Classification and application of filter paper for chemical experiments
Filter papers are often used in qualitative, quantitative, and chromatographic separation experiments. The filter paper has specifications of 70, 90, 110, 125, 150, 180 cm and different apertures. The filter paper for general qualitative folding is generally 3.5~l0u, and the diameter of the filter paper for quantitative analysis is 1~2.5u.
1, qualitative filter paper
The fiber of the qualitative filter paper has a high silicon content, and the ash weight after burning is large, and it is not suitable for weight analysis, and can be used for filtration, separation of inorganic precipitates and filtration of organic recrystallization.
2. Quantitative filter paper
The pulp of the Ding Dong filter paper is made by digesting with hydrochloric acid and hydrofluoric acid. The content of iron, aluminum and silicon in the paper is very low. The weight of ash after burning of domestic filter paper is less than or equal to 0.01 gram per sheet. In quantitative analysis, this weight is negligible, so it is often called “ashless filter paper”. The filtration speed of the quantitative filter paper is divided into three types: fast, medium and slow. The different color paper strips are marked on the filter paper tray.
The quality inspection method for quantitative ashless filter paper is as follows:
The ash test accurately weighed 10 pieces of ashless filter paper, and took two of them into pieces, and placed them in two accurately weighed platinum crucibles. In a high temperature furnace, it began to heat with a warm fire, and then added high temperature. After cooling, the crucible is weighed in a desiccator to room temperature, and the average weight of each filter paper ash can be obtained by subtraction.
The test for retaining sulphuric acid sputum heats 20 ml of sulfuric acid to boiling, and drops 20 liters of a solution of cesium chloride at a concentration of 1 ml/second, and continues to heat after the dropwise addition. After 30 seconds, the mixture was filtered through a filter paper to observe whether or not the filtrate had a white precipitate, indicating whether the filter paper could retain the acid sputum.
If starch is present in the starch test filter paper, it cannot be used as an analysis of carbohydrates. The method for the presence or absence of starch in the test paper is to shred the filter paper, azeotrope with distilled water, and drip 0.01N diluted iodine solution. If blue appears, it is confirmed that starch is present.
In the test of iron in filter paper, add a drop of paper ammonium solution to the filter paper, and add a drop of hydrochloric acid. If no iron exists, there will be no thirsty spots.