This method is the simplest and most commonly used, and it uses a glass funnel and filter paper for filtration. When filtering, fold the circular or square filter paper into four layers, then tear off the corner of the filter paper, and open the filter paper into a cone, with a single layer on one side and three layers on the other side, and put them in the funnel. The cone angle of the funnel should be 60 so that the filter paper can be completely attached to the funnel wall.
If the cone angle of the funnel is greater than 60, the folding angle of the filter paper should be appropriately changed to match the cone angle of the funnel. Then press the filter paper on the wall of the funnel with your index finger, and use a wash bottle to blow a small amount of distilled water to wet the filter paper. The edge of the filter paper should be slightly lower than the edge of the funnel.
If the filter paper is stuck on the wall of the funnel and there are still air bubbles between the two, you should press the filter paper gently with your fingers to remove the air bubbles, and then add water to the funnel almost to the top edge of the filter paper. At this time, the inside of the funnel neck should be completely filled with water, and after all the water on the filter paper has been drained, the water column in the funnel neck can still be maintained.
If it is unsuccessful, you can use your fingers to block the lower mouth of the funnel, lift the filter paper, and add water between the filter paper and the funnel wall, until most of the funnel neck and cone is filled with water, and the air bubbles are completely discharged. At this time, press the edge of the paper firmly, and then open the lower outlet, and the water column can be formed at this time. During the entire filtration process, the funnel neck must be filled with liquid at all times, so that the filtration can be performed quickly.
When filtering, pay attention to the funnel should be placed on the funnel rack, adjust the height of the funnel rack so that the outlet of the funnel rests on the inner wall of the receiver so that the filtrate can flow down the wall without splashing. The solution is transferred first, followed by the pellet. This will not slow down the filtration rate due to the clogging of the pores of the filter paper by precipitation.
Use a stir bar for both solution transfer and precipitation. When transferring the solution, the solution should be dropped on the side of the three layers of filter paper to prevent the liquid droplets from breaking through the single layer of filter paper. The solution added to the funnel must not exceed 2/3 of the total volume of the cone filter paper. Adding too much will cause the solution to flow into the receiver from between the filter paper and the inner wall of the funnel and lose the filtration effect of the filter paper.
Wash the pellet if necessary. After the solution is transferred, add a small amount of detergent to the container containing the precipitate, stir it thoroughly, and wait for the solution to settle. Then pour the upper solution into the funnel. Repeat this operation 3 times, and finally transfer the precipitate to Filter paper. You can also transfer the entire pellet to a filter paper, and then divide a small amount of detergent into several portions and add it to the funnel several times to wash the pellet.
When washing the precipitate, the principle of small and multiple times should also be followed to improve efficiency. Finally, after checking the impurities in the filtrate, you can judge whether the precipitate is washed.
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