The Classification, Folding, and Use of Filter Paper Sheets
Filter paper sheets are frequently used in lab experiments and HAWACH will talk about the classification, folding, and design of filter paper. Welcome to visit hawach.com to visit more.
Classification of filter paper sheets
As we know, there are two kinds of filter paper sheets, qualitative and quantitative filter papers. The difference lies in the ash content after ashing. Qualitative filter papers ash content is less than 0.15%, quantitative filter paper ash content is less than 0.01%.
For the quantitative filter paper, there is little residual ash after burning, which hardly affects the analysis results. It is suitable for precise quantitative analysis.
Qualitative filter paper generally has more residual ash, which is only used for general qualitative analysis and used for filtering precipitation or suspension in solution and cannot be used for quality analysis.
Qualitative and quantitative filter paper is divided into three types: fast, medium, and slow which is divided by the pore size of filter paper sheets.
Fast: the pore size is 80～120 microns
Medium speed: the pore diameter is 30-50 microns
Slow speed: pore diameter is 1～3 microns
The difference lies in the nature of the precipitation of the separated substances, fast filter paper for colloidal precipitation, slow filter paper for crystalline precipitation. Usually, the markings on the packaging box are white, blue, and red.
Folding and usage of filter paper sheets
There are many ways to fold the filter paper. Generally, the four-fold method is used. The main point is to make the folded filter paper fit and close to the inner wall of the funnel. When folding, the hands should be clean, and the cone of the folded filter paper should be consistent with the cone of the funnel used; the folded filter paper sheets have three layers on one half and one layer on the other half. Tear the outer two layers of the three layers.
Remove a small piece and make it fit better with the funnel wall after moistening it with water. The size of the filter paper sheets used should be about one centimeter below the edge of the funnel. Put the filter paper treated in this way into the display hopper, press it tightly by hand to make it tightly, and then use a washing bottle to add a little water to the filter paper to moisten it.
If the folding cone angle is appropriate, there should be no air bubbles between the filter paper and the funnel wall after water is injected, and a water column can be formed in the funnel neck, whereby the gravity of the water column can speed up the filtration speed. If there are bubbles, they should be driven out. The liquid level of the poured filtrate is generally two-thirds of the filter paper sheets. Please keep spare filter paper in the laboratory to prevent moisture or other material contamination.
Use of qualitative filter paper and quantitative filter paper
Why is the filter paper sheets lower than the edge of the funnel?
Filter paper sheets are lower than the edge of the funnel, which is considered from two aspects: one is that the support strength of the filter paper in the immersion state will be further reduced, which is likely to cause liquid spillage; the other is to facilitate the liquid level control in the filtration process.
For filter operation, we should pay attention to “two low”.
1.The edge of the filter paper sheets should be slightly lower than the edge of the funnel by about 5mm;
2.The liquid level in the funnel should be about 5mm lower than the edge of the filter paper sheets. The purpose is to prevent the liquid from flowing into the filtrate from the gap between the filter paper sheets and the inner wall of the funnel.
