Chemistry - chemistry of the environment

Two tests for water:

Cobalt chloride —> From blue to pink

Copper sulphate —> From white to blue

Formula Cobalt chloride: 6H2O + CoCl2 —> 6H2O.CoCl2

Formula copper sulphate: 5H2O + CuSO4 —> 5H2O.CuSO4

Purity of water

You can find the purity of water by checking the melting and boiling point of water. If the melting point decreases, it’s impure and if the boiling point increases, it’s impure. The graph will not be constant.

What is distilled water?

Contains fewer chemical impurities than tap water. It is evaporated and then condensed.

Water from natural sources contains:

1. Dissolved oxygen and other gases

2. Sewage

3. Plastics

4. Metal ions

5. Harmful microbes

6. Nitrates from fertilisers

7. Phosphates from detergents

Describe the water treatment steps

1. Screening - coarse grid removes big materials

2. Sedimentation - Coagulants are added, which stick to the mineral particles and make them heavier. This sinks to the bottom of the container and is removed.

3. Filtration - Passes through fine sand to remove any material that wasn’t during sedimentation.

4. Filtration through carbon - removes unpleasant odours and tastes.

5. Chlorination - eliminates harmful microorganisms.

What do NPK fertilisers have? How do each of these mineral ions benefit the plant?

1. Nitrogen - Promotes plant growth and required to make proteins.

2. Phosphorous - Promotes healthy roots

3. Potassium - Healthy growth of fruits and flowers

Examples of fertilisers:

Ammonium salts and nitrate salts -

Ammonium nitrate - NH4NO3

Ammonium phosphate - (NH4)3PO4

Potassium nitrate - KNO3

Describe the composition of the air

78% Nitrogen

21% Oxygen

1% Other

0.04% Carbon dioxide

0.9%.Argon and other noble gases

Gases present in the atmosphere due to human activity

• Carbon dioxide: Released by the complete combustion of fossil fuels, respiration, deforestation. Colourless heavy gas. Sharp smell when concentrated. Soluble in water.

• Carbon monoxide: Released by the incomplete combustion of fossil fuels. It is toxic, poisonous and combines with haemoglobin in the blood, preventing it from carrying oxygen. Colourless. Insoluble. No smell.

• Sulphur dioxide: An acidic gas with a sharp smell. Solub. Strong, sharp suffocating smell and colourless. Dissolves in rain to form acid rain.

• Nitrous oxides: Acidic gases. Form when the nitrogen and oxygen in air react together inside hot motor engines and furnaces. Causes respiratory problems, dissolves in rain to give acid rain, forms a brown haze called a photochemical smog.

• Particulates: Tiny solid particles that may appear as dark smoke. Forms in the incomplete combustion of fuels containing carbon. Linked to respiratory problems and cancer.

• Methane:

Three methods of tackling acid rain:

1. Flue gas desulfurisation - When fossil fuels are burnt, the sulphur dioxide can be trapped by being treated with a slurry of calcium oxide (CaO) or lime. This reacts with sulfur dioxide to give calcium sulphite and sulfur dioxide is not released into the atmosphere. Also called a SCRUBBER

2. Catalytic converters - Fitted into the exhaust system of cars. They convert nitrogen oxides to nitrogen and carbon monoxide to carbon dioxide. Deal with unburnt hydrocarbons as well.

Oxides of nitrogen are removed by reduction. Carbon monoxide is turned into carbon dioxide by oxidation.

NO + 2CO —> N2 + 2CO2

Unburnt hydrocarbons are oxidised to give water and carbon dioxide.

C8H18 + O2 —> CO2 + H2O

3. Using low-sulfur fuels - Coal, gas and fuels from petroleum are treated to remove as much sulfur as possible before being burnt.