Magnesium-potassium sulfate

Magnesium-potassium sulfate
Names:	dipotassium-magnesium sulfate magnesium-potassium Tutton's salt magnesium-potassium schoenite KMSH KMgSH
Formula:	K2Mg(SO4)2 (anhydrous) K2Mg(SO4)2 · 6H2O (hexahydrate)
Molar mass:	294.623 g/mol (anhydrous) 402.712 g/mol (hexahydrate)
Density:	2.201 g/cm3 (tetrahydrate) 2.028 g/cm3 (hexahydrate)
Crystal system:	monoclinic (hexahydrate, picromerite) a=6.1335 Å, b=12.2484 Å, c=9.0954 Åα=90°, β=104.88°, γ=90° monoclinic (tetrahydrate, leonite) a=9.889 Å, b=9.539 Å, c=11.769 Åα=90°, β=95.31°, γ=90°
Shapes:	https://en.crystalls.info/w/uploads/media/d/d0/Truncated_deformed_oblique_hexagonal_prism.json Truncated deformed oblique hexagonal prism https://en.crystalls.info/w/uploads/media/9/9a/Truncated_deformed_hexagonal_prism.json Truncated deformed hexagonal prism
Color:	colorless white
Decomposition point:	130 °C403.15 K <br />266 °F <br />725.67 °R <br /> (tetrahydrate) 47 °C320.15 K <br />116.6 °F <br />576.27 °R <br /> (hexahydrate)
Refractive index:	1.479 (tetrahydrate) 1.461 (hexahydrate)
Stability:	stable (hexahydrate) hygroscopic (anhydrous)
Hardness:	strong (2.5 on Moh's scale)
Toxicity:	non-toxic

Description

Inorganic compound, double salt of transitional metal magnesium, alkaline metal potassium and inorganic sulfuric acid. From water solutions crystallizes as hexahydrate.

Minerals

Occurs in nature as picromerite, schonite and leonite minerals.

Where to buy

Can be bought in fertilizers store (as "K-Mag" fertilizer).

Precursors

Reaction between magnesium and potassium sulfates

Chemical equation:

K₂SO₄ + MgSO₄ = K₂Mg(SO₄)₂↓

For preparation of 100.00g of magnesium-potassium sulfate hexahydrate

hexahydrate

anhydrous

а 79.56g of magnesium sulfate heptahydrate

heptahydrate

anhydrous

and 43.27g of potassium sulfate is required.

Dissolve compounds in hot water apart and then mix solutions into one container with intense stirring. Cooling or evaporation of a solution will cause double salt crystallyzation. Filter precipitate and wash it wish small amount of ethanol or acetone, then filter the solution and use it for crystal growing.

You could observe that compounds ratio is not equimolar. The cause is that firstly crystallizes potassium sulfate which is slight soluble, then begins crystallization of double sulfate. If there are some excess of magnesium, double salt crystallizes immediately at solution cooling.

Reaction between potassium chloride or nitrate and magnesium sulfate

Chemical equation:

2MgSO₄ + 2KCl = K₂Mg(SO₄)₂↓ + MgCl₂

2MgSO₄ + 2KNO₃ = K₂Mg(SO₄)₂↓ + 2MgNO₃

For preparation of 100.00g of magnesium-potassium sulfate hexahydrate

hexahydrate

anhydrous

а 37.02g of potassium chloride or 50.21g of potassium nitrate and 159.13g of magnesium sulfate heptahydrate

heptahydrate

anhydrous

is required.

Add to the flask with saturated potassium salt solution a magnesium sulfate solution with stirring. Freezing this mixture will cause forming a large amount of crystalline precipitateof potassium-magnesium sulfate. For purifying compound from unreacted compounds add large amount of cold ethanol or acetone to solution, salt will settle to the bottom in the form of fine crystals or powder. Filter precipitate and wash it with small amount of the same solvent, then filter the solution and use it for crystal growing.

Reaction between potassium sulfate and magnesium chloride

Chemical equation:

2K₂SO₄ + 2MgCl = K₂Mg(SO₄)₂↓ + 2KCl

For preparation of 100.00g of magnesium-potassium sulfate hexahydrate

hexahydrate

anhydrous

а 86.54g of potassium sulfate is required.

Dissolve compounds in hot water apart and then mix solutions into one container with intense stirring. Cooling or evaporation of a solution will cause double salt crystallyzation. For purifying compound from unreacted compounds add large amount of cold ethanol or acetone to solution, salt will settle to the bottom in the form of fine crystals or powder. Filter precipitate and wash it with small amount of the same solvent, then filter the solution and use it for crystal growing.

Influence of impurities

Small addition (~10%) of Tutton's salts, like nickel-potassium sulfate, cobalt(II)-potassium sulfate, copper(II)-potassium sulfate or magnesium-potassium sulfate-chromate can be used to change color of crystals. Adding large amounts of those sales may change crystal shape. It is also possible to cover crystals with a layer of other Tutton's salts, by placing the crystals into s saturated solution of other salt, producing a crystal-in-crystal.

Influence of pH level

Addition of surfactants has a positive influence on crystal shape and transparency. For example, addition of soap containing sodium lauryl sulfate makes crystal transparent and sharp-edged.

Storage conditions

Keep in its original form or under several layers of varnish at average humidity and room temperature. Do not keep crystals near heaters.

Solubility

TableGraph

Temperature	g/100,00 g water
0°C273.15 K <br />32 °F <br />491.67 °R <br />	14.1
20°C293.15 K <br />68 °F <br />527.67 °R <br />	18.3
80°C353.15 K <br />176 °F <br />635.67 °R <br />	43.8

Insoluble in ethanol, acetone and ethylene glycol.

Gallery

• 

  Magnesium-potassium sulfateDmitry Shintyakov, Personal crystal growing collectionDmitry ShintyakovPersonal crystal growing collection

• 

  Magnesium-potassium sulfateDmitry Shintyakov, Personal crystal growing collectionDmitry ShintyakovPersonal crystal growing collection

• 

  Magnesium-potassium sulfateDmitry Shintyakov, Personal crystal growing collectionDmitry ShintyakovPersonal crystal growing collection

• 

  Magnesium-potassium sulfateDmitry Shintyakov, Personal crystal growing collectionDmitry ShintyakovPersonal crystal growing collection

• 

  Magnesium-potassium sulfateDmitry Shintyakov, Personal crystal growing collectionDmitry ShintyakovPersonal crystal growing collection

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Sources

• R.A.Kiper Properties of compounds. Handbook
• Ferdinando Bosi, Girolamo Belardi, and Paolo Ballirano, Structural features in Tutton’s salts K2(M2+(H2O)6)(SO4)2, with M2+ = Mg, Fe, Co, Ni, Cu, and Zn
• W.Hertweck, The crystal structures of the low-temperature phases of leonite-type compounds

Navigation

Potassium compounds
Salts	Potassium bromate (KBrO3) • Potassium bromide (KBr) • Potassium chlorate (KClO3) • Potassium chloride (KCl) • Potassium chromate (K2CrO4) • Potassium dihydrophosphate (KH2PO4) • Potassium dichromate (K2Cr2O7) • Potassium iodide (KI) • Potassium hydrofluoride (KHF2) • Potassium hydrophosphate (K2HPO4) • Potassium hydrophthalate (KC8H6O4) • Potassium metavanadate (KVO3) • Potassium nitrate (KNO3) • Potassium sulfate (K2SO4) • Potassium thiocyanate (KNCS)
Double salts	Aluminum-potassium sulfate (KAl(SO4)2) • Antimony(III)-potassium tartrate (K2Sb2(C4H2O6)2) • Chromium(III)-potassium sulfate (KCr(SO4)2) • Cobalt(II)-potassium sulfate (K2Co(SO4)2) • Copper(II)-potassium sulfate (K2Cu(SO4)2) • Indium(III)-potassium sulfate (KIn(SO4)2) • Iron(II)-potassium sulfate (K2Fe(SO4)2) • Iron(III)-potassium sulfate (KFe(SO4)2) • Lithium-potassium sulfate (KLiSO4) • Magnesium-potassium sulfate (K2Mg(SO4)2) • Magnesium-potassium sulfate-chromate (K2CrO4 · MgSO4) • Manganese(II)-potassium sulfate (K2Mn(SO4)2) • Nickel-potassium sulfate (K2Ni(SO4)2) • Potassium-sodium tartrate (KNaC4H4O6) • Vanadium(III)-ammonium sulfate (NH4V(SO4)2) • Zinc-potassium sulfate (K2Zn(SO4)2)
Complexes	Potassium dioxalatocuprate(II) (K2[Cu(C2O4)2]) • Potassium hexanitrocobaltate(III) (K3[Co(NO2)6]) • Potassium hexachlororhodiate(III) (K3[RhCl6]) • Potassium hexacyanocobaltate(III) (K3[Co(CN)6]) • Potassium hexacyanoferrate(II) (K4[Fe(CN)6]) • Tripotassium-sodium hexacyanoferrate(II) (K3Na[Fe(CN)6]) • Potassium hexacyanoferrate(III) (K3[Fe(CN)6]) • Potassium hexacyanochromate(III) (K3[Co(CN)6]) • Potassium tetraiodobismuthate (К[BiI4]) • Potassium tetraiodomercurate(II) (K2[HgI4]) • Potassium trioxalatoaluminate (K3[Al(C2O4)3]) • Potassium trioxalatocobaltate(III) (K3[Co(C2O4)3]) Potassium trioxalatoferrate(III) (K3[Fe(C2O4)3]) • Potassium-sodium trioxalatoferrate(III) (K5Na[Fe(C2O4)3]2) • Dipotassium-sodium trioxalatoferrate(III) (K2Na[Fe(C2O4)3]) • Potassium trioxalatochromate(III) (K3[Cr(C2O4)3])