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The Dehydration of Methylene Glycol Clock Reaction

  • Page ID
    222016
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    Chemical Concepts Demonstrated

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

    Demonstration

    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.
    formal.gif

    Observations

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

    Explanation

    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)2 --> HCHO + H2O

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

    Contributors


    The Dehydration of Methylene Glycol Clock Reaction is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts.

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