4.3
ろ過
濾過は、液体から固体を分離するために多孔質媒体に懸濁液を通過させることを含む物理的分離プロセスです。濾過中、固体は多孔質媒体上に集まり、液体 (総称して濾液とも呼ばれます) が通過します。ろ過媒体は、ろ過の目的、量、沈殿物の性質に基づいて選択されます。適切な濾材の一般的な基準は、不活性で、機械的に強…
ろ過とは、ろ過媒体を使用して固体を流体から物理的に分離することです。
ろ過媒体は、固体のろ過目的、量、および粒子サイズに応じて選択されます。
一般に、ろ過効率は粒子サイズとともに増加します。
単純なろ過では、最初に沈殿物を沈殿させ、母液をガラス棒にデカントして濾紙を取り付けた漏斗に入れます。
次に、沈殿物はゴム製の警察官を使用して濾紙に移されます。
無灰濾紙は、計量が必要な場合に、沈殿物を回収するために点火することができます。
あるいは、Buchnerフラスコに固定された焼結ガラス漏斗(真空ポンプに接続できるサイドアーム付き)を使用して、沈殿物をトラップします。
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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.