(6th Edition) #12.19

[005115864]

Hi, the original question asks what is the difference of pH if HCl- were diluted by 12%.

I understand the pH equation is -log(H+) but in this case why is it that we divide the H+ concentrations?

The solutions manuel says we would use the equation,

pH = -log(0.12[H]+/[H+]) = -log(0.12) = 0.92



why do we divide by the H+ concentration within the pH equation?

[Chem_Mod]

In the solution manual, they use that equation to indicate the change in [H+]. If you started out with 1M H+ but diluted it to 12% concentration, then you would end up with .12M H+. The change in pH is thus the -log(new conc/old conc), which is -log(.12). You could also calculate the pH of the solution before and after dilution and then take the difference, and you would arrive at the same answer.