Apparatus Clock glass, Bunsen burner, tripod, gauze, beaker, salt and water
Salt solution Beaker
Gauze
Method 1. Wear safety goggles. 2. Add some salt into a beaker of water and stir. 3. Pour this solution onto a clock glass. 4. Place the clock glass over a beaker of water on a tripod and gauze and heat the beaker with a Bunsen burner.
Clock glass
Boiling water
Tripod
Bunsen burner
Fig. 8 Separating salt and water by evaporation.
p207 fig 9
5. Heat gently until the liquid in the clock glass is almost gone. Be careful as it can spit at the end.
6. Remove the Bunsen burner. The heat of the dish will evaporate the last few drops. 7. Note what is left behind.
Investigate this Work out how to separate a mixture of sand and salt.
Distillation We now know that the materials that make up solutions can be separated by evaporation. However, what happens if we want to keep the liquid part? Distillation is a method used to separate and collect the liquid part of a solution. Evaporation causes liquids to turn into gas and escape. With distillation, a piece of equipment called a Liebig condenser will trap the gas and turn it back into liquid – this is called condensation. A Liebig condenser is made of two tubes. There is an inner tube and an outer tube. The gas goes through the inner tube while cold water runs through the outer tube. The cold water cools the inner tube and condenses the gas in the inner tube back to a liquid. This condensed liquid is then collected. Distillation can also be used to separate liquids with different boiling points. Boiling points are covered in Chapter 21.
Gas Warm water out Condensation
Inner tube Outer tube
Cold water in Fig. 9 A Liebig condenser. Liquid Fig. 10 Distillation apparatus. 221
