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Science project on chromium electroplating


I am a Grade 11 student and I have to do a Culminating Performance Task (C.P.T.) about chromium electroplating. The exact question that I must answer is as follows: What chemicals are found in the bath of a chromium electroplating vat? Describe the chemical processes involved in preparing a bumper for re-chroming and in doing the re-chroming.

I'm not sure if you will be able to help me, but if you could it would be greatly appreciated. I have done a lot of research but only come up with minimal information. I also need to have a visual or experiment of some sort, so if it wouldn't be too much trouble could you offer some suggestions. I know I won't be able to use actual chromium in class, but if I used a simulation of some sort that would be great. Thank you very much!:)

Rosella G
student - Woodbridge, Ontario, Canada

A. Hi Rosella. For a short general discussion, please see our "Intro to Chrome Plating". Chromium plating baths contain about 33 oz/gal of chromic acid H2CrO4, with the balance mostly water. You can work out the oxidation state of the chromium in that compound from the known valences of hydrogen and oxygen. The oxidation state of the electrodeposited chrome metal is zero. There are also catalysts in the chrome plating solution; the best known and most common catalyst formulation is 1 part H2SO4 per 100 parts H2CrO4.

Bumpers are always nickel plated before they are chrome plated, and sometimes copper plated before that. See if your library can get you access to old issues of Products Finishing, Metal Finishing, or Plating & Surface Finishing magazine; if so, searching them will find you plant writeups of actual bumper plating shops.

The best plating demo is to plate zinc (which is a grayish to chrome-like color) onto copper pennies as described at

Lucks and regards,

Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey

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