TBR pH calc.?

[ModyzMalak]

im working through acid/base chapter in TBR, and having trouble with log calculations without a calculator. I'm not sure how else to quickly figure out how to do these calculations that ask for specific pH without memorizing table 4.7. is there a trick to pH problems I'm missing? for example question#29 in passage 5 and most of pH examples in the chapter.

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[justadream]

pH = 1/2 * pKa -log[HA]

pOH = 1/2 * pKa - log[A-]

10^-5 is pH = 5
10^-4 is pH = 4

3*10^-5 is pH = 4.5

For X*10^-5, if X is greater than 3, then pH <4.5
For X*10^-5, if X is less than 3, then pH >4.5

 

[popopopop]

Can you post the question?