Calcium carbonate is a chemical compound denoted by the chemical formula CaCO3. It is a carbonic salt of calcium and is also known as calcite or aragonite which are its mineral ores.
It is commonly found in rocks and also forms the main component of seashells, eggshells, snail shells, pearls, corals, etc. It is a non-toxic, odorless, white color compound. It reacts with acids to form carbon dioxide and is alkaline.
In this article, we will study whether CaCO3 is soluble in water or not.
So, is CaCO3 soluble in water? No, CaCO3 is insoluble in water because of the very strong electrostatic forces of attraction that exist in the calcium carbonate molecules. The forces are so strong that they make it impossible to break the bond between the calcium and carbonate ion, and do not let CaCO3 dissociate in water even when calcium carbonate is actually an ionic substance. The solubility product of CaCO3 is very low 3.3 * 10^-9 indicating that this compound is not soluble in water.
Most metal carbonates are insoluble in water.
Let us check the reasons for the insolubility of CaCO3 in water in further sub-topics. Keep Reading!
Why is CaCO3 not Soluble in Water?
The solubility of a substance i.e. a solute is its ability to form a solution when dissolved in another substance i.e. a solvent.
Most ionic compounds are soluble in water and split up to form ions. As calcium carbonate is an ionic compound, similar behavior is expected out of it, however, like most other metal carbonates CaCO3 molecules do not dissolve in water.
Water is a polar solvent and when any ionic compound is dissolved in water the original structure of that compound is broken and separate ions are formed.
Hence, the solubility of an ionic compound in water depends upon its hydration energy and lattice energy.
Hydration energy refers to the energy released when one mole of a substance is dissolved in water and depends upon the charge density of ions, while lattice energy is the energy responsible for binding the crystal lattice together in a compound and majorly depends upon the distance between the two atoms of a molecule.
If the hydration energy of a compound is higher than its lattice energy the substance becomes soluble in water while if the lattice energy surpasses the hydration energy the substance remains insoluble.
Therefore, the difference in the lattice energy and hydration energy of a compound lays the foundation of its solubility in water.
In the case of calcium carbonate, the value of lattice energy is 2860 KJ/mol while the hydration energy of Ca2+ is -189 KJ/mol, and that of CO32- ion is – 40 KJ/mol.
As the value of lattice energy is quite high in comparison to hydration energy the CaCO3 molecules do not dissolve in water.
Also, the solubility chart given below describes the solubility of various compounds formed by the combination of different anions and cations:
• S stands for Soluble
• I stand for Insoluble
• sS stands for Slightly soluble
• X stand for others
Looking at the combination of calcium and carbonate ions it is clear that the combination of these two ions is insoluble in water.
Also, looking at the trends of solubility it can be deciphered that carbonates are usually not soluble in water with an exception of sodium, potassium, and ammonium, which are alkali metal carbonates, while Magnesium carbonates are slightly soluble in water.
However, hydrogen carbonate of calcium viz. Ca(HCO3) is soluble in water.
Is CaCO3 Soluble in Cold Water?
The general trend in the solubility of a compound is that the solubility of a substance increases with temperature.
This is due to the extra amount of energy supplied by the kinetic energy of molecules that helps overcome the lattice energy and breaks the inter-atomic bonds in the molecule.
The solubility of calcium carbonate in pure water is very low, almost 0.013 g/L at 25 °C.
However, the trend of solubility for carbonate is opposite of the normal trend i.e. the solubility of calcium carbonate in water increases as the temperature decreases, and therefore, it is soluble in cold water.
The decrease in temperature results in the mobility of carbonate ions while the increase in temperature causes the carbonate ions to precipitate out from the solution.
Also, the pressure and pH of the solution play a vital role in the solubility of CaCO3 in water.
The solubility increases as the pressure increases.
Also, this is the reason why calcium carbonate molecules are easily soluble in rainwater. It is due to the presence of dissolved carbon dioxide which causes the formation of carbonic acid.
Does CaCO3 react with Water?
Under normal circumstances, calcium carbonate does not react with water.
When CaCO3 is added to water it results in precipitation of most calcium carbonate molecules on the bottom with only a negligible amount of molecules getting dissolved.
However, the CaCO3 molecules react with rainwater resulting in the formation of soluble calcium bicarbonate or hydrogen carbonate of calcium.
The reaction occurs due to the presence of carbon dioxide that gets dissolved in the rainwater from the atmosphere.
This decreases the pH of water due to the formation of carbonic acid.
The reaction for this can be written as:
CaCO3 + CO2 + H2O —> Ca(HCO3)2
This reaction is responsible for the erosion of rocks and the formation of caverns in the long run.
This is also the reason why a high amount of dissolved calcium is found in the water at some places (hard water).
What Increases the Solubility of CaCO3?
As calcium carbonate is insoluble in the water we will look at the factors affecting the solubility of CaCO3 molecules in rainwater as per the reaction mentioned in the previous section.
The various factors responsible are as follows:
• Temperature: As discussed earlier the increase in temperature decreases the solubility of calcium carbonate in the water while a decrease in temperature would increase its solubility.
You must also go through the article does temperature affect ph.
• Water: As the reaction is reversible in nature the increase in the concentration of water shifts the equilibrium towards the right i.e. more ions will get dissolved.
• Carbon dioxide: Again increase in the amount of dissolved CO2 would result in the dislocation of equilibrium towards the right and more ions will get dissolved in the solution.
• pH: As discussed earlier the dissolved CO2 results in the decline of the pH of the solution.
As the pH decreases with an increase in the amount of carbon dioxide, therefore, the solubility of calcium carbonate increases with a decline in pH and vice versa.
• Salts: The presence of different salts affect the solubility of CaCO3 differently.
If the salts present are comprised of common ions as present in calcium carbonate it will result in a decline in solubility while if other salts are present that do not have any common ions it would result in an increase in the solubility.
Which Carbonates are Soluble in Water?
Most metal carbonates do not dissolve in water, with a few exceptions while most alkaline metal carbonates are soluble in water.
For example, Potassium carbonate (K2CO3), Sodium carbonate (Na2CO3), and all other group 2 carbonates are soluble in water except Lithium carbonate.
The reason for this is the presence of a single electron in the valence shell of alkali metals due to which they have a charge value of +1 as it requires giving away only one electron to acquire stability.
The different ions of the salts of alkali metals (such as carbonates) are held together by the attraction between oppositely charged atoms.
As water has a high dipole moment, the alkali metal salts readily dissolve in water due to the separation of charges.
The lithium salts do not dissolve in water due to the very small size of its ion as it is not feasible energetically to break the bond at room temperature.
All alkaline earth metal compounds as well as the carbonates of p-block and d-block elements are insoluble in water and form a white precipitate when added to it.
Properties of CaCO3
Calcium carbonate naturally occurs as limestone, marble, etc. It is an alkaline salt of calcium.
The various properties of calcium carbonate are listed in the table below:
|Chemical Name||Calcium Carbonate|
|Molar Mass||100.0869 g/mol|
|Appearance||Fine white powder|
|Melting Point||1339 °C|
|Boiling Point||Decomposes before it boils|
|Density||2.711 g/cm3 for calcite
2.83 g/cm3 for aragonite
|Solubility||0.013 g/L at 25 °C|
|Solubility product||3.3 X 10-9|
Uses of CaCO3
A few important uses of calcium carbonate are given below:
• As limestone, marble, etc. calcium carbonate is extensively used as a building material. It forms an important part of many historical monuments.
• After its calcinations with anthracite, calcium carbonate is used in the refining of sugar from sugar beet.
• It is used as the bridging and filter cake-sealing agent in the oil industry.
• It also forms the main component of many antacids used for relieving acidity.
• It is also used as filler for many tablets and as a phosphate binder in the treatment of hyperphosphatemia.
• Calcium carbonate is used as agricultural lime for neutralizing acidic soil.
Calcium carbonate is not soluble in water as the lattice energy of the compound is very high in comparison to its hydration energy.
Also, the solubility product for the CaCO3 compound is very low 3.3 X 10-9 indicating that this compound cannot dissolve in water.
Mostly solubility increases with an increase in temperature but in the case of CaCO3, it increases with a decrease in temperature.
Calcium carbonate does not dissolve in pure water but is soluble in rainwater due to the presence of dissolved atmospheric carbon dioxide that lowers down the pH of water making it slightly acidic.
Most metal carbonates do not dissolve in water. However, the alkali metal carbonates dissolve in water with an exception of helium.
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