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Topic: Amount of NaOH needed to change pH  (Read 12863 times)

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Offline AL

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Amount of NaOH needed to change pH
« on: September 15, 2011, 09:08:18 PM »
I am trying to figure out the amount of 12.8M NaOH required to bring water from pH 7.2 to pH 10. Below is what I have done so far, but I am not sure if this is the right direction. I appreciate any help.

@ pH 7.2,
[H+] = 6.31*10-8
[OH-] = 1.6*10-4

@ pH 10
[H+] = 10-10
[OH-] = 10-4

I subtracted the [OH-] at pH 10 from pH 7.2
[OH-]10 - [OH-]7.2 = 9.98*10-5

Took that number and divided by concentration of NaOH to get the amount of 12.8M NaOH needed to change the pH of one liter of water.
9.98*10-5/12.8M = 7.8*10-6 liters needed.

Offline Borek

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Re: Amount of NaOH needed to change pH
« Reply #1 on: September 16, 2011, 04:47:27 AM »
Looks OK to me.
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Offline Pradeep

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Re: Amount of NaOH needed to change pH
« Reply #2 on: November 26, 2011, 11:37:02 AM »
Still you don't have considered about the medium. you have assumed the system as a solution of strong acid. If there is any un dissociated weak acid, or dissociated weak base ( I mean the buffering reaction) your solution will not be correct. The only thing you have to confirm is that, your assumption.

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