23)Quantitative analysis

In chemistry, quantitative analysis is the determination of the absolute or relative abundance (often expressed as a concentration) of one, several or all particular substance(s) present in a sample.

Once the presence of certain substance(s) in a sample is known, the study of their absolute or relative abundance can help in determining specific properties. Knowing the composition of a sample is very important and several ways have been developed to make it possible, like gravimetric and volumetric analysis. Gravimetric analysis yields more accurate data about the composition of a sample than volumetric analysis does, but the first one takes more time to perform in the laboratory. Volumetric analysis in the other side doesn't take that much time and the results that we obtain are in the most cases satisfactory.

Volumetric		analysis	can be		simply	a	titration	based	in
a	neutralization reaction but			it	can also be a precipitation or
a	complex	forming	reaction	as	well	as	a titration	based	in

a redox reaction. However, each method in quantitative analysis has a general specification, in neutralization reactions, for example, the reaction that occurs is between an acid and a base, which yields a salt and water, hence the name neutralization. In the precipitation reactions the standard solution is in the most cases silver nitrate which is used as a reagent to react with the ions present in the sample and to form a high insoluble precipitate. Precipitation methods are often called simply as Argentometry. In the two other methods the situation is the same. Complex forming titration is a reaction that occurs between metal ions and a standard solution that is in the most cases EDTA (ethylene diamine tetra acetic acid). In the redox titration that reaction is carried out between an oxidizing agent and a reduction agent.

Gravimetric methods of analysis

Gravimetry

Gravimetric methods are quantitative methods that are based on determining the mass of a pure compound to which the analyte is chemically related.

Gravimetric analysis is the quantitative isolation of a substance by precipitation and the weighing of the precipitate.

Gravimetric analysis: based upon mass measurements highly accurate and precise.

*Advantages

4. Accuracy

5. single fundamental chemical precipitation reaction ex: Cl- + Ag+ → AgCl(s)

6. Require no accuracy known standard solution

Classifications of Gravimetric methods

1-Precipitation gravimetry, the analyte is separated from a solution of the sample as a precipitate and is converted to a compound of known composition that can be weighed.

2-Volatilization gravimetry, the analyte is separated from other constituents of a sample by conversion to a gas of known chemical composition. The weight of this gas then serves as a measure of the analyte concentration.

3-Electrogravimetry, the analyte is separated by deposition on an electrode by an electrical current. The mass of this product then provides a measure of the analyte concentration.

Features or properties of Gravimetric Analysis

2. Traditional Method.

3. Cheap, easily available apparatus, simple to carry out.

4. Slow, especially when accurate results are required.

5. Wide range of sample concentrations (ng - kg).

6. No calibration required (except for the balance).

7. Accurate.