Projection Experiment: Oxidation of Hydroquinone by Ag Ions

Demonstration of Microscale Projection Experiments - Chemistry en miniature

Oxidation of Hydroquinone by Ag Ions

Peter Keusch

German version

Chemicals:
0.05 M aqueous hydroquinone solution (0.551 g / 100 mL H₂O)
0.1 M aqueous AgNO₃ solution (1.698 g / 100 mL H₂O)

A freshly prepared hydroquinone solution should be used.

Hazards and safety precautions:

Hydroquinone is probable carcinogen. Toxic. Severe skin irritant. Harmful by inhalation and ingestion. May cause sensitization. Eye and respiratory irritant.

Safety glasses, protective gloves. Effective ventilation. The hydroquinone solution should be prepared in a fume hood!

Experimental procedure:

Using a Pasteur pipette only few drops of 0.1 M AgNO₃ are added to a test tube containing a solution of hydroquinone.

Test tube 1 1 mL of AgNO₃ solution
Test tube 2 1 mL of hydroquinone solution some drops of AgNO₃ solution

Results:

The solution becomes turbid immediately (Photo 1). Finally gray "schlieren" turn black in color (Photo 2).

Photo 1

Photo 2

Discussion:

· Hydroquinone is oxidized by the strong oxidizing agent Ag⁺ to p-benzoquinone. Metallic silver is precipitated in fine particles.

· This reaction is used in the black-and-white photography. The developer solution is comprised of a combination of chemicals, consisting of alkali and metol (p-methylaminophenol sulfate) or hydroquinone mixed with water. Hydroquinone acts on the film by reducing the exposed silver bromide crystals to black metallic silver.

Reference:
Demonstration Experiment on Video Redox system Hydroquinone / Benzoquinone

General experimental instructions and index of experiments