Answer to Question #31020 in Organic Chemistry for dora

Question #31020
What chemical should I add to make the (calcium carbonate+water) solid? if you mix calcium carbonate and water, it can not make it solid?
Expert's answer
The tendency for metastable phases of calcium carbonate to be precipitated from aqueous solutions is increased not only by raising the rate of precipitation but also by increasing the concentration of certain added substances. Thus in the presence of small amounts of Calgon or magnesium-ion, and in saturated sodium chloride solution in the presence of magnesium-ion, a range of products is obtained according to the conditions of precipitation, particularly the stirring and the temperature. Calcite (the stable phase), aragonite, vaterite ( μ -calcium carbonate) and calcium carbonate hexahydrate have been prepared in this way together with a new hydrate, CaCO3*nH2O. By allowing reaction mixtures containing additive to stand until the first-formed gel has crystallized, metastable phases may be produced with considerable regularity. Metastable phase diagrams can be constructed which show the dependence of the phases on conditions of precipitation, e.g. sodium carbonate concentration and concentration of additive. In stirred conditions of reaction, calcium carbonate may be grown, without fresh nucleation, on seed crystals of calcite and vaterite at a much faster rate in the presence of limited amounts of Calgon than in its absence. At relatively high concentrations other phases may appear and growth of the calcite and vaterite ceases in spite of the presence of seed crystals. Compounds containing calcium carbonate formed in the presence of magnesium-ion or Calgon have been shown by analytical methods to contain magnesium or phosphorus in appreciable quantities. The presence of the additive leads to modification in the crystal habit of calcite and of the hexahydrate CaCO3*6H2O. It has also been noted that distortion of X-ray patterns of the crystalline species is common. These observations are explained on the grounds that germs of the crystalline phases are subject to varying degrees of distortion depending on the constitution of the solution. The growth is therefore hindered to different degrees in different cases. In the limit the effect of distortion may be such that growth of nuclei of certain types may be inhibited, and there is a corresponding change in the conditions for the spontaneous crystallization from solution of the various phases.

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