Addition of KNO3 to HF(aq)

[lanrete]

Hi,

in my lab i have a procedure by which excess KNO3 is added to an unknown HF
sample and then titrated with NaOH with phenolphthalein as indicator.

After this first titration, the sample is then placed in an 80oC waterbath
for 1 hour before conducting a 2nd titration with NaOH again with
phenolphthalein as indicator.

From my manual, it states that this procedure is to determine the HF and
H2SiF6 concentration in the sample.

So my question is what is the purpose of KNO3 in the procedure? Also can
someone deduce the formula of the reaction(s) taking place with KNO3 in this
procedure?

Thanks!

[c***@one.net.au]

Post by lanrete
Hi,
in my lab i have a procedure by which excess KNO3 is added to an unknown HF
sample and then titrated with NaOH with phenolphthalein as indicator.
After this first titration, the sample is then placed in an 80oC waterbath
for 1 hour before conducting a 2nd titration with NaOH again with
phenolphthalein as indicator.
From my manual, it states that this procedure is to determine the HF and
H2SiF6 concentration in the sample.
So my question is what is the purpose of KNO3 in the procedure? Also can
someone deduce the formula of the reaction(s) taking place with KNO3 in this
procedure?
Thanks!

Does the first titration determine both acids , and the second
titration the H2SiF6 ?
If so, I suspect the KNO3 complexes the H2SiF6, whilst allowing the HF
to be evaporated off.

Colthechemist

[Merlin]

Hi everybody
I just finished experiments of GC-MS, and I have 3 undetermined peaks. I
searched for oxysterols, but there are not (ecdysones??). Where can I
found a MS database; ie enter my peaks and get some clues?

cheers
Olivier