EXERCISE 1

Question 1

Major component of plant cell wall for structural support and is a water-insoluble polymer of glucose.

Answer 1

Cellulose

Question 2

What are organic acids?

Answer 2

Water-soluble organic compounds (phenolic compounds)

Question 3

Naturally occurring bases where N is present in an aliphatic chain or heterocyclic ring system.

Answer 3

Alkaloids

Question 4

Tea leaves have small amounts of what component?

Answer 4

Chlorophyll

Question 5

What is the major alkaloid component of tea?

Answer 5

Caffeine

Question 6

A common technique used to separate a desired compound from unwanted ones.

Answer 6

Extraction

Question 7

The separation process based on preferential dissolution of one or more components (analyte) of the solid mixture in a liquid solvent.

Answer 7

Solid-Liquid Extraction

Question 8

Why is the extracting solvent boiling H2O?

Answer 8

To separate caffeine from water-insoluble components and increase the solubility of caffeine for higher yield.

Question 10

Purpose for adding HCl.

Answer 10

Converts molecular caffeine to protonated form, increasing its solubility in water.

Question 11

What is the step that removes DCM-soluble unwanted compounds from the acidic aqueous layer?

Answer 11

Washing with dichloromethane.

Question 12

Dispersion of slightly miscible liquids due to vigorous shaking while mixture is hot.

Answer 12

Emulsion

Question 13

How to eliminate emulsion?

Answer 13

Use a stirring rod or add salt to lower the solubility of organic material or add alcohol to destabilize the emulsion.

Question 14

What test determines whether the bottom layer is aqueous or organic?

Answer 14

Water Test

Question 16

If bottom layer is miscible with water, it is _______?

Answer 16

Aqueous

Question 17

How to use a separatory funnel?

Answer 17

1. Vent occasionally to avoid pressure build-up from the vaporization of DCM due to being a very volatile organic solvent.
2. Shaking hastens the transfer of compounds between solvents.
3. Removal of stopper when draining allows liquid to flow.

Question 18

What method is used to separate substances based on their relative solubilities in 2 different immiscible liquids?

Answer 18

Liquid-liquid extraction

Question 19

Purpose of adding Na2CO3 until basic.

Answer 19

Transforms protonated caffeine to its molecular form with higher solubility in DCM compared to water.

Question 20

What is the extracting solvent in liquid-liquid extraction?

Answer 20

DCM

Question 21

Formula for distribution coefficient (Kd).

Answer 21

Solubility in phase 1 / Solubility in phase 2

Question 22

Value of Kd.

Answer 22

8.36

Question 23

Characteristics of a good extraction solvent.

Answer 23

1. High Kd value.
2. Immiscible with original solvent.
3. Chemically inert.
4. Volatile
5. Inexpensive
6. Nontoxic

Question 24

Why are extractions always done twice?

Answer 24

It has a higher extraction efficient in comparison to single-step extraction.

Question 25

Formula for % extraction efficiency.

Answer 25

)Amount extracted in new phase / original amount in original phase) x 100

Question 26

Drying agent used in recovery from organic phase.

Answer 26

Anhydrous sodium sulfate

Question 27

Characteristics of a good drying agent.

Answer 27

1. Chemically inert. 2. Absorbs water quickly upon contact. 3. Absorbs a large amount of water. 4. Wet drying agent can be separated easily.

Question 28

Purpose of evaporation to dryness.

Answer 28

To remove the solvent and separate volatile compound (DCM) from nonvolatile (caffeine) via simple distillation.

Question 29

Formula for % yield calculations.

Answer 29

(Grams of isolated caffeine / Grams of used tea leaves) x 100

Question 30

What aqueous solution is used in Wagner's Test?

Answer 30

I2 or KI

Question 31

Positive sign in Wagner's Test indicates what?

Answer 31

Formation of insoluble reddish-brown complex.

Question 32

Why is it recommended that Wagner's test is conducted together with other chemical tests?

Answer 32

Due to false positive results from other organic compounds.

Question 33

What test uses 2 M of HCl or KBiI4 and results in reddish brown precipitate if positive?

Answer 33

Dragendorff's Test

Question 34

What test uses saturated picric acid solution and results in yellow precipitate if positive?

Answer 34

Hager's Test

Question 35

What test uses K2HgI4 and results in cream-colored precipitate if positive?

Answer 35

Mayer's Test

Question 36

What test uses 10% tannic acid solution and results in pale orange-brown buff precipitate?

Answer 36

Tannic Acid Test