In this practical, students place a pool of acidified potassium dichromate(VI) in a Petri dish. After adding a few drops of cyclohexanol to this pool, they can see clear signs of the oxidation reaction taking place as cyclohexanone is formed
This is a quick microscale experiment to illustrate that alcohols like cyclohexanol react with acidified dichromate(VI). No attempt is made to identify the product. The experiment takes about 15 minutes.
- Eye protection (goggles)
- Petri dish, 5.5 cm size, plastic
- Dropping pipettes x2
- White paper
- Cyclohexanol (HARMFUL)
- Potassium dichromate(VI) (OXIDISING, VERY TOXIC, DANGEROUS FOR THE ENVIRONMENT), 2 g (note 4)
- Concentrated sulfuric acid (CORROSIVE)
Health, safety and technical notes
- Read our standard health and safety guidance.
- Wear eye protection (goggles) throughout.
- Cyclohexanol, C6H11OH(s) or (l) (HARMFUL) – see CLEAPSS Hazcard HC084C. Cyclohexanol has a melting point of 20–22 °C (about room temperature). If this experiment is done on a warm day the cyclohexanol is liquid and therefore easier to sample. In cold laboratories, warm the cyclohexanol first.
- Potassium dichromate(VI), K2Cr2O7(s), (OXIDISING, VERY TOXIC, DANGEROUS FOR THE ENVIRONMENT) – see CLEAPSS Hazcard HC078c. To make up the the acidified dichromate(VI) solution: dissolve 2 g of potassium dichromate(VI) in 80 cm3 of deionised or distilled water and slowly add 10 cm3 of concentrated sulfuric acid to the solution, with cooling. Label the solution TOXIC and CORROSIVE.
- Concentrated sulfuric acid, H2SO4(l), (CORROSIVE) – see CLEAPSS Hazcard HC098a.
- Place a Petri dish on a piece of white paper.
- Collect 1 cm3 of acidified potassium dichromate(VI) solution in a dropping pipette.
- Carefully, use the pipette to place ten drops of potassium dichromate(VI) in the centre of the dish.
- Use another pipette to place one drop of cyclohexanol into the pool of dichromate(VI) solution.
- Observe the pool over the next few minutes. Look for signs of reaction and of new substances being formed.
A great deal of surface activity is observed.
This is due to the differences in physical properties such as surface tension and viscosity of the product (cyclohexanone) compared to the reactant (cyclohexanol). A green colour, due to Cr3+(aq), will also be seen.
The reaction can be represented like this:
This is a resource from the Practical Chemistry project, developed by the Nuffield Foundation and the Royal Society of Chemistry. This collection of over 200 practical activities demonstrates a wide range of chemical concepts and processes. Each activity contains comprehensive information for teachers and technicians, including full technical notes and step-by-step procedures. Practical Chemistry activities accompany Practical Physics and Practical Biology.
© Nuffield Foundation and the Royal Society of Chemistry
Health and safety checked, 2016