During Recrystallization, insoluble impurities are removed by: explain it briefly and choose one
Select one:
A. Cooling.
B. gravity filtration.
C. suction filtration.
D. heating.
E. drying.
The Correct Answer and Explanation is :
The correct answer is B. gravity filtration.
Explanation:
In recrystallization, the goal is to purify a solid compound by removing impurities. The process typically involves dissolving the impure solid in a hot solvent, then allowing the solution to cool. During cooling, the pure substance crystallizes out of the solution, while impurities remain dissolved in the solvent.
Insoluble impurities, which do not dissolve in the solvent, are removed during the recrystallization process by gravity filtration. Here’s why gravity filtration is the correct method:
- Dissolution of the compound: First, the impure compound is dissolved in the solvent at high temperature. The solvent is chosen in such a way that the compound to be purified is soluble at high temperatures but becomes insoluble upon cooling, while impurities either remain dissolved or are insoluble throughout.
- Filtration: Once the compound is dissolved in the hot solvent, the mixture is typically passed through a filtration setup. Insoluble impurities such as dust or sand particles are removed using gravity filtration. In this method, the hot solution is poured through filter paper in a funnel. Gravity allows the liquid to pass through the filter paper while retaining the solid impurities. The solvent and dissolved compound flow through into a clean container, leaving behind the insoluble impurities on the filter paper.
- Crystallization: After filtration, the filtered solution is allowed to cool. As the temperature decreases, the solubility of the compound decreases, leading to the formation of crystals of the purified compound. The impurities, being either soluble or larger, stay in the solution and are not incorporated into the crystalline form of the desired substance.
Thus, gravity filtration is essential for removing any solid, insoluble impurities from the hot solution before crystallization occurs. Other methods like suction filtration (option C) are typically used to separate larger amounts of material, while drying, heating, and cooling do not directly remove insoluble impurities.