s[ o]*l[=u] sh[u^]n), n. [OE. solucion, OF. solucion, F. solution, fr. L. solutio, fr. solvere, solutum, to loosen, dissolve. See {Solve}.] 1. The act of separating the parts of any body, or the condition of undergoing a separation of …   The Collaborative International Dictionary of English

  • solution — UK US /səˈluːʃən/ noun [C] ► a way to solve a problem or deal with a difficult situation: a solution to/for sth »Education is seen as a solution to the state s economic and employment problems. find/have/offer a solution »She can not find a… …   Financial and business terms

  • solution — Solution. s. f. v. Denoüement d une difficulté. Donnez la solution de cet argument, de cette difficulté. la solution est bonne, n est pas bonne. On appelle, Solution de continuité, La division d un corps continu. Il se dit principalement des… …   Dictionnaire de l'Académie française

  • solution — [sə lo͞o′shən] n. [ME solucion < OFr < L solutio < solutus: see SOLUTE] 1. a) the act, method, or process of solving a problem b) the answer to a problem c) an explanation, clarification, etc. [the solution of a mystery] d) …   English World dictionary

  • solution — I (answer) noun clarification, decipherment, determination, eludication, explanation, explicatio, explication, exposition, finding, illumination, interpretation, key. reason, resolution, right answer, solutio associated concepts: equitable… …   Law dictionary

  • solution — [n1] answer, resolution Band Aid*, clarification, elucidation, explanation, explication, key, pay dirt*, quick fix*, result, solving, the ticket*, unfolding, unraveling, unravelment; concepts 230,661,712 Ant. doubt, problem, quandary, question,… …   New thesaurus

  • solution — Solution, ou payement, Solutio. Solution ou dissolution de mariage, Solutum coniugium vel abruptum …   Thresor de la langue françoyse

  • Solution — (lat.), Lösung (s.d.) …   Kleines Konversations-Lexikon

  • solution — late 14c., a solving or being solved, from O.Fr. solucion, from L. solutionem (nom. solutio) a loosening or unfastening, also a solving, from pp. stem of solvere to loosen, untie, solve, dissolve (see SOLVE (Cf. solve)). Meaning liquid containing …   Etymology dictionary

  • solution — ► NOUN 1) a means of solving a problem. 2) the correct answer to a puzzle. 3) a liquid mixture in which the minor component (the solute) is uniformly distributed within the major component (the solvent). 4) the process of dissolving or the state… …   English terms dictionary


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