This document discusses water resources, water purification processes, and water quality testing. It describes various water sources like lakes, rivers, and aquifers. It explains how water is used in industry for cooling, solvents, and as a raw material. It also lists common pollutants in water sources like nitrates, lead, and pesticides. The purification process removes insoluble solids through sedimentation, filters out smaller particles, and uses chlorination to kill microbes. Testing identifies ions that cause water hardness and determines which halide ions are present through precipitation reactions.

1. C4h How pure is our water?
Uses and Purification of Water
Different Types of Water Resources
• Lakes
• Rivers
• Reservoirs
• Aquifers – an underground water source
How is water used in industry?
• Coolant – to stop equipment overheating
• Solvent
• Cheap raw material
Pollutants in water sources
• Nitrate residues – from fertilisers
• Lead compounds – from lead pipes
• Pesticide residues – from spraying crops near water sources
What is in water before it is purified?
• Dissolved salts and minerals
• microbes
• pollutants
• insoluble solids
Before water is fit to drink it needs to be purified to remove these substances and
any from the list of pollutants.
The Purification Process
Water is purified in 3 main stages:
1. Sedimentation
2. Filtration
3. Chlorination

2. 1. Sedimentation:
Water contains insoluble solids that need to be removed first e.g. sand and soil.
This happens in sedimentation tanks. The larger particles settle to the bottom of
the tank and the water is run off from the top (see diagram above)
2. Filtration:
Some particles are too small and light to settle out in the sedimentation tank e.g.
clay.
So the water goes through a filter made from layers of grit, coarse sand and fine
sand. This traps smaller insoluble particles such as clay.
3. Chlorination:
To kill any microbes that may cause disease, a very small quantity of chlorine gas
is dissolved in the water.
NOTE:
Some soluble substances are not removed in the purification process and these
may be poisonous!

3. Testing for Dissolved Ions in Water
Hardness in water
• Some dissolved ions cause water to be “hard”
• When you wash your hands with soap the water makes bubbles. We say that the
water lathers.
• Hard water does not lather well with soap
• Soft water lathers very well
• The more soap solution needed to lather, the harder the water must be.
Experiment to find out which dissolved ions create hard water
Solution Volume of soap solution needed for a permanent
lather, cm3
sodium chloride 15cm3
magnesium chloride 3cm3
potassium nitrate 1cm3
sodium sulfate 7cm3
magnesium sulfate 10cm3
calcium sulfate 48cm3
Conclusion
Explain in as much detail as you can what these results tell you (or answer questions
from the practical sheet). Are there any anomalous (odd) results?

4. Uses and Purification of Water
Different Types of Water Resources
•
•
•
•
How is water used in industry?
•
•
•
Pollutants in water sources
•
•
•
What is in water before it is purified?
•
•
•
Before water is fit to drink it needs to be purified to remove these substances and
any from the list of pollutants.
The Purification Process
Water is purified in 3 main stages:
1.
2.
3.

5. 1. Sedimentation:
Water contains _____________ solids that need to be removed first e.g.
______ and ________. This happens in _________________________. The
larger particles settle to the ______________ of the tank and the water is run
off from the top (see diagram above)
2. Filtration:
Some particles are too small and light to settle out in the sedimentation tank e.g.
clay.
So the water goes through a filter made from layers of ________, __________
sand and ____________ sand. This traps ____________ insoluble particles such
as clay.
3. Chlorination:
To kill any _______________ that may cause disease, a very small quantity of
________________________ is dissolved in the water.
NOTE:
Some soluble substances are not removed in the purification process and these
may be poisonous!

6. Testing for Dissolved Ions in Water
Hardness in water
• Some dissolved ions cause water to be _____________
• When you wash your hands with soap the water makes bubbles. We say that the
water________________.
• ______________ water lather well with soap
• ______________ water lathers very well
• The more soap solution needed to lather, the ____________ the water must
be.
Experiment to find out which dissolved ions create hard water
Solution Volume of soap solution needed for a
permanent lather, cm3
sodium chloride
magnesium chloride
potassium nitrate
sodium sulfate
magnesium sulfate
calcium sulfate
Conclusion
Explain in as much detail as you can what these results tell you (or answer questions
from the practical sheet). Are there any anomalous (odd) results?

7. Testing for Sulphate Ions, SO42-
• Fertilisers contain sulphate ions and if they get into water supplies in large
quantities they can be harmful.
• We need to be able to test water to find out if sulphate ions are present
• Sulphate ions make a white precipitate with barium chloride
barium chloride + potassium sulphate barium sulphate + potassium chloride
(white ppt)
barium chloride + sodium sulphate barium sulphate + sodium chloride
(white ppt)
Testing for Halide Ions, Cl-, Br-, I-
Silver nitrate solution is used to test for halide ions:
 chloride ions give a white precipitate
 bromide ions give a cream precipitate
 iodide ions give a pale yellow precipitate
silver nitrate + potassium chloride silver chloride + potassium nitrate
(white ppt)
silver nitrate + potassium bromide silver bromide + potassium nitrate
(cream ppt)
silver nitrate + potassium iodide silver iodide + potassium nitrate
(pale yellow ppt)
Higher ONLY
You must be able to write balanced symbol equations (given the appropriate
formulae)