176 NON-METALLIC ELEMENTS IN BINARY COMPOUNDS- Reducing Action of Hydrogen Sulphide. Dilute 5 cc.
of a potassium permanganate solution with 100 cc. of water
and add 5 cc. of 6 N H2SO4. Bring the solution to boiling
and pass in hydrogen sulphide. The deep purple color of
the permanganate quickly disappears, and a white opalescent
precipitate appears.
Although sulphur in hydrogen sulphide has a range of eight pos-
sible points in valence, from —2 to +6, to go when it acts as
a reducing agent, it usually does not go beyond the zero stage of
valence in aqueous oxidizing agents, the obvious explanation
being that the free sulphur is precipitated and thus removed from
the sphere of action.
2KMnO 4 + 5H 2 S + 3H 2 SO 4 -»K 2 SO 4 + 2MnSO 4 + 8H 2 O + 5S
2Mn +7 to+2 2X(-5) = -10
5S -2 to 0 5X(+2) = +10
Total change = 0NITROGEN
Nitrogen is an extremely inactive element, combining directly
only with the most active of the metals. Nitrogen forms no
simple ions and it is impossible to give it an exact potential in the
electromotive series, but it is obvious that it is far less active
than sulphur or iodine. Under the influence of electric sparks
or of catalysts at about 400° nitrogen does combine sparingly
with hydrogen to form ammonia NH 3. It combines quite readily
with magnesium to give the nitride Mg 3 N 2 which compound bears
the same relation to ammonia (its formula should logically be
H 3 N) that magnesium chloride does to hydrogen chloride.
- Synthesis of Ammonia. Heat a mixture of 14 grams
of iron filings, 0.5 gram of powdered sodium hydroxide, and
0.5 gram of powdered potassium nitrate in a test tube, and
test the gas which escapes by holding a rod wet with con-
centrated hydrochloric acid near the mouth of the tube.
A white smoke is formed.
Test the action of iron on sodium hydroxide and potassium
nitrate respectively by heating 7-gram portions of iron
filings with 0.5 gram of each of these reagents separately.