Chem 237 Recrystallization Lab – Flashcards

There are four major methods of purification in the chemistry laboratory. Which of the following techniques is not included in the four most common methods for separation and purification? Distillation recrystallization chromatography extraction sublimation

When is recrystallization not a suitable method to purify an organic material? When the organic material is insoluble in water. When the organic material is thermally unstable near its melting point. When the organic material is a liquid instead of a solid. When the organic material is impure.

None of the following molecules display much solubility in water at room temperature. However, two of the molecules display appreciable solubility in boiling water. Based on its structure, which molecule will be the least soluble in hot water? acetaminophen salicylic acid 2-naphthol

Statements describing requirements for suitable solvents for recrystallization are listed below. Sort these requirements as either true or false.

During the recrystallization of a solid, the sample is dissolved in hot solvent then filtered while hot. The filtrate is allowed to cool and the mixture is filtered a second time. What is the purpose of the initial hot vacuum filtration in the recrystallization process? To obtain the maximum amount of the compound as a purified solid. To form larger crystals. To remove insoluble solid impurities. To remove soluble solid impurities.

During the recrystallization of a solid, the sample is dissolved in hot solvent then filtered while hot. The filtrate is allowed to cool and the mixture is filtered a second time. What effect will result if the filtrate solution is cooled too rapidly? Large impure crystals will form. Small impure crystals will form. The maximum amount of the compound as a purified solid will be obtained. Small pure crystals will form.

Recrystallization is a common laboratory method to purify solids by dissolving them in hot solvent, filtering while hot, then allowing the filtrate to cool so that crystals form. Use the pop-up menus to label the following statements about the practical aspects of recrystallization as either True or False. 1. Use clamps to secure the filter flask to avoid tipping and unnecessary exposure to hot liquids or the solute. 2.Recrystallization requires the material that is to be purified is a solid. 3.For hot vacuum filtration, the filter paper should be completely dry when pouring the hot solution into the Buchner funnel to filter. 4.Recrystallization is the process of dissolving a solid material into a suitable solvent or mixture of solvents and allowing the material to crystallize from this solution. 5.For recrystallization, rapid cooling gives the best crystals.

The solubility of acetanilide is 12.8 g in 100 mL of ethanol at 0 °C, and 46.4 g in 100 mL of ethanol at 60 °C. What is the maximum percent recovery that can be achieved for the recrystallization of acetanilide from ethanol?

A student was given a sample of crude acetanilide to recrystallize. The initial mass of the the crude acetanilide was 166 mg. The mass after recrystallization was 121 mg. Calculate the percent recovery from recrystallization.

List the procedural steps, from start to finish, that are required in the recrystallization of acetanilide.

Acetanilide was recrystallized from a minimum amount of hot water, then collected using vacuum filtration. Identify where the waste generated by this process should go. Drag and drop the chemical wastes generated in this reaction into the appropriate container.

During the recrystallization of an impure solid sample of acetanilide, the sample is dissolved in hot water then filtered while hot. The filtrate is allowed to cool and the mixture is filtered a second time. Which of the following actions will increase the percent recovery of the acetanide solute? After the first filtration, Place the solution in an ice-water bath for about 10 minutes. After the second filtration, warm the filtrate for about 10 minutes. Add additional hot water to the dissolved impure acetanilide and swirl occasionally. Place the solution in a hot-water bath for about 5 minutes.

During the recrystallization of an impure solid sample, the sample is dissolved in hot water then filtered while hot. The filtrate is allowed to cool and the mixture is filtered a second time. Which procedure should a student NOT do if they observe an oil forming as the solution cools? Place the solution in an ice-water bath for about 15 minutes. Once the oil has dissolved, allow the solution to cool slowly. Reheat the solution gently until the oil dissolves. Add a small amount of additional water to the flask containing the oil.