Water in the atmosphere-Acid rain
Water in the atmosphere- Acid rain
Ions in pure water autoionization H20 H+ OH neutralization Kea= [h] w=Keglh2O [H2O] =HOH =10 14
Ions in pure water H2O autoionization neutralization H+ + OH- [ ] [ ][ ] H2 O H OH Keq + − = 14 2 2 10 [ ][ ] [ ] M H OH Kw Keq H O − + − = = =
pH value of pure water HOH log Kw=-log h]-log oH] oK w=pH+pOH In pure water, autoionization is the only source of ions, therefore [F]=[OH]=107M pH=7 A pH of 7 defines neutrality pH<7 means acidic and pH>7 is basic
pH value of pure water pK pH pOH K H OH K H OH w w w = + − = − − = + − + − log log[ ] log[ ] [ ][ ] In pure water, autoionization is the only source of ions, therefore: 7 [ ] [ ] 10 7 = = = + − − pH H OH M A pH of 7 defines neutrality, pH<7 means acidic and pH>7 is basic
What is the pH of natural rain water? pH of natural rain water is determined by acidic and basic species that are CO2(8)+H20=H2CO3 naturally present in the TH2CO3 Unit: M atmosphere K ICOL,OI Equilibrium IH,CO3 constant Kell,oi CO2 partial pressure 1015=H2CO in unit of atm 370x10 C02: 370 ppm [H2CO3]=10-M
What is the pH of natural rain water? H CO M x H CO p H CO K H O CO H O H CO K CO g H O H CO CO eq eq 4.9 2 3 6 1.5 2 3 2 3 2 2 2 2 3 2 2 2 3 [ ] 10 370 10 [ ] 10 [ ] [ ] [ ][ ] [ ] ( ) 2 − − − = = = = + = pH of natural rain water is determined by acidic and basic species that are naturally present in the atmosphere. Equilibrium constant CO2 partial pressure in unit of atm Unit: M CO2: 370 ppm
What is the pH of natural rain water? ( Continued) H2CO3=H++HCO3(K=1064 K-[H* I lH,CO3 k=[+2 [H]≈[HCO31 [H,CO [H+]=K[H2CO3]=10-64x10-9 [H+]=10-37 pH=5.7 Rainwater is naturally acidic because its equilibrium with carbon dioxide
What is the pH of natural rain water? (Continued) 5.7 [ ] 10 [ ] [ ] 10 10 [ ] [ ] [ ] [ ][ ] ( 10 ) 5.7 6.4 4.9 2 3 2 2 3 2 2 3 3 6.4 2 3 3 = = = = = = = + = + − + − − + + − + − − pH H H K H CO x H CO H K H CO H HCO K H CO H HCO K a a a a Rainwater is naturally acidic because its equilibrium with carbon dioxide. [ ] [ ] 3 + − H HCO