If you like us, please share us on social media.
The latest UCD Hyperlibrary newsletter is now complete, check it out.

ChemWiki: The Dynamic Chemistry E-textbook > Development Details > Approaches > Demos > Additional Demos > The Chemistry of Chromium

Copyright (c) 2006-2014 MindTouch Inc.

This file and accompanying files are licensed under the MindTouch Master Subscription Agreement (MSA).

At any time, you shall not, directly or indirectly: (i) sublicense, resell, rent, lease, distribute, market, commercialize or otherwise transfer rights or usage to: (a) the Software, (b) any modified version or derivative work of the Software created by you or for you, or (c) MindTouch Open Source (which includes all non-supported versions of MindTouch-developed software), for any purpose including timesharing or service bureau purposes; (ii) remove or alter any copyright, trademark or proprietary notice in the Software; (iii) transfer, use or export the Software in violation of any applicable laws or regulations of any government or governmental agency; (iv) use or run on any of your hardware, or have deployed for use, any production version of MindTouch Open Source; (v) use any of the Support Services, Error corrections, Updates or Upgrades, for the MindTouch Open Source software or for any Server for which Support Services are not then purchased as provided hereunder; or (vi) reverse engineer, decompile or modify any encrypted or encoded portion of the Software.

A complete copy of the MSA is available at http://www.mindtouch.com/msa

The Chemistry of Chromium

Chemical Concepts Demonstrated

  • Cr2+, Cr 3+, and Cr (IV) oxidation states of chromium


  1. A Cr3+ solution is prepared.  Some is added to crystallizing dishes A and B.
  2. NaOH is added to the Cr3+ solution. Some is poured into dish C.
  3. More NaOH is added to the solution. Some of this is poured into dish D.
  4. 3% H2O2 is added to the rest of the solution. Some of this is pour into dish E.  HCl is added to this dish.
  • Solution E is compared with AC, and D, and HCl is added to them.
  • HCl and granulated Zn are added to dish B.
  • BaClis added to the remaining solution. HCl is then added.  Finally, Pb(NO3)2 is added.

Observations and Explanations


Dish Observation / Explanation
A + B

Violet solution of Cr(H2O)6 3+.


The color of the solution changes from violet to an "acid green".


Green Cr(OH)3 precipitates from the green solution.  More base will cause the solid to redissolve to give a green chromite Cr(OH)4 -solution. 


The green solution changes to orange as the CrO42-/Cr2O72- ions are formed.

E + HCl

After the HCl is added a series of erratic color changes are observed.  When the reaction is complete the solution is green.

AC, & D with HCl

Solution A remains violet. Solution C changes from green back to violet. Solution D produces another green solution.

B with HCl & Zn

When the solution becomes acidic, several pieces of Zn are added to the dish.  The bright blue color of Cr2+ (aq) will be visible momentarily, but air oxidation rapidly converts this to a green solution.

Original solution + BaCl2 + Pb(NO3)2

A yellow precipitate of BaCrO4 will form.  Adding HCl will redissolve the precipitate and produce an orange-yellow solution.  Pb(NO3)2 produces another yellow precipitate, PbCrO4.



You must to post a comment.
Last modified
10:30, 2 Oct 2013



(not set)
(not set)

Creative Commons License Unless otherwise noted, content in the UC Davis ChemWiki is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License. Permissions beyond the scope of this license may be available at copyright@ucdavis.edu. Questions and concerns can be directed toward Prof. Delmar Larsen (dlarsen@ucdavis.edu), Founder and Director. Terms of Use