GROUP V! 281- The hexacyanoferrate(III) ion is reduced in alkaline solution
to hexacyanoferrate(II):
[Fe(CN) 6 ]^3 " + H 2 O 2 + 2OH~ -> [Fe(CN) 6 ]^4 ~ + 2H 2 O ~h O 2 T
(Compare this reaction with (2) of the oxidising examples, where
iron(II) is oxidised to iron(III) in acid solution; change of pH, and
complex formation by the iron, cause the completed iron(III) to be
reduced.)- Manganate(VII) is reduced to manganese(II) ion in acid
solution (usually sulphuric acid):
2MnO4 4- 6H+ + 5H 2 O 2 -* 2Mn2+ + 8H 2 O + 5O 2 TIt has been shown in reaction (3) that all the evolved oxygen comes
from the hydrogen peroxide and none from the manganate(VII) or
water, by using H 218 O 2 and determining the^18 O isotope in the
evolved gas.
The reaction with acidified potassium manganate(VII) is used in
the quantitative estimation of hydrogen peroxide.TWO TESTS FOR HYDROGEN PEROXIDE- The oxidation of black lead(II) sulphide to the white sulphate
is a very sensitive test if the black sulphide is used as a stain on filter
paper. - Addition of dilute potassium dichromate(VI) solution,
K 2 Cr 2 O 7 , to a solution of hydrogen peroxide produces chromium
peroxide, CrO 5 , as an unstable blue coloration; on adding a little
ether and shaking this compcund transfers to the organic layer in
which it is rather more stable.
USES
Pure hydrogen peroxide (or highly concentrated solution) is used
together with oil as an under-water fuel. The fuel is ignited by
inducing the strongly exothermic decomposition reaction by
spraying it with a finely-divided solid catalyst. Mixtures of hydrazine
(p. 223) and hydrogen peroxide are used for rocket propulsion.
Hydrogen peroxide in aqueous solution has many uses, because
the products from its reaction are either water or oxygen, which are
generally innocuous. The chief use is bleaching of textiles, both
natural and synthetic, and of wood pulp for paper. Other uses are
the oxidation of dyestuffs, in photography and in the production of