Q. Why do we use watch glass in weighing solid chemicals?

Answer

To get an accurate reading of the sample weight, a watch glass is used to "tar" or "zero" the scale before the required quantity of solid is added. A watch glass may be used for both drying solids and viewing precipitation patterns and crystals. Chemists use watch glasses, which are circular, slightly concave pieces of glass, to cover beakers and allow liquids to evaporate while preparing samples. A laboratory watch glass has several purposes, such as a surface for evaporating liquids, for weighing solids, for heating chemicals or powders, and as a cover for a beaker to keep dust and other particles out of the container.