13. ELEMENTS OF SUBGROUP OF CHROME.

Atomic number	Name	Electronic configuration	ρ g/cm3	tpl. 0C	tkip. 0C	EO	Atomic radius, nanometer	Degree oxidations
26	Fe iron	[Ar] 3d64s2	7,87	1535	2750	1,64	0,128	+2,+3
27	Co cobalt	[Ar] 3d74s2	8,9	1495	2870	1,7	0,125	+2,+3
28	Ni nickel	[Ar] 3d8 4s2	8,9	1453	2732	1,75	0,124	+1,+2,+3,+4

 Receiving
metals of subgroup of iron

Recovery from oxides coal or carbon oxide (II)

FeO + C Fe + CO
_Fe2O3 + 3CO 2Fe + _3CO2
NiO + C Ni + CO
_Co2O3 + 3C 2Co + 3CO

Fe
d-group element VIII; order number – 26; atomic mass – 56; (26p; 30 n), 26e

1s22s22p63s23p63d64s2

 
Metal of average activity, reducer.
The main oxidation levels - +2, +3

Iron and its connections

Chemical properties

On air iron easily is oxidized in the presence of moisture (rustiness):

4Fe + _3O2 + _{6H2 O} 4Fe _(OH)3

The heated iron wire burns in oxygen, forming scale - iron oxide (II, III):

3Fe + _{2O2 Fe3O4}

At high ^{temperature (700-9000C)} iron reacts with water vapor:

3Fe + _{4H2O Fe3O4} + _4H2
Iron reacts with nonmetals when heating:

2Fe + _{3Br2  2FeBr3}
Fe + S FeS
Iron is easily dissolved in the hydrochloric and diluted with chamois acids:

Fe + 2HCl _FeCl2 + _H2
Fe + _H2SO4 (разб.) _FeSO4 + _H2

In the concentrated acids oxidizers iron is dissolved only when heating

2Fe + _6H2SO4 (конц.)  _Fe2(SO4)3 + _3SO2 + _6H2O
Fe + _6HNO3 (конц.)  _Fe(NO3)3 + _3NO2 + _3H2O

(on cold the concentrated nitric and sulfuric acids passivate iron).
Iron forces out the metals standing more to the right of it among tension from solutions of their salts.

Fe + _{CuSO4 FeSO4} + Cu

Ferro-compounds

Ferrous hydroxide (II)

It is formed at effect of solutions of alkalis on salt of iron (II) without air access:

FeCl + _{2KOH 2KCl + Fe (OH) 2}

_Fe(OH)2 - mild base, растворимо in strong acids:

_Fe(OH)2 + _{H2SO4 FeSO4} + _2H2O

When calcinating Fe(OH)2 without access of air FeO iron oxide (II) is formed:

_{Fe (OH) 2 FeO} + _H2O

In the presence of air oxygen white deposit _{of Fe (OH) 2}, being oxidized, grows brown – forming _{Fe (OH) 3 ferrous hydroxide (III)}:

4Fe _(OH)2 + _O2 + _2H2O 4Fe _(OH)3

Compounds of iron (II) have recovery properties, they easily turn into compounds of iron (III) under the influence of oxidizers:

_10FeSO4 + _2KMnO4 + _{8H2SO4 5Fe2(SO4) 3} + _K2SO4 + _2MnSO4 + _8H2O
6FeSO4 + _2HNO3 + _{3H2SO4 3Fe2(SO4) 3} + 2NO + _4H2O

Compounds of iron are inclined to complex formation (coordination number =6):

_FeCl2 + _{6NH3 [Fe(NH3)6] of Cl2}
Fe(CN)2 + 4KCN K4 [Fe(CN)6] (yellow blood salt)

Qualitative test on ^{Fe2 +}

At effect of hexacyanoferrate (III) _{of K2 potassium [Fe(CN)6]} (red blood salt) on solutions of salts of bivalent iron the blue deposit is formed (turnbuleva blue):

_3FeSO4 + _{2K3 [Fe(CN)6] of Fe3 [Fe(CN)6]} + _3K2SO4

Ferri-compounds

Iron oxide (III)

It is formed at combustion of iron sulfides, for example, when roasting pyrite:

_4FeS2 + _{11O2 2Fe2O3} + _8SO2

or when calcinating salts of iron:

_2FeSO4Fe2O3 + _SO2 + _SO3

_Fe2O3 - the main oxide in insignificant degree showing amphoteric properties

_Fe2O3 + 6HCl  _2FeCl3 + <sub>3H2O

Fe2O3</sub> + 2NaOH + _3H2O 2Na _[Fe(OH)4]

Ferrous hydroxide (III)

It is formed at effect of solutions of alkalis on salt of trivalent iron: drops out in the form of red-brown deposit

_Fe(NO3)3 + _{3KOH Fe(OH)3+ 3KNO3}

_Fe(OH)3 – more mild base, than ferrous hydroxide (II).
This results from the fact that at ^{Fe2 +} the ion charge more its radius is less, than at ^Fe3+ and therefore, ^{Fe2 +} holds hydroxide ions more weakly, i.e. _Fe(OH)2 dissociates more easily.
In this regard salts of iron (II) are hydrolyzed slightly, and salts of iron (III) - is very strong. Also color of solutions of Fe (III) salts is explained by hydrolysis: in spite of the fact that Fe3 ion + is almost colourless, the solutions supporting him are painted in yellow-brown color that is explained by presence of gidroksoion of iron or the molecules Fe (OH) 3 which are formed thanks to hydrolysis:

^{Fe3 +} + _H2O [Fe(OH)]2 ⁺ + H ⁺
_[Fe(OH)]2+ + _{H2O [Fe(OH)2]} ⁺ + H ⁺
_[Fe(OH)2] ⁺ + _{H2O Fe (OH) 3} + ^H+

When heating coloring darkens, and at addition of acids becomes lighter owing to hydrolysis suppression. Fe(OH)3 has poorly expressed amphoteric character: it is dissolved in diluted acids and in concentrated solutions of alkalis:

_Fe(OH)3 + 3HCl _FeCl3 + <sub>3H2O

Fe(OH)3 + NaOH Na [Fe(OH)3]</sub>

Compounds of iron (III) - weak oxidizers, react with strong reducers:

_2FeCl3 + H2S S + _2FeCl2 + 2HCl

Qualitative tests on Fe3 +

At effect of hexacyanoferrate (II) of K4 potassium [Fe(CN)6] (yellow blood salt) on solutions of salts of trivalent iron the blue deposit (Prussian blue) is formed:

_4FeCl3 + _{3K4 [Fe(CN)6] of Fe4} [_Fe(CN)6]3 + 12KCl

At addition to the solution containing Fe3 ions + potassium sulphocyanate or ammonium intensive blood-red coloring of ferric rhodanide (III) appears:

_FeCl3 + _{3NH4CNS 3NH4Cl} + _Fe(CNS)3

(at interaction with rhodanates of ions ^{Fe2 +} solution remains almost colourless).

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Cobalt and its connections

On reactivity cobalt concedes to iron. It is easily dissolved in acids - oxidizers and slowly in usual acids:

Co + 2HCl _CoCl2 + _H2

In simple connections at cobalt the oxidation level +2, in komplesny – +3 is steadiest. Aqueous solutions of salts of cobalt (II) are usually painted in pink color.

Cobaltic hydroxide (II)

It is formed at effect of alkalis on salt of cobalt (II):

_CoSO4 + _{2KOH K2SO4} + _Co(OH)2

On air the pink deposit of Co (OH) 2 gradually grows brown, turning into cobaltic hydroxide (III):

4Co _(OH)2 + _O2 + _2H2O 4Co _(OH)3

So _(OH)2 - mild base, soluble in strong acids:

_Co(OH)2 + 2HCl _CoCl2 + _2H2O

When calcinating _Co(OH)2 forms CoO cobalt oxide (II):

_{Co (OH) 2 CoO} + _H2O

Compounds of cobalt are inclined to complex formation (coordination number =6):

_Co(OH)2 + _{6NH3 [Co(NH3)] (OH)2}

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Nickel and its connections

Nickel is easily dissolved in the diluted nitric acid and slowly in hydrochloric and sulfuric acids

Ni + 2HCl _NiCl2 + _H2

The ion ^{of Ni2 +} in aqueous solutions has green coloring. Oxidation level +2 is most characteristic of nickel. Oxide and nickel hydroxide show the main character.

NiO + _{H2SO4 NiSO4} + _H2O
NiCl2 + 2NaOH _Ni(OH)2 (green) + 2NaCl
_Ni(OH)2 + _{H2SO4 NiSO4} + _2H2O

Nickelous compounds can give complexes with ammonia:

_Ni(OH)2 + _6NH3 [_{Ni(NH3)6](OH)2}

   

 

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