Shriver & Atkins: Inorganic Chemistry 4e 
3D Rotatable Molecular Structures
FiguresShriver & Atkins: Inorganic Chemistry 4e
Chapter 18
Paramagnetism
Diamagnetic zinc chloride is not attracted to the poles of a powerful magnet. Paramagnetic manganese(II) chloride, the manganese(II) ion having five unpaired electrons, is attracted to the magnet.
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Oxidation states of vanadium
Vanadium shows one of the widest range of commonly-accessible oxidation states of the transition metals. Using zinc as a reducing agent:
Zn (s) → Zn2+(aq) + 2e-
Pale yellow vanadium(V) (as the dihydrogen vanadate ion) is successively reduced to blue vanadium(IV) (as the vanadyl ion), to green vanadium(III), and finally to violet vanadium(II).
[H2VO4]- (aq) + 4H+(aq) + e-→ VO2+(aq) + 3H2O(l)
VO2+ (aq) + 2H+ (aq) + e- → V3+(aq) + H2O(l)
V3+(aq) + e-→ V2+(aq)
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The chromate-dichromate equilibrium I
The yellow chromate ion and orange dichromate ion are in equilibrium, with the chromate ion predominating in base and the dichromate ion in acid. Addition of hydrogen (hydronium) ion to chromate ion solution will drive the equilibrium towards dichromate:
2CrO42-(aq) + 2H+(aq) → Cr2O72-(aq) + H2O(l)
Addition of hydroxide ion to dichromate ion solution will drive the equilibrium towards chromate:
Cr2O72-(aq) + 2OH-(aq) → 2CrO42- (aq) + H2O(l)
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The chromate-dichromate equilibrium II
Barium chromate is insoluble while barium dichromate is soluble. Addition of hydroxide ion to dichromate ion solution increases the chromate ion concentration above the solubility product of barium chromate:
Cr2O72-(aq) + 2OH-(aq) → 2CrO42-(aq) + H2O(l)
Ba2+(aq) + CrO42-(aq) → BaCrO4(s)
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Dichromate ion as an oxidizing agent I
Dichromate ion is a strong oxidizing agent:
Cr2O72-(aq) + 14H+(aq) + 6e-→ 2Cr3+(aq) + 7H2O(l)
In this case, dichromate ion oxidizes iodide ion to iodine. The molecular iodine is extracted into dichloromethane to give the characteristic purple color.
2I-(aq) → I2(aq) + 2e-
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Dichromate ion as an oxidizing agent II
Yellow dichromate ion is reduced to green chromium(III) ion when ethanol is added.
Cr2O72-(aq) + 14H+(aq) + 6e-→ 2Cr3+ (aq) + 7H2O(l)
CH3CH2OH (aq) + H2O(l) → CH3CO2H (aq) + 4H+ (aq) + 4e-
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Decomposition of ammonium dichromate
Orange crystalline ammonium dichromate decomposes on heating to give the ‘fluffy’ green chromium(III) oxide. The reaction is non-stoichiometric but can be generally represented by the following equation.
(NH4)2Cr2O7(s) → Cr2O3 (s) + N2(g) + 4H2O(g)
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A specific test for chromate and dichromate ion
Cr2O72-(aq) + 3H2O(l) → 2CrO(O2)2 (ether) + 6H+ (aq) + 8e-
H2O2 (aq) + 2H+ (aq) + 2e-→ 2H2O (l)
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Oxidation states of manganese
Manganese(VII) in the form of the permanganate ion, can be reduced to manganese(VI), manganese(IV), and manganese(II) by the hydrogen sulfite (acidic solution) and sulfite (basic solution) ions. The product depends upon the pH of the solution.
Under very basic conditions, the green manganate ion is formed:
MnO4-(aq) + e-→ MnO42-(aq)
SO32-(aq) + 2OH-(aq) → SO42-(aq) + H2O(l) + 2e-
Under slightly basic conditions, a deep brown precipitate of manganese(IV) oxide is formed:
MnO4-(aq) + 2H2O(l) + 3e-→ MnO2(s) + 4OH-(aq)
SO32-(aq) + 2OH-(aq) → SO42-(aq) + H2O(l) + 2e-
Under acidic conditions, the colorless manganese(II) ion is formed:
MnO4-(aq) + 8H+(aq) + 5e-→ Mn2+(aq) + 4H2O(l)
HSO3-(aq) + H2O (l) → SO42-(aq) + 3H+ (aq) + 2e-
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Permanganate ion as an oxidizing agent I
In a kinetically slow reaction, purple permanganate ion oxidizes oxalate ion to carbon dioxide, itself being reduced to the colorless manganese(II) ion.
MnO4-(aq) + 8H+(aq) + 5e-→ Mn2+(aq) + 4H2O(l)
C2O42-(aq) → 2CO2 (g) + 2e-
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Permanganate ion as an oxidizing agent II
Purple permanganate ion oxidizes hydrogen peroxide in acidic solution to oxygen, itself being reduced to the colorless manganese(II) ion.
MnO4-(aq) + 8H+(aq) + 5e-→ Mn2+(aq) + 4H2O(l)
H2O2(aq) → O2(g) + 2H+(aq) + 2e-
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Permanganate ion as an oxidizing agent III
Purple permanganate ion oxidizes hydrogen peroxide in basic solution (in which it is present as the HO2- ion) to oxygen, itself being reduced to a precipitate of deep brown manganese(IV) oxide.
MnO4-(aq) + 2H2O(l) + 3e- → MnO2(s) + 4OH-(aq)
HO2-(aq) + OH-(aq) → O2(g) + H2O(l) + 2e-
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Permanganate ion as an oxidizing agent IV
Purple permanganate ion oxidizes sulfite ion in basic solution to sulfate ion, itself being reduced to the green manganate ion.
MnO4-(aq) + e-→ MnO42-(aq)
SO32-(aq) + 2OH-(l) → SO42-(aq) + H2O(l) + 2e-
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Reaction of cobalt(II) ion with hydroxide ion
Addition of hydroxide ion to the pink cobalt(II) chloride solution first results in the formation of a precipitate of blue cobalt(II) hydroxide chloride. warming with excess hydroxide ion gives the pink cobalt(II) hydroxide which upon standing converts to brown-black cobalt(III) hydroxide:
Co2+(aq) + OH-(aq) + Cl-(aq) → Co(OH)Cl (s)
Co(OH)Cl (s) + OH-(aq) → Co(OH)2(s) + Cl-(aq)
4Co(OH)2(s) + O2(g) + 2H2O(l) → 4Co(OH)3(s)
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Reaction of nickel(II) ion with hydroxide ion
Pale green nickel(II) ion reacts with hydroxide ion to give a gelatinous pale green precipitate of nickel(II) hydroxide.
Ni2+(aq) + 2OH-(aq) → Ni(OH)2(s)
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A specific test for nickel(II) ion
Nickel(II) ion gives a characteristic and quantitative red precipitate with the dimethyglyoximate reagent.
Ni2+(aq) + 2C4H6O2N22-(aq) → [Ni(C4H6O2N2)2] (s)
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Reaction of copper(II) ion with hydroxide ion
Blue copper(II) ion reacts with hydroxide ion to give a precipitate of gelatinous/flocculent pale blue copper(II) hydroxide. Warming the mixture results in formation of black copper(II) oxide.
Cu2+(aq) + 2OH-(aq) → Cu(OH)2(s)
Cu(OH)2(s) 
CuO(s) + H2O(l)
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Reaction of sulfide ion with copper(II) ion
Blue copper(II) ion reacts with sulfide ion to give a black precipitate of copper(II) sulfide.
Cu2+(aq) + S2-(aq) → CuS(s)
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A specific test for cadmium ion
Colorless cadmium ion gives a characteristic yellow to orange (depending upon particle size) precipitate of cadmium sulfide.
Cd2+(aq) + S2-(aq) → CdS(s)
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