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What is an aqueous solution?

An aqueous solution is any solution in which water (H 2 0) is the solvent or solvent. The symbol (aq) following the chemical formula of a species in a chemical equation indicates that it is in aqueous solution. The solute is called the compound that dissolves in the liquid medium, the solvent; water in the case of aqueous solutions. For example, the solution of table salt (NaCl), the solute, in water, the solvent, has the following chemical formula.

NaCl(s) → Na + (aq) + Cl – (aq)

Although water is often called a universal solvent, it only dissolves substances that have hydrophilic properties. Hydrophilic compounds are acids, bases, and many salts. Substances that are hydrophobic do not dissolve in water and therefore do not constitute aqueous solutions. Many organic compounds such as fats and oils are hydrophobic.

In the case of electrolytes such as NaCl or KCl, when dissolved in water the molecule completely dissociates into its ions (Na + and Cl – in the case of table salt, or into K + and Cl – in the case of the potassium salt) which, being free ions, which mobilize independently in the liquid medium, allow the solution to conduct electricity. Nonelectrolyte compounds, such as sugar, also dissolve in water, but the molecule does not dissociate and the solution is not conductive.

Characteristics of an aqueous solution

Chemical reactions that occur in an aqueous solution usually occur rapidly, because:

  1. The reactant molecules, the initial compounds in a chemical reaction, are dissociated in solution.
  2. The attractive forces on compounds are weaker when they are dissolved.
  3. The components that are obtained when the molecules dissociate in the solution can move freely in such a way that collisions between the reactants are favored, increasing the speed of the chemical reaction.

Examples of aqueous solutions

Salt in seawater, rain, acid solutions, basic solutions, and saline solutions are examples of aqueous solutions.

On the other hand, everyday examples of non-aqueous solutions, that is, solutions in which the liquid phase, the solvent, is not water, can be vegetable oil, toluene, acetone and carbon tetrachloride. If we have a material that does not dissolve when placed in water, it is simply a mixture, as is the case with sand and water. If there are two liquids that mix but one does not dissolve in the other, or the solid is in such fine particles that it does not settle, we have a suspension; for example, oil in water.

Font

American Chemical Society (2005). Chemistry: A Project of the American Chemical Society . Reverse, 2018.

Cristobal Valenzuela Calahorro. General Chemistry: An Introduction to Theoretical Chemistry . University of Salamanca, 1995.