Partition equilibrium
Encyclopedia
The most common chemical equilibrium
systems involve reactants and products in the same phase - either all gases or all solutions. However, it is also possible to get equilibria between substances in different phases, such as two liquids that do not mix (are immiscible). Partition equilibria are described by Nernst law.
(NH3) is soluble in both water (aq) and the organic solvent trichloromethane (CHCl3) - two immiscible solvents. If ammonia is first dissolved in water, and then an equal volume of trichloromethane is added, and the two liquids shaken together, the following equilibrium is established:
The equilibrium concentrations of ammonia in each layer can be established by titration
with standard acid solution. It can thus be determined that Kc remains constant, with a value of 0.4 in this case.
or polar
are more soluble in water than in non-polar organic solvents and vice-versa.
that is typically used in gas chromatography (GC) and high performance liquid chromatography
(HPLC). The stationary phase in GC is a high boiling liquid bonded to solid surface and the mobile phase is a gas.
Chemical equilibrium
In a chemical reaction, chemical equilibrium is the state in which the concentrations of the reactants and products have not yet changed with time. It occurs only in reversible reactions, and not in irreversible reactions. Usually, this state results when the forward reaction proceeds at the same...
systems involve reactants and products in the same phase - either all gases or all solutions. However, it is also possible to get equilibria between substances in different phases, such as two liquids that do not mix (are immiscible). Partition equilibria are described by Nernst law.
Example
For example, ammoniaAmmonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
(NH3) is soluble in both water (aq) and the organic solvent trichloromethane (CHCl3) - two immiscible solvents. If ammonia is first dissolved in water, and then an equal volume of trichloromethane is added, and the two liquids shaken together, the following equilibrium is established:
- Kc = [NH3 (CHCl3)]/[NH3 (aq)] (where Kc is the equilibrium constant)
The equilibrium concentrations of ammonia in each layer can be established by titration
Titration
Titration, also known as titrimetry, is a common laboratory method of quantitative chemical analysis that is used to determine the unknown concentration of an identified analyte. Because volume measurements play a key role in titration, it is also known as volumetric analysis. A reagent, called the...
with standard acid solution. It can thus be determined that Kc remains constant, with a value of 0.4 in this case.
Partition coefficient
This particular kind of equilibrium constant measures how a substance distributes or partitions itself between two immiscible solvents. It is called the partition coefficient or distribution coefficient.Polar and non-polar substances
Substances that are ionicIonic compound
In chemistry, an ionic compound is a chemical compound in which ions are held together in a lattice structure by ionic bonds. Usually, the positively charged portion consists of metal cations and the negatively charged portion is an anion or polyatomic ion. Ions in ionic compounds are held together...
or polar
Chemical polarity
In chemistry, polarity refers to a separation of electric charge leading to a molecule or its chemical groups having an electric dipole or multipole moment. Polar molecules interact through dipole–dipole intermolecular forces and hydrogen bonds. Molecular polarity is dependent on the difference in...
are more soluble in water than in non-polar organic solvents and vice-versa.
Partition equilibrium chromatography
Partition equilibrium chromatography is a type of chromatographyChromatography
Chromatography is the collective term for a set of laboratory techniques for the separation of mixtures....
that is typically used in gas chromatography (GC) and high performance liquid chromatography
High performance liquid chromatography
High-performance liquid chromatography , HPLC, is a chromatographic technique that can separate a mixture of compounds and is used in biochemistry and analytical chemistry to identify, quantify and purify the individual components of the mixture.HPLC typically utilizes different types of stationary...
(HPLC). The stationary phase in GC is a high boiling liquid bonded to solid surface and the mobile phase is a gas.