1. What effect would each of the following have on the success of the recrystall
ID: 795393 • Letter: 1
Question
1. What effect would each of the following have on the success of the recrystallization of benzoic acid from hexane?
a. The hot solution of the benzoic acid in hexane is immediately placed in an ice bath.
b. After crystallization has taken place, the cold solution is vacuum filtered and the product crystals are collected on a Buchner funnel, then the crystals are rinsed with hot hexane.
c. After isolation of the benzoic acid the crystals are rinsed with diethyl ether.
2. The solubility of acetanilide in hot and coldwater is given below. What is the maximum recovery if 4.50 g of acetanilide is recrystallized from 100 mL of water?
Temperature (
Temperature (
Explanation / Answer
The hot solution of the benzoic acid in hexane is immediately placed in an ice bath.
Immediately benzoic acid will start crystallising. since it is a polar compound, its solubility is high only in hot hexane, once it is cooled it will recrystallise.
b. After crystallization has taken place, the cold solution is vacuum filtered and the product crystals are collected on a Buchner funnel, then the crystals are rinsed with hot hexane.
Once the benzoic acid crystallises, its molecular packing become so dense, hence its solubility in hot hexane varies, hence it is better to wash with hot hexane to remove unwanted impurities,
c. After isolation of the benzoic acid the crystals are rinsed with diethyl ether.
Diethyl ether is polar aprotic solvent, it can remove the impurities as well as, it will wash the excess hexane away and the solid benzoic acid will crystallise fast. diethyl ether has very low boiling point, so it is used for this purpose.
What is a eutectic mixture?
A eutectic system is a mixture of chemical compounds or elements that have a single chemical composition that solidifies at a lower temperature than any other composition made up of the same ingredients
Suggest another solvent that could be used to recrystallize fluorene and explain why.
Methanol can be used.
Methanol is the best solvent for this crystallization. The nonpolar hydrocarbon (methyl) region interacts with the nonpolar fluorene, but at low temperatures the fluorene is significantly less soluble in MeOH than it is at high temperatures.Hence, methanol solution of fluorene will help in crystallisation.
Suggest another solvent that could be used to recrystallize benzoic acid and explain why
Water is the solvent of choice. since water has more hydrogen bonds with benzoic acid, while heating benzoic acid will soluble in water and then, it will crystallise while cooling.
6. Why is it better to extract with two times with 5.0 mL portions of NaOH than to extract one time with a 10.0 mL portion of NaOH? (This will be true for all extractions.)
The efficiency of extraction is depends on the number of times of the extraction and not depends on the volume of extraction. Hence, it is always necessary to do multiple times of extraction to ensure complete extraction.
7. In the extraction portion of the lab acids and bases were use to affect the solubility of fluorene and benzoic acid. Write the acid and base reactions for this experiment.
During the extraction portion, while adding base like NaOH will convert benzoic acid into sodium benzoate. To that sodium benzoate while you add the acids like HCl, you will get separated benzoic acid, your fluorene remain unaffected.
C6H5COOH + NaOH -> C6H5COONa
C6H5COONa + HCl -> C6H5COOH
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