Paper, KNO3, Flame

Name: Ateev
Status: student
Grade: 9-12
Location: KY

Question: When we write anything on a paper with KNO2 and then heat
the area with a very less flame such as a match stick then why does
the area on which the compound is applied turns black but not burn?
I want to know the reason for it turning black.
---------------------------------------
Ateev-
   If it was KNO3 (instead of KNO2), well, that is an oxidizer often used in
rocket fuel.
It causes some charring of the paper at temperatures lower than would
otherwise happen from the oxygen in air.
The paper can still turn black if you get it hotter, but you have not gone
to that temperature yet.
When the KNO3 melts the liquid is much more reactive than the solid
crystals could be.

KNO3 melts at 334 degrees C.
The combustion temperature for paper in air is something above 300C,
That order seems a little wrong.
Maybe the KNO3 does not need to melt completely to be reactive.
With water in the air and starch in the paper it might make a lower-melting
mix.
And for short times, the paper might not char from air as quickly as the
KNO3 reaction occurs.

I guess KNO2 might have some effects too.
It is also an oxidizer, and when it decomposes at 350C or less, what is left
is KOH or K2O or K2O2,
which are very strong bases and will catalyze cellulose oxidation in air.
I do not really know which reason is dominant.

Jim Swenson
====================================================================