Question

Question 11 Assume that the gas in a soda can is pure carbon dioxide at a pressure of 2.0atm . Estimate the pH of soda at 25 °C. Hint take advantage of the fact that soda is likely to be acidic and use appropriate carbonate system equation. Kh for carbon dioxide is 0.033363mol/L'atm A 3.675 B 3.714 C 3.763 D 3.825 E 3.641 Question 12

Answer 1

Solubility of CO2 = K * P = 0.033363 mol/L.atm * 2.0 atm = 0.066726 mol/L When CO, is soluble in water, H,CO2 (diprotic acid) is formed.

Kal of H2CO3 = 4.5 x 10-7 Ka2 = 4.8 x 10-11 The dissociation of diprotic acid is given by H2O H2o+ + HCO3 H2CO3 + 0.066726 Initial Change Equilibrium 0.066726-X -= 4.5x10-7 0.066726-X x? + 4.5x10-?x-3.00267x10-= 0 by solving we get x = 0.0001731 [H,0*]=0.0001731M [HCO, ]= 0.0001731M

HCO, will further dissociates into H+ and CO2:2 Let y be the change in the conc. of all species at equilibrium. H2O co, -2 HCO3 + 0.0001731 H2O+ + 0.0001731 Initial Change - y + y Equilibrium 0.0001731- y 0.0001731 + y y (0.0001731+y).y – 48x10-11 2 0.0001731- y Since y is very small,0.0001731- y = 0.0001731 and neglet y? 0.0001731y V=4.8x10-11 0.0001731 :: y=4.8x1041 [H,0*]=0.0001731+ y =0.0001731+4.8x10-11 =0.0001731 pH =-log(0.0001731)= 3.763 Option C is the right answer.