4.3
课程名称：过滤
过滤是一种物理的分离过程，其中涉及到使悬浮液通过多孔介质来将固体与流体进行分离。在过滤的过程中，其中的固体会聚集在多孔介质上，而液体（也统称为滤液）则会穿过多孔介质。根据其过滤的目的、沉淀物的数量和性质来选择合适的过滤介质。合适的过滤介质的一般标准是具有惰性、机械强度高、对溶解物质不具有吸收性并且能…
过滤是利用过滤介质将固体与流体进行物理分离的过程。
滤膜介质的选择取决于过滤的目的、固体量以及颗粒大小。
一般来说，过滤效率随着颗粒尺寸的增大而提高。
在简单过滤中，先让沉淀物沉降，然后将上清液沿玻璃棒倾入装有滤纸的漏斗中。
然后使用橡胶刮刀将沉淀物转移至滤纸上。
当需要称重时，可将无灰滤纸点燃以回收沉淀物。
或者，可使用带有侧臂的布氏烧瓶，其上固定一个烧结玻璃漏斗，侧臂可连接真空泵，用于收集沉淀物。
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Q1: What is filtration and how does it separate solids from liquids?
Filtration is a physical separation process that passes a suspension through a porous medium to separate solids from fluids. Solids collect on the porous medium while liquids, called the filtrate, pass through. The filtration medium is selected based on the filtration purpose, quantity, and nature of the precipitate to ensure effective separation.
Q2: How does particle size affect filtration efficiency?
Filtration efficiency increases with particle size. Larger particles are retained more effectively on the filtration medium, while smaller particles may pass through more easily. The choice of filtration medium depends on the particle size of the solid being separated to optimize efficiency.
Q3: What are the key properties of a suitable filtering medium?
A suitable filtering medium must be inert, mechanically strong, nonabsorbent toward dissolved materials, and permissive toward rapid filtration. These criteria ensure the medium does not react with the sample, maintains structural integrity during use, and allows efficient liquid passage while retaining solids.
Q4: Why is ashless filter paper preferred in gravimetric analysis?
Ashless filter paper is preferred because regular filter paper is hygroscopic and can absorb moisture, affecting mass measurements. Ashless filter paper can be ignited to recover the precipitate without leaving residue, making it ideal for gravimetric procedures that require accurate weighing of collected solids.
Q5: What is the difference between simple filtration and suction filtration?
Simple filtration uses gravity to pass liquid through filter paper in a funnel, with the precipitate settling first and mother liquor decanted. Suction filtration uses a Buchner flask connected to a vacuum pump with a sintered-glass funnel to trap the precipitate more rapidly and efficiently.
Q6: How do you recover and weigh solids collected in a crucible during suction filtration?
The solid is transferred to a glass or silica crucible containing a porous glass disc, then fitted into a Buchner flask for suction filtration. After filtration, the crucible is dried and weighed directly. The weight difference of the crucible before and after filtration gives the mass of the collected solid.
Q7: What is the purpose of using a rubber policeman during filtration?
A rubber policeman is used to dislodge any solid that adheres to the glass rod or beaker during the filtration process. This ensures complete transfer of the precipitate to the filter paper, preventing loss of sample and improving the accuracy of separation and subsequent gravimetric analysis. Filtration often precedes precipitation and co-precipitation procedures.