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Author: Subject: pH calculation (piece of cake for the experts)
Harmless

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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?

bbartlog
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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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Harmless

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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?
bbartlog
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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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zoombafu
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I'm pretty sure your calculations are correct. And yes pH can go above and below the normal 0-14 range

Harmless

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

Thanks guys.
ScienceSquirrel
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