Acid Rain https://www.twig-world.com/film/glossary/acid-rain-396/

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

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

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 SO2 + H2O = H2SO3 [sulphurous acid]

The sulphurous acid then reacts with oxygen in the air to become sulphuric acid 2 H2SO3 + O2 = 2 H2SO4 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

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

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

Problems caused by acid rain

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

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

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.

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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

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

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

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.

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.

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 [43]