KNO3 Solution pH

[Seibert]

Hi- I'm a high school physics/physical science teacher with a problem I
don't understand. Why does an aqueous solution of KNO3 test strongly
basic (litmus, pH papers, phenolphthalien, etc.) A collegue has
suggested salt hydrolysis, but that seems to apply more to a salt of a
weak acid/strong base (or vice versa.) Surely KOH and HNO3 are both
completely dissociated in aqueous solutions. KNO3 is a strong oxidizer;
does this affect the pH of its solution? I guess I'm just stuck. If
you can enlighten me please do so.
--
Ralph S. Seibert III
physics teacher and guitar player
pit...@mesh.net
http://www.mesh.net/~pituso

[Uncle Al]

Seibert wrote:
>
> Hi- I'm a high school physics/physical science teacher with a problem I
> don't understand. Why does an aqueous solution of KNO3 test strongly
> basic (litmus, pH papers, phenolphthalien, etc.) A collegue has
> suggested salt hydrolysis, but that seems to apply more to a salt of a
> weak acid/strong base (or vice versa.) Surely KOH and HNO3 are both
> completely dissociated in aqueous solutions. KNO3 is a strong oxidizer;
> does this affect the pH of its solution? I guess I'm just stuck. If
> you can enlighten me please do so.

KOH is a strong base, nitric acid is a strong acid. Pure KNO3 is a
neutral salt solution not prone to hydrolysis. Your KNO3 is
contaminated with excess base.

--
Uncle Al Schwartz
Uncl...@ix.netcom.com ("zero" before @)
http://uncleal.within.net/
http://pw2.netcom.com/~uncleal0/uncleal.htm
http://www.ultra.net.au/~wisby/uncleal.htm
http://www.guyy.demon.co.uk/uncleal/uncleal.htm
(Toxic URLs! Unsafe for children, Democrats, and most mammals)
"Quis custodiet ipsos custodes?" The Net!

[Colin Maxwell]

Seibert wrote in message <366F373A...@mesh.net>...

>Hi- I'm a high school physics/physical science teacher with a problem I
>don't understand. Why does an aqueous solution of KNO3 test strongly
>basic (litmus, pH papers, phenolphthalien, etc.) A collegue has
>suggested salt hydrolysis, but that seems to apply more to a salt of a
>weak acid/strong base (or vice versa.) Surely KOH and HNO3 are both
>completely dissociated in aqueous solutions. KNO3 is a strong oxidizer;
>does this affect the pH of its solution? I guess I'm just stuck. If
>you can enlighten me please do so.

>--
>Ralph S. Seibert III
>physics teacher and guitar player
>pit...@mesh.net
>http://www.mesh.net/~pituso
>

You obviously have cheap impure technical grade materal containing traces of
unreacted KOH supplied to schools.
If you did the same experiment with analytical grade ACS KNO3 the pH of a 5%
solution would be in the range 4.5-8.5
>Regards
Colin

[Bernhard Kuemel]

Seibert <pit...@mesh.net> wrote:
> Hi- I'm a high school physics/physical science teacher with a problem I
> don't understand. Why does an aqueous solution of KNO3 test strongly
> basic (litmus, pH papers, phenolphthalien, etc.)

Because it is not KNO3. My KNO3 tests to about 6.5 pH with ph1-14 test
stripes and does not turn phenolphtalein red. A drop of conc. NH3 turned
it red.

[Oscar Lanzi III]

If KNO3 actually does act as an oxidizer, the nitrate ion will produce
basic products, making te solution basic. To wit:

NO3- + 2e- + H2O --> NO2- + 2 OH-
NO3- + 3e- + (3/2) H2O --> NO + 3 OH-

And so on.

--OL