Buffer solution

See also: Plug

In Chemistry, a Buffer solution is a solution which maintains roughly same pH in spite of the addition of minor amounts of a Acide, of a bases or of a dilution. If one of these three criteria is not then checked the solution is a pseudo-plug.

In general the plugs are composed of a Weak acid and its combined Base, for example a solution of and of. One finds in human blood a carbon plug of Dioxide (H₂CO₃) and of Hydrogénocarbonate (HCO₃^-) which maintains the pH between 7,35 and 7,45.

The value maximum buffer of a solution is obtained for a équimolaire mixture. In this case pH is equal to the value of the pKa of the couple in solution. The more the buffer solution is concentrated, the more its value buffer is important.

There exist also plugs redox which will fix the potential of the solution roughly and of the ionic plugs which will roughly fix the force ionic of the solutions.

PH of a buffer solution

The pH is maintained constant thanks to the absorption or with the release of an ion H⁺ by the species in presence in the solution.

For example the acetic acid (which is one of the components of the vinegar) gives:

CH₃COOH = CH₃COO^- + H⁺

This reaction is reversible and balances of it. When a compound of this type is present in a solution, the two molecular species CH₃COOH and CH₃COO^- are thus present. Thus, if you add for example an acid to this solution part of those Ci will be consumed in the following reaction:

CH₃COO^- + H⁺ --> CH₃COOH

The proportion of molecules CH₃COO^- and CH₃COOH thus will be modified, but the pH as for him will vary much less than if these molecules were not present in water.

It is what one calls " the tampon" effect; .

See too

• Ampholytic

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