1. E NVIRONMENTAL CHEMISTRY E 11. acid deposition

2. A CID DEPOSITION Describe the mechanism of acid deposition caused by the oxides of nitrogen and oxides of sulfur. Explain the role of ammonia in acid deposition.

3. M ECHANISMS OF ACID DEPOSITION Hydroxyl free radicals are formed by the following two processes involving water, ozone and oxygen free radicals: H 2 O + O 3 → 2HO + O 2 or H 2 O + O → 2HO

4. M ECHANISMS ACID DEPOSITION Formation of nitric acid HO + NO 2 → HNO 3 also (HO + NO → HNO 2 )

5. M ECHANISM ACID DEPOSITION Formation of sulphuric acid – 3 steps HO + SO 2 → HOSO 2 then HOSO 2 + O 2 → HO 2 + SO 3 then: SO 3 + H 2 O → H 2 SO 4

6. R OLE OF NH 3 IN ACID DEPOSITION (1) Atmospheric NH 3, although an alkali, contributes to acid deposition. NH 3 neutralizes the strong acids in acid rain forming ammonium salts as shown in the equations below. 2NH 3 (aq) + H 2 SO 4 (aq) → (NH 4 ) 2 SO 4 (aq) 2NH 3 (aq) + H 2 SO 3 (aq) → (NH 4 ) 2 SO 3 (aq) NH 3 (aq) + HNO 3 (aq) → NH 4 NO 3 (aq)

7. R OLE NH 3 IN ACID DEPOSITION (2) (NH 4 ) 2 SO 4,(NH 4 ) 2 SO 3 and NH 4 NO 3 formed from strong acids and a weak alkali. salt hydrolysis occurs in acid rain drops ensuring rain droplets are still acidic, making the soil onto which the rain falls also acidic. salt hydrolysis equation: NH 4 + + H 2 O → NH 3 + H 3 O +

8. R OLE OF NH 3 IN ACID DEPOSITION ( LAST ONE ) additional acidic effect soil is further acidified as any NH 4 + not hydrolysed reacts with oxygen in the soil to form the nitrate ion (=nitrification) and hydrogen ions, H +, as shown by the equation below: NH 4 + +2O 2 → 2H + + NO 3 − +H 2 O