1. Enough of a monoprotic acid is dissolved in water to produce a 0.0127 M solut

Question

1. Enough of a monoprotic acid is dissolved in water to produce a 0.0127 M solution. The pH of the resulting solution is 6.30. Calculate the Ka for the acid.

2. Carbon dioxide dissolves in water to form carbonic acid. Estimate the thermodynamic equilibrium constant for this reaction using the Gf° values shown here.

Substance          ?Gf0

H2CO3(aq)        -616.1

H2O(l)               -237.1

CO2(g)               -394.4

K=

Carbonic acid then ionizes in water (Ka1 = 4.5× 10–7). Ignoring Ka2, estimate K for the overall process by which CO2 and H2O form H and HCO3–.

K=

What is the pressure of CO2 in equilibrium with carbonated water at 25 °C and pH = 4.87?

PCO2=

Explanation / Answer

1)

the dissociation equation

HA <-> H+ and A-

Ka = [H+][A-]/[HA]

[h+] = 10^-pH = 10^-6.3 = 5.01*10^-7

Note that by stoichiometr

[H+] = [A] = 5.01*10^-7

And

[HA] = 0.0127 - 5.01*10^-7 = 0.0127

Substitute in Ka

Ka = [H+][A-]/[HA] = (5.01*10^-7)(5.01*10^-7) /(0.0127) = 1.97*10^-11

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