Need #3 and #7 solutions (a) What is the effective Henry\'s law constant for SO_

Question

Need #3 and #7 solutions

(a) What is the effective Henry's law constant for SO_2 for an aqueous solution of pH 5.0? (b) What is the total concentration of S(IV) in solution under these conditions if the gas-phase SO_2 concentration is 10 ppb? Repeat Problem 3 for pH 2.0. Compare your answers to those for Problem 3 and explain based on the chemistry of S(IV) in solution. Calculate the mole functions of SO_2(aq), HSO^-_3, and SO^2-_3 in solution at pH of 3.0, characteristics of many fogs, as well as the total concentration of S(IV) in solution for 20 ppb SO_2 in the gas phase. Calculate the mole fractions of SO_2(aq), HSO^-_3, and SO^2-_3 in solution at a pH of 8.0, equal to that of seawater and therefore expected for airborne particles formed from seawater in clean regions as well as the total concentration of S(IV) in solution for 20 ppb SO_2 in the gas phase. Comment on the implications for the potential role of sea salt particles in the oxidation of SO_2 in the marine boundary layer. How fast is the oxidation of SO_2, in percent year hour, in the gas phase for an OH concentration in the lower troposphere? Comment on the significance of your calculated rate in light of observed rates of SO_2 oxidation of up to 30% h^-1 in the troposphere.

Explanation / Answer

These reactions have the equilibrium constants:

HSO2= [SO2.H2O ]/pSO2

Ks1 = [H+][HSO3-]/[SO2.H2O]

Ks2 = [H+][SO32- ]/[HSO3-]

Kw = [H+][OH-] ; This is called the ion product of water: Kw = 10-14 M2 @ 298 K.

The concentrations of the dissolved species are:

[SO2.H2O] = HSO2 pSO2

[HSO3-] = Ks1[SO2.H2O]/[H+] = HSO2 Ks1 pSO2/[H+]

[SO32- ] = Ks2[HSO3-]/[H+] = HSO2Ks1Ks2 pSO2 / [H+]2

Let total sulfur that is in the IV oxidation state in the aqueous solution be written as:

[S(IV)] = [SO2.H2O] + [HSO3-] + [SO32- ]

Writing all of the concentrations as a combination of constants and [H+]:

[S(IV)] = HSO2 pSO2 {1 + Ks1/[H+] + Ks1 Ks2 /[H+]2}

Therefore, we can write total dissolved sulfur as:

[S(IV)] = HS(IV)* pSO2

The effective Henry's Law coefficient is:

HS(IV)* = HSO2 {1 + Ks1/[H+] + Ks1 Ks2 /[H+2]

Hence from the plot of effective Henry's law constant for SO2 as a function of PH

we get , effective Henry's law constant for SO2 is around 103 M atm-1

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