Potassium dichromate (K2Cr2O7) is an inorganic chemical reagent that is normally used as an oxidizer in industrial and laboratory applications. It is used to oxidize alcohols and convert primary alcohols to aldehydes and sometimes carboxylic acids. Unlike similar processes that use permanganate, only carboxylic acids result. The secondary alcohols are converted into ketones and no further oxidation is required. Potassium dichromate does not oxidize tertiary alcohols. The chemical is potentially harmful to human health and is a crystalline ionic solid that is a bright, red-orange color.
Potassium Dichromate Uses
When the chemical is used in an aqueous solution, the color it changes to determines whether there is a ketone or aldehyde present. When aldehydes are in the mixture, the color will change from orange to green. Keytones will not result in a color change since they can no longer be oxidized, and the mixture will remain orange.
Potassium dichromate is also used in cleaning solutions. Similar to other compounds made from chromium VI (sodium dichromate and chromium trioxide), it can be used to help prepare chromic acid, which is used for etching materials and cleaning glassware. The chemical is also used in cement to help improve its texture and density as well as to retard the setting of concrete mixture. Other industries use the substance to tan leather and screen print.
How Postassium Dichromate is Used to Determine Ethanol Concentration
Potassium dichromate can be used to determine the concentration of ethanol in a sample. Acidified potassium dichromate is used in titration to accomplish this. When accomplished, all of the ethanol is oxidized to acetic acid and the excess dichromate is determined by titration against sodium thiosulfate. In order to determine the amount of ethanol present in the substance, the excess dichromate is subtracted from the original amount of ethanol present in the substance. This aspect of the substance is used in police breathalyzer tests as it changes from yellow to green in the presence of alcohol. The greater the level of alcohol in a person’s breath, the greater the color change will be.
Potassium Dichromate in Silver Testing and Wood Treatment
Potassium dichromate is also used to test silver. When the substance is dissolved in a nitric acid solution (also called Schwerter’s solution) it can be used to determine silver purity. If the metal or substance is pure, the solution will turn a bright red. If it is sterling silver, the color will change to dark red, and most silver coins will turn the liquid brown. If the substance being tested is 50% silver, the color will change to green. When used to treat wood, potassium dichromate changes the wood’s color and grain to a rich, deep appearance and even has this effect on mahogany.