Chromate Dichromate Equilibrium

 

 

Hazards: 

Chromium salts are considered carcinogenic.  Use care.

6M HCl and 6M NaOH are corrosive and toxic.  Avoid contact.

Chemicals and Solutions: 

Potassium chromate (K2CrO4) solution 0.1M

Potassium dichromate (K2Cr2O7) solution 0.1M

6M hydrochloric acid

6M Sodium hydroxide

Materials: 

2 ungraduated cylinders

Procedure: 

Add some 0.1M K2CrO4 to one cylinder and then add 6M HCl. The solution will shift from yellow to orange.

To the second cylinder add some 0.1M K2Cr2O7 and then add 6M NaOH.  The solution will shift from orange to yellow.

Hint: 

This demonstration can also be done on an overhead projector using petri dishes instead of cylinder.

Discussion: 

The Reaction:

2CrO42-(aq) + 2H+(aq) ---> Cr2O72-(aq) + H2O

yellow                        orange

 

To schedule a demonstration, please send an email to the demonstration lab.

 

Contact:

Eric Camp

Lecture Demonstration Technician

Bagley Hall 171

(206) 543-1606

ericcamp@uw.edu

 

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