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Student Question

Secondary II • 2yr.

What constitutes and doesn’t constitute a color change in a chemical reaction?


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Explanations (1)

  • Explanation from Alloprof

    Explanation from Alloprof

    This Explanation was submitted by a member of the Alloprof team.

    Team Alloprof • 2yr.

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    A change of color during a chemical reaction is a clue that a chemical change has occurred.

    For a color change to be considered significant (to such an extent as to suggest a chemical change), it must meet the following two criteria:

    • The combination of the colors of the two reagents must not be that of the product. For example, if one mixed magenta paint with yellow paint and obtained orange, one could not necessarily conclude that there had been a chemical change, since magenta combined with yellow gives an orange color. However, if one had mixed a magenta reactant with a yellow reactant and obtained a greenish color, a chemical change may have occurred, since yellow and magenta don’t give green when combined.

    • The change of color must not be a slight change of hue or tone. For example, mixing a red solution with a clear solution may result in a dilute pink solution, but this only indicates a dilution, and not necessarily a real chemical change.

    This is not to say that chemical changes can’t occur when a solution only slightly changes color, or when a solution is formed by the union of reactants whose combined colors are the colors of the final solution. It just means that this type of color change is not reliable enough to be a characteristic sign of chemical changes.

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