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. Sedimentation2. Filtration3. Chlorination

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!

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

ConclusionExplain 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?

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.

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!

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 chloridemagnesium chloridepotassium nitratesodium sulfatemagnesium sulfatecalcium sulfate

ConclusionExplain 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?

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 ONLYYou must be able to write balanced symbol equations (given the appropriate formulae)