Magnesium-potassium sulfate

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Crystal compoundsSaltsSulfatesMagnesium-potassium sulfate


  Magnesium-potassium sulfate   
Names: dipotassium-magnesium sulfate
magnesium сернокислый potassiumный
magnesium-potassium Tutton's salt
magnesium-potassium schoenite
NMSH

Formula: K2Mg(SO4)2 (anhydrous)
K2Mg(SO4)2 · 6H2O (hexahydrate)
SMILES: [O-]S(=O)(=O)[O-].[O-]S(=O)(=O)[O-].[Mg+2].[K+].[K+]
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=9.066 Å
9.0660 Å
0.9066 nm
, b=12.254 Å
12.2540 Å
1.2254 nm
, c=6.128 Å
6.1280 Å
0.6128 nm
α=90°
90°  
, β=104.78°
104°46′48.0″  
, γ=90°
90°  

monoclinic (tetrahydrate, leonite)
a=11.769 Å
11.7690 Å
1.1769 nm
, b=9.539 Å
9.5390 Å
0.9539 nm
, c=9.889 Å
9.8890 Å
0.9889 nm
α=90°
90°  
, β=95.31°
95°18′36.0″  
, γ=90°
90°  

Shapes:
https://media.crystalls.info/w/uploads/media/Truncated_deformed_oblique_hexagonal_prism.json
https://media.crystalls.info/w/uploads/media/Truncated_deformed_hexagonal_prism.json

Color: colorless
white
Decomposition point: 130 °C
403.15 K
266 °F
725.67 °R
(tetrahydrate)
47 °C
320.15 K
116.6 °F
576.27 °R
(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

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 а 79.56g of magnesium sulfate heptahydrate 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 а 37.02g of potassium chloride or 50.21g of potassium nitrate and 159.13g of magnesium sulfate heptahydrate 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 precipitationof 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 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.

Storage conditions

Store in its original form or under several layers of varnish at average humidity and room temperature. Do not store in matchboxes or cotton wool and do not heat.

Solubility

Temperatureгр/100,00 гр water
0°C
273.15 K
32 °F
491.67 °R
14.1
14.1 g/100g
12.358 %
10°C
283.15 K
50 °F
509.67 °R
~16.2
16.2 g/100g
13.941 %
15°C
288.15 K
59 °F
518.67 °R
~17.3
17.3 g/100g
14.749 %
20°C
293.15 K
68 °F
527.67 °R
18.3
18.3 g/100g
15.469 %
25°C
298.15 K
77 °F
536.67 °R
~20.4
20.4 g/100g
16.944 %
30°C
303.15 K
86 °F
545.67 °R
~22.5
22.5 g/100g
18.367 %
40°C
313.15 K
104 °F
563.67 °R
~26.8
26.8 g/100g
21.136 %
50°C
323.15 K
122 °F
581.67 °R
~31.1
31.1 g/100g
23.722 %
60°C
333.15 K
140 °F
599.67 °R
~35.3
35.3 g/100g
26.09 %
70°C
343.15 K
158 °F
617.67 °R
~39.6
39.6 g/100g
28.367 %
80°C
353.15 K
176 °F
635.67 °R
43.8
43.8 g/100g
30.459 %
Insoluble in ethanol, acetone and ethylene glycol.

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