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Question/Problem

I know that [H+][OH-]=$10^{-14}$

And the problem asks to find out the concentration of H+ when the concentration of OH- is $3.57*10^{-5}$M

By using the equation above i find that the concentration of H+ is 2.67E-10

But if I use a different method as follows:

-log[OH]=pOH so by substitution, -log[$3.57*10^{-5}$]

then that gives me 4.425.......

then i subtract 14 from that number to get 9.574......

which that is pH

then i set 9.574=-log[H+] so then you "e" everything which the answer comes to be 6.95E-5

why is this wrong?

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  • $\begingroup$ Do you know the difference between $$9.574 = -\log x$$ and $$9.574 = -\ln x?$$ $\endgroup$ – orthocresol Jan 8 '17 at 8:52
  • $\begingroup$ Oh no wonder, i get it now $\endgroup$ – John Rawls Jan 8 '17 at 8:54
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Well You have to note that you cannot simply "e" everything because the base of log in chemistry is base 10 while you assumed that it was all base e. Ie ln(x). in order to get x, we use e, while if we say log(x) we have to assume that it is base 10 which is the general norm

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