Chromium (III) -potassium sulfate

Chromium sulfate
Chromium sulfate
General
Systematic ; name	Chromium (III) -potassium sulfate
Traditional names	potassium chromium sulfate; potassium chromium alum
Chem. formula	KCr (SO 4 ) 2
Physical properties
condition	red crystals
Molar mass	283.22 g / mol
Density	hydr. 1,842 g / cm³
Thermal properties
T. melt.	hydr. 89 ° C
Enthalpy of Education	-5785.30 kJ / mol
Chemical properties
Solubility in water	12.51 25 g / 100 ml
Classification
Reg. CAS number	10141-00-1
PubChem
Reg. EINECS number
Smiles
Inchi
Reg. EC number	233-401-6
RTECS
ChemSpider

Chromium (III) -potassium sulfate is an inorganic compound, a salt of potassium and chromium metals and sulfuric acid with the formula KCr (SO ₄ ) ₂ , dark violet crystals soluble in water form crystalline hydrates - potassium chromium alum .

Crystal growth from chromium potassium alum

Getting

Formed during the evaporation of solutions of chromium and potassium sulfates :

{\mathsf {K_{2}SO_{4}+Cr_{2}(SO_{4})_{3}+24H_{2}O\ {\xrightarrow {}}\ 2(KCr(SO_{4})_{2}\cdot 12H_{2}O)\downarrow }}

{\ displaystyle {\ mathsf {K_ {2} SO_ {4} + Cr_ {2} (SO_ {4}) _ {3} + 24H_ {2} O \ {\ xrightarrow {}} \ 2 (KCr (SO_ { 4}) _ {2} \ cdot 12H_ {2} O) \ downarrow}}}

{\mathsf {K_{2}SO_{4}+Cr_{2}(SO_{4})_{3}+24H_{2}O\ {\xrightarrow {}}\ 2(KCr(SO_{4})_{2}\cdot 12H_{2}O)\downarrow }}

Recovery of potassium dichromate in an acidic environment:

{\mathsf {K_{2}Cr_{2}O_{7}+3CH_{3}CH_{2}OH+4H_{2}SO_{4}+17H_{2}O\ {\xrightarrow {}}}}

{\ displaystyle {\ mathsf {K_ {2} Cr_ {2} O_ {7} + 3CH_ {3} CH_ {2} OH + 4H_ {2} SO_ {4} + 17H_ {2} O \ {\ xrightarrow {} }}}}

\mathsf{K_2Cr_2O_7 + 3CH_3CH_2OH + 4H_2SO_4 + 17H_2O \ \xrightarrow{} }

{\mathsf {{\xrightarrow {}}\ 2KCr(SO_{4})_{2}\cdot 12H_{2}O\downarrow +3CH_{3}CHO}}

{\ displaystyle {\ mathsf {{\ xrightarrow {}} \ 2KCr (SO_ {4}) _ {2} \ cdot 12H_ {2} O \ downarrow + 3CH_ {3} CHO}}}

\mathsf{ \xrightarrow{}\ 2KCr(SO_4)_2\cdot 12H_2O\downarrow + 3CH_3CHO }

Physical Properties

Chromium (III) -potassium sulfate forms red crystals of trigonal syngony , space group P 32 , cell parameters a = 0.4737 nm, c = 0.8030 nm, Z = 1.

It forms crystalline hydrates of the composition KCr (SO ₄ ) ₂ • n H ₂ O, where n = 1, 2, 6, and 12.

The most studied crystalline hydrate is KCr (SO ₄ ) ₂ • 12H ₂ O — potassium chromium alum , dark violet crystals of cubic syngony , space group P a3 , cell parameters a = 1.2200 nm, Z = 4. When heated above 78 ° C, they turn into green modification.

Chemical Properties

Anhydrous salt is obtained by drying crystalline hydrate by heating:

{\mathsf {KCr(SO_{4})_{2}\cdot 12H_{2}O\ {\xrightarrow {350-400^{o}C}}\ KCr(SO_{4})_{2}+12H_{2}O}}

{\ displaystyle {\ mathsf {KCr (SO_ {4}) _ {2} \ cdot 12H_ {2} O \ {\ xrightarrow {350-400 ^ {o} C}} \ KCr (SO_ {4}) _ { 2} + 12H_ {2} O}}}

Decomposes on heating:

{\mathsf {4KCr(SO_{4})_{2}\ {\xrightarrow {700-900^{o}C}}\ 2K_{2}SO_{4}+2Cr_{2}O_{3}+6SO_{2}+3O_{2}}}

{\ displaystyle {\ mathsf {4KCr (SO_ {4}) _ {2} \ {\ xrightarrow {700-900 ^ {o} C}} \ 2K_ {2} SO_ {4} + 2Cr_ {2} O_ {3 } + 6SO_ {2} + 3O_ {2}}}}

In hot water it undergoes slow hydrolysis :

{\mathsf {2KCr(SO_{4})_{2}+6H_{2}O\ {\xrightarrow {\tau ,100^{o}C}}\ H_{2}[Cr_{2}(H_{2}O)_{4}(SO_{4})_{3}(OH)_{2}]+2K_{2}SO_{4}}}

{\ displaystyle {\ mathsf {2KCr (SO_ {4}) _ {2} + 6H_ {2} O \ {\ xrightarrow {\ tau, 100 ^ {o} C}} \ H_ {2} [Cr_ {2} (H_ {2} O) _ {4} (SO_ {4}) _ {3} (OH) _ {2}] + 2K_ {2} SO_ {4}}}}

Decomposed by diluted alkalis :

{\mathsf {KCr(SO_{4})_{2}+3KOH\ {\xrightarrow {}}\ Cr(OH)_{3}\downarrow +2K_{2}SO_{4}}}

{\ displaystyle {\ mathsf {KCr (SO_ {4}) _ {2} + 3KOH \ {\ xrightarrow {}} \ Cr (OH) _ {3} \ downarrow + 2K_ {2} SO_ {4}}}}

and concentrated:

{\mathsf {KCr(SO_{4})_{2}+6KOH\ {\xrightarrow {}}\ K_{3}[Cr(OH)_{6}]+2K_{2}SO_{4}}}

{\ displaystyle {\ mathsf {KCr (SO_ {4}) _ {2} + 6KOH \ {\ xrightarrow {}} \ K_ {3} [Cr (OH) _ {6}] + 2K_ {2} SO_ {4 }}}}

It is restored by atomic hydrogen :

{\mathsf {2KCr(SO_{4})_{2}+2H_{(Zn,H_{2}SO_{4})}^{0}\ {\xrightarrow {}}\ 2CrSO_{4}+K_{2}SO_{4}+H_{2}SO_{4}}}

{\ displaystyle {\ mathsf {2KCr (SO_ {4}) _ {2} + 2H _ {(Zn, H_ {2} SO_ {4})} ^ {0} \ {\ xrightarrow {}} \ 2CrSO_ {4} + K_ {2} SO_ {4} + H_ {2} SO_ {4}}}}

It is oxidized by concentrated hydrogen peroxide in an alkaline medium:

{\mathsf {2KCr(SO_{4})_{2}+3H_{2}O_{2}+10KOH\ {\xrightarrow {}}\ 2K_{2}CrO_{4}+4K_{2}SO_{4}+8H_{2}O}}

{\ displaystyle {\ mathsf {2KCr (SO_ {4}) _ {2} + 3H_ {2} O_ {2} + 10KOH \ {\ xrightarrow {}} \ 2K_ {2} CrO_ {4} + 4K_ {2} SO_ {4} + 8H_ {2} O}}}

Application

When tanning leather and as a mordant in the textile industry.

Literature

Chemical Encyclopedia / Editorial Board: Knunyants I.L. et al. - M .: Soviet Encyclopedia, 1990. - T. 2. - 671 p. - ISBN 5-82270-035-5 .
Chemistry Handbook / Editorial: Nikolsky B.P. et al. - 2nd ed., rev. - M.-L.: Chemistry, 1966. - T. 1. - 1072 p.
Chemistry Handbook / Editorial: Nikolsky B.P. et al. - 3rd ed., rev. - L .: Chemistry, 1971. - T. 2. - 1168 p.
Lidin R.A. and other Chemical properties of inorganic substances: Textbook. manual for universities. - 3rd ed., Rev. - M .: Chemistry, 2000 .-- 480 p. - ISBN 5-7245-1163-0 .
Ripan R., Chetyanu I. Inorganic chemistry. Chemistry of metals. - M .: Mir, 1972. - T. 2. - 871 p.