Question

Imagine you are breathing through a straw into a beaker of water. What does CO2 do to the pH of water?

Answer 1

The pH of the waterdrops because of the CO2 in exhaled breath. The CO2 dissolves in water where it acts as a Lewis acid and forms carbonic acid, a weak acid.pH of the water decreases

CO2(aq) + H2O(l) ' H2CO3(aq)

H2CO3(aq) + H2O(l) ' HCO3-(aq) + H3O+(aq)

The pH change does not occur instantly after the breathing out of CO2 because in each blowing their is only little amount of carbondioxide is coming out. so inorder to make significant change in the pH more number of breathing out is required.