Re: Practice 1 -- Chemistry

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Date Posted: 09:56:24 08/02/01 Thu
Author: Mr. Yeo Woei Ter
Subject: Re: Practice 1
In reply to: Shufei 's message, "Practice 1" on 07:52:29 08/02/01 Thu

Hi Shufei!

The correct place to insert the thermometer is near to the opening that is leading to the condenser (hope you know which position I'm refering to!).

The answer to question 2 is to fill the fractionating column (tube Q) with glass beads. The glass beads will provide a large surface area for condensation to occur.

Let's suppose that the mixture in the flask is a mixture of ethanol and water. When the flask is heated, the vapour coming off from the mixture will contain both ethanol and water molecules.

At first, this vapour will just condense on the surface of the glass beads in the fractionating column. But as the column warms up, molecules in the vapour state rise further before condensing. As we go up the column the temperature becomes lower and so the proportion of the more volatile ethanol molecules increases.

When the temperatuer at the top of the column reaches 78 degree celcius, only ethanol molecules can survive as vapour and these pass over into the condenser. Water molecules with the higher boiling point will keep on condensing on the surface of the glass beads and fall back into the flask. This continues until a large proportion of the ethanol is boiled off. When the temperature at the top of the column rises to 100 degree celcius, water passes into the condenser. It can then be collected in another receiver.

From the description above, you can see the function of the glass beads in the fractionating column. The presence of the glass beads helps to separate the two liquids.

Hope you understand!

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