It is important in this core practical to use apparatus and substances carefully and safely, and to observe chemical changes. Eye protection must be worn at all times.
|Water sample||pH||Mass of solid obtained by evaporating 50 cm3 of water sample (g)|
Which sample was sea water?
Sample B was sea water. It contained the highest mass of dissolved solids.
Which sample was obtained from a region affected by acid rain?
Sample C was acidic, so it could have been obtained from a region affected by acid rain.
Set up your distillation apparatus as demonstrated by your teacher.
You may be able to use a conventional condenser like this:
Or you might be using apparatus like this:
Heat your sea water until it boils gently.
After a period of time you should see pure water being produced.
Why is it not safe to drink the distilled water sample?
It might be contaminated because the apparatus might not have been cleaned properly before the practical.
Why was it important to heat the same volume of water to dryness in the first part of the practical?
So the mass of the dissolved solids could be compared in a valid test.
It is essential that the end of the delivery tube in the method described by the second diagram above is above the level of the distillate. This is for safety reasons. Describe what would happen if you stopped heating the sea water and the end of the delivery tube was below the surface of the distillate.
As the delivery tube cools the distillate will be sucked up the delivery tube. When this cool water reaches the hot glass, it may cause the glass to break.
It is important to evaluate the hazards and the precautions needed to reduce the risk of harm. For example:
|Hazard||Possible harm||Possible precaution|
|Acidic or alkaline water samples||Irritating to eyes or skin||Rinse off skin if contact occurs and wear eye protection|
|Hot apparatus||Burns||Allow hot apparatus time to cool before touching|