The metal cadmium resembles the metal zinc quite a lot, both in appearance and in chemical properties. The metal is somewhat less electropositive than zinc, but it also tarnishes in air and also dissolves easily in non-oxidizing acids with formation of hydrogen.

Compounds of cadmium have a somewhat more covalent character than the corresponding compounds of zinc. E.g. compounds like cadmium bromide and cadmium iodide hardly dissociate into their ions, when dissolved in water.

An important difference between zinc and cadmium is that the latter is much more toxic to humans and to the environment. The use of cadmium and its compounds is banned in most industrialized countries, due to its toxicity.

Cadmium can be purchased on eBay frequently for a very reasonable price and at very high purity. For the home chemist, cadmium is not the first element to play with, but it has some interesting properties, especially in its potential to form beautifully colored precipitates.

In its compounds, cadmium has the +2 oxidation state, just like zinc. The free cadmium ion is colorless. Cadmium ion has a strong tendency to hydrolyse. Compounds of cadmium resemble the similar compounds of zinc, but they usually have a more covalent character. Some compounds of cadmium, available to the public are the following:

  • cadmium sulfide, CdS
  • cadmium selenide, CdSe
  • cadmium bromide, CdBr2
  • cadmium iodide, CdI2

Although cadmium compounds are available for the public, it is better not to experiment with them. They only have limited interesting properties. Combining this with the toxicity of cadmium, it is best not to play with them. For experimenting one can better start with the metal itself and prepare solutions, containing cadmium ions, by means of dissolving some of the metal in a dilute mineral acid.

If one really wants to experiment with cadmium compounds, then the best option is to use cadmium sulfide. This is a bright yellow compound, available from art and paint shops as the pigment cadmium yellow. Sometimes more 'cadmium yellow' pigments are offered. The brightest yellow compound should be used. Lighter compounds frequently are cadmium sulfide, mixed with zinc sulfide or with barium sulfate. When the bright yellow compound is added to dilute hydrochloric acid (approximately 10% HCl), then it dissolves, while producing hydrogen sulfide. When the liquid is heated somewhat, then the hydrogen sulfide is driven off and the cadmium ions remain in solution. This must be done outside, due to toxicity of hydrogen sulfide. The remaining solution is clear and colorless. When the hydrogen sulfide is not driven off very well, then on dilution, the liquid will become yellow and turbid again, due to back-formation of cadmium sulfide from the free cadmium ions and remaining hydrogen sulfide.

The compound cadmium selenide is a dark red compound, available from art and paint shops as the pigment 'cadmium red'. Again, there are several shades of red, ranging from orange-red to dark red/brown. The darkest available cadmium red should be taken. Cadmium reds have composition CdSxSe1-x, with 0 < x < 1. The larger x, the lighter the color. For home chemistry experiments, where one is interested in cadmium chemistry, the use of cadmium red is strongly advised against. In order to release the cadmium, the selenium has to be driven off as hydrogen selenide. Do not do that at home, not even outside, see page on selenium.

Cadmium bromide is a white to slightly yellow powder. It is soluble in water. Solutions of this are only partially dissociated into cadmium and bromide ions. When one wants to experiment with cadmium salts, then this is not the compound to start with. The presence of the bromide counter-ion may strongly interfere with many experiments. Cadmium bromide is available from a few photography raw chemical suppliers. It is quite expensive.

Cadmium iodide also is a white to slightly yellow powder. It resembles cadmium bromide quite a lot. It is even less ionized than cadmium bromide, when it is dissolved in water.  When one wants to experiment with cadmium salts, then again this is not the compound to start with. The presence of the iodide counter-ion even interferes more strongly than the presence of bromide ion in many experiments. Cadmium iodide also is available from a few photography raw chemical suppliers. It also is quite expensive.


Compounds of cadmium are toxic. When experiments are conducted with cadmium, cadmium sulfide or solutions prepared with this, be sure not to breathe any fine particles or droplets of the (heated) solutions. Cadmium waste definitely must be brought to a proper waste processing facility.




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