1. UNIT IV
Acid Rain

2. Metal Oxides
Metal Oxides (or Basic Anhydrides) act as BASES in solution.
Group 1 and Group 2 Oxides are ionic. They dissociate to form the oxide ion (O2-).
Ex. Na2O (s)  2 Na+(aq) O2-(aq)
O2-(aq) H2O (l)  OH- (aq)
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3. Metal Oxides Ex. BaO (s)  Ba2+(aq) + O2-(aq)
O2-(aq) H2O (l)  OH- (aq)
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Ex. Write a balanced formula equation for the overall reactions of the following oxides with water: 
CaO:
Li2O:

4. Non-Metal Oxides
Non-Metal Oxides (or Acidic Anhydrides) act as ACIDS in solution.
Some common examples of non-metal oxides: NO2 , N2O5 , SO2 , SO3 , CO2 , Cl2O
Ex. SO2(g) + H2O(l)  H2SO3 (aq)
H2SO3 (aq) + H2O(l) H3O+(aq) + HSO3- (aq)

5. Non-Metal Oxides
Ex. 2NO2(g) + H2O(l)  HNO3 (aq) + HNO2 (aq)
HNO3 (aq) + H2O(l)  H3O+(aq) NO3-(aq)
Metalloid Oxides usually have LOW solubility so not many ions are freed to undergo hydrolysis. So very little hydrolysis occurs and they do not act AS acids or bases.
Hebden Textbook Page 185 Questions #

6. CO2(g) + 2H2O(l) H3O+(aq) + HCO3-(aq)
Acid Rain
Since our atmosphere naturally contains CO2 (an acidic anhydride), some of this reacts with water (rain) to make the rain slightly acidic:
CO2(g) + 2H2O(l) H3O+(aq) + HCO3-(aq) 
So natural rainwater (unaffected by human activities) can have a pH as low as 5.6 (due to the CO2 in air). 
If rain has a pH < 5.6 it is called ACID RAIN.

7. Acid Rain
The main human sources of acid rain are: 1. Burning fuels containing sulphur. (SOx) 2. Car exhaust. (NOx)

8. Acid Rain Read pages 186-189 of your textbook. Review:
Sources of Acidity in Acid Rain
Natural Protection Against Acid Rain
Problems Associated with Acid Rain
Possible Solutions
Hebden Textbook Page 188 Questions #