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Author: Subject: pH calculation (piece of cake for the experts)
madmanhere
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[*] posted on 7-3-2012 at 22:55
pH calculation (piece of cake for the experts)


According to Wikipedia, NaOH has a solubility of 1110g/L in water at 20'C. If I dissolve 1.1kg of NaOH pellets in 1L H2O, calculation of pH is as follows:

1.1kg NaOH = 1110/40 = 27.75 mol
=27.75 mol/ L

pOH= -log 27.75
pH + pOH=14

pH = 14 + log 27.75
= 15.44

pH > 14!!! What am I doing wrong?

[Edited on 8-3-2012 by madmanhere]
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bbartlog
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[*] posted on 7-3-2012 at 23:05


I don't think there's any theoretical reason why you can't have a pH above 14. Or below zero for that matter.



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madmanhere
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[*] posted on 7-3-2012 at 23:10


You mean to say that although 1.1kg can dissolve, only a small portion of it will dissociate and the rest will exist as undissociated NaOH?
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[*] posted on 7-3-2012 at 23:30


Uh, no. That's like the opposite of what I'm saying. Your calculation looks good, the NaOH is almost entirely dissociated, and the pH is 15+. So what's the problem? Did someone tell you that pH can only be in the range of 0-14 or something?



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[*] posted on 7-3-2012 at 23:43


I'm pretty sure your calculations are correct. And yes pH can go above and below the normal 0-14 range
source: http://books.google.com/books?id=eKtNUN1FeqEC&lpg=PA3&dq=pH%20above%2014&pg=PA3#v=onepage&q=pH%20above%2014&f=false




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madmanhere
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[*] posted on 8-3-2012 at 03:43


I didn't know pH could go higher than 14. My bad.

Thanks guys. :)
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ScienceSquirrel
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13-3-2012 at 05:06

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