What is the purpose of adding sodium carbonate to the water-tea extract?

Question

1) What is the purpose of adding sodium carbonate to the water-tea extract? Draw the general reaction equation that results from the addition of the sodium carbonate.

2) List one advantage and one disadvantage of shaking the separatory funnel during extraction

3) List two different types of analyses that could be carried out to confirm the recrystallized solid is indeed caffeine

4) List two different methods besides the one used in this experiment to isolate caffeine from tea.

[su_box title="♦ Relevant knowledge" box_color="#2d6ff7" radius="1"]Hardness of Water

Certain chemicals render water unusable for certain purposes, like washing clothes. Compounds like calcium sulphate hinder the creation of lather. Therefore, getting rid of these substances is a must prior to the use of water.

[/su_box]

Kyle Smith · Accepted Answer

Answer:

1)

Sodium carbonate is added into the extraction medium in order to make sure that the acidic components of the tea leaves are water solubilized and that caffeine remains free from base.

Sodium carbonate means basic. Tannins, which are acidic compounds of high molecular weight and have an -OH that is directly bound to an aromatic rings, are basic. To do this, add 10g of sodium carbonate into your aqueous tea extract. The first sodium carbonate should produce a distinctive fizzing sound. This is because it reacts contains acidic tannins that release carbon dioxide gas. Let the solution simmer for five minutes, then boil the majority of the water.

2)

The advantage of shaking the separatory channel

a) Ability to separate at most two immiscible liquids.

b) It is easy to use and can be done quickly.

It is transparent so you can easily see the layers.

You can choose to remove the upper or lower layers. The stopper removes the upper layer and the stopcock removes the lower.

A major drawback of shaking the separatory funnel may be that the phase separations might not be very accurate.

3)

a-Recrystalization Method -Add 5-8mL hot acetone in order to dissolve the crude caffeine. Then, pour the solution into a 50mL Erlenmeyer flask to make recrystallization. You can add a few drops petroleum ether to reach the cloud point (caffeine is less water-soluble in this mixture solvent and is just beginning precipitate). Cool the solution.

b-Recrystalization Method - Place the tea leaves into a Erlenmeyer flask of 125 ml. Mix 20 ml dichloromethane with 10 ml of 0.2 M NaOH. Extract: Seal the flask, and swirl it gently for 5-10 minutes. This will allow the solvent mixture into the leaves. Caffeine dissolves with the solvent. Most of the other compounds found in the leaves don't.

4) Procedure :- Isolation Of Caffeine From Tea

Reagents are required

Dichloromethane.
Anhydrous sodium sulfite.
Distilled water

Materials Required:

Tea bags
500ml Beaker
Hot plate
Separating funnel.
Melting point apparatus.
Allow the solution to cool to room temperature.
Keep the tea cool in an icebox. The tea should be cooled (20°C) before it comes in contact with dichloromethane (boiling temperature = 40°C).
Three times extract the solution with 30-mL portions dichloromethane(CH2Cl2) Do not touch dichloromethane.

This experiment uses tea bags as the source for caffeine.

Extraction step:

a. You add 20ml of dichloromethane to the tea solution. Because it is denser than tea, the mixture will split into two layers.

b. Take the funnel out of the stand. Keep your fingers on the stopper. Gently shake the funnel.

c. Ventilate the separating funnel every 30 seconds to reduce the vapour pressure inside the funnel.

d. Once the contents are sufficiently shaken, place the separating funnel on the ring stand. Then let the layers separate.

e. Pour the bottom layer into a conical Flask. This is where the caffeine is extracted from the dichloromethane. To prevent evaporation, cover the mouth of your conical flask.

f. Continue steps a-e twice.

9. Dry the mixture of dichloromethane and anhydrous sodium sulfite. Mix in about 1 teaspoon of the drying agents until the mixture is no longer lumpy at the bottom. Mix it well and let it sit for 10 minutes.

10.Convert the dichloromethane to a conical flask (100ml). In a hot water bath, evaporate the dichloromethane solvent.

11.A residue of yellowish-green - white crystalline caffeine will remain after all solvent has been removed.

Sublimation step:

a. Take the conical flask with crystalline caffeine.

b. Sublime the crude caffeine at atmospheric tension by placing the flask on a preheated hot plate. The caffeine melts at 238°C and is sublimed at 178°C.

c. Keep a test tube in the mouth of your conical flask to collect the sublimed caffeine d. The conical flask walls are observed to be covered with white caffeine vapour.

e. Now cool the conical flask.

12. Take a clean watchglass and weigh it in a weight balance.

13. Now, use a spatula to remove the caffeine from the conical flask.

14. Record the watch glass's weight + the caffeine in a weight balance. Next, calculate the extract pure caffeine weight.

15. The melting point apparatus is used to determine the caffeine's melting point.

Sign Up

Sign In

Forgot Password

ITtutoria Latest Questions

What is the purpose of adding sodium carbonate to the water-tea extract?