pH question (1 Viewer)

[toknblackguy]

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]

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-

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)

 

[eeyore]

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]

 

[ND]

But as MyLuv said, the second H+ doesn't disassociate completely.

 

[toknblackguy]

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

 

[inasero]

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

 

[Frigid]

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...

 

[ND]

Yeh there's no limit on pH.

edit: theoretically.

 

[toknblackguy]

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

 

[Frigid]

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!

 

[ND]

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]

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

i concur

 

[Frigid]

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]

edit2: i mean the [H+] --> 0.

then acidic nature of the solution approaches zero
pH=-log0.00000000000001= a very large number, simple!

 

[ND]

Yeh that's what i meant, therefore there is no limit, on the positive side anyway.