Carbonic acid is a diprotic acid and it can have a gaseous form. There are 6 spe
ID: 700571 • Letter: C
Question
Carbonic acid is a diprotic acid and it can have a gaseous form. There are 6 species you need to solve for.
1. CO2(g) Carbon Dioxide Gas
2. H2CO3* Carbonic Acid (H2CO3* = CO2(aq) + H2CO3)
3. HCO3- Bicarbonate
4. CO32- Carbonate
5. H+ Proton
6. OH- Hydroxide
To solve for six unknowns, you need six equations. Four of these are equilibrium constants.
1. CO2(g) + H2O = H2CO3*, KH = [H2CO3*] / PCO2 (Henry's Law) (gas concentrations are given as partial pressure)
2. H2CO3* = H+ + HCO3-, K1 = [HCO3- ][H+] / [H2CO3*]
3. HCO3- = H+ + CO32-, K2 = [H+][CO32-] / [HCO3-]
4. H2O = H+ + OH-, Kw = [H+][OH-] (ionic product of water = 10-14)
We can also define total CO2, CT = [CO2(aq)] + [HCO3- ] + [CO32-]
Explanation / Answer
b. An important issue in the geochemistry of solutions is the distribution of the ionic species. A typical example of a distribution of ionic species can be seen in the carbonate system. With reference to the carbonate system, draw a labeled-sketch that shows the variation in the activity and type of ionic species versus the pH (for the range of pH1-14).