The Amateur Chemist

Synthesis of Potassium Chlorochromate


In this experiment, I make an interesting chromium compound that can be prepared fairly easily. Potassium chlorochromate is soluble in multiple organic solvents which make for some interesting experiments. This synthesis only requires potassium dichromate and hydrochloric acid, but it is still quite dangerous. Both potassium dichromate and potassium chlorochromate are toxic and easily form dust. KCrO3Cl is a very interesting compound.



K2Cr2O7 + 2HCl  2KCrO3Cl + H2O




Ingredients

1 gram of potassium dichromate

6 ml 25% HCl (5 ml 30% + 1 ml water)


Preperation


Put 1 gram of potassium dichromate in a test tube. Make sure the dichroamte is crushed up into pieces less than 1 mm. Take the 6 ml of 25% hydrochloric acid and pour it into the test tube with the potassium dichromate. It will take some time for all of the dichromate to fully dissolve. 


Carefully heat the test tube with a small flame or hot plate, stirring constantly. Make sure you do not heat too strongly and make sure no hot spots are formed under the solid potassium dichromate crust. Break up the dichromate crust and stir with the stirring rod. If the solution becomes too hot or hot spots form, thr chromium oxidizes the acid and the experiment has failed.


As soon as the potassium dichromate has fully dissolved, stop heating. The liquid should have a deep red color. It should definately not be super dark or even green. Set the test tube aside and let it cool down. You can put it into an ice bath or the freezer to increase the yield even more. Crystals will form and fall to the bottom of the test tube. After 15 minutes in the ice bath, take the test tube out and decant all of the liquid.


When filtering to get rid of the extra liquid, make sure not to use any paper or fabric filters. The best way is to use a sintered glass filter, drain all of the liquid out, and press the bottom of the filter with paper towels to get rid of extra liquid. Scrape the solid out and put it on a watch glass to dry. It will form flaky, light orange crystals. The result should be just about 0.5 grams.


The paper that you used to squeeze the excess liquid out of the crystals will slowly reduce the chromium and turn green after about 15 minutes. By then it will be sage to dispose of.