Meteo 532 Atmospheric Chemistry

Problem set #4

assigned: 4 November 2002

due: 11 November 2002

1. F-P & P. chapter 8, problem 2

2. F-P & P. chapter 8, problem 3

3. F-P & P. chapter 8, problem 7

4. F-P & P. chapter 8, problem 8

5. F-P & P. chapter 8, problem 9

6. True acidity of rain. The pH of rain reported by monitoring agencies is based on analysis of rain samples that are collected weekly in buckets. The weekly collection schedule is fine for HNO₃ and H₂SO₄, which do not degrade; however, formic acid (HCOOH) is rapidly consumed by bacteria in the buckets and therefore escapes analysis. The Henry’s Law and acid dissociation equilibria for HCOOH are:

HCOOH(g) Û HCOOH(aq) H_hcooh = 3.7 x 10³ M atm^-2

HCOOH(aq) Û HCOO^‑ + H⁺ K₁ = 1.8 x 10^-4 M

If the monitoring agency reports a rainwater pH of 4.7, calculate the true pH of the rain. Assume 1 ppbv HCOOH in the atmosphere, a typical value for the eastern United States.