Chemistry of metals and their ions

Most metals have a rather interesting and colorful aqueous chemistry. Especially the transition metals form numerous interesting complexes and have interesting redox chemistry. Note, some experiments are mentioned two times on this page, because they both demonstrate redox properties of a certain metal and coordination chemistry of that metal in the same experiment. The lists below are ordered alphabetically, based on the chemical symbol of the element

List of fully worked out experiments, redox chemistry:

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Ag: Preparation of a high explosive . Silver ions react with acetylene gas, even at low pH (around 0), giving an off-white precipitate of impure silver acetylide. This precipitate is highly explosive, when it is dry.

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Cr: Divalent chromium, extreme sensitivity to aerial oxidation. From high purity chromium metal and hydrochloric acid a solution is made with chromium(II) ions as the main species in solution. It is shown that these chromium(II) ions are oxidized by oxygen from air very easily.

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Cr: Reduction of dichromate - different colors of reaction product. When orange dichromate is reduced, then the resulting chromium(III) ions almost always are coordinated to something in solution. It is shown that the color of the reduction product of dichromate strongly depends on which reductor is used.

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Cu: Redox chemistry and coordination chemistry of copper(II) and sulfite at different pH. Sulfite ion and copper(II) ion can react in different ways. Coordination complexes can be formed, but they also can interact in a redox reaction. Quite remarkable compounds can be formed in these reactions. The pH of the solutions has great influence on the actual reactions occurring.

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Cu: Unexpected colors with copper(II) ions in the presence of halogenide at high concentration. Copper(II) ions form intensely colored red/purple complex ions with bromide at low pH and high concentration.

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Cu: Copper redox and coordination chemistry. The element copper has a very rich aqueous chemistry, although it only has two oxidation states, which can be stabilized in aqueous solution. The combination of redox chemistry and extensive coordination chemistry makes this element very interesting.

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Cu: Formation of a complex of copper in oxidation state +3. Copper can be oxidized to the +3 oxidation state if it is coordinated to orthoperiodate ions. This complex is stable in aqueous solution, and it has a deep red color, which is very special for copper compounds.

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Cu, Zn: Zinc plating of copper coin. This is a classical experiment, but still, its explanation is not straightforward. In this experiment, a copper coin is plated with a thin zinc layer from a solution of alkaline zincate. This zinc plating is not done by means of electrolysis.

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Cu, Al: Influence of copper ions on reactivity of aluminium. Another interesting property of the element copper in aqueous solution. Copper ions, together with chloride ions, work extremely corrosively on aluminium. When alone, copper ion, or chloride ion, hardly affects aluminium, but when working together, the aluminium is eaten in a few minutes.

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Fe: Cyanotype, the dawn of photography. One of the oldest processes for making permanent images is demonstrated in this experiment. Using simple chemicals and tools an image (a blue print) is made from flat objects like leaves. The word 'blue print' originally stems from this process.

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Hg: Multiple compounds with a beautiful color, which depends on temperature . Mercury iodide and some derived compounds have beautiful colors, but even more surprising is the reversible change of color when the temperature is changed.

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Ir: Iridium -- goddess of the rainbow. One of the most colorful elements in its aqueous chemistry. All colors from the rainbow can be obtained from just one iridium compound (sold as "iridium(IV) chloride") as starting point, using common reagents only.

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Mn: Properties of manganese(II) ion at very high concentration. In this experiment it is shown that manganese(II) ions in aqueous solution are pale pink, also at very high concentration and in the presence of concentrated hydrochloric acid. This is different from what some textbooks claim, which mention the existence of green complexes.

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Mn: Liquid from hell -- fire on first contact . An organic solvent like acetone or ethanol inflames at once, when brought in contact with a mix of potassium permanganate and concentrated sulphuric acid.

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Mn: Chemical chameleon with permanganate. A classical but appealing experiment. A dilute solution of potassium permanganate is reduced by an alkaline sugar solution. The solution goes through many different colors while the permanganate ion is reduced.

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Mn, Fe: Oxidizing power of bleach. Bleach is a remarkably strong oxidizer. It is capable of oxidizing iron to its +6 oxidation state, and manganese to its +7 oxidation stage.

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Mn, Ce: Oscillating reaction. This is the classical Belousov-Zhabotinsky reaction, an oscillating reaction. Although it is well-known, it remains one of the most beautiful and remarkable demonstrations. The reaction, shown in this page, is based on the oxidation of malonic acid with bromate ions, with manganese(II/III) or cerium(III/IV) as a catalyst.

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Mo: Colorful compounds of molybdenum. This experiment demonstrates the very interesting and colorful, but also rather incompletely understood chemistry of molybdenum in aqueous solution. All colors of the rainbow can be produced with molybdenum in aqueous solution.

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Nb: Coloration of metallic niobium by means of electrolysis . This is really remarkable. When niobium is used as anode in an electrolysis setup, then the metal is covered by a very thin oxide layer, which can have bright colors. This is a simply, but very surprising experiment.

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Ni: Nickel in oxidation state +1. In this experiment, nickel is brought to the remarkable oxidation state +1, which is very special for this metal, which usually is in oxidation state +2 in aqueous solutions.

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Ni, Ag: Very high oxidation states with persulfate. Persulfate (better: peroxodisulfate) is a strong oxidizer, capable of oxidizing nickel to +3 or +4 oxidation state in alkaline solution, and capable of oxidizing silver to +3 oxidation state in acidic solution.

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Re: Rhenium chemistry. A set of experiments, which shows relevant parts of aqueous chemistry of this element. Rhenium metal is dissolved in nitric acid, giving a solution of perrhenic acid, and this solution in turn is used in a few redox chemistry experiments.

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Ru: Ruthenium chemistry. Ruthenium metal is dissolved in hot bleach, giving deep red ruthenate(VI) in solution. This solution, in turn is used for a large set of redox chemistry experiments. The chemistry of the element ruthenium is very rich and colorful.

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Pb: Electrolysis of a solution of lead nitrate, formation of metal crystals. This is a demonstration of the formation of pure lead metal from a solution of lead nitrate. The metal is deposited in the form of beautiful glittering crystals.

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Ti: Aqueous chemistry of titanium. A solution of a titanium(III) species is made by dissolving some titanium in hydrochloric acid, and this solution serves as a basis for further experiments, exploiting the redox chemistry of this element.

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V: Colorful oxidation states of vanadium. Vanadium can be in any of the oxidation states +2, +3, +4 and +5 in aqueous solution. Starting from vanadium pentoxide (easy to obtain from pottery suppliers) all oxidation states are prepared in this experiment.

 

List of fully worked out experiments, coordination chemistry:

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Bi: Bismuth complexes with halogens. The metal bismuth in the +3 oxidation states forms deeply colored precipitates and complexes, most notably with iodide ion.

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Co, Hg: Colorful and really remarkable chemistry. In this experiment some amazing color changes can be observed. A beautiful bright red solution is prepared from which slowly very bright blue crystals are precipitated. Beautiful contrasts are produced in this experiment.

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Cr: Volatile compounds of chromium - another colored gas . In this experiment, two volatile compounds of chromium are made from potassium dichromate, sodium fluoride, sodium chloride and concentrated sulphuric acid. One of them produces an orange/brown vapor, which very much resembles bromine vapor.

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Cr: More fun with volatile chromium - chromyl chloride . This is a really beautiful experiment. Chromyl chloride vapor is poured on a very dilute acidified solution of hydrogen peroxide. On the surface, the chromyl chloride vapor is absorbed by the liquid and heavy streams of a peroxo complex of chromium are formed, which produce nice deep blue patterns in the liquid.

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Cr: Reduction of dichromate - different colors of reaction product. When orange dichromate is reduced, then the resulting chromium(III) ions almost always are coordinated to something in solution. It is shown that the color of the reduction product of dichromate strongly depends on which reductor is used.

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Cr: Synthesis and properties of polychromates. Hexavalent chromium forms the well-known chromates and dichromates, but at very low pH and high concentration, the much more obscure trichromates can be made. These trichromates can be prepared remarkably easily and they keep remarkably well in the case of the potassium salt and ammonium salt.

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Cr: Chromium(III) coordination chemistry. This is a simple experiment which shows that by simple boiling an aqueous solution of chromium(III) ions forms a complex with anions present in solution by means of ligand exchange. The experiment demonstrates this effect with sulfate anions, but the effect also exists for many other anions. The ligand exchange is accompanied with a strong change of color.

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Cr: Synthesis of potassium tetraperoxo chromate(V) . A detailed description (recipe) for making the energetic compound K3CrO8.

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Cr: Synthesis of triammine diperoxo chromium(IV). This is a description of how to make another very energetic chromium peroxo compound. Also some properties of the prepared compound are shown.

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Cr: Synthesis of potassium chlorochromate(VI). The compound potassium chlorochromate(VI) can easily be prepared. In this webpage it is demonstrated how this can be done with acceptable yield. The resulting chemical compound can be kept indefinitely and may be interesting for further experiments.

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Cr: Chromium peroxo pyridine complex and its properties. A dark blue insoluble peroxo complex of chromium is made, and some further experiments are performed with this compound. This experiments shows some remarkable color combinations and the peroxo complex is remarkably stable under reducing conditions.

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Cu: Redox chemistry and coordination chemistry of copper(II) and sulfite at different pH. Sulfite ion and copper(II) ion can react in different ways. Coordination complexes can be formed, but they also can interact in a redox reaction. Quite remarkable compounds can be formed in these reactions. The pH of the solutions has great influence on the actual reactions occurring.

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Cu: Copper redox and coordination chemistry. The element copper has a very rich aqueous chemistry, although it only has two oxidation states, which can be stabilized in aqueous solution. The combination of redox chemistry and extensive coordination chemistry makes this elements very interesting.

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Cu: A fluorescent compound of copper. This is an experiment, which is not well known. The effect demonstrated in this experiment, however, is striking and it is a shame that so few people know it. A white compound is prepared which exhibits beautiful bright yellow fluorescence under black-light.

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Cu: Complex chemistry of copper in combination with thiocyanate. Copper exhibits an interesting chemistry when it is combined with thiocyanate ion. An intricate interplay of coordination chemistry and redox chemistry leads to many surprising compounds with nice colors.

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Cu: Inductive effect demonstrated by properties of copper acetate and related complexes. In this experiment, copper acetate, but also several substituted and related compounds are prepared. Their properties are compared and a good explanation can be given by the inductive effect.

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Cu, Al: Influence of copper ions on reactivity of aluminium. Another interesting property of the element copper in aqueous solution. Copper ions, together with chloride ions, work extremely corrosively on aluminium. When alone, copper ion, or chloride ion, hardly affects aluminium, but when working together, the aluminium is eaten in a few minutes.

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Cu, Cs: Red complex of copper and chloride. A really beautiful and remarkable solid chloro complex of copper is produced. The complex has copper in oxidation state +2 and has a bright red color, which is very special for copper in oxidation state +2. A few other similar complexes of other metals are described as well through this webpage.

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Hg: Mercury iodide, change of color and complex formation. Mercury iodide is made from mercury chloride and potassium iodide. When the precipitate of mercury(II)iodide is made, then at first it is yellow, but it quickly turns bright orange/red. When excess iodide is added, then the precipitate redissolves again, due to complex formation.

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Ir: Iridium -- goddess of the rainbow. One of the most colorful elements in its aqueous chemistry. All colors from the rainbow can be obtained from just one iridium compound (sold as "iridium(IV) chloride") as starting point, using common reagents only.

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K: Synthesis of potassium from magnesium and potassium hydroxide . This is an interesting and also remarkable synthesis of potassium, which can be carried out at very mild conditions and which only requires reactants which are not really hard to obtain.

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Mn: A volatile compound of manganese and corrosion of glass . In this experiment, a mix of potassium permanganate and sodium fluoride is treated with concentrated sulphuric acid. A green volatile compound is formed and the glass is heavily corroded. A dangerous, but also appealing experiment.

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Re: Rhenium chemistry. A set of experiments, which shows relevant parts of aqueous chemistry of this element. Rhenium metal is dissolved in nitric acid, giving a solution of perrhenic acid, and this solution in turn is used in a few redox chemistry experiments.

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Ru: Ruthenium chemistry. Ruthenium metal is dissolved in hot bleach, giving deep red ruthenate(VI) in solution. This solution, in turn is used for a large set of redox chemistry experiments. The chemistry of the element ruthenium is very rich and colorful.

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Sn: Tin chloride and iodide. Tin(II) ions and iodide ions give rise to formation of a yellow precipitate of tin(II) iodide, but at high concentrations of iodide, a nice orange/red compound is formed. No explanation can be given though. When hydrochloric acid is added, then the precipitate redissolves and a colorless solution is obtained, due to complex formation.

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Sn: Preparation of tin(IV) iodide, a volatile covalent compound. Tin and iodine are made to react in a suitable solvent for iodine. Under these conditions the interesting compound tin(IV) iodide is formed, which can easily be isolated. Some properties of this compound are shown.

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Ti: Aqueous chemistry of titanium. Some titanium is dissolved in hydrochloric acid, giving a deep blue/violet solution. This solution is used as a starting point for a range of experiments, demonstrating interesting redox and coordination chemistry of this metal.

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V: Isolation of peroxo complex of vanadium. In this experiment a peroxo complex of vanadium is made and this complex is isolated as a dry powdered solid. The isolated compound is stable on storage and has energetic properties. A mix with red phosphorus deflagrates on ignition.

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*: Peroxo complexes of transition metals in high oxidation states. This is a large set of experiments in which compounds of transition metals are treated with hydrogen peroxide. Many transition metals form beautiful peroxo complexes, sometimes of remarkable nature.

 

List of fully worked out experiments, miscellaneous:

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Ca: Explanation of what happens when hard water is heated. This experiment is a nice and safe demonstration and explanation of what happens when hard water is boiled.

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Cr: Nice dendritic crystal structures. A solution of ammonium chromate is allowed to evaporate to dryness. The solution looses ammonia, and hence ammonium dichromate is formed. Very interesting fractal patterns are produced, with the yellow ammonium chromate having a rather different structure than the orange ammonium dichromate.

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Fe: Preparation of a compound with magnetic properties. Only very mundane chemicals and equipment are needed in this simple, but funny experiment. A precipitate of magnetite is prepared and the precipitate is drawn through a test tube by moving a strong magnet around the test tube.

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Nd: Narrow absorption bands of neodymium ions. In this experiment it is shown that the appearance of a solution of neodymium salts strongly depends on the type of light source, used for viewing the solution. The effect is really striking!

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Pb: "Golden" crystals of lead iodide. A precipitate of lead iodide is dissolved in boiling water. On cooling down, many beautiful glittering gold-like crystals are formed, which slowly settle on the bottom.

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Pb: Lead iodide: color depending on temperature and decomposition. Some lead iodide is heated. This gives rise to a change of color from bright yellow to deep red. On cooling down, the color reverses to bright yellow. When the heating is much stronger, then the lead iodide decomposes.

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Pr: Praseodymium chemistry. Some praseodymium metal is dissolved in hydrochloric acid, and some solid praseodymium chloride is made. The color of the solution deepens when concentrated hydrochloric acid is used.

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V: Volatile vanadium compound, leading to green gas and red smoke. Phosphorus pentachloride is capable of chlorinating vanadium pentoxide and the resulting compound is volatile and gives rise to formation of interesting green vapor and red smoke when it is heated.

 

Tidbits and raw material with some nice results and ideas:

  • Colorful precipitates with periodate ion. In this experiment, many solutions of metal salts are added to a solution of sodium metaperiodate. Many precipitates, made in this way, have highly unexpected colors.
  • Beautiful effects with potassium dichromate and hydrogen peroxide. Small crystals of potassium dichromate are sprinkled on the surface of a very dilute acidified solution of hydrogen peroxide. The crystals remain floating on the surface, slowly releasing dichromate in solution. This reacts with the hydrogen peroxide and this gives beautiful effects.
  • Explosive properties of peroxo chromates. A recipe is given for making potassium tetraperoxochromate (V) and it is shown how this compound explodes on heating.
  • Nice effects in petri dish with yellow precipitate. A small amount of potassium iodide is put in a petri dish, filled with water, and a small amount of lead nitrate is put in the petri dish at the other side. The compounds dissolve and slowly diffuse towards each other. When they reach each other, a yellow precipitate of lead(II)iodide is formed. The slow diffusion results in a nice effect.
  • Formation of a silver mirror. Ammoniacal silver nitrate is mixed with a solution of glycerol or glucose and the test tube then is slightly heated. This results in a shiny silver mirror on the inside of the test tube.
  • Anhydrous chromium(III) sulfate from concentrated sulphuric acid? In this experiment, it is shown that a precipitate is formed from concentrated sulphuric acid, by dissolving chromium compounds and then strongly heating. It is expected that this precipitate is anhydrous, highly insoluble, chromium(III) sulfate.
  • Preparation of anhydrous cobalt(II) chloride. Anhydrous cobalt(II) chloride is prepared from the hydrated salt by very careful heating. It is possible to make the anhydrous salt, also without an atmosphere of HCl, but one has to work carefully.
  • Thionyl chloride and potassium dichromate. Potassium dichromate is dissolved in thionyl chloride and some sulphuric acid is added. This gives some chromyl chloride and a deep red solution. When this mix is added to water, then a violent, but rather spectacular and in some sense beautiful reaction starts, giving a cloud of HCl and chromyl chloride.
  • Sodium skirting over water surface. This is a very simple experiment. Some sodium is thrown in a tank, filled with water, in which some pH indicator is dissolved. This results in a nice visual effect.

 

 

   

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