(A) The solubility of CO₂(g) in H₂O at 25 °C and under a CO₂(g) pressure of 1 atm is 1.45 g CO₂/L. Air contains 0.037% CO₂ by volume. Use this information, together with data from Table 16.5, to show that rainwater saturated with CO₂ has a pH ≈ 5.6 (the normal pH for rainwater).

Table 16.5

(B) Often the following generalization applies to oxoacids with the formula EO_m(OH)_n (where E is the central atom): If m = 0, K_a ≈ 10^-7; if m = 1, K_a ≈ 10^-2; if m = 2, K_a is large; and if m = 3, K_a is very large.

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TABLE 16.5 Ionization Constants of Some Polyprotic Acids Acid lonization Equilibria H₂S + H₂O HS + H₂O = Hydrosulfurica Carbonicb Citric Phosphoric Oxalic Sulfurouse Sulfuricd H₂CO3 + H₂O H₂O+ + HS¯ H₂O+ + S²- H₂SO4+H₂O HSO4+H₂O = HCO3+H₂0 H3C6H507 + H₂0 H₂CH²Ð‚¯ + H₂0 — HC H₂0₂2 + H₂0 — H₂PO4+H₂O H₂PO4+H₂O → HPO42- + H₂O = H₂C₂O4 + H₂0 — HC₂04 + H₂0 H₂SO3 + H₂O → H3O+ + HSO3- HSO3 + H₂0 H3O+ + SO3²- H₂0+ + HCO3- H3O+ + CO3²- H3O+ + H₂CH₂O, H3O+ + HC¿H₂0,²- K₁₂ H₂O+ + C₂H₂0,³- H₂O+ + H₂PO4¯ H3O+ + HPO4²- H3O+ + PO4³- H30+ + HC₂04¯ H30+ +C₂04²- lonization Constants, K K₁₁ = 1.0 × 10-7 = 1 × 10-19 Kaz Ka₁ H₂O+ + HSO4- H₂O+ + SO₂²- Kaz K₁₁ = 7.5 x 10-4 = 1.7 x 10-5 Ka Kal Kaz Kaj = 4.4 x 10-7 Kaz Kay Kaz Kaz Kay K₂ = 4.7 x 10-11 = 4.0 x 10-7 = 7.1 x 10-3 = 6.3 × 10-8 = 4.2 X 10-13 = 5.6 x 10-2 = 5.4 x 10-5 = 1.3 x 10-2 = 6.2 × 10-8 = very large = 1.1 x 10-2 pk pka₁ = 7.00 pka₂ = 19.0 pka₁ = 6.36 pka2 = 10.33 pK₁₁ = 3.12 PK₁₂ = 4.77 PK₁₂ = 6.40 PK₁₁ = 2.15 PK₁₂ = 7.20 pKaz = 12.38 pka = 1.25 PK₁₂ = 4.27 pk = 1.89 PK₁₂ = 7.21 PK₁₁ <0 pk az = 1.96 Acid strength