According to the different degrees of tightness, qualitative filter paper, and quantitative filter paper can be divided into three kinds: fast, medium, and slow. Because qualitative filter paper contains more ash, usually used for precipitation or residue filtration without burning weighing.
Quantitative filter paper is used in precipitation weight analysis. Because the quantitative filter paper has been treated with hydrochloric acid and hydrofluoric acid, the ash content after burning is negligible, so it is also called ashless filter paper.
The following are the specific methods for choosing filter paper:
1. The effective area is large, that is, the filter paper uses a large area, and the dust holding capacity is large, the resistance is small, and the service life is long. Of course, the cost will increase accordingly. 2. The finer the fiber diameter, the better the interception effect and the correspondingly higher filtration efficiency. 3. If the content of the binder in the filter material is high, the tensile strength of the paper is high, the filtering efficiency is high, the linting phenomenon is less, the background dust of the filter material is small, the resistance is good, but the resistance increases accordingly.
Generally speaking, the filter paper of amorphous precipitation (such as Fe (OH)3 and Al (OH)3) can be chosen loosely so as to avoid too slow filtration speed. For fine-grained precipitation such as CaC2O4 and BaSO4, close slow-speed filter paper should be selected to prevent precipitation leakage.
Medium-sized crystalline precipitation, such as K2SiF6 and SiO2, can be selected as medium-speed filter paper discs. The size of the filter paper should be selected according to the amount of sediment. In the analysis of cement and raw materials, the circular filter paper with a diameter of 9-11 cm should be selected.
How to use the laboratory filter paper
The filter paper roll used in the lab is usually used together with instruments such as a filter funnel and a Buchner funnel. Filter paper used in the laboratory, it needs to be folded into a shape that is suitable for the experiment. To fold the filter paper into a flower-like shape is frequently seen. The more details, please see the How To Fold, Use, and Separation Filter Paper?
The filter paper’s folding degree is in direct proportion to the usable surface area and the filtering effect. But one thing needs to be noticed- not over-fold and rupture the filter paper. Place the drained glass rod on the multi-layer filter paper and apply even force to avoid damage to the filter paper.
1. Fold the filter paper in half, twice in a row, and fold it into a 90° center angle.
2. Put the stacked filter paper into three layers on one side and one layer on the other to form a funnel.
3. Then the filter will be in a funnel shape and put into the funnel. Pour some water into the funnel mouth to make the wet filter paper abut against the inner wall of the funnel, and then pour off the remaining water for use
4. Place the funnel with the filter paper on the filter funnel holder (such as the ring of the iron stand), place the beaker or test tube that receives the filter under the funnel neck, and place the tip of the funnel neck against the wall of the receiving container.
5. When injecting the liquid to be filtered into the funnel, hold the liquid beaker on the right hand, and hold the glass rod on the left. The lower end of the glass rod is close to the lower side of the three layers of the funnel so that the cup mouth is close to the glass rod, and the liquid to be filtered flows out along the cup mouth. Then, the glass rod is inclined, and the liquid flows into the funnel. The liquid level cannot exceed the height of the filter paper in the funnel.
6. Check to see if the liquid flows down the wall of the cup and feed it to the bottom of the cup when the liquid passes through the filter paper and flows down the funnel neck. Otherwise, the beaker should be moved or funnel rotated to make the tip of the funnel is firmly attached to the wall of the beaker to allow the liquid to slowly flow down the inner wall of the beaker.