Why does CO2 lowers the pH of water below 7?
Carbon Dioxide (CO2) readily dissolve in water and form Carbonic Acid (i.e H2CO3 (aq) )


This is the formation of bonds.



Then Carbonic Acid (i.e H2CO3  (aq)  ) dissociate in water as follows.



So water gets H+ ions, so that cause water acidic.

The following shows dissociation of Carbonic Acid (i.e H2CO3 (aq) ) more clearly.



Carbon Monoxide (CO) do not readily react with water in room temperature in standard conditions. So it do not dissolve in water.