Gravimetric Analysis

                Precipitation is a very valuable method of separating a sample into its components. The process involved process by which substances to be separated use to form a solid precipitate. Precipitation reaction has been used extensively in analytical chemistry, especially in argentometry and gravimetric methods. Gravimetry are also part of the quantitative analysis related to weight measurements by separating analysts from all the other components that can be specified level of a substance. In addition to inorganic substances, organic compounds have also been analyzed by gravimetric techniques, for example determination of cholesterol levels in cereals and lactose in dairy products.

Gravimetric analysis is a method of weight measurement by separating the analyte from other components so that all levels of a substance can be determined using a gravimetric factor. A gravimetric analysis is usually based on the reaction:
 aA + bB → AaBb

                With the provisions of a is the analyte A reacts with b molecule B. The results is a substance with a solubility usually so small that it can be weighed in that form after dried or baked into other compounds of known structure and then weighed. A B excess reagent is usually added to suppress the solubility of the precipitate, for example in the determination of Ca2 +.

Ca²⁺+C₂O₄^2-→CaC₂O₄

CaC₂O₄ → CaO + CO₂ + CO

Requirements of the gravimetric method are:
A. In the separation must be perfect enough so that the quantity of analyte that does not settle the analyte is not specified.
B. Substances that must have weighed a certain arrangement and must be pure. If no result can not be obtained.

2. Aplication of Gravimetric Analysis
                Gravimetry can be carried out on organic substances such as cholesterol determination in grains. Besides the analysis of elements and organic compounds is usually also done this way. For example C in organic compounds can be determined by burning the sample in oxygen and absorb CO2 and H2O are produced in a suitable absorption. Absorption tubes were weighed before and after combustion for CO2 and H2O are produced.

3. The advantage of gravimetric
Although it has been superseded in terms of gravimetric routine as an instrumental, but gravimetric actually faster and accurately than an instrument that needs to be calibrated. Tools generally provide only a relative measurement and must be calibrated on the basis of gravimetric or titimetri classical way. If the analyte is a first konstata (> 1%) accuracy of the various parts per thousand can be expected, if the sample is not too complex. If the analyte minority of less than 1%, gravimetric way is usually not use.

4.  Theory of Coprecipitation, Peptisasi, Post Precipitation
Coprecipitation is a process brought down a substance which is usually dissolved when the desired deposition of sediment. Suppose that nitrate ions on the precipitation of barium sulfate precipitate containing lead barium nitrate so nitrate is said to have coprecipitation with sulfate or due to adsorption of ions when the deposition process. In this event the cause of impurity substances into the side of the crystal and the absorbed ions dragged down at the time of coagulation.

The procedure used to reduce coprecipitation:
A. The method of determining these two reagents can be used to control the concentration of the regulator and the electric charge carried by the primary particles in the sediment is controlled by using the appropriate pH.
B. Expansion with gelatin blob and must be with an electrolyte solution in the wash solution to avoid precipitation.
C. Pollution is a major benefit of crystalline precipitates, the benefits are large enough to sediment clotted remain unused for gelatin.
D. Repeated if the sediment precipitation can easily be dissolved again, especially for the oxidation hydrolysis and crystalline salts of fatty acids.

credits: Book of PDTK 1 Chemical Engineering 2011 Diponegoro University