vineri, 10 mai 2013

QUALITATIVE CHEMICAL ANALYSIS


QUALITATIVE CHEMICAL ANALYSIS


QUALITATIVE CHEMICAL ANALYSIS - aims to identify elements and groups of elements that are found in an unknown substance. Isolate on all elements (ions) with similar properties using group reagents, after which the separation continues in each group to reach each cation in part that identifies with specific reagents.
Qualitative analysis begins with a series of preliminary tests in order to obtain information about analytes.
After you run these samples, the dissolution reaches a mixture of cations and anions that are subject to a systematic review.
In general any qualitative analysis of substances takes place in two stages, namely, preliminary analysis and the analysis itself.

PRELIMINARY ANALYSIS METHODS

Preliminary research done on the substance in the solid state.If it is in a state of solution, focuses on water bath to dryness and the residue research are obtained.Preliminary tests consist of the following operations:1 - heating tubules (closed tube)2 - heating coal3 - as pearls,4 - stain flame5 - behavior from H2SO46 - heating with alkali

Preliminary analysis should be performed in the above order.Information obtained in the preliminary analysis are particularly useful when reliable, but not always obtained conclusive indications for an item, especially when considering mixtures. In analyzes using mixtures containing flame of a gas burner.

Lamp Teclu - is formed in the combustion tube, for adjusting the flow rate of the air brake, DMIS gas pipe, a base, a screw for adjusting the flow rate of gas.
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Bunsen lamp - contains the same components, except the adjusting screw for the gas and air adjustment is provided with a sleeve. These bulbs are used in the various Laboratory (evaporation, boiling, roasting) allowing heating to temperatures of 1000-1200 degrees C. The flame is the combustion gas. It consists of three distinct areas:1 - the inner, colorless gas formed by combustion and unreacted still having a temperature somewhere from 350 - 400 degrees C.2 - the middle, bright interior and the surrounding region is made up of CO gas and incandescent particles of carbon, because the combustion is incomplete, insufficient oxygen.This area is about 520 degrees C.
3 - the outer, less bright because it is devoid of incandescent carbon particles, containing end-products of combustion to CO2 and water vapor having high temperature.

These three areas are distinguished not only by their temperature but 
by how different chemical action of substances.
Thus, in the outer region, where burning is complete and 
highest temperature, flame oxidant in nature. In this region substances oxidize. In the middle region due existence of incandescent carbon particles and CO flame Reducing. A chemical bring in this area is reduced.


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