Difference between revisions of "Calcium sulfate"

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'''Calcium sulfate''' is a virtually insoluble inorganic compound with the formula CaSO<sub>4</sub>. It is commonly formed as a by-product of reactions.
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| Name = Calcium sulfate
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| Reference =
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| IUPACName = Calcium sulfate
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| SystematicName =
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| OtherNames = Drierite (anhydrous)<br>Gypsum<br>Plaster of Paris
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| Section1 = {{Chembox Identifiers
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| Section2 = {{Chembox Properties
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| AtmosphericOHRateConstant =
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| Appearance = White solid
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| BoilingPt =
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| BoilingPtC =
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| BoilingPt_notes = Decomposes
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| Density = 2.96 g/cm<sup>3</sup> (anhydrous)<br>2.32 g/cm<sup>3</sup> (dihydrate)
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| Formula = CaSO<sub>4</sub>
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| HenryConstant =
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| LogP =
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| MolarMass = 136.14 g/mol (anhydrous)<br>145.15 g/mol (hemihydrate)<br>172.172 g/mol (dihydrate)
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| MeltingPt_notes = ''anhydrous''<br>1,460 °C (2,660 °F; 1,730 K)<hr>''hemihydrate''<br>180 °C (356 °F; 453 K) (decomposes)<hr>''dihydrate''<br>100–150 °C (212–302 °F; 373–423 K) (decomposes)
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| Odor = Odorless
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| pKa = 10.4 (anhydrous)<br>7.3 (dihydrate)
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| pKb =
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| Solubility = 0.21 g/100 ml at 20 °C (anhydrous)<br>0.24 g/100 ml at 20 °C (dihydrate)
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| SolubleOther = ''dihydrate''<br>Slightly soluble in [[glycerol]]
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| DeltaHf = -1,433 kJ/mol
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| Entropy = 107 J·mol<sup>−1</sup>·K<sup>−1</sup>
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| AutoignitionPt = Non-flammable
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| ExploLimits = Non-explosive
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| ExternalMSDS = [https://www.docdroid.net/mGpTgLd/calcium-sulfate-anhydrous-sa.pdf.html Sigma-Aldrich] (drierite)<br>[https://www.docdroid.net/XDuFe6j/calcium-sulfate-hemihydrate-sa.pdf.html Sigma-Aldrich] (hemihydrate)<br>[https://www.docdroid.net/uZK74UP/calcium-sulfate-dihydrate-sa.pdf.html Sigma-Aldrich] (dihydrate)
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| FlashPt = Non-flammable
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| OtherCompounds = [[Magnesium sulfate]]<br>[[Strontium sulfate]]<br>[[Barium sulfate]]
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'''Calcium sulfate''' is a virtually insoluble inorganic compound with the formula '''CaSO<sub>4</sub>'''. It is commonly formed as a by-product of reactions. Since it's hygroscopic, it's commonly encountered as hydrate.
  
 
==Properties==
 
==Properties==
 
===Chemical===
 
===Chemical===
 
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A very exothermic [[thermite]] reaction occurs with [[aluminium]] powder, which is used to 'heat boost' reactions such as a [[titanium dioxide]] thermite, where the extra heat is needed to reduce the oxide all the way to [[titanium]] metal.
A very exothermic [[thermite]] reaction occurs with [[aluminium]] powder, which is used to 'heat boost' reactions such as a [[titanium dioxide]] thermite, where the extra heat is needed to reduce the oxide all the way to [[titanium]] metal
+
  
 
Double displacement reactions often are chosen to form calcium sulfate as the precipitation of the solid not only drives the reaction but makes the two formed chemicals easy to separate by simply filtering off the sulfate:
 
Double displacement reactions often are chosen to form calcium sulfate as the precipitation of the solid not only drives the reaction but makes the two formed chemicals easy to separate by simply filtering off the sulfate:
  
:Ca(OCl)<sub>2</sub> + K<sub>2</sub>SO<sub>4</sub> → CaSO<sub>4</sub> + 2KOCl
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:Ca(OCl)<sub>2</sub> + K<sub>2</sub>SO<sub>4</sub> → CaSO<sub>4</sub> + 2 KOCl
 +
 
 +
Anhydrous calcium sulfate (drierite) is one of the few [[desiccant]]s that can be safely used to dry [[acetone]], as most common desiccants tend to cause it to self-condense. Neutral calcium sulfate (no traces of bisulfate or hydroxide) is necessary, as any impurities like bisulfate or hydroxide will cause minor self-condensation.
  
 
===Physical===
 
===Physical===
It is generally considered to be insoluble, but does have a very low solubility of 0.21g/100ml @20 degrees (Wikipedia)
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It is generally considered to be insoluble, but does have a very low solubility of 0.21 g/100ml at 20 °C.<ref>https://en.wikipedia.org/wiki/Calcium_sulfate</ref>
  
Calcium sulfate exists in three hydrates, a dihydrate, a hemihydrate and a anhydrous form. Over 100 degrees the hemihydrate is formed and it looses water to form the anhydrous over 180 degrees. These two forms will slowly absorb water at room temperature to revert back to the dihydrate.
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Calcium sulfate exists in three hydrates, a dihydrate, a hemihydrate and a anhydrous form. Over 100 degrees the hemihydrate is formed and it looses water to form the anhydrous over 180 degrees Celsius. These two forms will slowly absorb water at room temperature to revert back to the dihydrate.
  
 
==Availability==
 
==Availability==
The hemihydrate is easily available as 'plaster of Paris' in hardware stores. The dihydrate is heavily used as 'drywall', a calcium sulfate construction material. A chalk is made from calcium sulfate (a chalk is not made from [[Calcium carbonate|chalk]], who knew) and in many locations it can be found on the ground as the mineral gypsum
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The hemihydrate is easily available as 'plaster of Paris' in hardware stores. The dihydrate is heavily used as 'drywall', a calcium sulfate construction material. Chalk sticks tend to contain calcium sulfate rather than calcium carbonate (a chalk is not made from [[calcium carbonate|chalk]], who knew), though some formulas may contain traces of calcium carbonate and in many locations it can be found in the ground as the mineral gypsum.
  
 
==Preparation==
 
==Preparation==
A solutions of a soluble sulphate salt such as [[ammonium sulfate]] and [[calcium chloride]] will precipitate calcium sulfate, which can be washed with cold water and dried.
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A solutions of a soluble sulphate salt such as [[ammonium sulfate]] and [[calcium chloride]] will precipitate calcium sulfate, which can be filtered and washed with cold water, then dried. To obtain perfectly neutral CaSO<sub>4</sub>, add a slight excess of ammonium sulfate to make sure all the calcium has precipitated, filter it, thoroughly wash the CaSO<sub>4</sub> precipitate and dry it in an oven at 180 °C.
  
 
==Projects==
 
==Projects==
 
*Calcium sulfate [[thermite]], from which elemental [[calcium]] can be obtained.
 
*Calcium sulfate [[thermite]], from which elemental [[calcium]] can be obtained.
 
*Sulfur dioxide generation
 
*Sulfur dioxide generation
*Dry acetone
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*Dry [[acetone]]
  
 
==Handling==
 
==Handling==
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<references />
 
<references />
 
===Relevant Sciencemadness threads===
 
===Relevant Sciencemadness threads===
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*[http://www.sciencemadness.org/talk/viewthread.php?tid=21332 Calcium Sulfate and Titanium Thermite]
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*[http://www.sciencemadness.org/talk/viewthread.php?tid=66628 Calcium Sulfate as a desiccant - Will anhydrous work?]
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*[http://www.sciencemadness.org/talk/viewthread.php?tid=8338 anhydrous calcium sulfate or alumina silicate]
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*[https://www.sciencemadness.org/whisper/viewthread.php?tid=6255 What form of Calcium sulfate?]
  
 
[[Category:Chemical compounds]]
 
[[Category:Chemical compounds]]
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[[Category:Calcium compounds]]
 
[[Category:Calcium compounds]]
 
[[Category:Sulfates]]
 
[[Category:Sulfates]]
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[[Category:Desiccants]]
 
[[Category:Easily prepared chemicals]]
 
[[Category:Easily prepared chemicals]]
 
[[Category:Readily available chemicals]]
 
[[Category:Readily available chemicals]]
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[[Category:Essential reagents]]
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[[Category:Neutral salts]]

Revision as of 22:01, 25 August 2018

Calcium sulfate
Names
IUPAC name
Calcium sulfate
Other names
Drierite (anhydrous)
Gypsum
Plaster of Paris
Properties
CaSO4
Molar mass 136.14 g/mol (anhydrous)
145.15 g/mol (hemihydrate)
172.172 g/mol (dihydrate)
Appearance White solid
Odor Odorless
Density 2.96 g/cm3 (anhydrous)
2.32 g/cm3 (dihydrate)
Melting point anhydrous
1,460 °C (2,660 °F; 1,730 K)
hemihydrate
180 °C (356 °F; 453 K) (decomposes)
dihydrate
100–150 °C (212–302 °F; 373–423 K) (decomposes)
Boiling point Decomposes
0.21 g/100 ml at 20 °C (anhydrous)
0.24 g/100 ml at 20 °C (dihydrate)
Solubility dihydrate
Slightly soluble in glycerol
Acidity (pKa) 10.4 (anhydrous)
7.3 (dihydrate)
Thermochemistry
107 J·mol−1·K−1
-1,433 kJ/mol
Hazards
Safety data sheet Sigma-Aldrich (drierite)
Sigma-Aldrich (hemihydrate)
Sigma-Aldrich (dihydrate)
Flash point Non-flammable
Related compounds
Related compounds
Magnesium sulfate
Strontium sulfate
Barium sulfate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Calcium sulfate is a virtually insoluble inorganic compound with the formula CaSO4. It is commonly formed as a by-product of reactions. Since it's hygroscopic, it's commonly encountered as hydrate.

Properties

Chemical

A very exothermic thermite reaction occurs with aluminium powder, which is used to 'heat boost' reactions such as a titanium dioxide thermite, where the extra heat is needed to reduce the oxide all the way to titanium metal.

Double displacement reactions often are chosen to form calcium sulfate as the precipitation of the solid not only drives the reaction but makes the two formed chemicals easy to separate by simply filtering off the sulfate:

Ca(OCl)2 + K2SO4 → CaSO4 + 2 KOCl

Anhydrous calcium sulfate (drierite) is one of the few desiccants that can be safely used to dry acetone, as most common desiccants tend to cause it to self-condense. Neutral calcium sulfate (no traces of bisulfate or hydroxide) is necessary, as any impurities like bisulfate or hydroxide will cause minor self-condensation.

Physical

It is generally considered to be insoluble, but does have a very low solubility of 0.21 g/100ml at 20 °C.[1]

Calcium sulfate exists in three hydrates, a dihydrate, a hemihydrate and a anhydrous form. Over 100 degrees the hemihydrate is formed and it looses water to form the anhydrous over 180 degrees Celsius. These two forms will slowly absorb water at room temperature to revert back to the dihydrate.

Availability

The hemihydrate is easily available as 'plaster of Paris' in hardware stores. The dihydrate is heavily used as 'drywall', a calcium sulfate construction material. Chalk sticks tend to contain calcium sulfate rather than calcium carbonate (a chalk is not made from chalk, who knew), though some formulas may contain traces of calcium carbonate and in many locations it can be found in the ground as the mineral gypsum.

Preparation

A solutions of a soluble sulphate salt such as ammonium sulfate and calcium chloride will precipitate calcium sulfate, which can be filtered and washed with cold water, then dried. To obtain perfectly neutral CaSO4, add a slight excess of ammonium sulfate to make sure all the calcium has precipitated, filter it, thoroughly wash the CaSO4 precipitate and dry it in an oven at 180 °C.

Projects

Handling

Safety

Anhydrous calcium sulfate will release large amounts of heat if mixed with water.

Storage

Should be stored in closed containers, away from moisture.

Disposal

Unless it's contaminated with heavy metals or sodium ions, calcium sulfate can be safely dumped in the ground or trash. Do not pour it down the drain as it may clog the pipes.

References

  1. https://en.wikipedia.org/wiki/Calcium_sulfate

Relevant Sciencemadness threads