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

Question

Aaron Allen · Accepted Answer

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

Aria Johnson · Answer

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#

Addison Adams · Answer

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

On the other hand, because carbon dioxide and water combine to form carbonic acid, an aqueous solution of carbon dioxide has a pH. A complicated set of equilibria exists: #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. This is a pH table at three significant 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

Adeline Allen · Answer

undefined The pH of pure carbon dioxide dissolved in water is approximately 5.65.