chemistry - quant.

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I need help calculating the pH of a solution that is .0400M Na3AsO4

I was trying to calculate the pH with [H30+]=sqrt(ka1*ka2)

What is the correct way to calculate this?
Thankyou

  • chemistry - quant. -

    What you have finds the pH for a solution of NaH2AsO4.
    For a solution of Na3AsO4,
    write the hydrolysis equation.
    AsO4^-3 + HOH ==> HAsO4^-2 + OH^-
    Kb = Kw/K3 = (OH^-)^2/(AsO4^-3)
    You know Kw, K3 (look up K3 for H3AsO4), and (AsO4^-3= 0.0400 M)
    This gives (OH^-). Convert to pOH and then to pH. Post your work if you get stuck.

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