Calculate the concentration of all species in a 0.160M solution of H2CO3.?

NetherCraft 0

These are the species: [H2CO3], [HCO−3], [CO2−3], [H3O+], [OH−]

1 Answer

  • H2CO3 ionizes in two steps:

    H2CO3 <—> H+ + HCO3- Ka = 4.3X10^-7

    HCO3- <—> H+ + CO32- Ka = 5.6X10^-11

    Using the first Ka:

    Ka = [H+][HCO3-]/[H2CO3] = 4.3X10^-7

    [H+] = [HCO3-] = x Then,

    x^2/0.160 = 4.3X10^-7

    x = [H+] = [HCO3-] = 2.6X10^-4 M

    A small amount of the HCO3- will ionize by the second equation, but this will be very small relative to the first ionization. So,

    5.6X10^-11 = [H+][CO32-]/[HCO3-]

    Since from the first ionization, [H+] = [HCO3], and because these will not change significantly because of the second ionization,

    [CO32-] = 5.6X10^-11

    Since [H+] = 2.6X10^-4, [OH-] = 1X10^-14 / 2.6X10^-4 = 3.8X10^-11

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