general chemistry

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general chemistry

Post by mrpeepers » Sat Feb 17, 2007 5:37 am

:?: Can anyone explain this to me in a way that I might understand??? I know, tough question. I am a middle aged college student, who hasn't had chemistry since grade school (7th to be exact). I am taking a general biology class and a question on one quiz was:

"A solution has a hydroxide concentration of 1 x 10-4(exponent of -4) M. Which if the following is NOT correct about the solution?
A) the solution has 1000 times less hydrogen ions than pure water
B) the solution has a pH of 10
C) the solution has 1000 times more hydroxide ions than pure water
D) the solution has 1000 more hydroxide ions than hydrogen ions
E) the solution would be considered basic

I know the answer is D, but what I don't know is how to obtain this answer. I can't find it in our text book, so my question is how do I figure something like this out. I know it has something to do with logarithims, and the instructor tried to explain it, but it was at the end of know that goes.

So, any help would be appreciated. Thanks.

King Cobra
King Cobra
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Post by sdekivit » Sat Feb 17, 2007 10:30 am

the pOH of the solution is 4, thus the pH = 10

-->A: water has a pH = 7 --> every pH-step is 10 times a difference H(+) (log-units --> log 10 =, log 100 = 2 and so on): true.

--> B: pH is indeed 10

--> C: true: three pH-units more basic is equal to 1000 tim es OH(-)ions more.

--> D: At pH = 10 [H(+)] = 10^-10, whereas the pOH = 4 -->? [OH(-)] = 10^-4
--> that's not a difference of 10^3, but 10^6

--> E: pH > 7, thus true.

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