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Actually, it turns out to be not that simple.
Some references make a distinction between verdigris (copper acetate) and the green on copper roofs, which some claim is basic copper carbonate (as ChuckFickens says) and others claim is a mixture of copper carbonate and copper oxide.
Odd that there seems no agreement.
Some references make a distinction between verdigris (copper acetate) and the green on copper roofs, which some claim is basic copper carbonate (as ChuckFickens says) and others claim is a mixture of copper carbonate and copper oxide.
Odd that there seems no agreement.
Ha, the great verdigris debate. This has always been a contentious issue and has caused many a row during pub quizzes � I took part in one recently myself and won �50 because of it. So, if you�ll allow me, I�ll try to clarify it.
First of all, it�s important to know that there are so-called true verdigris and false verdigris (yes, plural). Let�s discuss them one by one.
True verdigris comes in the form of three distinct varieties, each with a different chemical formula. The first is known as blue verdigris and has the approximate formula Cu(CH3COO)2.CuO.6H2O. The second is known as green verdigris and has the approximate formula 2Cu(CH3COO)2.CuO.6H2O. The third is known as neutral verdigris which has the approximate formula Cu(CH3COO)2.H2O.
Now as you can see, all of these compounds are basic acetates (aka ethanoates) of copper, but what is important to note is that each of them or a mixture of them may be correctly termed true verdigris.
(continued)
First of all, it�s important to know that there are so-called true verdigris and false verdigris (yes, plural). Let�s discuss them one by one.
True verdigris comes in the form of three distinct varieties, each with a different chemical formula. The first is known as blue verdigris and has the approximate formula Cu(CH3COO)2.CuO.6H2O. The second is known as green verdigris and has the approximate formula 2Cu(CH3COO)2.CuO.6H2O. The third is known as neutral verdigris which has the approximate formula Cu(CH3COO)2.H2O.
Now as you can see, all of these compounds are basic acetates (aka ethanoates) of copper, but what is important to note is that each of them or a mixture of them may be correctly termed true verdigris.
(continued)
False verdigris is the �verdigris� that we�re all familiar with on uncleaned copper vessels and church roofs. This compound has the formula Cu(OH)2.CuCO3 and is a basic cupric carbonate. To complicate matters further, on buildings near the sea, the compound is often mixed with a basic cupric chloride. It should also be noted that the compound will form on brass, copper and bronze just as readily as copper if the article is exposed to a moist atmosphere or buried in the ground long enough.
Incidentally, if you want to see the difference in true and false verdigris on copper vessels, the classic method is to boil some vinegar or vegetables in vinegar in the vessel on a stove. True verdigris will form in the vessel due to the action of the acetic (ethanoic) acid. Leaving a clean vessel in a moist atmosphere or burying it in soil allows false verdigris to form.
Finally, having had a quick look at the Wikipedia article on verdigris, I�m afraid it�s not strictly correct, which is not unusual given the fact that it�s user editable. I�ve just checked my copy of Hawley�s Chemical Dictionary � the recognised, definitive reference source for chemists- to see if my grey cells were wanting and found that what I�ve written complies with Hawley�s definition. Clearly senility hasn�t set in yet!
Incidentally, if you want to see the difference in true and false verdigris on copper vessels, the classic method is to boil some vinegar or vegetables in vinegar in the vessel on a stove. True verdigris will form in the vessel due to the action of the acetic (ethanoic) acid. Leaving a clean vessel in a moist atmosphere or burying it in soil allows false verdigris to form.
Finally, having had a quick look at the Wikipedia article on verdigris, I�m afraid it�s not strictly correct, which is not unusual given the fact that it�s user editable. I�ve just checked my copy of Hawley�s Chemical Dictionary � the recognised, definitive reference source for chemists- to see if my grey cells were wanting and found that what I�ve written complies with Hawley�s definition. Clearly senility hasn�t set in yet!
Hi chakka
What happened was that the quizmaster gave the answer "copper carbonate" at the end of the quiz was over and as I'd consumed a good few ales, I stood up and told him he was wrong. The wife looked like she wanted the ground to swallow her up, but the beer got the better of me and I gave him a cut-down version of what I typed above.
There was a fair bit of scepticism mainly because I seemed to be the only person with academic chemistry qualifications in the room. All the same, the landlord went off to check on the internet and after returning twenty minutes later, announced that I was right. I was given the �50 that night on a point basis. When I called into my local a few weeks later, quite a few people told me that they had always thought copper carbonate was the only right answer.
So now I'm not just a university professor and dean at my pub but a big-head as well!
What happened was that the quizmaster gave the answer "copper carbonate" at the end of the quiz was over and as I'd consumed a good few ales, I stood up and told him he was wrong. The wife looked like she wanted the ground to swallow her up, but the beer got the better of me and I gave him a cut-down version of what I typed above.
There was a fair bit of scepticism mainly because I seemed to be the only person with academic chemistry qualifications in the room. All the same, the landlord went off to check on the internet and after returning twenty minutes later, announced that I was right. I was given the �50 that night on a point basis. When I called into my local a few weeks later, quite a few people told me that they had always thought copper carbonate was the only right answer.
So now I'm not just a university professor and dean at my pub but a big-head as well!
I am peeved that there is a pub quiz book somewhere that states that copper is used to make the green colour in fireworks. I have argued a number of times that this is incorrect and that Barium salts are used for green and copper is used to make blue (in chlorine vapour).
I worked in a fireworks factory for 8 years, but usually get the answer "I have to take what the book says".
Bah!
I worked in a fireworks factory for 8 years, but usually get the answer "I have to take what the book says".
Bah!
MortartubeI sympathise and I know how infuriating this can be. I've always felt the blame rests with indolent chemistry/general science teachers during a child's first year at comprehensive schools, who select a mere three or four compounds for a flame test demonstration.
Yes, they all know that copper imparts blue and green colours to the flame, but they won't have seen the flame test colours of molybdenum, barium, boron and arsenic compounds.
Whilst I realise that it would be impractical to see a demonstration of flame tests with many such compounds due to time restraints, children should at least be required to learn a dozen or so even if the knowledge is gained from the child's own class notes. Unless the child goes on to study chemistry at A level, they simply don't appreciate that other elements provide spectacular flame test results too.
Yes, they all know that copper imparts blue and green colours to the flame, but they won't have seen the flame test colours of molybdenum, barium, boron and arsenic compounds.
Whilst I realise that it would be impractical to see a demonstration of flame tests with many such compounds due to time restraints, children should at least be required to learn a dozen or so even if the knowledge is gained from the child's own class notes. Unless the child goes on to study chemistry at A level, they simply don't appreciate that other elements provide spectacular flame test results too.
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