12.2 Water safe to drink + RP
No description yet. This curated deck is ready for daily study.
Card preview (10)
What does potable water mean
water thats safe to drink
Is potable water pure
no it has other dissolved substances in it
What are the three criteria that make water potable
• levels of dissolved substances need to be fairly low • no micro-organisms • pH between 6.5 - 8.5
Example of a surface water source
Lakes Rivers Resevoirs
Three stages involved in treating water to make it potable
• Pass fresh water through wire mesh to filter out any big things • Pass untreated water through filter beds made of sand and gravel to remove solid particles • Sterilise it to kill any microbes using chlorine gas or ozone of ultraviolet light
Why use desalination
No natural sources of water apart from ocasional rain water
Disadvantages associated with desalination
Require lots of energy and very expensive
Describe how desalination is achieved by means of reverse osmosis
Salty water passes through membrane, larger molecules get trapped and separated
How can water be purified
Distillation, but it requires lots of energy so it is very expensive
Water purification required practical
• Pour 1cm depth of the salt water into the test tube in the rack. Dip the nichrome wire into this solution, and then hold the tip of the wire in a blue Bunsen burner flame. • Now add a few drops of dilute nitric acid to this solution, followed by 1cm depth of silver nitrate solution. • Place the remaining salt water in the conical flask and set up the apparatus for distillation. Make sure conical flask is held on the tripod and gauze using the clamp stand. Place a mixture of ice and water in the beaker surrounding the test tube. • Heat the water with the Bunsen burner until it starts to boil. Then reduce the heat so that the water boils gently. Distilled water will collect in the cooled test tube. Collect about 1cm depth of water then stop heating. • Repeat steps 1 and 2 again using the distilled water, making sure that the nichrome wire and test tube have been cleaned. Record your results in a table.