Air and Water
- Created by: Lucy Sands
- Created on: 29-05-14 15:59
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- Air and Water
- Gases in the atmosphere
- 200million years ago
- proportions of gases in Earth's atmosphere had stabilised
- much the same as they are today
- Nitrogen 78%
- Oxygen 21%
- Argon 0.9%
- Carbon Dioxide 0.04%
- also small % of pollutant gases e.g. Carbon Monoxide, Sulfur Dioxide and oxides of Nitrogen
- as well as varying amounts of water vapour
- proportions of gases in Earth's atmosphere had stabilised
- 200million years ago
- Separating gases in the air
- In industry - fractional distillation
- process in which liquids with different boiling points are separated
- firstly, have to get air cold enough to condense into liquid
- cooled to below -200°C
- two stage process
- 1. compress air to about 150 times atmospheric pressure
- actually warms it up, so cooled down to normal temp
- by passing over air pipes carrying cold water
- actually warms it up, so cooled down to normal temp
- 2. provides main cooling, takes place when pressure is released
- air allowed to expand rapidly, similar to aerosol cans
- temp drops far enough for even gases in air to condense to liquids
- CO? and water can be removed easily from mixture before frac. dist. takes place
- these two are solids at room temp.
- CO? and water can be removed easily from mixture before frac. dist. takes place
- temp drops far enough for even gases in air to condense to liquids
- air allowed to expand rapidly, similar to aerosol cans
- 1. compress air to about 150 times atmospheric pressure
- Boiling points of main substances
- Nitrogen: -196°C
- Argon: -186°C
- Oxygen: -183°C
- Column colder at top than bottom so at -196°C nitrogen boils 1st
- -185°C oxygen still cold enough to be liquid as it boils at -183C
- so O? can be separated off as a liquid from bottom of column
- small amount of argon can be collected from column
- Untitled
- -185°C oxygen still cold enough to be liquid as it boils at -183C
- Uses of 3 main gases
- Liquid Nitrogen
- cool things down at very low temp.
- at these temps most things solidify
- used to store sperm in hospitals to help in fertility treatment
- cool things down at very low temp.
- Nitrogen Gas
- very unreactive
- sealed food packaging to stop decay
- oil tankers
- when oil pumped ashore to reduce risk of explosion
- ammonia
- convert into fertilisers
- very unreactive
- Oxygen
- help people breathe, often at scene of accident or hospital
- help things react
- high temp welding and steel making process
- Liquid Nitrogen
- In industry - fractional distillation
- Oxygen and Oxides
- reactive gas in air is oxygen
- when any substance burns, it reacts with oxygen gas in air to form compounds
- i.e. oxides
- elements burn more vigorously in pure oxy than air as only 21% oxy
- metallic elements burn to form solid oxides
- 2Mg + O? ? 2MgO
- 4Li + O? ? 2Li?O
- known as combustion reactions
- non-metallic elements burn often form oxides which are produced as gases
- C + O? ? CO?
- S + O? ? SO?
- OXIDATION
- opposite is reduction - important for extraction of metals from ores
- non-metallic elements burn often form oxides which are produced as gases
- non-metallic elements burn often form oxides which are produced as gases
- C + O? ? CO?
- S + O? ? SO?
- when any substance burns, it reacts with oxygen gas in air to form compounds
- Metal Oxides
- if dissolved in water, makes an alkaline solution
- however some do not dissolve in water
- e.g. copper oxide
- test neutral with UI
- however does react with acid
- test neutral with UI
- also known as a BASE
- e.g. copper oxide
- amphoteric oxides
- react like both acids and bases
- do not dissolve in water
- cannot test pH of solutions formed
- do not dissolve in water
- react like both acids and bases
- Non-metal Oxides
- most dissolve in water to form acids
- In general, Metal oxides are basic, Non-metal oxides are acidic
- reactive gas in air is oxygen
- Water Treatment
- Water from natural resources contains dissolved minerals and microbes
- have to be reduced to meet safety standards
- best sources contain low levels of minerals and microbes to start with
- when taken from rivers and reservoirs needs to be treated to be safe to drink
- treatment involves...
- passing untreated water through filter beds made of sand to remove solid particles
- addition of chlorine to sterilise water by killing microbes
- people often have filter jugs at home
- usually have top part into which you put tap water
- as water goes from top to bottom, passes through a filter cartridge
- often contains activated carbon, an ion-exchange resin and silver
- carbon reduces levels of chlorine, pesticides and other organic impurities
- ion-exchange removes calcium, magnesium, lead, copper and aluminium ions
- silver nano particles discourage growth of bacteria within filter
- cartridge should be changed every few weeks
- often contains activated carbon, an ion-exchange resin and silver
- as water goes from top to bottom, passes through a filter cartridge
- usually have top part into which you put tap water
- treatment involves...
- Pure water
- water can be made pure by distillation
- boiling followed by condensation of steam
- however expensive process due to energy costs involved in heating large vols of water
- in countries with few sources of freshwater, seawater is made usable
- process known as desalination
- seawater undergoes distillation at industrial plant
- but at reduced pressure to lower b.p. and save energy
- however still caro
- seawater undergoes distillation at industrial plant
- process known as desalination
- water can be made pure by distillation
- Fluoride in water
- Arguments for
- some areas have had fluoridated water for about 50 years - no one has seen harmful effects
- 30% reduction of cavities in teeth
- need fluoridation to protect teeth of those who don't have good dental hygiene habits and don't visit dentists regularly
- bacteria associated with tooth decay will also cause some types heart disease
- fluoride is only added in tiny amounts anyway
- Arguments against
- Fluorosis is a condition caused when children take too much fluoride
- white streaks/tips appear on teeth - deposits of calcium fluoride
- these are porous and can become stained
- white streaks/tips appear on teeth - deposits of calcium fluoride
- benefit of fluoridation is not significant, so why should we risk our health?
- ethically wrong to give people treatments they have not consented to
- some excess fluoride can affect the brain, producing learning difficulties and Alzheimer's
- Fluorosis is a condition caused when children take too much fluoride
- Arguments for
- Water from natural resources contains dissolved minerals and microbes
- Rusting
- both air (oxygen) and water are needed for iron to rust
- providing a barrier between iron and air and water protects iron from rusting
- paint, oil/grease, plastic, a less/more reactive metal
- sacrificial protection provides protection against rusting even when the iron is exposed to air and water. The iron needs to be attached to a more reactive metal
- i.e. zinc, aluminium or magnesium
- galvanisation
- i.e. zinc, aluminium or magnesium
- rust = hydrated iron oxide
- Gases in the atmosphere
- 200million years ago
- proportions of gases in Earth's atmosphere had stabilised
- much the same as they are today
- Nitrogen 78%
- Oxygen 21%
- Argon 0.9%
- Carbon Dioxide 0.04%
- also small % of pollutant gases e.g. Carbon Monoxide, Sulfur Dioxide and oxides of Nitrogen
- as well as varying amounts of water vapour
- proportions of gases in Earth's atmosphere had stabilised
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