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 Dehydration of Methylene Glycol Clock Reaction

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 Dehydration of Methylene Glycol Clock Reaction


Chemical Concepts Demonstrated

  • Concentration effects on reaction rate
  • Addition reactions across a C=O double bond


The first set of beakers contains varying amounts of solution A and water. The second set of beakers contains varying amounts of solution B and water. One set has green indicator, the other red.

  • Solution A: Formalin (37% formaldehyde) diluted.
  • Solution B: NaHSO3, Na2SO3, and disodium EDTA dissolved in water and diluted.
  • Green Indicator: Thymolphthalein mixed withp-nitrophenol solution.
  • Red Indicator: Phenolphthalein mixed with p-nitrophenol solution.


The clock reaction shown proceeds in a linear fasion.  The beakers on the left change first while the beakers on the right change last.


The beakers change color at different rates because of the different concentrations of starting materials, particularly the materials involved in the rate-limiting step, the production of formaldehyde:

CH2(OH)--> HCHO + H2O

The faster the formaldehyde is produced, the faster the beakers change color.



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