1. We are all aware of the fabulous work done by
charities such as Water Aid in developing countries.
But water also needs to be purified in the UK

2. Need to know (for the UK):
Water sources
Pollutants in water
Purifying water
Testing water for sulphates and group 7 ions

3. Water resources in the UK
• Use page 94 of your revision guide to:
– Find 4 places where we get our water
– Explain why it is important to conserve water
– List 3 impurities that can be found in tap water and
explain how they get there
– Describe the water purification process:
• Filtration; Sedimentation; Chlorination
• Ext: Explain why some soluble substances are not removed
from water during purification
• Ext: Explain the disadvantage of obtaining fresh water by
distilling sea water

4. Testing water for dissolved ions
Precipitates
A precipitate is a ____________ that forms when
two dissolved i_ _ _ react together
Sulphate ions SO42-
Group 7 (halide) ions Cl-, Br-, I-

5. Testing water for dissolved ions
Precipitates
A precipitate is a solid that forms when
two dissolved ions react together
Sulphate ions SO42-
Group 7 (halide) ions Cl-, Br-, I-

6. Testing water for dissolved ions
Precipitates
Sulphate ions SO42- Group 7 (halide) ions Cl-, Br-, I-
Add acidified barium chloride Add acidified silver nitrate
video

7. Testing water for dissolved ions
Precipitates
Sulphate ions SO42-
Add acidified barium chloride
Barium chloride + potassium sulfate →
Barium sulfate + potassium chloride
White precipitate

8. Testing water for dissolved ions
Precipitates
Sulphate ions SO42-
Add acidified barium chloride
Barium chloride + potassium sulfate →
Barium sulfate + potassium chloride
BaCl2 + K2SO4 → BaSO4 + 2KCl
White precipitate

9. Testing water for dissolved ions
Precipitates
Sulphate ions SO42-
Add acidified barium chloride
Barium chloride + potassium sulfate →
Barium sulfate + potassium chloride
BaCl2 + K2SO4 → BaSO4 + 2KCl
Ba2+(aq) + SO42-(aq) → BaSO4 (s)
White precipitate

10. Testing water for dissolved ions
Precipitates
Group 7 (halide) ions Cl-, Br-, I-
Add acidified silver nitrate
Silver nitrate + sodium chloride →
sliver chloride + sodium nitrate
Cl- Br- I-
Silver chloride → white precipitate
Silver bromide → cream precipitate
Silver iodide → yellow precipitate video

11. Testing water for dissolved ions
Precipitates
Group 7 (halide) ions Cl-, Br-, I-
Add acidified silver nitrate
Silver nitrate + sodium chloride →
sliver chloride + sodium nitrate
Cl- Br- I-
AgNO3 + NaCl → AgCl + NaNO3
Silver chloride → white precipitate
Silver bromide → cream precipitate
Silver iodide → yellow precipitate video

12. Testing water for dissolved ions
Precipitates
Group 7 (halide) ions Cl-, Br-, I-
Add acidified silver nitrate
Silver nitrate + sodium chloride →
sliver chloride + sodium nitrate
Cl- Br- I-
AgNO3 + NaCl → AgCl + NaNO3
Ag+(aq) + Cl-(aq) → AgCl(s)
Silver chloride → white precipitate
Silver bromide → cream precipitate
Silver iodide → yellow precipitate video

13. Water sources
Pollutants in water
Purifying water
Testing water for sulphates and group 7 ions
Quick test