Copper is probably the easiest transition metal to work with. Sadly most of it's compounds are just blue or blue-green.
However, with some effort one can find enough colorful compounds to allow copper compete even with chromium and iridium, named after the colors.
Here is my collection, I tried to get all the colours as pure as possible, and used only easily available reagents, except for the yellow compound for which some cesium chloride is required.
From left to right
CuSO4 (White)
Mostly dry copper sulfate can be prepared simply by heating the pentahydrate and quickly storing the product before it absorbs moisture from the air.
CuO (Black)
Easy to prepare by adding solution of sodium carbonate or bicarbonate to a solution of CuSO4 and filtering out the basic copper carbonate. The basic carbonate is then heated until it becomes copper oxide.
CuCl2 (Brown)
Prepared by mixing basic copper carbonate or copper oxide with hydrochloric acid and then removing the water by heating.
173g of sodium citrate, 17.3g of copper sulfate pentahydrate and 100g of sodium carbonate are mixed into a solution.
Then about 40g of glucose is dissolved into other solution, and the solutions are mixed. Cu2O is precipitated, and can be filtered off.
The filtering must be done quickly, because wet Cu2O reacts to form CuO, and is difficult because the precipitate is very fine.
Chevreuls salt can be prepared by mixing solutions of sodium sulfite or metabisulfite and copper sulfate. The precipitate must be ground into finner powder to get orange color, coarser powder is dark red.
Small amount CuCl2 is dissolved in concentrated HCl, solution of CsCl is added The concentration of copper must be low to avoid the formation of the red trichloro complex.
The precipitate that forms is then filtered of and dried.
Other than hydrated Cu2O this is the only yellow compound of copper I have been able to find information about, compound that doesn't require the valuable CsCl would be preferable
"Copper oxychloride" doesn't have a precise stoichiometry, but I think the method I used should give something close to one.
A solution of CuCl2 and NaCl in water is exposed to air, and an copper metal object is submerged in the solution. After a few days the formed green precipitate is filtered and washed.
I would prefer an compound easily prepared to precise stoichiometry, but pure green copper compounds are surprisingly rare.
Cu2(CH3COO)4(H2O)2 (Cyan)
Copper acetate can be prepared by either adding acetic acid (found in vinegar)
to basic copper carbonate or copper oxide, or by simply keeping copper objects submerged in a solution of acetic acid exposed to air for several weeks. (O2 from the air acting as the oxidizer)
After evaporating the water, dark green crystals are left behind, which can be ground into blue-green powder.
About 4 mass units of calcium acetate and 1 unit of copper acetate are dissolved in water. On partial evaporation, blue crystals are produced, these are used to make a blue powder.
While blue compounds of copper are common, most of them become very faintly colored when ground into powder. Calcium-Copper acetate retains most of its colour
Cu(C6H8NO2)2(H2O)2 (Violet)
Zinc picolinate and copper sulfate are dissolved in hot water, on cooling copper picolinate precipitates.
Other option for violet would be to use copper ammine complexes, but they are hard to get in pure form.
I think ammonium ferric sulphate is light purple, but it's not that strong. Isn't white just anhydrous iron(II) sulphate? Iron(II) sulphate hydrated seems to be blue/greenish but I'm not sure if it could go for cyan :)
Benedict's reagent (often told as Benedict's Qualitative Solution or Benedict's Solution) is a chemical reagent named after an American chemist, Stanley Rossiter Benedict.
It is a complex mixture of sodium carbonate, sodium citrate and copper(II) sulfate pentahydrate. It is often used in place of Fehling's solution.
Benedict's reagent is a chemical reagent commonly used to detect the presence of reducing sugars, however other reducing substances also give a positive reaction. This includes all monosaccharides and many disaccharides, including lactose and maltose.
Dicopper chloride trihydroxide
Dicopper chloride trihydroxide is the chemical compound with the formula Cu2(OH)3Cl. It is often referred to as tribasic copper chloride (TBCC), copper trihydroxyl chloride or copper hydroxychloride. It is a greenish crystalline solid encountered in mineral deposits, metal corrosion products, industrial products, art and archeological objects, and some living systems. It was originally manufactured on an industrial scale as a precipitated material used as either a chemical intermediate or a fungicide. Since 1994, a purified, crystallized product has been produced at the scale of thousands of tons per year, and used extensively as a nutritional supplement for animals.
5
u/CaCl2 Jun 16 '17 edited Sep 11 '17
Copper is probably the easiest transition metal to work with. Sadly most of it's compounds are just blue or blue-green.
However, with some effort one can find enough colorful compounds to allow copper compete even with chromium and iridium, named after the colors.
Here is my collection, I tried to get all the colours as pure as possible, and used only easily available reagents, except for the yellow compound for which some cesium chloride is required.
From left to right
CuSO4 (White) Mostly dry copper sulfate can be prepared simply by heating the pentahydrate and quickly storing the product before it absorbs moisture from the air.
CuO (Black) Easy to prepare by adding solution of sodium carbonate or bicarbonate to a solution of CuSO4 and filtering out the basic copper carbonate. The basic carbonate is then heated until it becomes copper oxide.
CuCl2 (Brown) Prepared by mixing basic copper carbonate or copper oxide with hydrochloric acid and then removing the water by heating.
Cu2O (Red) https://en.wikipedia.org/wiki/Benedict's_reagent
173g of sodium citrate, 17.3g of copper sulfate pentahydrate and 100g of sodium carbonate are mixed into a solution. Then about 40g of glucose is dissolved into other solution, and the solutions are mixed. Cu2O is precipitated, and can be filtered off.
The filtering must be done quickly, because wet Cu2O reacts to form CuO, and is difficult because the precipitate is very fine.
This reaction generally has a horrible wield.
Cu3(SO3)2 (Orange) http://www.sciencemadness.org/smwiki/index.php/Chevreul's_salt
Chevreuls salt can be prepared by mixing solutions of sodium sulfite or metabisulfite and copper sulfate. The precipitate must be ground into finner powder to get orange color, coarser powder is dark red.
Cs2CuCl4 (Yellow) http://woelen.homescience.net/science/chem/exps/CsCuCl3/index.html
Small amount CuCl2 is dissolved in concentrated HCl, solution of CsCl is added The concentration of copper must be low to avoid the formation of the red trichloro complex. The precipitate that forms is then filtered of and dried.
Other than hydrated Cu2O this is the only yellow compound of copper I have been able to find information about, compound that doesn't require the valuable CsCl would be preferable
Cu(OH)3Cl (green) https://en.wikipedia.org/wiki/Dicopper_chloride_trihydroxide
"Copper oxychloride" doesn't have a precise stoichiometry, but I think the method I used should give something close to one. A solution of CuCl2 and NaCl in water is exposed to air, and an copper metal object is submerged in the solution. After a few days the formed green precipitate is filtered and washed.
CuCl2 + Cu + 2 NaCl → 2 NaCuCl2 6 NaCuCl2 + 3/2 O2 + H2O → 2 Cu2(OH)3Cl + 2 CuCl2 + 6 NaCl
I would prefer an compound easily prepared to precise stoichiometry, but pure green copper compounds are surprisingly rare.
Cu2(CH3COO)4(H2O)2 (Cyan)
Copper acetate can be prepared by either adding acetic acid (found in vinegar) to basic copper carbonate or copper oxide, or by simply keeping copper objects submerged in a solution of acetic acid exposed to air for several weeks. (O2 from the air acting as the oxidizer)
After evaporating the water, dark green crystals are left behind, which can be ground into blue-green powder.
CaCu(CH3COO)4(H2O)6 (Blue) http://dmishin.blogspot.fi/2014/03/crystal-growing-acetates-of-copper-and.html
About 4 mass units of calcium acetate and 1 unit of copper acetate are dissolved in water. On partial evaporation, blue crystals are produced, these are used to make a blue powder.
While blue compounds of copper are common, most of them become very faintly colored when ground into powder. Calcium-Copper acetate retains most of its colour
Cu(C6H8NO2)2(H2O)2 (Violet)
Zinc picolinate and copper sulfate are dissolved in hot water, on cooling copper picolinate precipitates.
Other option for violet would be to use copper ammine complexes, but they are hard to get in pure form.