Question

Estimate the pH of natural rainwater, assuming the only substance effecting it is the adsorption of CO2 from the atmosphere. Assume the concentration of CO2 is 390 ppm, and the temperature and pressure are 25 "C and 1 atmosphere. Steps. Assume the absorption of CO2 adds only the carbonate system ions so the ionic present must balance, and are due to Ht, OH, HCO3, and CO32. Establish your charges charge balance equation-+'s = -'s i. Assuming the rainfall is slightly acidic make an assumption about the relative magnitude CO32 to HCO3, simplify your charge balance equation in step i. of ii. Use a known relationship to express [OH-] in terms of [H+] iv. Recognize that H2CO is approximated as CO2 (aq), therefore apply air-water equilibrium (Henry's Law) to estimate H2CO3 . v. Estimate [HCO3] from the carbonate system equilibrium reaction with H2CO3 vi. Solve for the pH from the simplified charge balance equation.

Answer 1

An v en 390 pm 390 m/L 30 S/ v(L) 0 390 너니 8.8G X LO M cidic ih weak ea 2-5 x1o 25 C 2) Fon a weak acid [h"J。/au

0g 148 x1O 2-82 n Wa 2 82