Potassium Polysulfides

Potassium Polysulfides
Potassium Polysulfides
Are common
Systematic ; name	Potassium polysulfide
Traditional names	Potassium sulphide
Chem. formula	K 2 S n

Potassium polysulfide - yellow-brown, solid crystals with the formula K ₂ S _n , where n = 2 ÷ 6.

Content

Getting

The fusion of potassium sulfide with sulfur produces a mixture of polysulfides:

{\mathsf {K_{2}S+{\mathit {n}}S\ {\xrightarrow {T}}\ K_{2}S_{{\mathit {n}}+1}}}

{\ displaystyle {\ mathsf {K_ {2} S + {\ mathit {n}} S \ {\ xrightarrow {T}} \ K_ {2} S _ {{\ mathit {n}} + 1}}}}

the result can be controlled by the amount of sulfur and the reaction temperature. Also, this reaction can be carried out in an alkalized boiling aqueous solution.

Physical Properties

Potassium polysulfides are yellow to yellow-orange solid substances. Well soluble in water, higher polysulfides are soluble in ethanol .

Properties of some potassium polysulfides
Polysulfide	Molar mass	Density	Temperature melting point (° C)	Appearance	Crystal hydrate
K ₂ S ₂	142.33	1,973	520; 470; 477	reddish yellow	K ₂ S ₂ • 3H ₂ O
K ₂ S ₃	174.39	2,102	292; 252; 295	yellow brown
K ₂ S ₄	206.46		159; 145	red brown	K ₂ S ₄ • 2H ₂ O
K ₂ S ₅	238.53	2,128	211; 206; 207	Orange	K ₂ S ₅ • H ₂ O
K ₂ S ₆	270.59	2.02	196; 197

Chemical Properties

With strong heating, decompose with the release of sulfur:

{\mathsf {K_{2}S_{\mathit {n}}\ {\xrightarrow {>600^{o}C}}\ K_{2}S+({{\mathit {n}}-1})S}}

{\ displaystyle {\ mathsf {K_ {2} S _ {\ mathit {n}} \ {\ xrightarrow {> 600 ^ {o} C}} \ K_ {2} S + ({{\ mathit {n}} - 1 }) S}}}

Aqueous solutions have an alkaline reaction due to anion hydrolysis :

{\mathsf {S_{\mathit {n}}^{2-}+H_{2}O\ \rightleftarrows \ HS_{\mathit {n}}^{-}+OH^{-}}}

{\ displaystyle {\ mathsf {S _ {\ mathit {n}} ^ {2 -} + H_ {2} O \ \ rightleftarrows \ HS _ {\ mathit {n}} ^ {-} + OH ^ {-}}} }

At room temperature they decompose with dilute acids, releasing sulfur:

{\mathsf {K_{2}S_{\mathit {n}}+2\ HCl\ {\xrightarrow {20^{o}C}}\ 2\ KCl+H_{2}S\uparrow +({{\mathit {n}}-1})S\downarrow }}

{\ displaystyle {\ mathsf {K_ {2} S _ {\ mathit {n}} + 2 \ HCl \ {\ xrightarrow {20 ^ {o} C}} \ 2 \ KCl + H_ {2} S \ uparrow + ( {{\ mathit {n}} - 1}) S \ downarrow}}}

At low temperature and concentrated acid, polysulfanes can be obtained:

{\mathsf {K_{2}S_{\mathit {n}}+2\ HCl\ {\xrightarrow {-15^{o}C}}\ 2\ KCl+H_{2}S_{\mathit {n}}}}

{\ displaystyle {\ mathsf {K_ {2} S _ {\ mathit {n}} + 2 \ HCl \ {\ xrightarrow {-15 ^ {o} C}} \ 2 \ KCl + H_ {2} S _ {\ mathit {n}}}}}

In a humid environment and in the light, potassium polysulfides are oxidized by atmospheric oxygen:

{\mathsf {2\ K_{2}S_{\mathit {n}}+2\ H_{2}O+O_{2}\ {\xrightarrow {\ }}\ 4\ KOH+2{\mathit {n}}S}}

{\ displaystyle {\ mathsf {2 \ K_ {2} S _ {\ mathit {n}} + 2 \ H_ {2} O + O_ {2} \ {\ xrightarrow {\}} \ 4 \ KOH + 2 {\ mathit {n}} S}}}

Without water, the oxidation reaction proceeds differently:

{\mathsf {2\ K_{2}S_{\mathit {n}}+3\ O_{2}\ {\xrightarrow {\ }}\ 2\ K_{2}S_{2}O_{3}+(2{\mathit {n}}-4)S}}

{\ displaystyle {\ mathsf {2 \ K_ {2} S _ {\ mathit {n}} + 3 \ O_ {2} \ {\ xrightarrow {\}} \ 2 \ K_ {2} S_ {2} O_ {3 } + (2 {\ mathit {n}} - 4) S}}}

Application

For sulphidation of steel and cast iron products.
For the treatment of skin diseases (Sulfur Liver).
Like a pesticide .

Literature

Chemical Encyclopedia / Editorial Board: Knunyants I.L. et al. - M .: Soviet Encyclopedia, 1990. - T. 2. - 671 p. - ISBN 5-82270-035-5 .
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 .
Chemistry Handbook / Editorial: Nikolsky B.P. et al. - 3rd ed., rev. - L .: Chemistry, 1971. - T. 2. - 1168 p.
Ripan R., Chetyanu I. Inorganic chemistry. Chemistry of metals. - M .: Mir, 1971. - T. 1. - 561 p.