Ch. 23 + Atmospheric Chemistry

Question 1

What is the fractional distillation of liquid air used for?

Answer 1

The fractional distillation of liauid air is used to obtain O and N gas from air. Air is liquified before being distilled.

Question 2

What are the steps involves in the fractional distillation of liquid air?

Answer 2

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.

Question 3

What are the uses for oxygen?

Answer 3

Pure oxygen is mixed with ethyne in oxyacetylene torches, used in welding. Also used in hospitals.

Question 4

What makes N2 so stable.

Answer 4

N2 has a triple bond.

Question 5

What is N gas and liquid used for?

Answer 5

N gas is used in food packaging(crisps). N liquid is used in refrigerant, storage of sperm, and in medicine to kill damaged cells.

Question 6

What is N fixation?

Answer 6

N fixation is the conservation of atmospheric N to compounds that can be used by plants.

Question 7

How does N fixation occur?

Answer 7

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).

Question 8

How is CO formed?

Answer 8

When C is burned in limited O,
C + 0.5O2 = CO
(CO prevents the uptake of O by haemoglobin)

Question 9

How is CO emitted?

Answer 9

Vehicle exhausts, cigarette smoke, incomplete combustion of hydrocarbons.

Question 10

How is CO2 formed?

Answer 10

C + O2 = CO2 in combustion
C6H12O6 = 2C2H5OH + 2CO2 in fermentation

Question 11

What is CO2 used for?

Answer 11

Carbonated drinks

Question 12

What is an acid oxide?

Answer 12

An acid oxide is an oxide that increases the H ion concentration in water.

Question 13

How are the three forms of CO2 found in water formed?

Answer 13

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.

Question 14

What is the greenhouse effect?

Answer 14

The greenhouse effect is the prevention of escape of infrared radiation by gases in the atmosphere.

Question 15

What is a greenhouse gas?

Answer 15

A greenhouse gas is a gas in the atmosphere that absorbs heat and contributes to global warming.

Question 16

What gas is the largest contributor to global warming?

Answer 16

Water vapour

Question 17

Where is CH4 produced?

Answer 17

Digestive tracts of cattle, compost heaps.

Question 18

How are the oxides of N formed?

Answer 18

From car exhausts,
N2 + O2 = 2NO
When lightning discharges,
2NO + O2 = 2NO2
Dissolution water to form nitrous/nitric acid,
2NO2 + H2O = HNO2 + HNO3

Question 19

How are the oxides of S formed?

Answer 19

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)

Question 20

How is scrubbing used to reduce waste gas emissions?

Answer 20

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.

Question 21

What is the pH of unpolluted rainwater?

Answer 21

5.7 (approx.)

Question 22

How is ozone(O3) formed?

Answer 22

O3 is formed in the stratosphere in a series of photochemical reactions,
O2 + energy = O. + O.
O2 + O. = O3
O3 + uv = O2 + O.

Question 23

What substances damage the ozone layer?

Answer 23

NO and CFCs

Question 24

How do CFCs damage the ozone layer?

Answer 24

CFCs are broken down into Cl. by uv radiation.
Cl. + O3 = ClO. + O2
ClO. + O. = Cl. + O2
This induces a chain reaction.

Question 25

In what layer are CH4 molecules harmful and beneficial and why?

Answer 25

CH4 has a greenhouse effect in the troposphere, hence harmful. In the stratosphere, they react with Cl atoms,
CH4 + Cl. = CH3. + HCl
HCl does not destroy O3.

Question 26

What are the replacements for CFCs, since they have uses like aerosol cans and refrigerants.

Answer 26

HCFCs and HFCs, an example of a HFC is tetrafluoroethane (CH2FCF3).