Chemical Forums
Chemistry Forums for Students => Inorganic Chemistry Forum => Topic started by: Smokin on April 05, 2008, 07:33:02 PM
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First off forgive my ignorance. I'm no chemist, just a wannabe artist tyring to understand the chemistry of my pigments. I'm confused as to a formula I am looking at.
(PbCO3)2 · Pb(OH)2
I know PbCO3 = Lead Carbonante, and Pb(OH) = Lead Hydrate. But what does the 2 stand for at the end of each substance...compound, ...molecule? Does that mean for every two particles of PbCO3 there is two particles of Pb(OH) which means 50% carbonate and 50% hydrate? Also, why does the MSDS sheet for 100g of this formula described as Basic Lead Carbonate, say 100% PbCO3?
Also, is (Pb H2O2) the same as Pb(OH)2?
Lastly, does this link for a substance coined lead hydroxide carbonate = to about 66% carbonate to 33% lead hydroxide? Am I reading this correctly?
http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?sid=158089&loc=ec_rcs
This is my first post here, so let I hope we can do a lil less socrates on this one ;D.
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From the link it seems that your pigment is actually a mixture of two compounds
PbCO3 lead (II) carbonate
Pb(OH)2 (known to chemists as lead II hydroxide) - the 2 indicates that there are 2OH groups for every Pb in this compound
Pb(H2O2) would not be the same as Pb(OH)2 - Pb(H2O2) would imply lead peroxide - if that exists.
Also, why does the MSDS sheet for 100g of this formula described as Basic Lead Carbonate, say 100% PbCO3?
Perhaps because you just looked up PbCO3 and not the pigment name?
The format (PbCO3)2 . Pb(OH)2 indicates this mixture as 2 parts PbCO3 and 1 part Pb(OH)2
this is consistent with the 66% lead carbonate and 33% lead hydroxide (2:1 mixture)
Lastly, does this link for a substance coined lead hydroxide carbonate = to about 66% carbonate to 33% lead hydroxide? Am I reading this correctly?
http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?sid=158089&loc=ec_rcs
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First off forgive my ignorance. I'm no chemist, just a wannabe artist tyring to understand the chemistry of my pigments. I'm confused as to a formula I am looking at.
(PbCO3)2 · Pb(OH)2
I know PbCO3 = Lead Carbonante, and Pb(OH) = Lead Hydrate. But what does the 2 stand for at the end of each substance...compound, ...molecule?
An OH group is called an hydroxide, a hydrate has a · H2O. The 2 after the parenthesis means the same as the 2 after the H in water -- we need two of the groups to balance the charge.
Does that mean for every two particles of PbCO3 there is two particles of Pb(OH) which means 50% carbonate and 50% hydrate?
No, this particular compound, or mineral, is made of one molecule of lead carbonate and one molecule of lead hydroxide bound together. These lead salts can also be found separately, but I don't think they were reacted with each other, probably, the rock or mineral is mined that way, or a reaction produces the combined salt you have here.
Also, why does the MSDS sheet for 100g of this formula described as Basic Lead Carbonate, say 100% PbCO3?
Many reasons are possible for the 100% PbCO3. The assay may want to express the dual salt as lead carbonate equivalents. Also, basic lead carbonate is the name for this dual salt, the OH group makes any inorganic salt a base.
Also, is (Pb H2O2) the same as Pb(OH)2?
Nope, not even if it exists, which it probably doesn't. Different atoms, different molecule, no exceptions.
Lastly, does this link for a substance coined lead hydroxide carbonate = to about 66% carbonate to 33% lead hydroxide? Am I reading this correctly?
Yep, that explains this salt properly.
This is my first post here, so let I hope we can do a lil less socrates on this one ;D.
Not a problem, you have a lot to digest here.
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From the link it seems that your pigment is actually a mixture of two compounds
I would not call it a mixture. It probably crystallizes with this exact formula, so it has strictly defined composition of Pb2CO3(OH)2. Formula given as PbCO3·Pb(OH)2 is just an alternate notation, quite often used in mineralogy. Orthoclase is KAlSi3O8, sometimes written as K2O·Al2O3·6SiO2. Mohr's salt is (NH4)2Fe(SO4)2·6H2O, sometimes written as FeSO4·(NH4)2SO4·6H2O and so on.
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Thx you so much for the help. Im sure Ill have new questions for this wonderful group soon. Trying to figure out pigments isnt as easy as I hoped. Ill look this site more, but is there a good source anyone can recomend to learrn basic terminology or basic chemistry so I can minimize confusion when asking questions?
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Since the original form of the formula you listed was (PbCO3)2 · Pb(OH)2,
I'm wondering if you are referring to "white lead" which has the formula Pb3(CO3)2(OH)2. It has been used in pigments and was a common ingredient in makeup 200 years ago or so.