6. Separation by Distillation
We can obtain salt from salt-water mixture (or salt solution) by evaporation but water cannot be recovered during evaporation, it is lost into the air. In order to recover both, salt as well as water, from a salt-water mixture (or salt solution), the process of distillation is used.
Distillation is the process of heating a liquid to form vapour,and then cooling the vapour to get back liquid. Distillation can be represented as :
The liquid obtained by condensing the vapour is called 'distillate'. From this discussion we conclude that in order to obtain both, solid as well as liquid from the 'mixture of a solid and a liquid', the process of distillation has to be used. When the homogeneous mixture of solid and a liquid is heated in a closed distillation flask, the liquid, being volatile, forms vapour. The vapours of liquid are passed through a 'condenser' where they get cooled and condense to form pure liquid. This pure liquid is collected in a separate vessel. The solid, being non-volatile, remains behind in the distillation flask.
Before we describe the process of distillation, we should know something about the 'water condenser'which is also known as 'Liebig condenser'. The water condenser is a long glass tube surrounded by a wider glass tube (called water jacket) having an inlet and outlet for water. During distillation, cold water from tap is circulated through the outer tube of condenser. This water takes away heat from the hot vapour passing through the inner tube of condenser and causes its condensation (vapour to liquid change).
We will now describe how a 'salt and water mixture' (or 'salt-solution') can be separated into 'salt' and 'water' by distillation.
Notes
Matter in Our Surroundings - Notes
1. 11. Metals Usually Have a Silver or Grey Colour
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2. The Case of a Liquid Solute Dissolved in a Liquid Solvent
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8. 7. Non-Metals may be Solid, Liquid or Gases at the Room Temperature.
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10. 3. Non-Metals are Bad Conductors of Heat and Electricity.
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11. 6. Metals are Usually Strong. They Have High Tensile Strength.
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18. Chemical Formula for daily use material
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24. To Study the Properties of a Compound of Iron and Sulphur
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28. 4. Metals are Lustrous (or Shiny), and can be Polished.
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30. To Separate a Mixture of Alcohol and Water
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31. To Study the Properties of a Solution
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34. 7. Metals are Solids at the Room Temperature
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38. To Study the Properties of a Suspension
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40. To Separate the Salt-Water Mixture (or Salt-Solution)
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48. 6. Non-Metals are Not Strong. They Have Low Tensile Strength.
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50. Solutions, Suspensions And Colloids
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