Ch. 23 + Atmospheric Chemistry Flashcards
What is the fractional distillation of liquid air used for?
The fractional distillation of liauid air is used to obtain O and N gas from air. Air is liquified before being distilled.
What are the steps involves in the fractional distillation of liquid air?
Air is filtered to remove dust. Then cooled, then CO2 and H2O vapour are removed(as solids). Then air is compressed. Air is cooled again. Liquid N and O have boiling points of 77K and 90K respectively. (N being the higher fraction). This is a continuous process.
What are the uses for oxygen?
Pure oxygen is mixed with ethyne in oxyacetylene torches, used in welding. Also used in hospitals.
What makes N2 so stable.
N2 has a triple bond.
What is N gas and liquid used for?
N gas is used in food packaging(crisps). N liquid is used in refrigerant, storage of sperm, and in medicine to kill damaged cells.
What is N fixation?
N fixation is the conservation of atmospheric N to compounds that can be used by plants.
How does N fixation occur?
Lightning splits the N2 bond, to make N oxides and then these dissolve in water to make nitrous/nitric acid. The roots of legumes are colonised by N fixing bacteria(they use nitrogenase).
How is CO formed?
When C is burned in limited O,
C + 0.5O2 = CO
(CO prevents the uptake of O by haemoglobin)
How is CO emitted?
Vehicle exhausts, cigarette smoke, incomplete combustion of hydrocarbons.
How is CO2 formed?
C + O2 = CO2 in combustion
C6H12O6 = 2C2H5OH + 2CO2 in fermentation
What is CO2 used for?
Carbonated drinks
What is an acid oxide?
An acid oxide is an oxide that increases the H ion concentration in water.
How are the three forms of CO2 found in water formed?
CO2 + H2O = H2CO3 (carbonic acid)
H2CO3 = H+ + HCO3- (hydrogencarbonate ion)
HCO3- = H+ + CO3 2- (carbonate ion)
These are all reversible reactions.
They are more likely to occur under alkaline conditions.
What is the greenhouse effect?
The greenhouse effect is the prevention of escape of infrared radiation by gases in the atmosphere.
What is a greenhouse gas?
A greenhouse gas is a gas in the atmosphere that absorbs heat and contributes to global warming.
What gas is the largest contributor to global warming?
Water vapour
Where is CH4 produced?
Digestive tracts of cattle, compost heaps.
How are the oxides of N formed?
From car exhausts,
N2 + O2 = 2NO
When lightning discharges,
2NO + O2 = 2NO2
Dissolution water to form nitrous/nitric acid,
2NO2 + H2O = HNO2 + HNO3
How are the oxides of S formed?
From combustion of fossil fuels, they go on to dissolve in water,
SO2 + H2O = H2SO3 (sulfurous acid)
Oxidation of SO2,
SO2 + O2 = 2SO3
Dissolution of SO3 in rainwater,
SO3 + H2O = H2SO4 (sulfuric acid)
How is scrubbing used to reduce waste gas emissions?
Limestone is used to reduce SO2 emissions from coal combustion.
High temperatures cause limestone to decompose,
CaCO3 = CaO + CO2
CaO + SO2 = CaSO3 (calcium sulfite)
In scrubbing, SO2 is prevented from releasing into the atmosphere.
What is the pH of unpolluted rainwater?
5.7 (approx.)
How is ozone(O3) formed?
O3 is formed in the stratosphere in a series of photochemical reactions,
O2 + energy = O. + O.
O2 + O. = O3
O3 + uv = O2 + O.
What substances damage the ozone layer?
NO and CFCs
How do CFCs damage the ozone layer?
CFCs are broken down into Cl. by uv radiation.
Cl. + O3 = ClO. + O2
ClO. + O. = Cl. + O2
This induces a chain reaction.
