Aqueous and non aqueous solution

Aqueous

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Aqueous means pertaining to, related to, similar to, or dissolved in water.
An aqueous solution is a solution in which the solvent is water (rather than, for example, alcohol or ether). It is usually shown in chemical equations as a subscript (aq).
Aqueous humor is the transparent fluid occupying the space between the crystalline lens and the cornea of the eye.





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Non-aqueous titration

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Non-aqueous titration is the titration of substances dissolved in non-aqueous solvents. It is the most common titrimetric procedure used in pharmacopoeial assays and serves a double purpose:

it is suitable for the titration of very weak acids and very weak bases, and
it provides a solvent in which organic compounds are soluble.
The most commonly used procedure is the titration of organic bases with perchloric acid in anhydrous acetic acid. These assays sometimes take some perfecting in terms of being able to judge the endpoint precisely.





Contents[hide]

1 Theory

1.1 Acid-base reactions
1.2 Organic solvents
2 Non-aqueous solvents used
3 Titration of Halogen Acid Salts of Bases
4 Visual indicators
5 Potentiometric titration
6 See also



[edit] Theory

[edit] Acid-base reactions
The theory is that water behaves as both a weak acid and a weak base; thus, in an aqueous environment, it can compete effectively with very weak acids and bases with regard to proton donation and acceptance, as shown below:

H2O + H+ ⇌ H3O+
Competes with RNH2 + H+ ⇌ RNH3+
or

H2O + B ⇌ OH- + BH+
Competes with ROH + B ⇌ RO- + BH+
The effect of this is that the inflection in the titration curves for very weak acids and very weak bases is small, because they approach the pH limits in water of 14 or 0 respectively , thus making endpoint detection relatively more difficult.
A general rule is that bases with pKa < 7 or acids with pKa > 7 cannot be determined accurately in aqueous solution.
Substances which are either too weakly basic or too weakly acidic to give sharp endpoints in aqueous solution can often be titrated in non-aqueous solvents. The reactions which occur during many non-aqueous titrations can be explained by means of the concepts of the Lowry-Bronsted Theory. According to this theory an acid is a proton donor, i.e. a substance which tends to dissociate to yield a proton, and a base is proton acceptor, i.e. a substance which tends to combine with a proton. When an acid HB dissociates it yields a proton together with the conjugate base B of the acid:

HB ⇌ H+ + B-
acid proton base
Alternatively, the base B will combine with a proton to yield the conjugate acid HB of the base B, for every base has its conjugate acid and, every acid has its conjugate base.
It follows from these definitions that an acid may be either:

an electrically neutral molecule, e.g. HCl, or
a positively charged cation, e.g. C6H5NH3+, or
a negatively charged anion, e.g. HSO4-.
A base may be either:

an electricially neutral molecule, e.g. C6H5NH2, or
an anion, e.g. Cl-.
Substances which are potentially acidic can function as acids only in the presence of a base to which they can donate a proton. Conversely basic properties do not become apparent unless an acid also is present.

An aqueous solution is a solution with water as the solvent.
e.g. coca cola is an aqueous solution of carbon dioxide, sugar... as carbon dioxide and sugar... dissovle in water.
Non aqueous solution is a solution with liquid, which is not water, as the solvent
e.g. Iodine solution is actually a solution of iodine in alcohol, which is an organic solvent