1. Acid Rain

2. Naturally slightly acidic
As rain falls through air CO2 dissolves in it
H2O + CO2 = H2CO3
carbonic acid
pH might be about 6.5
This is NOT Acid Rain

3. Difference between Acid Lake and Healthy Lake
is 2 pH units
Acid Lake is 100 times more acidic than a Healthy Lake
pH is a log scale

4. Acid Rain Formation SO2 Sulphur dioxide gas
Produced by burning Fossil Fuels
Fossil fuels [oil, turf, coal] contain varying amounts of sulphur (natural gas contains very little S)
When they burn
S + O2 = SO2
This SO2 dissolves in the rain as it falls
SO H2O = H2SO [sulphurous acid]

6. The sulphurous acid then reacts with oxygen in the air to become sulphuric acid
2 H2SO3 + O2 = 2 H2SO Sulphuric acid
Sulphuric acid is a strong acid and quickly lowers the pH of the rain
When the pH gets below 5 then the rain is Acid Rain

7. The other important cause is NO2 – nitrogen dioxide gas
Produced in areas where there is high temperature combustion [incinerators and petrol engines]
As a waste product of many industrial processes [e.g. fertiliser production]
Also produced from air by lightning

8. N2 + O2 = 2 NO [nitrogen monoxide]
2 NO + O2 = 2 NO2 [nitrogen dioxide]
2 NO2 + H2O = HNO HNO2
nitric acid nitrous acid
2 HNO O2 = 2 HNO3
Nitric acid is also a strong acid
So it quickly lowers the pH of the rainwater and forms acid rain

10. Problems caused by acid rain

11. 1. Corrosion of stonework and metals
a. Stonework
Particularly CaCO3 (limestone and marble)
CaCO3 + 2 HNO3 = Ca(NO3)2 + H2O + CO2
Calcium nitrate is soluble in water and washes away easily
Much, much faster than carbonic acid at wearing away limestone and marble
Sulphuric acid similar

13. b. Metals 2 Fe + 6 HNO3 = 2 Fe(NO3)3 + 3 H2
Iron is insoluble but iron nitrate is soluble so the pole dissolves away

14. 2 Respiratory Problems
Acid rain forming gases in the atmosphere dissolves in the water of the eyes and lungs
This acid irritates both the lungs and eyes
especially of the old and sick [and very young.]
irritation leaves open to infections which can kill
The “pea-souper” of London smog in 1950 officially caused 10,000 deaths but recent studies suggest the actual death toll was much greater.

17. Bejing

18. 3. Aquatic Life
Fish eggs [roe] and very young fish [fry] are very susceptible to pH changes.
If the pH drops below six they can be severely damaged
They do not develop properly
Many are affected by fungal attacks
Crayfish and shrimps are first to die off
As the pH gets lower more and more species die off

21. pH 7 6.5 6 5.5 5 4.5 4 Normal pH Crayfish and shrimp Snails and mayfly
Salmon, Minnows, Roach
Trout
Perch and Pike
Normal pH
Bog moss and certain insects

24. 4. Terrestrial Life - Plants
Damage to trees - tops show damage first by going yellow and then dying e.g. Black Forest.
Pine trees actually make the problem worse - rainwater running off them is more acidic than that which falls onto them

26. 5. Groundwater Effects
The acid in the rain reacts with metals in the soil and puts them into solution
They can now work their way out of the soil into our drinking water
This washing of metals out of the soil is called Leaching
If the metals are toxic e.g. Pb, Cd, Hg or Al then this is a big problem.

27. Normal rain is acidic . What is its pH? [1]
What makes normal rain acidic and write an equation? [4]
At what pH does rain become acid rain [1]
Name the 2 gases that are the cause of acid rain and in each case give major source of the gas. [4]
By means of equations show how the two gases mentioned above become acid rain.
Give five problems caused by acid rain.

28. Normal rain is acidic . What is its pH? [1] 6.5
What makes normal rain acidic and write an equation? [4] CO2, CO2 + H2O = H2CO3,
At what pH does rain become acid rain [1] 5
Name the 2 gases that are the cause of acid rain and in each case give major source of the gas. [4] SO2, burning fossil fuels, volcanoes // NO2 /cars, high tempeature combustion, lightning, car engines,
By means of equations show how the two gases mentioned above become acid rain. [10+17]
Give five problems caused by acid rain. [6] corrosion stone / metal/ kills aquatic life/ kills plants / respiratory problems / groundwater effects
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