{2}O + 2Cl,

MnO_{2} + H_{2}SO_{4} = MnSO_{4} + H_{2}O + O.

The sulphide, carbonate, and hydroxide, being insoluble, may be prepared
from a solution of the chloride or sulphate by precipitation with the
appropriate reagents. Most of the manganous salts are rose colored. They
not only have formulas similar to the ferrous salts, but resemble them
in many of their chemical properties.

~Compounds containing manganese as an acid-forming element.~ Manganese
forms two unstable acids, namely, manganic acid and permanganic acid.
While these acids are of little interest, some of their salts,
especially the permanganates, are important compounds.

~Manganic acid and manganates.~ When manganese dioxide is fused with an
alkali and an oxidizing agent a green compound is formed. The equation,
when caustic potash is used, is as follows:

MnO_{2} + 2KOH + O = K_{2}MnO_{4} + H_{2}O.

The green compound (K_{2}MnO_{4}) is called potassium manganate, and is
a salt of the unstable manganic acid (H_{2}MnO_{4}). The manganates are
all very unstable.

~Permanganic acid and the permanganates.~ When carbon dioxide is passed
through a solution of a manganate a part of the manganese is changed
into manganese dioxide, while the remainder forms a salt of the unstable
acid HMnO_{4}, called permanganic acid. The equation is

3K_{2}MnO_{4} + 2CO_{2} = MnO_{2} + 2KMnO_{4} + 2K_{2}CO_{3}.

Potassium permanganate (KMnO_{4}) crystallizes in purple-black needles
and is very soluble in water, forming an intensely purple solution. All
other permanganates, as well as permanganic acid itself, give solutions
of the same color.

~Oxidizing properties of the permanganates.~ The permanganates are
remarkable for their strong oxidizing properties. When used as an
oxidizing agent the permanganate is itself reduced, the exact character
of the products formed from it depending upon whether the oxidation
takes place (1) in an alkaline or neutral solution, or (2) in an acid
solution.

1. _Oxidation in alkaline or neutral solution._ When the solution is
either alkaline or neutral the potassium and the manganese of the
permanganate are both converted into hydroxides, as shown in the
equation

2KMnO_{4} + 5H_{2}O = 2Mn(OH)_{4} + 2KOH + 3O.

2. _Oxidation in acid solution._ When free acid such as sulphuric is
present, the potassium and the manganese are both changed into salts of
the acid:

2KMnO_{4} + 3H_{2}SO_{4} = K_{2}SO_{4} + 2MnSO_