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Laboratory assigment alcohols

I am preparing for a lab practical that I'm doing tomorrow.
Can someone help me with some questions please?

Preparation of 2-chloro-2-methylpropane

Methylpropan-2-ol is used and concentrated hydrochloric acid is added and anhydrous calcium chloride.

1.Why is anhydrous calcium chloride added to the reaction mixture?

The mixture is then shaken.
2. What causes the pressure build-up in the mixture when it's shaken?

Allow the mixture to stand until separation in 2 layers has been achieved and then discart the spent acid.
The organic layer is first washed with cold 5% sodium hydrogen carbonate solution and then with cold water.

3. What is the purpose of the sodium hydrogen carbonate solution?
4. What is the purpose of washing the layer with water AFTER washing with sodium hydrogen carbonate solution?

5. I need to give 2 reasons why the reagents used for washing should be cold?

The mixture is then transfered to a container and anhydrous sodium sulphate added. The stopper is replaced, the mixture is shaken and allowed to stand. The product is decanted off and distilled to collect the fraction boiling between 49 and 51C. Then the mass or volume of the product is measured and used to calculate the % yield.

6. Anhydrous sodium sulphate plays no part in the reaction. Why is then used?

I appreciate your help so much.
THANK YOU!! :smile:
Reply 1
Can someone guide me on this one, please?!
Reply 2
criscea
I am preparing for a lab practical that I'm doing tomorrow.
Can someone help me with some questions please?

Preparation of 2-chloro-2-methylpropane

Methylpropan-2-ol is used and concentrated hydrochloric acid is added and anhydrous calcium chloride.

1.Why is anhydrous calcium chloride added to the reaction mixture?
This will remove the water produce and thus produces a dry sample of 2-chloro-2-methylpropane
CH3C(CH3)OHCH3 + HCl -----> CH3C(CH3)ClCH3 + H2O


The mixture is then shaken.
2. What causes the pressure build-up in the mixture when it's shaken?
The pressure build up is normally the result of a gas being produced but I don't see where any gas could be produced in this reaction. Perhaps from any carbonate impurites reacting with the HCl to produce carbon dioxide?

Allow the mixture to stand until separation in 2 layers has been achieved and then discart the spent acid.
The organic layer is first washed with cold 5% sodium hydrogen carbonate solution and then with cold water.

3. What is the purpose of the sodium hydrogen carbonate solution?
This will remove acid impurities

4. What is the purpose of washing the layer with water AFTER washing with sodium hydrogen carbonate solution?
The NaCl produced from the reaction with sodium hydrogen carbonate will dissolve in the water and thus be removed.

5. I need to give 2 reasons why the reagents used for washing should be cold?
I can't think of anything specififc but I suppose you would prefer to keep things cooler to prevent evaporation/loss of the organic liquid.

The mixture is then transfered to a container and anhydrous sodium sulphate added. The stopper is replaced, the mixture is shaken and allowed to stand. The product is decanted off and distilled to collect the fraction boiling between 49 and 51C. Then the mass or volume of the product is measured and used to calculate the % yield.

6. Anhydrous sodium sulphate plays no part in the reaction. Why is then used?
It is used to dry the mixture, i.e. remove any water present.

I appreciate your help so much.
THANK YOU!! :smile:


The details are little lacking as its been so long since I last did an organic preparation. I don't understand why the product is dried twice? perhaps the anyhdrous calcium chloride has another purpose