Proust copper carbonate

Joseph-Louis Proust reported preparing a copper carbonate compound. He analyzed the compound by heating it, driving off first water and then "carbonic acid"; what was left was a copper oxide. He said that from 180 pounds[1] of copper carbonate he drove off 10 pounds of water and 46 of "carbonic acid" (carbon dioxide); the residual copper oxide contained 100 pounds copper and 25 oxygen.

For the following exercise, let us work with 180 g of Proust's compound. We are supposing that 180 g of compound yields 10 g H2O, 46 g CO2, 100 g Cu, and 25 g "additional" O (that is, oxygen not in water or carbon dioxide).

a) Compute the number of moles of H2O, CO2, Cu, and additional O. Express the molar proportions as a ratio of small whole numbers.
b) Compute the number of moles of Cu, C, H, and O (total). What is the empirical formula of Proust's compound?
c) The empirical formula gives the proportions of elements in a compound, but does not tell us how the elements are arranged into groups. The ions that make up this compound are actually Cu2+, CO32- ions, and OH- ions. That is, we can write its formula as Cux(CO3)y(OH)z. Write the compound's formula in this way, filling in x, y, and z.


Joseph-Louis Proust, "Researches on Copper," Ann. chim. 32, 26-54 (1799).
[1]He was certainly not working in microscale!
Copyright 2003 by Carmen Giunta. Permission is granted to reproduce for non-commercial educational purposes.

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