1. Learning Objectives Key Words – Cobalt paper Filtration Chlorination
To describe chemical tests for water
To outline the treatment of the water supply in terms of filtration and chlorination
Testing for and cleaning water
Key Words –
Cobalt paper
Filtration
Chlorination
Pollutant
Do you know?
Some of the uses of water in industry and in the home?
5 Minute Task

2. The raft of the Medusa was stuck at sea for 2 weeks
The raft of the Medusa was stuck at sea for 2 weeks. Why is this such a drastic scene? There seems to be plenty of water around?
Transition filler

3. Key Reactions of Water
In your book, write the equation for CuSO4 and CoCl2 combining with water
How is this a test for water?
Name 4 uses of water

4. Water purifying
Design a water purifying system with the equipment in the room.
You have 10 minutes to design and build your device
Then we test them with dirty muddy water
What other steps are needed to make this drinkable?
Draw, label and explain your design

5. Purifying Water – How we make water safe to drink
Starter (5mins)
State 3 things that are likely to be wrong with this water
Suggest how you could remedy each of these problems
a) Water of the correct quality is essential for life. For
humans, drinking water should have sufficiently low
levels of dissolved salts and microbes.
b) Water filters containing carbon, silver and ion
exchange resins can remove some dissolved
substances from tap water to improve the taste
and quality.
c) Chlorine may be added to drinking water to reduce
microbes and fluoride may be added to improve
dental health.
d) Pure water can be produced by distillation.

6. Learning Objective Learning Outcomes
How water is made safe to drink
I can recall that drinking water needs to be clean, odourless, tasteless and free from microbes to avoid disease
I can describe the process of water purification as coagulation, sedimentation, filtration, disinfection and fluoridation
I can explain why purification by distillation as a main source of potable water is restricted to wealthy countries
I can explain what happens at each stage of the normal purification process of water
I can present an argument for the continued fluoridation of water

7. Instructions for Market Place Activity Split into small groups.
Each group is provided detailed information regarding 1 aspect of how water is made safe to drink
You have 10mins to make a poster/diagram conveying as much information on your sheet as possible
You can not use more than 15 words (excluding the title), but you can use as many chemical symbols and numbers as you like
task 2 (10mins)

8. Gathering your information
task 3 (8mins)
You have 2mins per poster to capture as much information as possible
Overview
You have 5mins to make a poster/diagram conveying as much information on water filtration as possible
You can not use more than but you can use as many chemical symbols and numbers as you like

9. The floc settles to the bottom of the tank under gravity.
Coagulation
The coagulant Aluminium Sulphate is added
This causes impurities to clump or coagulate together
Impurities sink to the bottom as “floc”
Adding Aluminium Sulphate (Alum) causes clay, dirt and other organic matter to clump together to form large particles of floc.
The floc settles to the bottom of the tank under gravity.
This helps the subsequent removal of particles by sedimentation and filtration.

10. Sedimentation
The large tanks allow the floc to settle to the bottom as sludge under gravity.
The water spends a total of about 5 hours in the tank. The flow is continuous.
The dripping of the water into the tank allows extra oxygen to mix with the water.
This provides more oxygen for microbial respiration in bacteria which are responsible for decomposing organic matter that enters the sedimentation tank.

11. Relatively clean water leaves the filtration bed
This is the final step in removing suspended particles and any unsettled floc
Water moves through a layer of charcoal or coal before being further filtered by the sand. This acts as an excellent microfilter, trapping air which again increases available oxygen for microbial respiration, thus helping decomposition
Most particles pass through surface layers but are trapped in pore spaces or stick to sand particles.
Relatively clean water leaves the filtration bed

12. Disinfection and Fluoridation
The disinfection of water by adding chlorine gas is called chlorination. Chlorine was used for the first time in 1850 when John Snow used it in London’s water system to combat cholera.
This has resulted in a significant decrease in the number of deaths caused by cholera, typhoid, diarrhoea and hepatitis A. Today, chlorination is used to treat most of drinking in the world since it is easy, inexpensive and reliable.
Fluorine is also added to water to strengthen teeth. This prevents tooth decay. Some people are against the fluoridation of because they believe it could be linked to cancer and tooth flecking. Scientists are divided as there seems to be insufficient evidence and no difference in levels of cancer in fluoridated and unfluoridated areas

13. Questions of water safety
State 3 things that make water unfit to drink
List the stages involved in water purification
Why is chlorine added to water?
Why is fluorine added to water?
Why do some people campaign against the fluoridation of water?
What is sedimentation and why is it useful?
How does aluminium sulphate help sedimentation
Why is unclean water dripped slowly over large filter beds at sanitation plants
plenary (4min)
C3.2.2 Purifying water
a) Water of the correct quality is essential for life. For
humans, drinking water should have sufficiently low
levels of dissolved salts and microbes.
b) Water filters containing carbon, silver and ion
exchange resins can remove some dissolved
substances from tap water to improve the taste
and quality.
c) Chlorine may be added to drinking water to reduce
microbes and fluoride may be added to improve
dental health.
d) Pure water can be produced by distillation.
Suggested ideas for practical work to develop skills and understanding include the following:
■ investigation of which ions cause hard water, eg adding soap solution to solutions of NaCl, CaCl2, KCl, and
MgCl2
■ making temporary hard water by adding excess carbon dioxide to limewater
■ determining hardness of samples of water – shake with soap solution – measuring cm3 of soap to get
permanent lather
■ the removal of hardness:
– temporary hardness: test before and after boiling, with soap
– permanent hardness: test before and after addition of sodium carbonate
■ testing hard water before and after passing through an ion exchange column
■ using conductivity sensors to analyse different samples of hard and soft water
■ design and carry out an investigation to compare the effectiveness of commercial water softeners using soap
titration
■ investigating the various types of water ‘filters’ that are commercially available
■ distillation of seawater – design a simple apparatus to do the distillation and check the quality of the distillate
(boiling point and evaporation to dryness of a sample on a watch glass).

14. Water Purification
What percentage of the Earth’s water is drinkable
What percentage of the Earth’s drinkable water is locked in Icecaps and glaciers
What percentage of this is accessible(surface water)?
What percentage of the Earth’s fresh water is found in lakes
And what percentage is found in rivers?
Much of the drinking water in Saudi Arabia is obtained by distillation of sea water. Explain why this is not an option for a country like Zimbabwe
Suggest a reason why each of the following might be found in drinking water: Nitrates, Lead and Pesticides
To be done by students waiting for others to finish
Why don’t we just evaporate sea water on an industrial scale to make fresh drinkable water?

15. Homework
Find out how water filters containing carbon and silver ions are used as exchange resins to remove dissolved particles to improve the taste of water