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1.
Solubility and hydrolysis
Strong acid salts of iron-based elements are easily soluble in water, such as sulfate , nitrate and chloride
.
The weak acid salts, hydroxides and oxides of iron-based elements are insoluble in water
The hydrated ions of iron-based elements have characteristic colors, such as [Fe(H 2 O) 6] 2+ light green, [Fe(H 2 O) 6 ] 3+ lavender, [Co(H 2 O) 6 ] 2 + Pink, [Ni(H 2 O) 6 ] 2+ Bright green
.
Co(OH) 2 and Ni(OH) 2 are easily soluble in ammonia water, while Fe(OH) 2 and Fe(OH) 3 are insoluble in ammonia water
.
The hydrolysis of the salt is related to the charge level of the metal ion.
The higher the charge of the metal ion, the stronger the polarization ability, and the easier the salt is to be hydrolyzed
FeCl 2 ·6H 2 O and NiCl 2 ·6H 2 O cannot be hydrolyzed to obtain anhydrous salt when heated
.
The highly charged Fe 3+ has strong hydrolysis ability, and its salt aqueous solution is strongly acidic
.
Mixing FeCl 3 solution with ammonia or carbonate solution will produce hydroxide Fe(OH) 3 precipitation
The strong acid salt of Fe 3+ is soluble in water, and the lavender [Fe(H 2 O) 6 ] 3+ cannot be obtained, but a light yellow solution is obtained.
[Fe(OH)(H 2 O ) is formed due to gradual hydrolysis.
)5] 2+ and dimer [Fe 2 (OH) 2 (H 2 O) 8 ] 4+ are both yellow; as the pH of the solution rises, a brown β-FeOOH colloid is formed, at higher pH , And finally produce Fe 2 O 3 ·nH 2 O precipitation
2.
Redox
Fe 3+ is a medium to weak oxidant, E Θ (Fe 3+ /Fe 2+ )=0.
77V, which can oxidize strong reducing agents KI, H 2 S, SO 2 , Sn 2+ etc.
, and can corrode metals Copper
.
Cobalt and nickel with oxidation state +3 are strong oxidants under acidic conditions, which can oxidize HCI and Mn 2+, etc.
, in an aqueous solution
Under alkaline conditions, iodine, hydrogen peroxide and oxygen in the air can easily oxidize Fe(OH) 2 and Co(OH) 2 , but cannot oxidize Ni(OH) 2.
Use bromine water and chlorine water and other strong oxidants In order to oxidize Ni(OH) 2
.
In a strong base, Fe(OH) 3 can be oxidized by Cl 2 or CIO - to produce purple-red FeOF 4 2- ; FeO 4 2- is unstable under acidic conditions and has strong oxidizing ability; FeO 4 2- and Ba 2+ A reddish brown BaFeO 4 precipitate is formed
.
If the high-valent metal complex is more stable than the low-valent metal complex, the reducibility of the low-valent metal is enhanced when the ligand is present.
For example, I 2 cannot oxidize Fe 2+ and Co 2+ , but can oxidize [Fe(CN) 6 ] 4 - and [of Co (NH2 .
3 ) .
6 ] 2+
.
