Difference between revisions of "Calcium hydroxide"

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(Created page with "'''Calcium fluoride''' is an inorganic salt of calcium, with the chemical formula CaF<sub>2</sub>. It occurs in nature as the mineral known as '''fluorite''' or '''fluorspar''...")
 
 
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'''Calcium fluoride''' is an inorganic salt of calcium, with the chemical formula CaF<sub>2</sub>. It occurs in nature as the mineral known as '''fluorite''' or '''fluorspar'''.
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| Name = Calcium hydroxide
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| IUPACName = Calcium hydroxide
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| OtherNames = Slaked lime
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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_ref =
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| BoilingPt_notes = Decomposes
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| Density = 2.211 g/cm<sup>3</sup>
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| Formula = Ca(OH)<sub>2</sub>
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| HenryConstant =
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| LogP =
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| MolarMass = 74.093 g/mol
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| MeltingPt =
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| MeltingPtC = 580
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| MeltingPt_notes = (decomposes)
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| pKa =
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| pKb = 1.37 (first OH–)<br>2.43 (second OH–)
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| Solubility = 0.189 g/100 ml (0 °C)<br>0.173 g/100 ml (20 °C)<br>0.066 g/100 ml (100 °C)
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| SolubleOther = Reacts with acids<br>Slightly soluble in [[glycerol]]<br>Insoluble in alcohols, alkanes
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| CrystalStruct = Hexagonal, hP3
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| Section4 = {{Chembox Thermochemistry
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| DeltaGf =
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| DeltaHc =
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| DeltaHf = −987 kJ/mol
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| Entropy = 83 J·mol<sup>−1</sup>·K<sup>−1
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| AutoignitionPt = Non-flammable
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| ExternalMSDS = [https://www.docdroid.net/KhRaX9b/calcium-hydroxide-sa.pdf.html Sigma-Aldrich]
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| FlashPt = Non-flammable
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| LD50 = 7,340 mg/kg (oral, rat)<br>7,300 mg/kg (mouse)
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| MainHazards = Irritant
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| OtherCompounds = [[Magnesium hydroxide]]
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'''Calcium hydroxide''', also known by the names '''slaked lime''' and '''hydrated lime''', is an inorganic compound with chemical formula '''Ca(OH)<sub>2</sub>'''. It serves as an intermediate amongst basic calcium compounds, as it can be converted to both [[calcium oxide]] or [[calcium carbonate]] with relative ease. It is a great starting point for other calcium compounds.
  
 
==Properties==
 
==Properties==
 
===Chemical===
 
===Chemical===
Calcium fluoride will react with a strong acid, such [[sulfuric acid]] to yield [[calcium sulfate]] and hydrogen fluoride.
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Calcium hydroxide, which is usually produced by the hydration of calcium oxide, can be re-converted to the oxide by heating it above 512°C for a substantial period of time. Despite its low solubility, calcium hydroxide is a strong [[base]], and produces saturated solutions with a pH of 12.4. This solution, often referred to as limewater, gradually absorbs carbon dioxide from the air, precipitating the less soluble calcium carbonate. Limewater reacts easily with acids to form other calcium compounds, and has an advantage over calcium oxide because these reactions are not intensely exothermic, and an advantage over calcium carbonate in that no carbon dioxide is evolved. It reacts violently with some metals such as [[Aluminium|aluminium]] in a manner similar to [[sodium hydroxide]]. Calcium hydroxide can be made into sodium hydroxide by combining a saturated solution of it with excess aqueous [[sodium carbonate]], leaving and precipitating the calcium ions out as [[calcium carbonate]], which can be used to make more calcium hydroxide.
:CaF<sub>2</sub> + H<sub>2</sub>SO<sub>4</sub> → 2 HF + CaSO<sub>4</sub>
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===Physical===
 
===Physical===
Calcium fluoride is a white solid compound. Single crystals are transparent. It is extremely poorly soluble in water (0.0016 g/100 mL at 20 °C) and insoluble in organic solvents. It has a melting point of 1,418 °C and boils at 2,533 °C.
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Calcium hydroxide is typically encountered as a fine white powder or as a saturated solution called limewater. When wet or in solution it readily absorbs carbon dioxide, limiting its shelf life.
  
 
==Availability==
 
==Availability==
Calcium fluoride occurs naturally as the mineral fluorite, that can be purchased from mineral sellers. Certain homeopathy tablets also contain calcium fluoride. Purer calcium fluoride is available from chemical suppliers.
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Calcium hydroxide is usually referred to outside of the chemistry profession as slaked lime or hydrated lime, and is a very commonly used material in construction, where it is used for cement and concrete. As such, it can be purchased at builders supplies or hardware stores as builder's lime or any of its other names. Calcium hydroxide can also sometimes be bought, but usually in impure form, as a pH increasing agent for lawns and gardens. These products usually contain magnesium carbonate/hydroxide, or calcium sulfate/carbonate as impurities.
  
Calcium fluoride optic objects, such as lens, windows, filters, prisms are an interesting application of the substance. At least [http://www.globalopticsuk.com/calcium-fluoride.htm one website] offers many such items.
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Food-grade calcium hydroxide or a mixture of calcium hydroxide and other bases may be found in some Latin American groceries or specialty stores, where it is used in the treatment of corn to produce masa.
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Calcium hydroxide sometimes occurs naturally as the mineral ''Portlandite''.
  
 
==Preparation==
 
==Preparation==
Calcium fluoride can be prepared by reacting a fluoride, such as sodium fluoride with a soluble calcium salt.
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Calcium hydroxide is usually prepared by the highly exothermic addition of [[calcium oxide]] to water, in a process called slaking. The temperature of this reaction is more than enough to boil water and can produce a caustic spray of limewater that can seriously injure an overenthusiastic chemist, so the addition must be slow and the temperature must be watched.
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For those that cannot make calcium oxide, calcium hydroxide can be precipitated by the combination of a solution of sodium hydroxide to one of either [[calcium chloride]] or [[calcium nitrate]], taking advantage of the low solubility of calcium hydroxide. When this reaction is done, the resulting precipitate can be very difficult to filter and dry, so dilute solutions should be used. However, calcium hydroxide is soluble enough such that there will be significant losses. It is possible, however, to make calcium oxide by strongly heating calcium hydroxide.
  
 
==Projects==
 
==Projects==
*Make [[hydrofluoric acid]]
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*Make your own cement
*Store elemental fluorine
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*Chemical scrubbers
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*Make alkali metal hydroxides
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*Make copper hydroxide
  
 
==Handling==
 
==Handling==
 
===Safety===
 
===Safety===
Calcium fluoride has poor solubility in water. Contact with strong acids should be avoided, as it will generate hydrofluoric acid.
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Calcium hydroxide is a strong base, and while it's claimed that can cause burns in contact with bare skin, this is more of a problem in dry solid form, and less of a problem when mixed with water (like in the form of slaked lime), as it's poor solubility in water limits its corrosive effects, compared to other alkali bases. If consumed orally it is not very toxic but again is dangerous due simply to the basicity of the compound. Reaction with stomach acid is exothermic, and the heat released may cause injuries if consumed in large amounts. Fine dry calcium hydroxide is very dangerous without a facemask as the dust can cause severe respiratory injury if inhaled and may cause blindness if it contacts the eyes, though these risks aren't quite as high as those of calcium oxide, which reacts much more exothermically. Dry calcium hydroxide is a very strong irritant, and will rapidly dry the skin.
  
 
===Storage===
 
===Storage===
Calcium fluoride should be stored away from strong acids.
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Since it will absorb carbon dioxide and other corrosive gases from air and react with them, it's best to store it in a sealed container. Make sure it's perfectly dry, as it will tend to solidify inside its container if wet.
  
 
===Disposal===
 
===Disposal===
Calcium fluoride does not require any special disposal.
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Calcium hydroxide can be left in air or treated with carbon dioxide to convert it to calcium carbonate, which is harmless and can be disposed of very easily.  
  
 
==References==
 
==References==
 
<references/>
 
<references/>
 
===Relevant Sciencemadness threads===
 
===Relevant Sciencemadness threads===
*[http://www.sciencemadness.org/talk/viewthread.php?tid=24869 Fluorine salts aqcuisition?]
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*[http://www.sciencemadness.org/talk/viewthread.php?tid=64128 OTC Calcium Hydroxide]
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*[http://www.sciencemadness.org/talk/viewthread.php?tid=14104 Calcium hydroxide impurities and Baking soda reaction]
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[[Category:Chemical compounds]]
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[[Category:Inorganic compounds]]
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[[Category:Calcium compounds]]
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[[Category:Bases]]
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[[Category:Alkalis]]
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[[Category:Hydroxides]]
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[[Category:Minerals]]
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[[Category:Corrosive chemicals]]
 +
[[Category:Readily available chemicals]]
 +
[[Category:Essential reagents]]
 +
[[Category:Irritants]]
 +
[[Category:Air-sensitive materials]]

Latest revision as of 20:51, 6 June 2018

Calcium hydroxide
Calcium hydroxide wiki.jpg
Names
IUPAC name
Calcium hydroxide
Other names
Slaked lime
Properties
Ca(OH)2
Molar mass 74.093 g/mol
Appearance White solid
Density 2.211 g/cm3
Melting point 580 °C (1,076 °F; 853 K) (decomposes)
Boiling point Decomposes
0.189 g/100 ml (0 °C)
0.173 g/100 ml (20 °C)
0.066 g/100 ml (100 °C)
Solubility Reacts with acids
Slightly soluble in glycerol
Insoluble in alcohols, alkanes
Thermochemistry
83 J·mol−1·K−1
−987 kJ/mol
Hazards
Safety data sheet Sigma-Aldrich
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
7,340 mg/kg (oral, rat)
7,300 mg/kg (mouse)
Related compounds
Related compounds
Magnesium hydroxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Calcium hydroxide, also known by the names slaked lime and hydrated lime, is an inorganic compound with chemical formula Ca(OH)2. It serves as an intermediate amongst basic calcium compounds, as it can be converted to both calcium oxide or calcium carbonate with relative ease. It is a great starting point for other calcium compounds.

Properties

Chemical

Calcium hydroxide, which is usually produced by the hydration of calcium oxide, can be re-converted to the oxide by heating it above 512°C for a substantial period of time. Despite its low solubility, calcium hydroxide is a strong base, and produces saturated solutions with a pH of 12.4. This solution, often referred to as limewater, gradually absorbs carbon dioxide from the air, precipitating the less soluble calcium carbonate. Limewater reacts easily with acids to form other calcium compounds, and has an advantage over calcium oxide because these reactions are not intensely exothermic, and an advantage over calcium carbonate in that no carbon dioxide is evolved. It reacts violently with some metals such as aluminium in a manner similar to sodium hydroxide. Calcium hydroxide can be made into sodium hydroxide by combining a saturated solution of it with excess aqueous sodium carbonate, leaving and precipitating the calcium ions out as calcium carbonate, which can be used to make more calcium hydroxide.

Physical

Calcium hydroxide is typically encountered as a fine white powder or as a saturated solution called limewater. When wet or in solution it readily absorbs carbon dioxide, limiting its shelf life.

Availability

Calcium hydroxide is usually referred to outside of the chemistry profession as slaked lime or hydrated lime, and is a very commonly used material in construction, where it is used for cement and concrete. As such, it can be purchased at builders supplies or hardware stores as builder's lime or any of its other names. Calcium hydroxide can also sometimes be bought, but usually in impure form, as a pH increasing agent for lawns and gardens. These products usually contain magnesium carbonate/hydroxide, or calcium sulfate/carbonate as impurities.

Food-grade calcium hydroxide or a mixture of calcium hydroxide and other bases may be found in some Latin American groceries or specialty stores, where it is used in the treatment of corn to produce masa.

Calcium hydroxide sometimes occurs naturally as the mineral Portlandite.

Preparation

Calcium hydroxide is usually prepared by the highly exothermic addition of calcium oxide to water, in a process called slaking. The temperature of this reaction is more than enough to boil water and can produce a caustic spray of limewater that can seriously injure an overenthusiastic chemist, so the addition must be slow and the temperature must be watched.

For those that cannot make calcium oxide, calcium hydroxide can be precipitated by the combination of a solution of sodium hydroxide to one of either calcium chloride or calcium nitrate, taking advantage of the low solubility of calcium hydroxide. When this reaction is done, the resulting precipitate can be very difficult to filter and dry, so dilute solutions should be used. However, calcium hydroxide is soluble enough such that there will be significant losses. It is possible, however, to make calcium oxide by strongly heating calcium hydroxide.

Projects

  • Make your own cement
  • Chemical scrubbers
  • Make alkali metal hydroxides
  • Make copper hydroxide

Handling

Safety

Calcium hydroxide is a strong base, and while it's claimed that can cause burns in contact with bare skin, this is more of a problem in dry solid form, and less of a problem when mixed with water (like in the form of slaked lime), as it's poor solubility in water limits its corrosive effects, compared to other alkali bases. If consumed orally it is not very toxic but again is dangerous due simply to the basicity of the compound. Reaction with stomach acid is exothermic, and the heat released may cause injuries if consumed in large amounts. Fine dry calcium hydroxide is very dangerous without a facemask as the dust can cause severe respiratory injury if inhaled and may cause blindness if it contacts the eyes, though these risks aren't quite as high as those of calcium oxide, which reacts much more exothermically. Dry calcium hydroxide is a very strong irritant, and will rapidly dry the skin.

Storage

Since it will absorb carbon dioxide and other corrosive gases from air and react with them, it's best to store it in a sealed container. Make sure it's perfectly dry, as it will tend to solidify inside its container if wet.

Disposal

Calcium hydroxide can be left in air or treated with carbon dioxide to convert it to calcium carbonate, which is harmless and can be disposed of very easily.

References

Relevant Sciencemadness threads