Modern inorganic chemistry

382 THE TRANSITION ELEMENTS

[2Cr(H 2 0) 6 ]3+ + 20H- =2

OH

H,0

(H 2 0) 4 Cr

OH

H,O

(H 2 O) 4 Cr'

OH

/ x.

(H 2 O) 4 Cr X''x /Cr(H 2 O) 4

^O^

finally

2H,O

(13.1)

2H 2 O

(13.2)

HO OH OH OH OH

XCr C/ Cr Cr C/ (13.3)

/ \ / \ / \ / \

HO OH OH OH OH

Chromium(III) hydroxide, like aluminium hydroxide, possesses

(Wsorptive power, and the use of chromium compounds as mordants

is due to this property.

Chromium(III) hydroxide dissolves in acids to form hydrated

chromium(III) salts; in concentrated alkali, hydroxo-complexes

[Cr(OH) 6 ]^3 ~ are formed.

CHROMIUM(III) SULPHATE. Cr 2 (SO 4 )3.18H.O

Hydrated chromium(III) sulphate exhibits different colours and
different forms from which varying amounts of sulphate ion can be
precipitated by barium chloride, due to the formation of sulphato-
complexes. Chromium(III) sulphate can form alums.

HYDRATED CHROMIUM(lIl) NITRATE, Cr(NO 3 ) 3 .9H 2 O

Hydrated chromium)III) nitrate is a dark green, very deliquescent

solid, very soluble in water. The anhydrous nitrate is covalent.

Oxidation state + 2

This state is strongly reducing, often coloured, and paramagnetic.