The oxidation of cyclohexanol by potassium dichromate(VI)

Read our standard health & safety guidance

Lesson organisation

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.

Apparatus and chemicals

Eye protection: goggles

Each group of students will need:

Petri dish, 5.5 cm size, plastic
Dropping pipettes, 2
White paper

Access to:

Cyclohexanol (Harmful) (see note 1)
Potassium dichromate(VI) solution (Toxic) in concentrated sulfuric acid (Corrosive) (see note 2)

Technical notes

Cyclohexanol (Harmful) Refer to CLEAPSS Hazcard 84C
Potassium dichromate(VI) solution (Toxic) Refer to CLEAPSS Hazcard 78 and Recipe card 53
Concentrated sulfuric acid (Corrosive) Refer to CLEAPSS Hazcard 98A

1 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!

2 Make up the acidified dichromate(VI) solution by dissolving 2 g of potassium dichromate(VI) (Oxidising, Very toxic, Dangerous for environment) in 80 cm³ of deionised or distilled water and slowly add 10 cm³ of concentrated sulfuric acid (Corrosive) to the solution, with cooling.

Procedure

HEALTH & SAFETY: Wear goggles throughout.

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.

Teaching notes

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, February 2008