acid deposition • State what is meant by the term acid deposition and outline its origins. • Discuss the environmental effects of acid deposition and possible methods to counteract them.
rainwater normally acidic Write equations to show that rain water is normally acidic.
rainwater normally acidic • Rain is naturally slightly acidic because of the carbon dioxide dissolving into rain water to form carbonic acid according to the equation: CO2 (g) + H2O (l) H2CO3 (aq) • Carbon acid is a weak acid that dissociates partially to produce H+ ions to make rain water slightly acidic. H2CO3 (aq) HCO3- (aq) + H+(aq) Acidic rain is rain with a pH of less than 5.6 as it contains nitric acid and sulphuric acid.
acid deposition • Acid deposition refers to the process by which acid particles (acid solution particles or particles which can form acidic solutions i.e. H+(aq))leave the atmosphere as they are brought back down to earth e.g. on the ground, on trees, buildings, inside plants (e.g. stomata) or animals (e.g. your lungs). • There are two types of acid deposition: • wet deposition: acid rain, fog, sleet and snow – involves water. • dry deposition: gas molecules or acidic particles attached onto small airborne particles such as dust.
Nitric acid Write equations to show how nitric acid is formed in the atmosphere.
acid deposition: origins NO/NO2: formed as a result of high temperatures in internal combustion engines, i.e. cars and jet engines. 1. Production of nitrogen oxides: N2 (g) + O2 (g) 2NO (g) 2NO(g) + O2 (g) 2NO2 (g) 2. The following equations show two ways in which nitric (V) acid is formed in the atmosphere 2NO2(g) + H2O (l) HNO3 (aq) + HNO2 (aq) (=nitrous acid) Or 4NO2(g) + 2H2O (l) + O2 (g) 4 HNO3 (aq)
Sulphuric acid • Equations!!
acid deposition: origins SO2/SO3: from burning of coal which contains sulphur and from smelting plants • Production of oxides: S (g) + O2 (g) SO2 (g) 2SO2 (g) + O2 (g) 2SO3 (g) • Formation of atmospheric sulphuric (VI) acid and sulfurous acid SO3 (g) + H2O (l) H2SO4 (aq) 2SO2 (g) + 2H2O (l) + O2 (g) 2H2SO4 (aq) SO2 (g) + H2O (l) H2SO3(aq)
acid deposition: action • Cutting down emissions of nitrogen oxides by using catalytic converters, lean burn engines and thermal exhaust systems (lowers operating temperature). • Use of low sulphurfuels or remove sulphur before use. • Removal of sulphur oxides from exhaust fumes (factories, powr station stacks, incinerators) ; alkali scrubbers, limestone based fluidized bed. • Use of alternative sources of energy which do not involve fossil fuels and the production of very high temperatures. • Dealing with acid rain itself: neutralization of lakes using calcium carbonate or calcium oxide, e.g. CaO + H2SO4 (aq) CaSO4 (s) + H2O (l)