[cncbmb]

I noticed for question 7f on page 15 on this pdf, http://www.icho.hu/Files/prep_problems_icho40_0521.pdf that its solution on page 58 does not include [OH-] in the charge balance equation.

However, for the 7g solution, [OH-] is included in the charge balance equation.
In this specific example, for 7f, how would we know that we don't include hydroxide concentration in the charge balance equation?

Also, you might want to use adobe reader's or any similar program's option that allows you to go directly to a page number instead of scrolling down to page 15 to 58 to back up.