EXPERIMENTS 347
The decomposition of cobalt carbonate gives cobaltous oxide,
COCO3 —• CoO + CO 2 , but this is easily oxidizable in the air to a
higher oxide. The higher oxide reacts as an oxidizing agent to-
wards HCl and the chloride corresponding to CoO is obtained:
CO2O3 + 6HC1 -»2C0CI2 + 3H 2 O + Cl 2
The monoxides CrO, MnO, FeO, CoO, NiO are all easily oxidiz-
able in contact with air. The higher oxides of manganese and
nickel behave as the cobaltic oxide above. On the other hand,
the chlorides CrCl 3 and FeCl 3 are stable, and the treatment of
Fe 2 O 3 and Cr 2 O 3 with HCl produces no free chlorine.
Note. In Experiment 1 a higher oxide of nickel was probably
formed in the same manner, although to a considerably less extent.
- Properties of the Hydroxides. In separate test tubes
take 2 cc. each of IN solutions of (a) CrCl 3 , (6) MnCl 2 ,
(c) FeCl 2 , (d) FeCl 3 , (e) CoCl 2 , (/) NiCl 2. Add 10 cc. of
water to each tube and 6 N NaOH until the solution is alka-
line in each case.
(a) Chromic hydroxide, Cr(OH) 3 , a light greenish gray vo-
luminous precipitate. Soluble in excess of cold NaOH. Re-
precipitated on boiling.
(6) Manganous hydroxide, Mn(0H) 2 , a light buff-colored pre-
cipitate. Insoluble in excess of NaOH. Oxidizes easily, turning
dark brown or black as it comes in contact with air, Mn(0H) 3.
(c) Ferrous hydroxide, Fe(OH) 2 , a gray-green precipitate in-
soluble in excess NaOH. Oxidizes easily, turning reddish brown
as it comes in contact with air, (FeOH) 3.
(d) Ferric hydroxide, Fe(OH) 3 , a reddish brown voluminous
precipitate insoluble in excess of NaOH.
(e) Cobaltous hydroxide, Co(OH) 2 , insoluble in excess of
NaOH.
(/) Nickelous hydroxide, Ni(0H) 2 , an apple green precipitate
insoluble in excess NaOH, not oxidized by air.
- Action of Aqueous Alkaline Oxidizing Agents. Pre-
pare a sodium hypochlorite solution by stirring bleaching
powder and an excess Na 2 CO 3 solution and filtering. Place
about 2 cc. of thin suspensions of each of the hydroxides pre-
pared in Experiment 4 in separate test tubes and treat each
with excess NaOH and the sodium hypochlorite solution.
