pH question (1 Viewer)

toknblackguy

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say if a qyestion says yuo've got 0.01 M H2SO4
does you say pH = -log[0.02]
??
and if you had a 2M HCl wha't it's pH? -0.3?!?
 

MyLuv

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say if a qyestion says yuo've got 0.01 M H2SO4
does you say pH = -log[0.02]
Nope.Since HSO4- is moderately weak(not ionised completely) so PH will be between -log(0.02) and -log(0.01).U cant find unless they give u acid constance of HSO4- :p

and if you had a 2M HCl wha't it's pH? -0.3?!?
er..yes,i've seen sumwhere said actual PH scale is -1 to 14 (or 0 to 15):eek:
 

eeyore

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H2SO4 is a strong acid. That means it's completely ionised, so if it's 0.01M then ph= -log[0.01]

If you have 2M HCl then ph= -log[2]
 
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But as MyLuv said, the second H+ doesn't disassociate completely.
 

toknblackguy

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but eeyore...it's diprotic...so after the first ionisation...there's the second equilbrium
so then we can't work that out??
 

inasero

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yes...y luv is right...also it IS possible to have negative pH values..just not at all common....
 

Frigid

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in terms of neutralisation reactions we can assume that H2SO4 is diprotic...

and yes, the pH scale does range beyond and below 1 to 14, but 1 and 14 is the more practical range (since most of the time we're using ~1 molar solutions)... i had a discussion with phenol about this a while ago...
 

toknblackguy

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cool
then i think i'll have a quick read through my notes and i'm set!
good luck to all of us!!!
 

Frigid

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Originally posted by ND
Yeh there's no limit on pH.

edit: theoretically.
bs! hahaha, there's only so much ions (hydronium or otherwise) you can put into water before it becomes saturated! :)
 
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ND

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Originally posted by Frigid

bs! hahaha, there's only so much ions (hydronium or otherwise) you can put into water before it becomes saturated! :)
Yeh you're right, but how high would that be?

edit: also, what about appoachgin zero?

edit2: i mean the [H+] --> 0.
 

inasero

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bs! hahaha, there's only so much ions (hydronium or otherwise) you can put into water before it becomes saturated!
i concur
 

Frigid

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Originally posted by ND
Yeh you're right, but how high would that be?

edit: also, what about appoachgin zero?
haha, i think phenol would be in a better position to answer that than me... after all, i have only studied lower-order 2-unit hsc chemistry... :)
 

inasero

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edit2: i mean the [H+] --> 0.
then acidic nature of the solution approaches zero
pH=-log0.00000000000001= a very large number, simple!
 
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Yeh that's what i meant, therefore there is no limit, on the positive side anyway.
 

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