Chemistry · Ch 3 — Some Analytical Techniques
Simple distillation
Simple distillation
The Process
Simple distillation is used to purify liquids that boil without decomposing at atmospheric pressure. The liquid is first converted into vapour by boiling, and the vapour is then condensed back into liquid by cooling; the resulting pure liquid trickles down into a receiver.
The Apparatus
The liquid to be distilled is taken in a round-bottom flask, held in place by a clamp on a stand, and heated using a water bath, an oil bath, or sometimes a wire gauze placed directly beneath it. The flask is fitted with a cork carrying a thermometer, whose bulb is positioned just below the level of the flask's side arm. This side arm connects the flask to a condenser, which has an outer jacket with two outlets through which cooling water is continuously circulated. The lower end of the condenser is connected to a receiver flask, which collects the purified liquid.
How It Runs
As the flask is heated and the liquid's boiling point is reached, it starts to boil; the vapours rise into the neck of the flask, pass through the side arm, and enter the cooler parts of the condenser, kept cool by the circulating water in its jacket. There, the vapours condense back into liquid, which is collected in the receiver.
Worked Activity: Separating Acetone and Water …
What this figure shows. A round-bottom flask, held by a clamp on a stand and heated from below by a water bath, oil bath, or wire gauze, is fitted with a cork carrying a thermometer whose bulb sits just below the level of the flask's side arm; the side arm connects the flask to a condenser, an outer jacket around a central tube with two water outlets through which cooling water is circulated in the opposite direction to the vapour flow; the lower end of the condenser feeds into a receiver flask that collect …
Worked out. Apparatus: distillation flask with condenser, two receivers, thermometer. Chemicals: a mixture of acetone and water. Principle: acetone (boiling point 56 degrees C) and water (boiling point 100 degrees C) are miscible liquids with a wide difference in boiling point, so heating the mixture first drives off the acetone at 56 degrees C, and once all the acetone has distilled over, continued heating raises the temperature to 100 degrees C, at which point the water distils off. Procedure: place the water-acetone mixture in the distillation flask, arrange the apparatus, and heat carefully on a water bath; collect the acetone that distils at 56 degrees C in receiver number 1, then change the receiver (discarding the first few mL collected in between) and …