what is a solvents, solvent classifications.

     A solvent is a chemical substance that dissolves another chemical substance to form a solution of a homogeneous mixture.  The solvent is the component in the solution that is present in the largest amount and determines the physicochemical form of the substance as either solid, liquid or gas.

     The solvent is the part that normally consists of more than 50% of a solution, whereas the solvent is the part that is blended into the solvent.  Typically, this is less than 50% of the solution.

SOLVENT CLASSIFICATIONS:

     Organic solvents and inorganic solvents are two types of solvents.  Inorganic solvents dont contain the element carbon.  

     The most common inorganic solvents are water, and liquid ammonia where as organic solvents, such as alcohols, glycol ether, contain carbon and oxygen in their structure.

     Solvents can be broadly classified into two categories: Polar and non-polar.  A special case is mercury, whose solutions are known as amalgams.

    1) POLAR SOLVENTS :

     A polar solvent is a type of solvent that has large partial charges or dipole moments.  A polar solvent can dissolve ions and other polar compounds.

     Polar solvents are strong dipolar molecules that, as an interface form, also use hydrogen bonding.  Polar solvents also often work by breaking the solutes covalent bonds, inducing ionisation of the solute.

     The most common solvents used in drug delivery systems water, alcohol, aldehydes sugar ketones and other compounds of -OH groups, are typical solutes for which polar solvents are used.

     2) NON POLAR SOLVENTS:

     Non-polar solvents possess little or no dipolar character.  Although they tend to be unable to independently form dipoles, they can utilize induced dipole-induced dipole interactions for dissolving appropriate solutes.

     Ionic and polar solutes have little to non solubility in non-polar solvents.  However, oils, fats and fatty acids dissolve well in non-polar solvents.

     3) APROTIC SOLVENTS:

     Aprotic solvents do not release protons, but may act either as a simple solvent, where polarity constant is significant or they may act as a proton acceptor.

     Chemical bodies such as O-H and N-H bonds are absent from these solvents.  Therefore, hydroxide groups(-OH) and amine groups (-NH2) are absent from aprotic solvents and are unable to form hydrogen bonds.

     4) PROTIC SOLVENTS:

     A protic solvent is made up of molecules that may serve as donors of hydrogen-bonds. Examples of protic solvents contain water, alcohol, and carboxylic acids.  Solvents that are unable to serve as donors to hydrogen-bonds are considered aprotic solvents.  Examples of aprotic solvents include ether, methyene chloride and hexane.