Question

What percent of pure water is ionized?

Obviously at pH 7; please be very clear on how you arrive at your answer and explain what's wrong with my reasoning. What I did was see that the concentration of OH- and H3O+ were both 1E-7M and so together were twice that. The concentration of water is 55.5M so I did (2E-7)/(55.5) all time 100. Thanks in advance

Answer 1

The water ionization equation is as follows:

In normal conditions when the pH is equal to 7 the H₃O⁺ and HO^- concentration are the same and it is equal to 10^-7 M. This concentration is so low because the water is a weak electrolyte that dissociates very little. So,

2 mol       1 mol     1mol

?           10^-7 mol 10^-7 mol

2 mol H₂O------------- 1 mol H₃O⁺

2x10^-7mol H₂O------- 10^-7 mol H₃O⁺

If the H₂O concentration in the pure water is 55,55 moles/L, in 1 L of pure water only 2x10^-7moles of H₂O are ionized. So,

55,55 moles H₂O------------------ 100%

2x10^-7moles H₂O----------------- 3.6x10^-7 %                  Percent of H₂O ionized