(a) From Kw in Table 6-1, calculate the pH of pure water at 0°, 20°, and 40°C.

(b) For the reaction D₂O ⇌ D⁺ + OD^-, K = [D⁺][OD^-] =1.35 × 10^-15 at 25°C. In this equation, D stands for deuterium, which is the isotope ²H. What is the pD (= –log[D⁺]) for neutral D₂O?

Table 6-1

Temperature (C) Kw pKw = -log Kw Temperature (C) pKw = -log Kw 15 2.88 x 10-14 3.94 X 10 5.31 X 10 5.43 x 10-13 2.30 X 10 12 5.14 X 10-12 6.44 X 10 3.93 X 10-12 1.15 X 10 14.938 40 13.541 1.88 X 10-15 2.97 X 10 4.57 X 10 6.88 X 10-15 14 14.726 45 13.405 15 14 10 14.527 50 13.275 15 15 14.340 100 12.265 20 14.163 150 11.638 1.01 x 10-14 1.46 x 10-14 2.07 X 1014 25 13.995 200 11.289 12 30 13.836 250 11.191 35 13.685 300 11.406 a. Concentrations in the product [H* ][OH ] in this table are expressed in molality rather than in molarity. Accuracy of log Kw is 0.01. To convert molality (mol/kg) into molarity (mol/L), multiply by the density of H20 at each temperature. At 25C, K = 10-13.995 (molkg) (0.997 05 kg/L) = 10 13.998(mol/L. SOURCE: W. L. Marshall and E. U. Franck, "lon Product of Water Substance, 0-1 000C, 110,000 Bars," J. Phys. Chem. Ref. Data 1981, 10, 295. For values of K over a temperature range of 0-800C and a density range of 0-1.2 g/cm, see A. V. Bandura and S. N. Lvov, "The lonization Constant of Water over Wide Ranges of Temperature and Pressure," J. Phys. Chem. Ref. Data 2006, 35, 15.