Answers to Study Questions

ANSWERS TO STUDY QUESTIONS

Exercise 1: Isolation of Caffeine from Tea 1.

a. 10% sodium carbonate - Sodium carbonate, as a base, converts the acids to their sodium salts making it highly soluble in water. b. anhydrous sodium sulfate - absorbs all excess water c. 10% hydrochloric acid - adding HCl turns caffeine into a hydrochloride salt, which increases its solubility in water

2.

Characteristic of dichloromethane as a good extracting solvent: good solubility of caffeine immiscible with water - relatively low toxicity

3.

In single step extraction more amount of solvent is left in the process (which should not happen). Doing multiple extraction will leave lesser amount of solvent, retaining more product.

4.

Emulsions are mixture of two or more immiscible liquids. Emulsions are formed during extractions because of the conversion of tannins into salt – salt  – they become surfactants. Surfactants cause water-insoluble materials to form an emulsion. Gently shaking the separatory funnel can minimize the formation of emulsion.

5.

It is necessary to remove a stopper from a separatory funnel when liquid is being drained so that vacuum will not be created and air w ill not try to come in, making t he separation of liquids undisturbed.

Exercise 2: Recrystallization and Melting Point Determination 1. OPERATIONS a. In the solution step, an unnecessary large volume of  solvent is used. b. The crystals obtained by suction filtration are allowed to dry without being washed with cold solvent. c. The crystals referred to in (b) are washed with hot solvent.

2. 3.

EFFECT ON PURITY Not affected

Lower purity: Impurities would still be adhered to the surface of  crystals. Not affected

EFFECT ON RECOVERY Lower recovery: A large amount of the compound should still be dissolved in the solution. Not affected

Lower recovery: Crystals collected would be dissolved.

Hot-gravity filtration keeps the set-up hot preventing crystals from forming prematurely. Fluted filter paper maximizes flow rate during filtration because of it has larger surface area. Suction filtration is useful when a fast filtration of a mixture that is not hot is desired.

4. 5.

The substance is much visible in a watch glass. a. sample was heated too fast b. too much of the sample was placed

Exercise 3: Simple Distillation and Steam Distillation 1.

The substance should be less reactive. It should not be soluble in water in order to form a separate layer or to precipitate after distillation. 2. The heat of the steam helps to release the aromatic molecules from t he plant material. The steam forces the “pockets” to open in which the essential oils are kept. 3. Simple Distillation is used to separate two liquids with boiling points that differ by fair amount. It is also used to separate a liquid from a nonvolatile compound with higher viscosity. Steam distillation is used in the production of alcoholic beverages. On the other hand, Steam distillation is used to distill compounds that are sensitive to heat. It is used to extract oils from natural products.