UNIT IV Acid Rain

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) 2 OH- (aq)

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METAL OXIDES

Ex. BaO (s) Ba2+(aq) + O2-

(aq)

O2-(aq) + H2O (l) 2 OH- (aq)

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Ex. Write a balanced formula equation for the overall reactions of the following oxides with water: 

• CaO:  • Li2O:

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)

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 #144-145

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.

ACID RAIN

The main human sources of acid rain are:1. Burning fuels containing sulphur. (SOx)

2. Car exhaust. (NOx)

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 #146-147