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March 29, 2017

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Calculate the pH of 0.215 M carbonic acid (H2CO3). (HINT: do NOT worry about the second H+ in this acid!)

How would I solve this?

  • Chemistry - ,

    Carbonic acid is a weak acid.

    H2CO3 + H2O---> HCO3 +H30+

    Initial H2CO3=0.215 M
    Final H2CO3=0.215-x
    Initial HCO3=0
    Final HCO3= x
    Initial H30+=0
    Final H30+= x

    ka=4.3 x 10-7=[H30+][HCO3]/H2CO3]

    4.3 x 10-7=[x][x]/0.215M-x]

    5% rule allows for ignoring -x

    4.3 x 10-7=[x][x]/0.215M]
    sqrt(4.3 x 10-7 *0.215M])=x

    x=H3O+

    pH=-log[H3O+]

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