A pool of acidified potassium dichromate(VI) is placed in a Petri dish. A few drops of cyclohexanol are added to the pool. There are clear signs of reaction as the 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
Each group of students will need:
Petri dish, 5.5 cm size, plastic
Dropping pipettes, 2
Potassium dichromate(VI) (OXIDISING, VERY TOXIC, DANGEROUS FOR THE ENVIRONMENT), 2 g (Note 1)
Concentrated sulfuric acid (CORROSIVE)
Refer to Health & Safety and Technical notes section below for additional information.
Health & Safety and Technical notes
Wear goggles throughout.
Cyclohexanol, C6H11OH(s) or (l) (HARMFUL) - see CLEAPSS Hazcard. 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.
Concentrated sulfuric acid, H2SO4(l), (CORROSIVE) - see CLEAPSS Hazcard.
1 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.
a Place a Petri dish on a piece of white paper.
b Collect 1 cm3 of acidified potassium dichromate(VI) solution in a dropping pipette.
c Carefully, use the pipette to place ten drops of potassium dichromate(VI) in the centre of the dish.
d Use another pipette to place one drop of cyclohexanol into the pool of dichromate(VI) solution.
e 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:
Health & Safety checked, 2016
This Practical Chemistry resource was developed by the Nuffield Foundation and the Royal Society of Chemistry.
© Nuffield Foundation and the Royal Society of Chemistry
Page last updated October 2015
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 .