October 31, 2024, 07:41:01 PM
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Topic: concentration of [OH-]  (Read 3517 times)

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Offline Farid

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concentration of [OH-]
« on: April 05, 2007, 05:34:45 AM »
Could u help me witch this  task?

prepared 2 solutions, where concentration of [H+] was:
a) 4 * 10 -9
b) 8 *10    -5
How many times the concentration of [OH-] is bigger  in a) then in b).

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Offline Sam (NG)

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Re: concentration of [OH-]
« Reply #1 on: April 05, 2007, 05:41:19 AM »
Use the equation for the Equilibrium constant of the self ionisation of water (Kw) to find the concentration of OH- ions in each case:

Kw=[H+][OH-]

Kw=10-14

Offline Farid

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Re: concentration of [OH-]
« Reply #2 on: April 05, 2007, 05:49:37 AM »
a) [OH-] =2,51 * 10-6
b) [OH-] = 1,25 *10 -10

And i think a is 20080 times bigger than b, but in my book there is write: anwser is 20 000.
So, i don't where is mistake? Did i make it, ore mistake is in book.
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Offline Sam (NG)

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Re: concentration of [OH-]
« Reply #3 on: April 05, 2007, 06:51:33 AM »
Check your concentration for (a), it is slightly wrong (think about what number you get if you divide 10 by 4).  Once you have this correct then you will get the answer in your book.

Offline Farid

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Re: concentration of [OH-]
« Reply #4 on: April 05, 2007, 07:02:45 AM »
Thank youvery much :). Yes, in a there is 2,5 * 10-6, and now the result is good.
 Thanks again :)
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