SAM4CH - 17-12-2005 at 02:31
1. I tried to prepare Lead Carbonate, I added Pb(NO3)2 solution to a saturated solution of NaHCO3, is the resulted white ppt. lead carbonate "PbCO3"
or Basic white lead "(PbCO3)2.Pb(OH)2".
2. Trying to prepare Copper Carbonate, I added saturated Copper Sulfate pentahydrate solution to second solution of NaHCO3, is the resulted green/blue
ppt copper carbonate "CuCO3" or CUPRIC CARBONATE BASIC "CuCO3.Cu(OH)2".
Note: I filtered my solution after the reaction completed immediatly.
[Edited on 17-12-2005 by SAM4CH]
woelen - 17-12-2005 at 02:47
The problem with these compounds is that it is hard to obtain a composition of precisely determined stoichiometry. The real stoichiometry will be of
the form M(CO3)x(OH)y, where 2x + y = 2. With NaHCO3 you'll most likely get a compound with x quite close to 1 and y almost zero. With Na2CO3 you'll
get a compound with x around 0.5 and y close to 1. The precise composition also depends on the concentration of the reactants and the temperature.
SAM4CH - 17-12-2005 at 03:08
If i use 30% CuSO4.5H2O solution (30g/100mL), and 20% NaHCO3 (20g/100mL), at 20 degree.
What is the correct formula of that salts.
woelen - 17-12-2005 at 06:52
The only way to know that is performing the experiment and trying yourself. Maybe there has been someone, who determined (x,y) as function of
concentrations and temperature, but I have severe doubts on that.
In chemistry, I have learnt that the number of reactions, which nicely and quantitatively proceed according to some stoichiometry, is very small. Even
the simple reaction, where copper (II) ions are precipitated with solution of NaOH is not so nice and simple as one is tought on high-school. A lot of
other effects, such as coprecipitation and intercalation of water molecules and formation of bridged structures like -Cu-(μ-OH)-Cu- give rise to
complex mixtures. So, in your case, you will have something I posted in my previous post, but it will also contain Na(+) and SO4(2-) ions,
coprecipitated. There also will be water-molecules in the precipitate, so what you really end up with is a complicated mix for which only an empirical
formula can be given, which needs to be determined by analysis of the compound.
Btw, precipitation in general is a bad way to obtain pure chemicals, especially if the precipitates are slimy or flocculent. Coprecipitation is
considerable in such cases and you need a lot of rinsing.
unionised - 17-12-2005 at 10:50
You probably have basic copper sulphate in the mixture too.