Question

What is the pH of carbon dioxide? What is the pH of carbon dioxide?

Answer 1

depends on what it becomes, but cannot be below 6.

Answer 2

Carbon dioxide does not have a pH, because it is a gas.

Explanation:

However, an aqueous solution of carbon dioxide has a pH, because the carbon dioxide reacts with the water to form carbonic acid.

There is a complex series of equilibria:

`bb((1))color(white)(m)"CO"_2"(g)" ⇌ "CO"_2"(aq)"; k_text(H) = "29.76 L·atm·mol"^"-1"`

`bb((2))color(white)(m)"CO"_2"(aq)" ⇌ "H"_2"CO"_3"(aq)"; K_text(h) = 1.7 ×10^"-3"`

`bb((3))color(white)(m)"H"_2"CO"_3"(aq)" + "H"_2"O(l)" ⇌ "H"_3"O"^"+""(aq)" +"HCO"_3^"-""(aq)"; K_text(a₁) = 2.5 ×10^"-4"`

`bb((4))color(white)(m)"HCO"_3^"-""(aq)" + "H"_2"O(l)" ⇌ "H"_3"O"^"+" + "CO"_3^"2-""(aq)"; K_text(a₂) = 4.47 ×10^"-7"`

Thus, the pH of a pure `"CO"_2` solution depends on the partial pressure of `"CO"_2`above the solution.

Here's a table of the pH at three important partial pressures:

`bbul(color(white)(mml)p_text(CO₂)"/atm"color(white)(ml)"pH"color(white)(m))`
`bb((1))color(white)(ml)3.5 × 10^"-4"color(white)(ml)5.65`
`bb((2))color(white)(ml)1.0 ×10^0color(white)(mll)3.92`
`bb((3))color(white)(ml)2.5 × 10^0color(white)(mll)3.72`

`bb((1)) =` the normal atmospheric partial pressure
`bb((2)) =` a partial pressure of 1 atm
`bb((3)) =` the partial pressure in bottled carbonated drinks

Answer 3

Carbon dioxide exists as a gas at room temperature, I have never heard gases having some pH . This is the same reason why litmus test of dry HCl gas doesn't yield any result .
If you perform a combination reaction of `CO_2` and `H_2O` to form `H_2CO_3` . H2CO3 is a diprotic acid. The pKa for H2CO3 is 6.35, and the pKa for HCO3- is 10.33. pH depends on molarity now .

pH of `H_2CO_3`

10mM `=>` `4.68`
100mM `=> 4.18`
1000mM `=> 3.68`