Topic 10: Chemistry of the environment

Chemical tests for water Using cobalt(ll)chloride

Cobalt chloride paper turns blue to pink in water

Test of water

Using copper(ll)sulfate

Anhydrous copper(ll)sulfate turns white to blue on the addition of water

Pour drops of copper sulfate using a pipette

It turns blue in presence of water

Equation of cobalt chloride and water

Anhydrous cobalt(ll)+water=hydrated cobalt(ll)chloride

CoCl2(s)+6H2O(l)=CoCl2.6H2O(s)

Equation of copper(ll)sulfate and water

Anhydrous copper(ll)sulfate+water=hydrated copper(ll)sulfate

CuSO4(s)+5H2O(l)=CuSO4.5H2O(s)

Testing for purity

• Pure substances melt and boil at specific temperatures

• Melting and boiling points data can be use to determine the purity of water

• Impurities tend to increase the bp of water-boils over 100°C

• Impurities tend to decrease the mp of water-melts below 0°C

Distilled Water

• Water that has been heated to form vapor and condensed back into liquid

• It contains very few impurities

• It is used in practical chemistry because of its high purity

• Tap water contains many impurities which can interfere with chemical reactions

What is a rock that stores water called?

Aquifer

Substances which water from natural sources may contain

• Dissolved oxygen

• Metal compounds

• Plastic

• Sewage

• Harmful microbes

• Nitrates from fertilisers

• Phosphates from fertilisers and detergents

Beneficial substances in water

• Dissolved oxygen-essential for aquatic life

• Metal compounds-some provide essential minerals necessary for life such as calcium and magnesium

Harmful substances in water

Metal compounds-some are toxic such as Aluminium and lead

Plastic-harmful to aquatic life

Sewage-contains harmful microbes which cause diseases

Nitrate & phosphates from fertilisers-promote the growth of aquatic plant life which lead to deoxygenation of water(eutrophication)

How is domestic water treated

• Filtration(removes insoluble solids)

• Sedimentation(particles fall to the bottom due to gravity and form a layer called sediment)

• Further filtered and addition of carbon(to remove taste and odours)

• Chlorination(kills bacteria)(controlled amount as too much chlorine is toxic, too little doesn’t kill bacteria)

Diseases that can arise from consumption of untreated water

Cholera and typhoid

What does fertilisers contain

NPK

Nitrogen Potassium Phosphorus

Functions of NPK

Nitrogen-makes chlorophyll and protein to grow healthy leaves

Potassium-promotes growth and healthy fruits and flowers

Phosphorus-promotes healthy roots

Composition of air

78% Nitrogen

21% Oxygen

0.04% CO2

0.9% other noble gases

Pollutants of air

• Carbon dioxide(from combustion-causes global warming)

• Particulates(from incomplete combustion-increases risk of respiratory problems and cancer)

• Carbon monoxide(from incomplete combustion-toxic)

• Methane(formed from waste gases of animals, decomposition of vegetation)

• Sulfur dioxide(produced by combustion of fuels containing sulfur-causes acid rain)

• Oxides of nitrogen(formed when nitrogen and oxygen react at high temps-causes acid rain and photochemical smog)

Effects of greenhouse gases

• The sun emits energy in the form of radiation that enters the earth’s atmosphere

• Some thermal energy is reflected from the earth’s surface

• Most energy is absorbed and re emitted back from the earth’s surface

• The energy passes through atmosphere where some thermal energy passed straight through and it emitted in space

• But some thermal energy is absorbed by greenhouse gases and remitted in all directions

• This keeps the earth warm(greenhouse effect)

• As greenhouse gases increase=more thermal energy trapped in earth’s atmosphere leading to global warming(enhanced greenhouse effect)

Dealing with climate change

• Plating trees

• Reduction in livestock farming

• Decrease use of fossil fuels

• Increase use of renewable energy

Dealing with acid rain

• Use of catalytic converters in vehicles

• Reduce emissions of sulfur dioxide by using low sulfur fuels

Photosynthesis

• Endothermic reaction

  carbon dioxide+water=glucose+oxygen

Symbol equation for photosynthesis

6CO2+6H2O=C6H12O6+6O2

Oxides of nitrogen

• Formed when nitrogen and oxygen react with high pressure and temperature conditions of internal combustion engines and blast furnaces

Oxides of nitrogen are reduced to N2 gas:

2NO=N2+O2