10. Chemistry of the environment Flashcards
Air
In clean dry air there is…
78% Nitrogen (N²)
21% Oxygen (O²)
1% Other noble gases + CO²
(Argon - 0.93%, CO² - 0.04%)
Clean dry air - Characteristics
Temperature = 15C
Doesn’t contain any water
Doesn’t contain any polluting gases
It is a mixture of gases
Nitrogen is unreactive at this temperature, meaning the level of nitrogen is constant.
Oxygen levels are still constant (despite being reactive) → This is because these compounds are often broken down so O2 is returned to the air.
How are gases separated from air
Fractional distillation
Photosynthesis
carbon dioxide + water → glucose + oxygen
6CO2 + 6H2O → C6H12O6 + 6O2
Chlorophyll transfers light energy from the sun into stored chemical energy (glucose) through photosynthesis.
How the greenhouse effect occurs
- Visible light from Sun travels through vacuum of space + Earth’s atmosphere (without being absorbed because both are transparent) Infrared light = also sent out from sun
2- Visible sunlight = absorbed by molecules on surface of Earth → changed into thermal energy. Surface becomes warmer. - Some infrared light from sun = reflected by Earth
- Reflected light = either trapped by greenhouse gases (earth becomes warmer) or finds a path through the atmosphere + lost to outer space (no effect on Earth’s temp)
As the surface of earth cools…
- Infrared radiation = emitted. If it hits a molecule of a greenhouse gas → it is absorbed + converted into heat energy + makes the molecule warmer. (temperature of earth increases)
- These greenhouse molecules eventually cool by emitting infrared radiation → which gets absorbed by the earth’s surface + warms the earth
- Some of the infrared radiation = lost to space (not all is absorbed by earth.
How do human impacts increase greenhouse gases?
CO2 = combustion of fossil fuels
(Naturally emitted through respiration)
Methane = waste gas by the intensive farming of animals (eg. cattle + sheep)
(Naturally emitted through decomposition of vegetation)
How is acid rain created
- Acid rain = almost pure water
- (Not dangerous to people) → in large amounts and over years = dissolves rocks eg. limestone + makes soil + rivers more acidic.
- Can kill fish in rivers + trees (too acidic soil)
- Damages ancient buildings
Oxides of nitrogen (from burning fossil fuels in car engines) + sulfur dioxide (combustion of coal to generate electricity) cause acid rain
What is photochemical smog
Some chemicals (eg. nitrogen oxides) react with other chemicals and then light energy from the sun to create photochemical smog.
- Main cause of these chemicals = vehicle engines burning fossil fuels (why there is more smog in highly populated areas with large amounts of traffic → Becomes worse during the end of the day since sunlight is high + traffic increases)
- Photochemical smog can cause respiratory problems
How is carbon monoxide creates? (+ what is the effect of CO)
Carbon burns to create water + CO2
However, when there isn’t enough oxygen, incomplete combustion occurs and carbon monoxide is created.
CO = toxic gas + greenhouse gas
This often happens within forest fires or inside engines as the combustion of carbon containing fuels is inefficient.
What are particules, how are they created and what effect do they have?
Particulates = particles of solid or liquid material that are small enough to remain airborne (causing pollution)
- Examples include soot (microscopic particles of impure carbon)
- Produced by engines burning diesel / other heavy fuels (fuel oils in ships)
- Also smoke from forest fires.
Particulates → can cause respiratory diseases + cancer
Catalytic convertors
Exhaust fumes of car engines contain a variety of dangerous gases that are toxic and polluting.
Catalytic converters → reduce some of the most dangerous pollutants by reacting them together to make non-toxic gases, as shown in the reaction below.
(Therefore cars now always have catalytic converters)
carbon monoxide + nitrogen oxide → carbon dioxide + nitrogen
2CO + 2NO → 2CO2 + N2
Carbon dioxide (CO2) (Main source, Harmful effects, Solutions)
Main source
Complete combustion of fossil fuels
Harmful effects
Increases global warming (greenhouse effect)
Solutions
Planting more trees
Renewable energy sources (burning less fossil fuels)
Carbon monoxide (CO) (Main source, Harmful effects, Solutions)
Main source
Incomplete combustion of fossil fuels (+ wood)
Harmful effects
Toxic gas
Solutions
Catalyctic convertors on cars
Particulates (Main source, Harmful effects, Solutions)
Main sources
Burning of fossil fuels
Harmful effects
Respiratory problems (eg. asthma) + increases amounts of cancer
Solutions
Air filters
Methane (CH4) (Main source, Harmful effects, Solutions)
Main sources
Decomposition of plants + Waste products of digestion in farm animals
Harmful effects
Increases global warming
Solutions
Reduce livestock farming + Eating less meat + dairy foods
Oxides of nitrogen (NO, NO2, NOx) (Main source, Harmful effects, Solutions)
Main sources
Inside car engines, nitrogen + oxygen from the air react together
Harmful effects
Respiratory problems, forms acid rain, produces photochemical smog
Solutions
Catalytic convertors in cars
Sulfur dioxide (SO2) (Main source, Harmful effects, Solutions)
Main sources
Burning sulfur-containing fossil fuels like coal
Harmful effects
Forms acid rain
Solutions
Burning low-sulfur fuels instead
Flue gas desulfurisation by passing gases through solid calcium oxide.
Physical tests for water…
Cobalt (II) Chloride (paper)
Anhydrous = Blue
Hydrous = Pink
Copper (II) Sulfate (solid)
Anhydrous = White
Hydrous = Blue
Physical tests for the purity of water
Water freezes at 0 C
Water boils at 100 C
Impure substances (eg. seawater) has a boiling range
Substances found in water…
Dissolved oxygen - Allows aniamls (eg. fish) to respire
Metal compounds - Some are needed for plants to live eg. magnesium ions. Other are toxic. Eg. lead compounds (typically industrial waste)
Plastics - Eaten by marine animals + fish (can come from rubbish + from the fishing industry)
Sewage + harmful microbes - Human sewage = dangerous microbes. Can cause infectious diseases. (released from broken sewage pipes/ directly into river)
Nitrates + phosphates (from fertilisers) - Eutrophicaiton (phosphate source = detergents)
Why is distilled water used during experiments?
Tap water contains impurities which could change the outcome of your experiment.
How is distilled water created?
Water is boiled at 100 C.
The steam is collected.
It is then condensed back into a liquid.
Stages of water purification
- Source of water - Rivers/ lakes/ reservoirs
- Water filtered through screen to remove larger solids (eg. fish, sand, wood)
- Sedimentation tanks in which water stands still. This allows finer sediment to fall to the bottom of the tank.
- Filtration - Water flows through smaller and smaller sized sand particles → remove small insoluble solid impurities.
- Water is pushed through carbon particles. Molecules that give the water an unusual taste/ smell bond with the carbon particles.
- Small quantity of chlorine gas bubbles into water. Kills bacteria + destroys viruses.
- Water undergoes several additional steps. (Improves teeth, makes sure water flows through pipes well) →
- Water in pipes is still not 100% pure.
Why is fertilisation needed?
Atoms + molecules are extracted from the soil by growing plants.
After plants are harvested, atoms + molecules aren’t returned to the soil –> soil becomes less fertile.
Natural processes (eg. nitrogen cycle) can replace this –> but its slow.
Fertilisation can be used to replace this.
Why can’t plants absorb nitrogen gas?
N2 - Strong triple covalent bond.
Therefore, although it’s 78% of air –> plants absorb water soluble ions from their roots to create nitrogen-containing molecules (eg. DNA)
NPK fertilisers
Most important fertilisers = NPK
contains….
- Nitrogen (N)
- Phosphorous (P)
- Potassium (K)
(contains salts like KNO³, NH⁴, PO⁴)
