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Calcium Nitrate, Ca(NO3)2
Calcium Nitrate, Ca(NO3)2, does not occur as a mineral form but is often found in natural waters and in the soil as a product of putrefaction and bacterial nitrification. The tetrahydrate forms part of the efflorescence often seen on damp walls, especially on the walls of stables.
It is prepared by the neutralisation of calcium hydroxide or calcium carbonate by nitric acid. The anhydrous salt, which may be obtained by drying the hydrated salt at 170° C., is very deliquescent. The melting-point is 499° C., at which temperature decomposition has already set in to a slight extent. The eutectic mixture of potassium and calcium nitrates, containing 25.36 per cent, of the latter, melts at 251° C.
The heat of formation of anhydrous calcium nitrate from its elements is 216.7 Cal., and the heat of solution 3.95 Cal. The density is 2.240 – 2.504. The anhydrous salt crystallises from a hot aqueous or nitric acid solution in microscopic regular octahedra.
Calcium nitrate is very readily soluble in water and tends to form supersaturated solutions. The properties of aqueous calcium nitrate solutions have been extensively investigated with reference to their boiling-points, freezing-points, vapour pressures, densities, refractive indices, viscosities, electrical conductivities, and degree of dissociation. The boiling-point of the saturated solution at 760 mm. pressure is 151° C., and the solution contains 79 per cent, of calcium nitrate.
It is prepared by the neutralisation of calcium hydroxide or calcium carbonate by nitric acid. The anhydrous salt, which may be obtained by drying the hydrated salt at 170° C., is very deliquescent. The melting-point is 499° C., at which temperature decomposition has already set in to a slight extent. The eutectic mixture of potassium and calcium nitrates, containing 25.36 per cent, of the latter, melts at 251° C.
The heat of formation of anhydrous calcium nitrate from its elements is 216.7 Cal., and the heat of solution 3.95 Cal. The density is 2.240 – 2.504. The anhydrous salt crystallises from a hot aqueous or nitric acid solution in microscopic regular octahedra.
Calcium nitrate is very readily soluble in water and tends to form supersaturated solutions. The properties of aqueous calcium nitrate solutions have been extensively investigated with reference to their boiling-points, freezing-points, vapour pressures, densities, refractive indices, viscosities, electrical conductivities, and degree of dissociation. The boiling-point of the saturated solution at 760 mm. pressure is 151° C., and the solution contains 79 per cent, of calcium nitrate.
The Hydrates of Calcium Nitrate
Calcium nitrate forms several hydrates. The tetrahydrate crystallises from solution at ordinary temperatures in long monoclinic needles. The density is 1.82. The heat of hydration of calcium nitrate is 11.200 Cal., and the heat of solution of the tetrahydrate –7.250 Cal.
From vapour pressure measurements Lescoeur concluded that a di- and tri-hydrate probably exist. More recent work has not only confirmed this, but has revealed the existence of a second and unstable modification of the tetrahydrate. The nature of the solid phases in contact with saturated solutions of calcium nitrate at different temperatures is indicated by the curves in Fig.
The cryohydric temperature indicated by point A is -28.7° C. at a concentration of 42.9 per cent, of anhydrous salt.
The melting-point of the stable α-tetrahydrate (point B) is 42.7° C., and of the β-form (point B'), 39.6° C.
The trihydrate, the stable hydrate between C and E, which forms flattened prismatic crystals apparently belonging to the triclinic system, melts at 51.1° C. (point D).
The dihydrate in smaller prismatic crystals has no true melting- point, as can be seen from the diagram where the range of existence is line EF lying between the temperatures 48.4° and 51.3° C.
As the line FG shows, there is only a very slight increase in the solubility of the anhydrous salt with rise of temperature.
A hexahydrate, Ca(NO3)2.6H2O, of melting-point 26.4° C., is mentioned by Tilden, but there does not appear to be any confirmatory evidence.
Calcium nitrate, known as " air-saltpetre," is obtained technically in the fixation of atmospheric nitrogen by the arc process, the nitrous gases being absorbed by calcium oxide or calcium carbonate. It is as effective a fertiliser as sodium nitrate, but it has not appeared to any great extent in the English country markets. The difficulties caused by its hygroscopic nature have to some extent been overcome.
The preparation of calcium nitrate on a commercial scale by the bacterial oxidation of calcium cyanamide, or of ammonium compounds in the presence of calcium carbonate, has also been suggested.
A patent has been taken out for neutralising nitric acid with a mixture of rock phosphate and limestone. A hard dry mass of considerable fertilising value is said to be obtained.
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| Equilibria in the system, calcium nitrate: water |
The cryohydric temperature indicated by point A is -28.7° C. at a concentration of 42.9 per cent, of anhydrous salt.
The melting-point of the stable α-tetrahydrate (point B) is 42.7° C., and of the β-form (point B'), 39.6° C.
The trihydrate, the stable hydrate between C and E, which forms flattened prismatic crystals apparently belonging to the triclinic system, melts at 51.1° C. (point D).
The dihydrate in smaller prismatic crystals has no true melting- point, as can be seen from the diagram where the range of existence is line EF lying between the temperatures 48.4° and 51.3° C.
As the line FG shows, there is only a very slight increase in the solubility of the anhydrous salt with rise of temperature.
A hexahydrate, Ca(NO3)2.6H2O, of melting-point 26.4° C., is mentioned by Tilden, but there does not appear to be any confirmatory evidence.
Calcium nitrate, known as " air-saltpetre," is obtained technically in the fixation of atmospheric nitrogen by the arc process, the nitrous gases being absorbed by calcium oxide or calcium carbonate. It is as effective a fertiliser as sodium nitrate, but it has not appeared to any great extent in the English country markets. The difficulties caused by its hygroscopic nature have to some extent been overcome.
The preparation of calcium nitrate on a commercial scale by the bacterial oxidation of calcium cyanamide, or of ammonium compounds in the presence of calcium carbonate, has also been suggested.
A patent has been taken out for neutralising nitric acid with a mixture of rock phosphate and limestone. A hard dry mass of considerable fertilising value is said to be obtained.
Addition Compounds of Calcium Nitrate
Calcium nitrate solutions absorb ammonia more readily than does pure water, evidently as the result of the formation of a complex cation Ca(NH3)n.
Calcium nitrate is very soluble in ethyl alcohol and forms an alcoholate, Ca(NO3)2.2C2H5OH. It also dissolves readily in methyl, propyl, isobutyl, and amyl alcohols, and in acetone, but not in ether and paracetaldehyde.
Calcium nitrate is very soluble in ethyl alcohol and forms an alcoholate, Ca(NO3)2.2C2H5OH. It also dissolves readily in methyl, propyl, isobutyl, and amyl alcohols, and in acetone, but not in ether and paracetaldehyde.
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