Chemical elements
  Carbon
    Isotopes
    Energy
    Production
    Application
    Physical Properties
    Chemical Properties
      Methane
      Ethylene
      Acetylene
      Coal-Gas
      Carbon Tetrafluoride
      Tetrafluoromethane
      Carbon Tetrachloride
      Tetrachloromethane
      Carbon Tetrabromide
      Tetrabromomethane
      Carbon Tetraiodide
      Tetraiodomethane
      Carbon Oxychloride
      Carbonyl Chloride
      Phosgene
      Carbon Oxybromide
      Carbonyl Bromide
      Carbon Suboxide
      Carbon Monoxide
      Carbon Dioxide
        Preparation
        Physical Properties
        Liquid Carbon Dioxide
        Solid Carbon Dioxide
        Decomposition
        Carbonic Acid
        Carbonates
        Physiological Action
        Detection and Estimation
      Percarbonic Acid
      Carbamic Acid
      Carbamide
      Urea
      Carbon Disulphide
      Carbonyl Sulphide
      Carbon Oxysulphide
      Thiocarbonyl Chloride
      Thiocarbonic Acid
      Thiocarbamic acid
      Thiourea
      Thiocarbamide
      Perthiocarbonates
      Carbon Monosulphide
      Carbon Subsulphide
      Carbon Sulphidoselenide
      Carbon Sulphidotelluride
      Carbon Nitrides
      Cyanogen
      Dicyanogen
      Hydrocyanic Acid
      Prussic Acid
      Cyanogen Chloride
      Chlorocyanogen
      Cyanogen Bromide
      Bromocyanogen
      Cyanogen Iodide
      Iodocyanogen
      Polymerised Cyanogen Halides
      Cyanamide
      Cyanic Acid
      Cyanuric Acid
      Cyamelide
      Fulminic Acid
      Thiocyanic Acid
      Sulphocyanic Acid
      Isoperthiocyanic Acid
      Cyanogen Sulphide
      Thiocyanic Anhydride
    Diamonds
    Graphite
    Amorphous Carbon
    Coal

Carbonates






Carbon dioxide might be expected to undergo hydroxylation in two stages, producing respectively metacarbonic acid, CO(OH)2, and orthocarbonic acid, C(OH)4.

It has been shown, however, that even the former acid is unstable, and neither the latter acid nor its inorganic salts exist. Alkyl ortho-carbonates are, however, known, e.g. ethyl orthocarbonate, C(OC2H5)4.

Carbonic acid, H2CO3, readily decomposes into H2O and CO2, and the carbonates tend to undergo a similar reversible reaction:

MCO3MO + CO2.

The stability of a carbonate depends on the strength of the base contained in it. Thus the alkali carbonates are scarcely decomposable at a white heat; the alkaline earth carbonates lose carbon dioxide at a red heat, barium carbonate being the most stable of the three; carbonates of magnesium, zinc, copper, etc., lose carbon dioxide even more readily, and are prone to form basic carbonates, the formation of the normal salt by precipitation requiring the presence of excess of carbonic acid. Metalloids such as tin and antimony, and extremely electronegative metals like gold and platinum, form no carbonates.

The carbonates of the alkali metals are readily soluble in water; other carbonates are very slightly soluble, or practically insoluble. So far as water can act on carbonates, it hydrolyses them into free base or basic salt and free carbonic acid or hydrogen salt. Thus sodium and calcium carbonates undergo the following reactions with water - the former considerably, the latter, owing to its small solubility, very slightly:

Na2CO3 + H2ONaOH + NaHCO3
CaCO3 + 2H2OCa(OH)2 + Ca(HCO3)2.

The former of these reactions has been carefully studied. It may be otherwise represented:

Na2CO3 ⇔ 2Na + CO3'
CO3' + H2OOH' + HCO3'

The extent of hydrolysis in aqueous solution is indicated by the amount of alkalinity developed, that is by the excess of OH' over H ions in the solution. Such alkalinity cannot be estimated by titration because the disturbance of equilibrium by the addition of H ions is accompanied by further hydrolysis till equilibrium is restored.

The saponification of an ester, however, is a reaction which may be utilised, since neither H nor OH' ions are thereby added to the solution, and the rate of such saponification is directly proportional to the concentration of OH' ions. This method has been employed by Shields, who found that the sodium carbonate in a N/10 solution is hydrolysed at 25° to the extent of 3.17 per cent.


Bicarbonates

Only the most electropositive metals form bicar- bonates or hydrogen carbonates. The bicarbonates of the alkali metals, excepting lithium, are known in the solid state, and are less soluble in water than the corresponding carbonates. They show a progressive stability with increase in electropositiveness from sodium to caesium. The bicarbonates of lithium, calcium, strontium, barium, and ferrous iron exist only in solution, and are more soluble in water than the normal carbonates.

Double or Complex Carbonates

Salts of the type MKH(CO3)2, where M is cobalt, nickel, or magnesium, were obtained by Deville, and were converted into salts of the type MK2(CO3)2 by heating their solutions. Other complex salts of the same type, whose constitution is probably KCO3MCO3K, were prepared by Reynolds.

The metallic carbonates, bicarbonates, and complex carbonates will be dealt with under the individual metals.
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