Water Purity

This set of cards will show the equations needed to show how to test for different ions within water.

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Testing for Chloride Ions

Sodium Chloride + Silver Nitrate --> Silver Chloride + Sodium Nitrate

NaCl + AgNO3 --> AgCl +NaNO3


Sodium Chloride - clear

Silver Nitrate - silver/grey

Silver Chloride - white

Sodium Nitrate - clear

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Testing for Bromide Ions

Sodium Bromine + Silver Nitrate --> Silver Bromide + Sodium Nitrate

NaBr + AgNO3 --> AgBr + NaNO3


Sodium Bromine - clear

Silver Nitrate - silver/grey

Silver Bromide - cream

Sodium Nitrate - clear

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Testing for Iodide Ions

Sodium Iodide + Silver Nitrate --> Silver Iodide + Sodium Nitrate

NaI + AgNO3 --> AgI + NaNO3


Sodium Iodide - clear

Silver Nitrate - silver/grey

Silver Iodide - pale yellow

Sodium Nitrate - clear

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Testing for Sulphate ions

Sodium Sulphate + Barium Chloride --> Barium Sulphate + Sodium Chloride

Na2SO4 + BaCl2 --> BaSO4 + 2NaCl


Sodium sulphate - clear

Barium chloride - clear

Barium sulphate - white

Sodium chloride - clear

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Explanation of Equations

The equations shown for each of the different ions are when there is an ion present in the reaction. If there is no ion present, the reaction will not occur.

There is a different reaction for the sulphate ions so be careful not to get them mixed up or forget about it. Chloride, Bromide and Iodide ions are tested with Silver Nitrate as a Reagent in the reaction. For the sulphate reaction, the Reagent is Barium Chloride.

A Reagent is a substance used in a chemical reaction to detect, measure, examine or produce other substances.

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Overview of Water Purity

Water is purified in water treatment plants. Ground water is usually not needed to be treated because it is from aquifers. Surface water needs lots of treatment.

The process of water treatment:

1. Filtration - A wire mesh screens out large twigs etc. and then gravel and sand beds filter out any other solid bits.

2. Sedimentation - Iron Sulphate or Aluminium Sulphate is added to the water which makes fine particles clump together and settle at the bottom.

3. Chlorination - Chlorine gas is bubbled through to kill harmful bacteria and other microbes.

The water that comes out of our taps has to meet strict safety standards.Although this process has taken place, some pollutants are still found in tap water. These pollutants come from various sources.

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