Gravimetric methods of analysis
Define direction of the redox reactions
Define direction of redox reactions is Defined by electric driving force (EDF)(electromotive force) and equilibrium constant, if EDF > 0, reaction occurs forward direction, if EDF < 0, reaction occurs reverse direction. For example.
Cupper ion – oxidation, iron ion – reduction.
EDF = EOx- ERed= 0.34 – (-0.44) = 0.78 B ˃0
When set (reach) equilibrium, the redox pair potential gets to equal on oxidation – reduction reaction.
Electric driving force is just defined direction of reactions, but equilibrium constant is defined direction of reactions and completion.
Кredox0 ˃1 – forward reaction happened. Кredox0 ≥ 108 – reaction occurs completely For example:
So reaction occurs completely.
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 silvernitrate 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 oxidizingagent and a reduction agent.
Gravimetric methods of analysis
Gravimetry
Gravimetric methods are quantitative methods that are based ondetermining 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
Accuracy
5. single fundamental chemical precipitation reactionex: Cl- + Ag+ → AgCl(s)