Fossil
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Diferentiating between carbonates and basic carbonates
I know that there are two different plumbous carbonates, lead II carbonate and basic lead II carbonate. My problem is: how would I differentiate
between the two and know which one I have? I have the same problem with cupric carbonate. If there is no easy test, how would I prepare the carbonate
without the basic carbonate? I have read that cooling the solution of lead acetate before the introduction of CO2 works, but the source did not
specify what temperature it must be cooled to and I am unsure if it is effective in suppressing the formation of the basic carbonate.
Any help is appreciated!
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kavu
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If you have a good balance gravimetric analysis should be an easy one. Upon heating copper carbonate decomposes to yield copper(II)oxide. Some
stoichiometry and that's it. Same could be done with lead as it should decompose utimately to lead(II)oxide.
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Fossil
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I'm assuming that the basic carbonates will not decompose to their respective oxides, or will it not affect the reaction and will still decompose to
the oxide. I would like to know a sure fire way to differentiate the two still, as determining the density first means finding the volume and I am
simply not down to go through the trouble.
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kavu
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When torched in a red hot curcible heavy metal hydroxides are usually destined to become corresponding oxides. Density is of little or no use as the
packing of such solids is far from ideal. The gravimetric difference comes from the mass of the oxide residue as basic carbonates and carbonates have
different molar masses.
Dissolving and precipitation of metals as insoluble compounds is also an option. Titration might also give good results.
[Edited on 2-7-2012 by kavu]
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Fossil
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Thanks again, and it seems that I misunderstood what you meant by gravimetric analysis. Still, is there a way to ensure the formation of only the
carbonate and not the basic carbonate.
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AJKOER
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To distinguish between CuCO3.Cu(OH)2 (or 2CuCO3.Cu(OH)2) and CuCO3, perhaps a mild heating test will work. As long the temperature is above 185 C and
well below 290 C, it is known that pure Cu(OH)2 decomposes in part to CuO (black), while the blue-green CuCO3 should not breakdown.
Also, in addition to the color change, heating the dry CuCO3.Cu(OH)2 salt may produce water vapor that can be condensed on a cooled area of the flash.
However, all of the above may be a relative differentiation as per the "Concise Encyclopedia Chemistry" by De Gruyter, to quote: "Copper (II)
carbonate has not been obtained in pure form".
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