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Encyclopedia > Calcium carbonate
Calcium carbonate
Calcium carbonate
General
Systematic name Calcium carbonate
Other names Limestone,
calcite,
aragonite,
chalk,
marble
Molecular formula CaCO3
Molar mass 100.087 g/mol
Appearance White powder.
CAS number [471-34-1]
Properties
Density and phase 2.83 g/cm3, solid.
Solubility in water Insoluble
Melting point 825°C (1098 K)
Boiling point Decomposes
Acidity (pKa)  ?
Basicity (pKb)  ?
Thermochemistry
ΔfH0liquid
-1154 kJ/mol
ΔfH0solid
-1207 kJ/mol
S0solid
93 J/mol·K
Structure
Molecular shape Linear
Coordination
geometry
Tetrahedral
Dipole moment  ? D
Hazards
MSDS External MSDS
Main hazards Not hazardous.
NFPA 704
Flash point Non-flammable.
R/S statement R: R36, R37, R38
S: S26, S36
RTECS number  ?
Supplementary data page
Structure and
properties
n, εr, etc.
Thermodynamic
data
Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
Related compounds
Other anions Calcium bicarbonate
Calcium sulfate
Other cations Magnesium carbonate (dolomite)
Strontium carbonate
Related compounds Calcium oxide
Except where noted otherwise, data are given for
materials in their standard state (at 25°C, 100 kPa)
Infobox disclaimer and references

Calcium carbonate is a chemical compound, with the chemical formula CaCO3. It is a common substance found as rock in all parts of the world, and is the main component of shells of marine organisms and snails. Calcium carbonate is the active ingredient in agricultural lime, and is usually the principal cause of hard water. It is commonly used medicinally as a calcium supplement or as an antacid. ImageMetadata File history File links Calcium_carbonate. ... IUPAC nomenclature is a system of naming chemical compounds and of describing the science of chemistry in general. ... -1... Doubly refracting Calcite from Iceberg claim, Dixon, New Mexico. ... Aragonite Aragonite is a polymorph of the mineral calcite, both having the chemical composition CaCO3. ... The Needles,situated on the Isle Of Wight, are part of the extensive Southern England Chalk Formation. ... Venus de Milo, front. ... This article or section does not cite any references or sources. ... This article does not cite any references or sources. ... CAS registry numbers are unique numerical identifiers for chemical compounds, polymers, biological sequences, mixtures and alloys. ... In physics, density is mass m per unit volume V. For the common case of a homogeneous substance, it is expressed as: where, in SI units: ρ (rho) is the density of the substance, measured in kg·m-3 m is the mass of the substance, measured in kg V is... In the physical sciences, a phase is a set of states of a macroscopic physical system that have relatively uniform chemical composition and physical properties (i. ... Solubility refers to the ability for a given substance, the solute, to dissolve in a solvent. ... This article describes water from a scientific and technical perspective. ... The melting point of a crystalline solid is the temperature at which it changes state from solid to liquid. ... Italic text This article is about the boiling point of liquids. ... The acid dissociation constant (Ka), also known as the acidity constant or the acid-ionization constant, is a specific equilibrium constant for the reaction of an acid with its conjugate base in aqueous solution [1]. // When an acid dissolves in water, it partly dissociates forming hydronium ions and its conjugate... The acid dissociation constant (Ka), also known as the acidity constant or the acid-ionization constant, is a specific equilibrium constant for the reaction of an acid with its conjugate base in aqueous solution [1]. // When an acid dissolves in water, it partly dissociates forming hydronium ions and its conjugate... The standard enthalpy of formation or standard heat of formation of a compound is the change of enthalpy that accompanies the formation of 1 mole of a substance in its standard state from its constituent elements in their standard states (the most stable form of the element at 1 atmosphere... The joule (IPA pronunciation: or ) (symbol: J) is the SI unit of energy. ... The mole (symbol: mol) is the SI base unit that measures an amount of substance. ... The joule (IPA pronunciation: or ) (symbol: J) is the SI unit of energy. ... The mole (symbol: mol) is the SI base unit that measures an amount of substance. ... four sp³ orbitals three sp² orbitals In chemistry, hybridisation or hybridization (see also spelling differences) is the concept of mixing atomic orbitals to form new hybrid orbitals suitable for the qualitative description of atomic bonding properties. ... The coordination geometry of an atom is the geometrical pattern formed by its neighbors in a molecule or a crystal. ... The Earths magnetic field, which is approximately a dipole. ... The debye (symbol: D) is a non-SI and non-CGS unit of electrical dipole moment. ... An example MSDS in a US format provides guidance for handling a hazardous substance and information on its composition and properties. ... The examples and perspective in this article or section may not represent a worldwide view. ... NFPA 704 is a standard maintained by the U.S. National Fire Protection Association. ... The flash point of a flammable liquid is the lowest temperature at which it can form an ignitable mixture with air. ... Risk and Safety Statements, also known as R/S statements, R/S numbers, R/S phrases, and R/S sentences, is a system of hazard codes and phrases for labeling dangerous chemicals and compounds. ... R-phrases are defined in Annex III of European Union Directive 67/548/EEC: Nature of special risks attributed to dangerous substances and preparations. ... S-phrases are defined in Annex IV of European Union Directive 67/548/EEC: Safety advice concerning dangerous substances and preparations. ... RTECS, also known as Registry of Toxic Effects of Chemical Substances, is a database of toxicity information compiled from the open scientific literature that is available for charge. ... The refractive index (or index of refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves) is reduced inside the medium. ... The relative dielectric constant of a material under given conditions is a measure of the extent to which it concentrates electrostatic lines of flux. ... Ultraviolet-Visible Spectroscopy or Ultraviolet-Visible Spectrophotometry (UV/ VIS) involves the spectroscopy of photons (spectrophotometry). ... Infrared spectroscopy (IR Spectroscopy) is the subset of spectroscopy that deals with the IR region of the EM spectrum. ... Nuclear Magnetic Resonance Spectroscopy most commonly known as NMR Spectroscopy is the name given to the technique which exploits the magnetic properties of nuclei. ... Mass spectrometry (also known as mass spectroscopy (deprecated)[1] or informally, mass-spec and MS) is an analytical technique used to measure the mass-to-charge ratio of ions. ... An electrostatic potential map of the nitrate ion (NO3−). Areas coloured red are lower in energy than areas colored yellow An ion is an atom or group of atoms which have lost or gained one or more electrons, making them negatively or positively charged. ... Calcium bicarbonate (Ca(HCO3)2), also called calcium hydrogencarbonate, is a compound which exists only in solution. ... Calcium sulfate is a common laboratory and industrial chemical. ... An electrostatic potential map of the nitrate ion (NO3−). Areas coloured red are lower in energy than areas colored yellow An ion is an atom or group of atoms which have lost or gained one or more electrons, making them negatively or positively charged. ... Magnesium carbonate, MgCO3, is a white solid that occurs in nature as a mineral. ... Flash point Not applicable Except where noted otherwise, data are given for materials in their standard state (at 25 Â°C, 100 kPa) Infobox disclaimer and references Strontium carbonate (SrCO3) is a the carbonate salt of strontium that has the appearance of a white or grey powder. ... Calcium oxide (CaO), commonly known as lime, quicklime or burnt lime, is a widely used chemical compound. ... In chemistry, the standard state of a material is its state at 1 bar (100 kilopascals) and 25 degrees Celsius (298. ... A chemical compound is a chemical substance of two or more different chemically bonded chemical elements, with a fixed ratio determining the composition. ... This article or section does not cite any references or sources. ... General Name, Symbol, Number calcium, Ca, 20 Chemical series alkaline earth metals Group, Period, Block 2, 4, s Appearance silvery white Standard atomic weight 40. ... General Name, symbol, number carbon, C, 6 Chemical series nonmetals Group, period, block 14, 2, p Appearance black (graphite) colorless (diamond) Standard atomic weight 12. ... General Name, Symbol, Number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless (gas) very pale blue (liquid) Standard atomic weight 15. ... This balancing rock, Steamboat Rock stands in Garden of the Gods park in Colorado Springs, CO The rocky side of a mountain creek near Orosí, Costa Rica. ... The hard, rigid outer calcium carbonate covering of certain animals is called a shell. ... The name snail applies to most members of the molluscan class Gastropoda that have coiled shells. ... Agricultural lime is a soil additive made from pulverized limestone or chalk. ... Hard water water that has a high mineral content (water with a low mineral content is known as soft water). ... General Name, Symbol, Number calcium, Ca, 20 Chemical series alkaline earth metals Group, Period, Block 2, 4, s Appearance silvery white Standard atomic weight 40. ... A bottle of antacid tablets An antacid is any substance, generally a base, which counteracts stomach acidity. ...

Contents

Occurrence

Calcium carbonate is found naturally as the following minerals and rocks: A mineral is a naturally occurring substance formed through geological processes that has a characteristic chemical composition, a highly ordered atomic structure and specific physical properties. ...

Eggshells are composed of approximately 95% calcium carbonate. Aragonite Aragonite is a polymorph of the mineral calcite, both having the chemical composition CaCO3. ... Doubly refracting Calcite from Iceberg claim, Dixon, New Mexico. ... Vaterite (CaCO3) is a mineral and polymorph of aragonite and calcite. ... The Needles,situated on the Isle Of Wight, are part of the extensive Southern England Chalk Formation. ... -1... Venus de Milo, front. ... Travertine Travertine terraces at Mammoth Hot Springs, Yellowstone National Park A carving in travertine Travertine is a sedimentary rock. ...


To test whether a mineral or rock contains calcium carbonate, strong acids, such as hydrochloric acid, can be added to it. If the sample does contain calcium carbonate, it will fizz and produce carbon dioxide and water. Weak acids such as acetic acid will react, albeit less vigorously. All of the rocks/minerals mentioned above will react with acid. The chemical compound hydrochloric acid is the aqueous (water-based) solution of hydrogen chloride gas (HCl). ...


Preparation

The vast majority of calcium carbonate used in industry is extracted by mining or quarrying. Pure calcium carbonate (e.g. for food or pharmaceutical use), can be produced from a pure quarried source (usually marble) or it can be prepared by passing carbon dioxide into a solution of calcium hydroxide: the calcium carbonate precipitates out, and this grade of product is referred to as a precipitate (abbreviated to PCC). In order to meet Wikipedias quality standards, this article requires cleanup. ... It has been suggested that Portlandite be merged into this article or section. ...

Ca(OH)2 + CO2 → CaCO3 + H2O

Chemical properties

See also: Carbonate

Calcium carbonate shares the typical properties of other carbonates. Notably: In organic chemistry, a carbonate is a salt of carbonic acid. ...

  1. it reacts with strong acids, releasing carbon dioxide:
    CaCO3 + 2HCl → CaCl2 + CO2 + H2O
  2. it releases carbon dioxide on heating (to above 840 °C in the case of CaCO3), to form calcium oxide, commonly called burnt lime:
    CaCO3 → CaO + CO2

Calcium carbonate will react with water that is saturated with carbon dioxide to form the soluble calcium bicarbonate. Calcium oxide (CaO), commonly known as lime, quicklime or burnt lime, is a widely used chemical compound. ... Calcium bicarbonate (Ca(HCO3)2), also called calcium hydrogencarbonate, is a compound which exists only in solution. ...

CaCO3 + CO2 + H2O → Ca(HCO3)2

This reaction is important in the erosion of carbonate rocks, forming caverns, and leads to hard water in many regions. Severe soil erosion in a wheat field near Washington State University, USA. For erosion as an operation of Mathematical morphology, see Erosion (morphology) Erosion is displacement of solids (soil, mud, rock and other particles) by the agents of ocean currents, wind, water, or ice by downward or down-slope movement... Carbonate rocks are a class of sedimentary rocks composed primarily of carbonate minerals. ... Alternate meanings: Cave (disambiguation) This article is about natural caves; for artificial caves used as dwellings, such as those in north China, see yaodong. ... Hard water water that has a high mineral content (water with a low mineral content is known as soft water). ...


Uses

The main use of calcium carbonate is in the construction industry, either as a building material in its own right (e.g. marble) or limestone aggregate for roadbuilding or as an ingredient of cement or as the starting material for the preparation of builder's lime by burning in a kiln . A common contaminate is magnesium carbonate. Venus de Milo, front. ... In the most general sense of the word, cement is a binder, a substance which sets and hardens independently, and can bind other materials together. ...


Calcium carbonate is widely used as an extender in paints, in particular matte emulsion paint where typically 30% by weight of the paint is either chalk or marble.


Calcium carbonate is also widely used as a filler in plastics. Some typical examples include around 15 to 20% loading of chalk in uPVC drain pipe, 5 to 15% loading of stearate coated chalk or marble in uPVC window profile. Fine ground calcium carbonate is an essential ingredient in the microporous film used in babies' diapers and some building films as the pores are nucleated around the calcium carbonate particles during the manufacture of the film by biaxial stretching. This article is about the garment. ...


Calcium carbonate is also used in a wide range of trade and DIY adhesives, sealants, and decorating fillers. Ceramic tile adhesives typically contain 70 to 80% limestone. Decorating crack fillers contain similar levels of marble or dolomite. It is also mixed with putty in setting Stained glass windows, and as a resist to prevent glass from sticking to kiln shelves when firing glazes and paints at high temperature. Strictly speaking, stained glass is glass that has been painted with silver stain and then fired. ...


Calcium carbonate is widely used medicinally as an inexpensive dietary calcium supplement, antacid, and/or phosphate binder. It is also used in the pharmaceutical industry as a base material for tablets of other pharmaceuticals. A bottle of antacid tablets An antacid is any substance, generally a base, which counteracts stomach acidity. ... Phosphate binders are a group of medications used to reduce the absorption of phosphate and taken with meals and snacks. ... This article or section does not adequately cite its references or sources. ...


Calcium carbonate is known as whiting in ceramics/glazing applications, where it is used as a common ingredient for many glazes in its white powdered form. When a glaze containing this material is fired in a kiln, the whiting acts as a flux material in the glaze. Ancient Egyptian ceramic art: Louvre Museum. ... flux in science and mathematics. ...


Used in swimming pools as a pH corrector for maintaining alkalinity "buffer" to offset the acidic properties of the disinfectant agent.


It is commonly called chalk as it has been a major component of blackboard chalk. Chalk may consist of either calcium carbonate or gypsum, hydrated calcium sulfate CaSO4·2H2O. The Needles,situated on the Isle Of Wight, are part of the extensive Southern England Chalk Formation. ... It has been suggested that Selenite be merged into this article or section. ... Calcium sulfate is a common laboratory and industrial chemical. ...


In North America, calcium carbonate has begun to replace kaolin in the production of glossy paper. Europe has been practicing this as alkaline papermaking or acid-free papermaking for some decades. Carbonates are available in forms: ground calcium carbonate (GCC) or precipitated calcium carbonate (PCC). The latter has a very fine and controlled particle size, on the order of 2 micron in diameter, useful in coatings for paper. Kaolinite is a clay mineral with the chemical composition Al2Si2O5(OH)4. ...


As a food additive, it is used in some soy milk products as a source of dietary calcium. Food additives are substances added to food to preserve flavor or improve its taste and appearance. ... A can of Yeos soy milk, poured into a glass Soymilk (also called soya milk or soybean milk, and sometimes referred to as soy drink/beverage and even soy latte) is a beverage made from soybeans originating from China. ...


In 1989, a researcher introduced CaCO3 into the Whetstone Brook in Massachusetts [citation needed]. His hope was that the calcium carbonate would counter the acid in the stream from acid rain and save the trout that had ceased to spawn. Although his experiment was a success, it did increase the amounts of aluminum ions in the area of the brook that was not treated with the limestone. This shows that CaCO3 can be added to neutralize the effects of acid rain in river ecosystems. Nowadays, calcium carbonate is used to neutralise acidic conditions in both soil and water. [citation needed] This bridge across the Danube River links Hungary with Slovakia. ...


Calcination Equilibrium

Equilibrium Pressure of CO2 over CaCO3[1]
550 °C 0.055 kPa
587 °C 0.13 kPa
605 °C 0.31 kPa
680 °C 1.80 kPa
727 °C 5.9 kPa
748 °C 9.3 kPa
777 °C 14 kPa
800 °C 24 kPa
830 °C 34 kPa
852 °C 51 kPa
871 °C 72 kPa
881 °C 80 kPa
891 °C 91 kPa
898 °C 101 kPa
937 °C 179 kPa
1082 °C 901 kPa
1241 °C 3961 kPa

Calcination of limestone using charcoal fires to produce quicklime has been practiced since antiquity by cultures all over the world. The answer to the question, "how hot does the fire have to be?" is usually given as 825 °C, but stating an absolute threshold is misleading. Calcium carbonate exists in equilibrium with calcium oxide and carbon dioxide at any temperature. At each temperature there is a partial pressure of carbon dioxide that is in equilibrium with calcium carbonate. At room temperature the equilibrium overwhelmingly favors calcium carbonate, because the equilibrium CO2 pressure is only a tiny fraction of the partial CO2 pressure in air, which is about 0.035 kPa. At temperatures above 550 °C the equilibrium CO2 pressure begins to exceed the CO2 pressure in air. So above 550 °C, calcium carbonate begins to outgas CO2 into air. But in a charcoal fired kiln, the concentration of CO2 will be much higher than it is in air. Indeed if all the oxygen in the kiln is consumed in the fire, then the partial pressure of CO2 in the kiln can be as high as 20 kPa. The table shows that this equilibrium pressure is not achieved until the temperature is nearly 800 °C. For the outgassing of CO2 from calcium carbonate to happen at an economically useful rate, the equilibrium pressure must significantly exceed the ambient pressure of CO2. And for it to happen rapidly, the equilibrium pressure must exceed total atmospheric pressure of 101 kPa, which happens at 898 °C.
The pascal (symbol: Pa) is the SI derived unit of pressure or stress (also: Youngs modulus and tensile strength). ... The pascal (symbol: Pa) is the SI derived unit of pressure or stress (also: Youngs modulus and tensile strength). ... The pascal (symbol: Pa) is the SI derived unit of pressure or stress (also: Youngs modulus and tensile strength). ... The pascal (symbol: Pa) is the SI derived unit of pressure or stress (also: Youngs modulus and tensile strength). ... The pascal (symbol: Pa) is the SI derived unit of pressure or stress (also: Youngs modulus and tensile strength). ... The pascal (symbol: Pa) is the SI derived unit of pressure or stress (also: Youngs modulus and tensile strength). ... The pascal (symbol: Pa) is the SI derived unit of pressure or stress (also: Youngs modulus and tensile strength). ... The pascal (symbol: Pa) is the SI derived unit of pressure or stress (also: Youngs modulus and tensile strength). ... The pascal (symbol: Pa) is the SI derived unit of pressure or stress (also: Youngs modulus and tensile strength). ... The pascal (symbol: Pa) is the SI derived unit of pressure or stress (also: Youngs modulus and tensile strength). ... The pascal (symbol: Pa) is the SI derived unit of pressure or stress (also: Youngs modulus and tensile strength). ... The pascal (symbol: Pa) is the SI derived unit of pressure or stress (also: Youngs modulus and tensile strength). ... The pascal (symbol: Pa) is the SI derived unit of pressure or stress (also: Youngs modulus and tensile strength). ... The pascal (symbol: Pa) is the SI derived unit of pressure or stress (also: Youngs modulus and tensile strength). ... The pascal (symbol: Pa) is the SI derived unit of pressure or stress (also: Youngs modulus and tensile strength). ... The pascal (symbol: Pa) is the SI derived unit of pressure or stress (also: Youngs modulus and tensile strength). ... The pascal (symbol: Pa) is the SI derived unit of pressure or stress (also: Youngs modulus and tensile strength). ... Calcination is the process of heating a substance to a high temperature, but below its melting or fusing point, to bring about thermal decomposition or a phase transition in its physical or chemical constitution. ... Calcium oxide (CaO), commonly known as lime, quicklime or burnt lime, is a widely used chemical compound. ... In a mixture of ideal gases, each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume. ... The pascal (symbol: Pa) is the SI derived unit of pressure or stress (also: Youngs modulus and tensile strength). ... The pascal (symbol: Pa) is the SI derived unit of pressure or stress (also: Youngs modulus and tensile strength). ... The pascal (symbol: Pa) is the SI derived unit of pressure or stress (also: Youngs modulus and tensile strength). ...


Solubility of calcium carbonate in water

Solubility in pure water with varying CO2 pressure

Calcium carbonate is poorly soluble in pure water. The equilibrium of its solution is given by the equation (with dissolved calcium carbonate on the right):

CaCO3 Ca2+ + CO32– Ksp = 3.7×10–9 to 8.7×10–9 at 25 °C

where the solubility product for [Ca2+][CO32–] is given as anywhere from Ksp = 3.7×10–9 to Ksp = 8.7×10–9 at 25 °C, depending upon the data source.[2][3] What the equation means is that the product of molar concentration of calcium ions (moles of dissolved Ca2+ per liter of solution) with the molar concentration of dissolved CO32– cannot exceed the value of Ksp. This seemingly simple solubility equation, however, must be taken along with the more complicated equilibrium of carbon dioxide with water (see carbonic acid). Some of the CO32– combines with H+ in the solution according to: Solubility equilibrium is any chemical equilibrium between solid and dissolved states of a compound at saturation. ... The mole (symbol: mol) is the SI base unit that measures an amount of substance. ... In order to meet Wikipedias quality standards, this article requires cleanup. ... Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... Carbonic acid (ancient name acid of air or aerial acid) has the formula H2CO3. ...

HCO3 H+ + CO32–    Ka2 = 5.61×10–11 at 25 °C

HCO3 is known as the bicarbonate ion. Calcium bicarbonate is many times more soluble in water than calcium carbonate -- indeed it exists only in solution. For baking soda, see Sodium bicarbonate In inorganic chemistry, a bicarbonate (IUPAC-recommended nomenclature: hydrogencarbonate) is an intermediate form in the deprotonation of carbonic acid. ... Calcium bicarbonate (Ca(HCO3)2), also called calcium hydrogencarbonate, is a compound which exists only in solution. ...


Some of the HCO3 combines with H+ in solution according to:

H2CO3 H+ + HCO3    Ka1 = 2.5×10–4 at 25 °C

Some of the H2CO3 breaks up into water and dissolved carbon dioxide according to:

H2O + CO2(dissolved) H2CO3    Kh = 1.70×10–3 at 25 °C

And dissolved carbon dioxide is in equilibrium with atmospheric carbon dioxide according to:

frac{P_{mathrm{CO}_2}}{[mathrm{CO}_2]} = k_mathrm{H} where kH = 29.76 atm/(mol/L) at 25°C (Henry constant), scriptstyle P_{mathrm{CO}_2} being the CO2 partial pressure.
Calcium Ion Solubility
as a function of CO2 partial pressure at 25 °C
scriptstyle P_{mathrm{CO}_2} (atm) pH [Ca2+] (mol/L)
10−12 12.0 5.19 × 10−3
10−10 11.3 1.12 × 10−3
10−8 10.7 2.55 × 10−4
10−6 9.83 1.20 × 10−4
10−4 8.62 3.16 × 10−4
3.5 × 10−4 8.27 4.70 × 10−4
10−3 7.96 6.62 × 10−4
10−2 7.30 1.42 × 10−3
10−1 6.63 3.05 × 10−3
1 5.96 6.58 × 10−3
10 5.30 1.42 × 10−2

For ambient air, scriptstyle P_{mathrm{CO}_2} is around 3.5×10–4 atmospheres (or equivalently 35 Pa). The last equation above fixes the concentration of dissolved CO2 as a function of scriptstyle P_{mathrm{CO}_2}, independent of the concentration of dissolved CaCO3. At atmospheric partial pressure of CO2, dissolved CO2 concentration is 1.2×10–5 moles/liter. The equation before that fixes the concentration of H2CO3 as a function of [CO2]. For [CO2]=1.2×10–5, it results in [H2CO3]=2.0×10–8 moles per liter. When [H2CO3] is known, the remaining three equations together with In chemistry, Henrys law is one of the gas laws, formulated by William Henry. ... General Name, Symbol, Number calcium, Ca, 20 Chemical series alkaline earth metals Group, Period, Block 2, 4, s Appearance silvery white Standard atomic weight 40. ... An electrostatic potential map of the nitrate ion (NO3−). Areas coloured red are lower in energy than areas colored yellow An ion is an atom or group of atoms which have lost or gained one or more electrons, making them negatively or positively charged. ... Solubility refers to the ability for a given substance, the solute, to dissolve in a solvent. ... In order to meet Wikipedias quality standards, this article requires cleanup. ... In a mixture of ideal gases, each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume. ... The correct title of this article is . ... The pascal (symbol: Pa) is the SI derived unit of pressure or stress (also: Youngs modulus and tensile strength). ...

H2O H+ + OH K = 10–14 at 25 °C

(which is true for all aqueous solutions), and the fact that the solution must be electrically neutral,

2[Ca2+] + [H+] = [HCO3] + 2[CO32–] + [OH]

make it possible to solve simultaneously for the remaining five unknown concentrations (note that the above form of the neutrality equation is valid only if calcium carbonate has been put in contact with pure water or with a neutral pH solution; in the case where the origin water solvent pH is not neutral, the equation is modified).


The table on the right shows the result for [Ca2+] and [H+] (in the form of pH) as a function of ambient partial pressure of CO2 (Ksp = 4.47×10−9 has been taken for the calculation). At atmospheric levels of ambient CO2 the table indicates the solution will be slightly alkaline. The trends the table shows are

1) As ambient CO2 partial pressure is reduced below atmospheric levels, the solution becomes more and more alkaline. At extremely low scriptstyle P_{mathrm{CO}_2}, dissolved CO2, bicarbonate ion, and carbonate ion largely evaporate from the solution, leaving a highly alkaline solution of calcium hydroxide, which is more soluble than CaCO3.
2) As ambient CO2 partial pressure increases to levels above atmospheric, pH drops, and much of the carbonate ion is converted to bicarbonate ion, which results in higher solubility of Ca2+.

The effect of the latter is especially evident in day to day life of people who have hard water. Water in aquifers underground can be exposed to levels of CO2 much higher than atmospheric. As such water percolates through calcium carbonate rock, the CaCO3 dissolves according to the second trend. When that same water then emerges from the tap, in time it comes into equilibrium with CO2 levels in the air by outgassing its excess CO2. The calcium carbonate becomes less soluble as a result and the excess precipitates as lime scale. This same process is responsible for the formation of stalactites and stalagmites in limestone caves. It has been suggested that Portlandite be merged into this article or section. ... Hard water water that has a high mineral content (water with a low mineral content is known as soft water). ... A stalactice hanging above subterranean water. ... The Witchs Finger in the Carlsbad Caverns A stalagmite (from the Greek stalagma (Σταλαγμίτης), drop or drip) is a type of speleothem that rises from the floor of a limestone cave due to the dripping of mineralized solutions and the deposition of calcium carbonate. ...


Two hydrated phases of calcium carbonate, monohydrocalcite, CaCO3.H2O, and ikaite, CaCO3.6H2O, may precipitate from water at ambient conditions and persist as metastable phases. Monohydrocalcite is a mineral that is a hydrous form of calcium carbonate, CaCO3. ... Ikaite is the mineral name for the hexahydrate of calcium carbonate, CaCO3·6H2O. Ikaite is colorless when pure. ...


Solubility at atmospheric CO2 pressure with varying pH

We now consider the problem of the maximum solubility of calcium carbonate in normal atmospheric conditions (scriptstyle P_{mathrm{CO}_2} = 3.5 × 10−4 atm) when the pH of the solution is adjusted. This is for example the case in a swimming pool where the pH is maintained between 7 and 8 (by addition of NaHSO4 to decrease the pH or of NaHCO3 to increase it). From the above equations for the solubility product, the hydratation reaction and the two acid reactions, the following expression for the maximum [Ca2+] can be easily deduced:

showing a quadratic dependence in [H+]. The numerical application with the above values of the constants gives

pH 7.0 7.2 7.4 7.6 7.8 8.0 8.2 8.27 8.4
[Ca2+]max (10-4mol/L or °f) 1590 635 253 101 40.0 15.9 6.35 4.70 2.53
[Ca2+]max (mg/L) 6390 2540 1010 403 160 63.9 25.4 18.9 10.1

Comments:

  • decreasing the pH from 8 to 7 increases the maximum Ca2+ concentration by a factor 100
  • note that the Ca2+ concentration of the previous table is recovered for pH = 8.27
  • keeping the pH to 7.4 in a swimming pool (which gives optimum HClO/OCl- ratio in the case of "chlorine" maintenance) results in a maximum Ca2+ concentration of 1010 mg/L. This means that successive cycles of water evaporation and partial renewing may result in a very hard water before CaCO3 precipitates. Addition of a calcium sequestrant or complete renewing of the water will solve the problem.

Hypochlorous acid is a weak, unstable acid with chemical formula HOCl. ... Hard water water that has a high mineral content (water with a low mineral content is known as soft water). ...

References

  1. ^ CRC Handbook of Chemistry and Physics 44th ed., p2292
  2. ^ CSUDH
  3. ^ CRC Handbook of Chemistry and Physics, 44th ed.

See also

Travertine calcium carbonate deposits from a hot spring
Travertine calcium carbonate deposits from a hot spring

Image File history File links Metadata Size of this preview: 800 × 513 pixelsFull resolution (2321 × 1488 pixel, file size: 392 KB, MIME type: image/jpeg) File historyClick on a date/time to view the file as it appeared at that time. ... Image File history File links Metadata Size of this preview: 800 × 513 pixelsFull resolution (2321 × 1488 pixel, file size: 392 KB, MIME type: image/jpeg) File historyClick on a date/time to view the file as it appeared at that time. ... Aragonite Aragonite is a polymorph of the mineral calcite, both having the chemical composition CaCO3. ... Doubly refracting Calcite from Iceberg claim, Dixon, New Mexico. ... -1... Change in sea surface pH caused by anthropogenic CO2 between the 1700s and the 1990s Ocean acidification is the name given to the ongoing decrease in the pH of the Earths oceans, caused by their uptake of anthropogenic carbon dioxide from the atmosphere. ... Gesso is the Italian word for chalk (akin to the Greek word gypsum), and is a powdered form of the mineral calcium carbonate used in art. ... This article needs additional references or sources for verification. ... Cuttlebone from Sepia sp. ...

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Linus Pauling Institute at Oregon State University (5486 words)
Although calcium stone formers have been advised to restrict calcium intake in the past, a cross-sectional study of 282 patients with calcium oxalate stones found that dietary salt, as measured by urinary sodium excretion, was the dietary factor most strongly associated with urinary calcium excretion (23).
Until the relationship between calcium and prostate cancer is clarified, it is reasonable for men to consume a total of 1,000 to 1,200 mg/day of calcium (diet and supplements combined), which is the adequate intake level recommended by the Food and Nutrition Board of the Institute of Medicine (3).
These studies were not designed to examine the effect of calcium on obesity or body fat, and their significance was unclear until recent studies in cell culture and animal models indicated that low calcium intakes could result in hormonal and metabolic changes that increase the tendency of fat cells to accumulate fat (46).
Calcium Carbonate (222 words)
Calcium carbonate has a number of applications besides its natural ones, including as an antacid, lime for farm fertilization, a construction material (marble or cement, for instance), and a base for many pharmaceuticals.
Chalk is composed of either calcium carbonate or of gypsum, a form of calcium carbonate found naturally in caves.
Most caves are calcium carbonate formations, created when water dripped through limestone cracks, dissolving the stone to form weak carbonic acid from the carbonate.
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