Purifying and testing water

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

Need to know (for the UK):Water sourcesPollutants in waterPurifying waterTesting water for sulphates and group 7 ions

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

Testing water for dissolved ions

Sulphate ions SO42-

A precipitate is a ____________ that forms when

two dissolved i_ _ _ react together

Group 7 (halide) ions Cl-, Br-, I-

Precipitates

Testing water for dissolved ions

Sulphate ions SO42-

A precipitate is a solid that forms when

two dissolved ions react together

Group 7 (halide) ions Cl-, Br-, I-

Precipitates

Testing water for dissolved ions

Sulphate ions SO42-

Add acidified barium chlorideGroup 7 (halide) ions Cl-, Br-, I-

Add acidified silver nitrate

video

Precipitates

Testing water for dissolved ions

Sulphate ions SO42-

Add acidified barium chloride

Barium chloride + potassium sulfate → Barium sulfate + potassium chloride

Precipitates

White precipitate

Testing water for dissolved ions

Sulphate ions SO42-

Add acidified barium chloride

Barium chloride + potassium sulfate → Barium sulfate + potassium chloride

BaCl2 + K2SO4 → BaSO4 + 2KCl

Precipitates

White precipitate

Testing water for dissolved ions

Sulphate ions SO42-

Add acidified barium chloride

Barium chloride + potassium sulfate → Barium sulfate + potassium chloride

BaCl2 + K2SO4 → BaSO4 + 2KCl

Ba2+(aq) + SO4

2-(aq) → BaSO4 (s)

Precipitates

White precipitate

Testing water for dissolved ions

Silver nitrate + sodium chloride → sliver chloride + sodium nitrate

Group 7 (halide) ions Cl-, Br-, I-

Add acidified silver nitrate

video

Precipitates

Silver chloride → white precipitateSilver bromide → cream precipitateSilver iodide → yellow precipitate

Cl- Br- I-

Testing water for dissolved ions

Silver nitrate + sodium chloride → sliver chloride + sodium nitrate

AgNO3 + NaCl → AgCl + NaNO3

Group 7 (halide) ions Cl-, Br-, I-

Add acidified silver nitrate

video

Precipitates

Silver chloride → white precipitateSilver bromide → cream precipitateSilver iodide → yellow precipitate

Cl- Br- I-

Testing water for dissolved ions

Silver nitrate + sodium chloride → sliver chloride + sodium nitrate

AgNO3 + NaCl → AgCl + NaNO3

Ag+(aq) + Cl-

(aq) → AgCl(s)

Group 7 (halide) ions Cl-, Br-, I-

Add acidified silver nitrate

video

Precipitates

Silver chloride → white precipitateSilver bromide → cream precipitateSilver iodide → yellow precipitate

Cl- Br- I-

Water sourcesPollutants in waterPurifying waterTesting water for sulphates and group 7 ions

Quick test