Chem 111

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Why would NaOH solution need to be added when preparing the K2CrO4 stock solution

  • Chem 111 -

    Because the second ionization of H2CrO4 is not 100%; i.e., it is a weak acid.
    H2CrO4 ==> H^+ + HCrO4^-
    HCrO4^- ==> H^+ + CrO^2-
    k1 = 100%
    k2 = about 5E-7 in my set of tables.
    When CrO4^2- is added to water it hydrolyzes to form an equilibrium between CrO4^2- and HCrO4^-. Adding base keeps essentially 100% or the Cr in the form of CrO4^2-.

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