Heating of solution in a beaker.
The Bunsen burner, which typically burns natural gas and employs air as an oxygen supply, is a common equipment for heating at the laboratory bench. The size of the flame is determined by the amount of gas supplied to the burner, which is regulated by the valve on the desk to which the burner is connected. Depending on the type of burner that you have, the amount of air is regulated by a metal ring with holes that may be rotated at the base of the burner barrel, or by a piece of metal that may be slipped to one side or the other to vary the extent to which the base of the burner barrel is uncovered to admit air A yellow, smoky flame is unclean and not very hot; it indicates lack of air. A flame that roars and readily blows itself out is likewise bad; it indicates excess of air. A correctly burning flame is almost invisible blue in hue, with a vivid blue cone blazing inside it. The hottest part of the flame is at the apex of the brilliant blue cone.
When heating liquids in a beaker or flask using a burner, place the container on a wire gauze to uniformly distribute the heat from the burner. This reduces the danger of the container shattering or the liquid splattering. When it is critical that no loss occurs as a result of splashing, it is usual to set a watch glass over the container. If necessary, the watch glass can be supported by glass stirrups to allow vapour from the container to escape. At the end of the heating time, any condensate on the watch glass may be washed back into the beaker with distilled water.
An electric hot plate, particularly one fitted with a magnetic stirrer, is a very handy and convenient means of heating. Because of the typically delayed first warm-up period, the learner must be warned of the tendency to raise the temperature regulator to an excessively high number; the resulting overheating may result in loss through splattering or thermal breakdown.
When evaporating a solution to dryness or near dryness, considerable care must be taken to avoid "bumping," which is characterised by superheating followed by violent bursts of splattering. This is best accomplished by slowly heating the liquid while continually spinning it, to shield the fingers from the heated glass, an appropriate holder, such as a folded paper strip, must be used in this process. When acids or other solutions that generate unpleasant fumes are evaporated in this manner, the procedure must be carried out beneath a hood with adequate ventilation.
Comparison between Soft glass and Borosilicate glass
Borosilicate glass is a sort of "engineered" glass that was created especially for use in labs and applications where the thermal, mechanical, and chemical conditions are too severe for normal, household-type soda-lime glass. It is a kind of glass whose principal ingredients are silica and boron trioxide. Borosilicate glasses withstand thermal stress better than other types of common glass. It can be moved from the freezer to the oven and back again. Its excellent heat resistance stems from its extremely low coefficients of thermal expansion. It is commonly used in the manufacture of reagent bottles because it is less susceptible to heat stress and fits the needs of the majority of laboratories.
When using a Bunsen burner to heat materials in a test tube, the test tube should be held with a wire test tube holder, the mouth of the test tube should be directed away from yourself and your neighbour, and the heating should be done carefully.
The standard safety requirements for heating are
