Acid Deposition

pH Scale

7 is neutral As numbers decrease, acidity increases As numbers increase, alkalinity

increases

pH Scale

Q - How much more acidic is a pH of 3 than a pH of 7?

A – 10,000 times pH is a logarithmic scale

Rain From a natural and unpolluted

atmosphere has a pH of close to 6.0 Results form reaction of water vapor

and CO2 in the atmosphere forming a weak carbonic acid (H2CO3): CO2(g) + H2O(l) H2CO3(aq)

Since carbonic acid is a weak acid it partially dissociates: CO2(g) + H2O(l) H+(aq) + HCO3

-(aq)

Acid Rain

Has a pH below 5.6 Reaction of water vapor with sulfur

dioxide (SOx) and nitrogen oxides (NOx)

Acid Rain form Sulfur compounds (SOx) Sulfur dioxide reacts with water to form

sulfurous acid (H2SO3): SO2(g) + H2O(l) H2SO3(aq)

Sulfur dioxide (SO2) can be oxidized gradually to sulfur trioxide (SO3): 2SO2(g) + O2(g) 2SO3(g)

Sulfur trioxide (SO3) reacts with water to form sulfuric acid (H2SO4): SO3(g) + H2O(l) H2SO4(aq)

Acid Rain from Nitrogen compounds (NOx) Oxides of nitrogen, particularly nitrogen

dioxide (NO2) react with water to form nitrous acid (HNO2) and nitric acid (HNO3): 2NO2(g) + H2O(l) HNO2(aq) + HNO3(aq)

Effects of Acid Rain

Damages buildings and marble statues by reacting with calcium carbonate to from soluble calcium hydrogen carbonate (calcium bicarbonate, Ca(HCO3)2): CaCO3 + acid rain Ca(HCO3)2

Effects of Acid Rain

Effects of Acid Rain

Leaches aluminum and calcium form the soil into the ground water, lakes and rivers; poisoning fish and plant roots Aluminum reacts negatively with the gills of

the fish irritating them causing a build up of mucous resulting in suffocation

Effects of Acid Rain

Disrupts the process of photosynthesis Damages plant life

Slows the production of chlorophyll Sulfuric acid kills plants

“Crown dieback” Leaves at the top (crown) of trees die Leaving a sparse thin crown that progressively

increases and moves its way down the tree

Crown Dieback

Assignment

3.5.1 and 3.5.2 – Chemistry of acid Precipitation and Possible Effects