Depending on the degree of tightness, we can also tell different types of filter paper apart by their filtration rate as in fast, medium speed and slow speed. Since the qualitative filter paper contains more ash, it is often used for precipitate filtering or filtering residue that doesn’t need burning and weighing. Since the quantitative filter paper is treated with hydrochloric acid and hydrofluoric acid, the ash content after burning is extremely slim and negligible, it is also called ashless filter paper.
Selection of filter paper :
In general, amorphous precipitates such as Fe(OH)3, Al(OH)3 can be filtered with looser filter papers to avoid ultra-slow filtration. For fine crystals like CaC2O4 and BaSO4, a compact slow filter paper should be used to prevent precipitation loss. For medium-sized crystal precipitates like K2SiF6 or SiO2, a medium-speed filter paper can be used. The size of the filter paper should be selected according to the amount of precipitate. For example, a circular shape with a diameter of 9 to 11 cm can be selected for the analysis of cement and its raw materials.