Admin Table of Contents
- 1 Why do you have to cool the solution before filtering?
- 2 Why is a vacuum sometimes used in filtration?
- 3 What are the reasons why suction filtration vacuum is preferred than gravity filtration?
- 4 Why is it important to cool the solution to room temperature before place it in an ice bath?
- 5 Why should the washing solvent be cold in the suction filtration?
- 6 Why should you use a stemless funnel during the gravity filtration step?
- 7 Why is it necessary to cool hot supersaturated solution slowly?
- 8 Why is crystallization done in an ice bath?
- 9 How do you add NaOH to vanillin?
- 10 What happens when vanillin and NaBH4 are mixed together?
Why do you have to cool the solution before filtering?
An impure compound is dissolved (the impurities must also be soluble in the solvent), to prepare a highly concentrated solution at a high temperature. The solution is cooled. Decreasing the temperature causes the solubility of the impurities in the solution and the substance being purified to decrease.
Why is a vacuum sometimes used in filtration?
Vacuum filtration is used primarily to collect a desired solid, for instance, the collection of crystals in a recrystallization procedure. Vacuum filtration is faster than gravity filtration, because the solvent or solution and air is forced through the filter paper by the application of reduced pressure.
How does a stemless funnel is used to filter off impurities from the hot saturated solution can improve the amount of crystal recovered?
Crystallization in the stem hinders filtration, and can act as a plug on the bottom of the funnel. An advantage of hot filtration is that the boiling solvent in the filter flask helps to dissolve crystals that prematurely form in the stem of the funnel.
What are the reasons why suction filtration vacuum is preferred than gravity filtration?
Advantages: 1) Suction filtration is much faster than gravity filtration, often taking less than one minute with good seals and a good vacuum source. 2) Suction filtration is more efficient at removing residual liquid, leading to a purer solid.
Why is it important to cool the solution to room temperature before place it in an ice bath?
It is important to slowly cool the flask first to room temperature and then in ice-water. A rushed crystal formation will trap impurities within the crystal lattice. Furthermore, the resulting crystals will be smaller.
How does a vacuum filter work?
Vacuum filtration is an operation of evacuating the air below the filter paper to maintain the pressure differential across the filter medium. It increases the rate of filtration through the force on the solution over gravity.
Why should the washing solvent be cold in the suction filtration?
Once the suction filtration process is complete the collected crystals should be washed with a little more ice–cold solvent to remove final soluble impurities which would otherwise be left on the surface of the crystals.
Why should you use a stemless funnel during the gravity filtration step?
A stemless funnel is used because crystals can form in the cool stem of a long-stem funnel and clog it. Cooling immediately in an ice bath may result in crystals so small that they pass through filter paper, or crystals that still have a lot of impurities. After cooling for a few minutes, set up a vacuum filtration.
What would happen if the hot solution was allowed to cool rapidly?
If a saturated hot solution is allowed to cool, the solute is no longer soluble in the solvent and forms crystals of pure compound. Impurities are excluded from the growing crystals and the pure solid crystals can be separated from the dissolved impurities by filtration.
Why is it necessary to cool hot supersaturated solution slowly?
It is imperative to cool a hot supersaturated solution slowly during a recrystallization because rapid cooling will cause precipitation rather than the crystallization of the solid.
Why is crystallization done in an ice bath?
Usually, the flask containing the dissolved solid product is placed in an ice bath made from small pieces of ice and water. Recall from general chemistry that lower temperatures decrease the solubility of a solute in a solvent. The decrease in solubility induces crystallization.
When do you use a vacuum filtration system?
Vacuum filtration is generally used after you have crystallized a solid from a solvent. Usually, the flask containing the dissolved solid product is placed in an ice bath made from small pieces of ice and water. Recall from general chemistry that lower temperatures decrease the solubility of a solute in a solvent.
How do you add NaOH to vanillin?
EXPERIMENTAL PROCEDURE: Place 380 mg (0.380 g) of vanillin in a clean 5 mL conical reaction vial containing a spin vane. Using the color-coded syringe provided in the hood, add 2 mL of 1 M NaOH to the vanillin in the conical vial.
What happens when vanillin and NaBH4 are mixed together?
After Vanillin and NaBH4have been mixed together in the presence of aqueous NaOH, the reaction mixture is stirred at room temperature for about 20 minutes to ensure complete reduction of the carbonyl group. During the reaction process, small bubbles of hydrogen gas should be observed rising through the reaction mixture.