Liquids which are miscible

Liquids which are miscible

If miscible liquids are to be separated, then this can be done by fractional distillation. The apparatus used for this process is shown in the photo and diagram in Figure, and could be used to separate a mixture of ethanol and water. 

Fractional distillation relies upon the liquids having different boiling points. When ethanol and the water mixture is heated the vapours of ethanol and water boil off at different temperatures and can be condensed and collected separately. 

Ethanol boils at 78 °C whereas water boils at 100 °C. When the mixture is heated the vapour produced is mainly ethanol with some steam. Because water has a higher boiling point of the two, it condenses out from the mixture with ethanol. This is what takes place in the fractionating column.

The water condenses and drips back into the flask while the ethanol vapour moves up the column and into the condenser, where it condenses into liquid ethanol and is collected in the receiving flask as the distillate. When all the ethanol has distilled over, the temperature reading on the thermometer rises

steadily to 100 °C, showing that the steam is now entering the condenser. At this point, the receiver can be changed and the condensing water can now be collected.

Fractional distillation is used to separate miscible liquids such as those in crude oil, and the technique can also separate individual gases, such as nitrogen, from the mixture we call air.

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Md. Saifur Rahman

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