Potassium sulfate

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  Potassium sulfate   
Names: potassium sulfate
dipotassium sulfate

Formula: K2SO4
SMILES: [O-]S(=O)(=O)[O-].[K+].[K+]
Molar mass: 174.257 g/mol
Density: 2.663 g/cm3
Crystal system: orthorhombic (α)
a=5.7704 Å
5.7704 Å
0.5770 nm
, b=10.0712 Å
10.0712 Å
1.0071 nm
, c=7.4776 Å
7.4776 Å
0.7478 nm
α=90°
90°  
, β=90°
90°  
, γ=90°
90°  

hexagonal (β)
a=5.947 Å
5.9470 Å
0.5947 nm
, b=5.947 Å
5.9470 Å
0.5947 nm
, c=8.375 Å
8.3750 Å
0.8375 nm
α=90°
90°  
, β=90°
90°  
, γ=120°
120°  

Shapes:
https://media.crystalls.info/w/uploads/media/Hexagonal_bipyramid.json
https://media.crystalls.info/w/uploads/media/Hexagonal_pyramid.json
https://media.crystalls.info/w/uploads/media/Deformed_tetragonal_bipyramid.json

Color: colorless
Melting point: 1069 °C
1,342.15 K
1,956.2 °F
2,415.87 °R

Boiling point: 1689 °C
1,962.15 K
3,072.2 °F
3,531.87 °R

Decomposition point: 583 °C
856.15 K
1,081.4 °F
1,541.07 °R
(α)
Refractive index: 1.495
Magnetic properties: diamagnetic
χ=-6.70 · 10-5cm³/mol
Stability: stable
Hardness: relatively strong
(2 on Moh`s scale)
Toxicity: non-toxic
LD50=6600mg/kg

Description

Inorganic compound, salt of alkaline metal potassium and inorganic sulfuric acid. Doesn`t form water hydrates.

Minerals

Occurs in nature as arcanite mineral.

Where to buy

In fertilizers store (as "Potassium sulfate").

Precursors

Reaction between hydroxide or potassium carbonate and sulfuric acid

Chemical equation:

H2SO4 + 2KOH = K2SO4 + 2H2O
H2SO4 + K2CO3 = K2SO4 + H2O + CO2

For preparation of 100.00g of potassium sulfate а 64.39g of hydroxide or 79.31g of carbonate and 152.12g of 37% sulfuric acid is required.
Add acid to the flask, then add small parts of potassium compound with stirring until it will totally dissolve or, if you use carbonate, until carbon dioxide emission will stop. After reaction will stop, filter the solution and use it for crystal growing.

Recrystallization of "Potassium sulfate" fertilizer

Add fertilizer to the flask with boiling water until solution become saturated. Then filter out the solution and cool slowly. Excess of compound precipitates as a crystalline precipitate, most of impurities remain in the solution.

Separate this precipitate from the stock solution, and repeat this process for several times, use the same solution at each next step. Finally, the precipitated compound is used for crystal growing.

Due to potassium carbonate impurity in fertilizer, it is recommended to add sulfuric acid to fertilizer solution before recrystallization.

Reaction between potassium chloride or nitrate and ammonium nitrate

Chemical equation:

(NH4)2SO4 + KCl = K2SO4↓ + 2NH4Cl
(NH4)2SO4 + KNO3 = K2SO4↓ + 2NH4NO3

For preparation of 100.00g of potassium sulfate а 42.78g of potassium chloride or 58.02g of potassium nitrate and 75.83g of ammonium sulfate is required.
Add to the flask with hot ammonium sulfate solution a potassium chloride or nitrate solution with heating and stirring. Cooling this mixture will cause forming a large amount of crystalline precipitation. Filter precipitate and wash it wish small amount of cold water, then filter the solution and use it for crystal growing.

Reaction between potassium chloride or nitrate and sulfuric acid

Chemical equation:

H2SO4 + 2KCl = K2SO4 + 2HCl↑
H2SO4 + 2KNO3 = K2SO4 + 2HNO3

For preparation of 100.00g of potassium sulfate а 85.56g of potassium chloride or 116.04g of potassium nitrate and 152.12g of 37% sulfuric acid is required.
Add to the flask acid and then add small parts of hot acid solution with heating and stirring. Emission of large amount of gas will begin.Attention, exuding gas irritates eyes and lungs! The synthesis should be carried out only in a fume hood or outdoors! After reaction will stop, filter the solution and use it for crystal growing.

Reaction between ammonium sulfate and potassium hydroxide or carbonate

Chemical equation:

(NH4)2SO4 + 2KOH = K2SO4 + 2H2O + 2NH3
(NH4)2SO4 + K2CO3 = K2SO4 + H2O + CO2↑ + 2NH3

For preparation of 100.00g of potassium sulfate а 64.39g of potassium hydroxide or 79.31g of carbonate and 75.83g of ammonium sulfate is required.
Add to the flask saturated solution of ammonium sulfate and then add small parts of hot potassium compounds solution with heating and stirring. Emission of large amount of ammonia will begin.Attention, exuding ammonia irritates eyes and lungs! The synthesis should be carried out only in a fume hood or outdoors! After reaction will stop, filter the solution and use it for crystal growing.

Notes

Used as a substratum for microbes and fungi, so mold can grow easily in the solution. It is recommended to boil solution for 15 minutes and change vessel to another one.

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 waterгр/100,00 гр ethanol 40%гр/100,00 гр methanolгр/100,00 гр glycerolгр/100,00 гр formic acid 95%гр/100,00 гр sulfuric acidгр/100,00 гр hydrazineгр/100,00 гр hydroxylamine
0°C
273.15 K
32 °F
491.67 °R
7.18
7.18 g/100g
6.699 %
10°C
283.15 K
50 °F
509.67 °R
9.3
9.3 g/100g
8.509 %
15°C
288.15 K
59 °F
518.67 °R
~10.2
10.2 g/100g
9.256 %
20°C
293.15 K
68 °F
527.67 °R
11.1
11.1 g/100g
9.991 %
1.317
1.317 g/100g
1.3 %
36.5
36.5 g/100g
26.74 %
5
5 g/100g
4.762 %
3.5
3.5 g/100g
3.382 %
25°C
298.15 K
77 °F
536.67 °R
12.1
12.1 g/100g
10.794 %
0.0596
0.0596 g/100g
0.0596 %
30°C
303.15 K
86 °F
545.67 °R
13
13 g/100g
11.504 %
40°C
313.15 K
104 °F
563.67 °R
14.8
14.8 g/100g
12.892 %
0.16
0.16 g/100g
0.16 %
11.61
11.61 g/100g
10.402 %
50°C
323.15 K
122 °F
581.67 °R
~16.5
16.5 g/100g
14.163 %
60°C
333.15 K
140 °F
599.67 °R
18.2
18.2 g/100g
15.398 %
70°C
343.15 K
158 °F
617.67 °R
19.9
19.9 g/100g
16.597 %
80°C
353.15 K
176 °F
635.67 °R
21.4
21.4 g/100g
17.628 %
90°C
363.15 K
194 °F
653.67 °R
22.9
22.9 g/100g
18.633 %
100°C
373.15 K
212 °F
671.67 °R
24.1
24.1 g/100g
19.42 %
41.42
41.42 g/100g
29.289 %
Slightly soluble in glycerol. Insoluble in ethanol, acetone, benzene, carbon disulfide, ethylene glycol and ammonia.

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