Problem 4. (5 points) Two waters at 25°C are in equilibrium with air, one at pH

Question

Problem 4. (5 points) Two waters at 25°C are in equilibrium with air, one at pH 9.0 and one at pH 7.0. These waters are then mixed in equal proportions. (a) (2 points) Assuming that both solutions behave ideally, that carbonate species dominate the acid/base behavior of both (b) (2 point) Determine whether the mixed solution will be undersaturated, supersaturated, or in equilibrium with atmospheric solutions, and that no gas transfer occurs when they are mixed, what is the alkalinity and pH of the mixture? 2- (c) I points) How much CO2 will dissolve into or volatilize out of the solution as it equilibrates with the atmosphere? Express your answer in moles CO2 transferred per liter of solution.

Explanation / Answer

a) For pH = 9.0, [H+] = 10-9 M, and for pH = 7.0, [H+] = 10-7 M

Therefore, total [H+] = 10-9 + 10-7 M = 1.01e-7 M

Therefore, resulting pH = -log [H+] = -log (1.01e-7) = 6.99

Thus alkalanity of the resulting solution = 6.99

b) As the solution is acidic already, it is saturated and will equilibrium with atmospheric CO2.

c)

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