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    Diprotic Acids and Solution Equlibria

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    2. A 1.200 M solution of HCl is added to a solution containing 0.150 moles of sodium phosphate (Na3PO4). The resulting solution is then diluted to exactly 0.500 L, at which time the pH was found to be pH 8.00. What is the concentration of H2PO4- and HPO4-2 in the solution and how many mL of HCl were added?
    (For phosphoric acid, Ka1 = 7.11 × 10-3, Ka2 = 6.32 × 10-8, and Ka3 = 4.22 × 10-13)

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    Solution Preview

    quantitative analysis
    2. A 1.200 M solution of HCl is added to a solution containing 0.150 moles of sodium phosphate (Na3PO4). The resulting solution is then diluted to exactly 0.500 L, at which time the pH was found to be pH 8.00. What is the concentration of H2PO4- and HPO4-2 in the solution and how many mL of HCl were added?
    (For phosphoric acid, Ka1 = 7.11 × 10-3, Ka2 = 6.32 × 10-8, and Ka3 = 4.22 × 10-13)

    This problem looks complex at first because phosphoric acid is triprotic and has three Ka values. You can simplify it with some simple logic though. The pH is 8.00, which means any protons that dissociate easily will be removed. This means you ...

    Solution Summary

    This solution explains how to calculate the concentration of H2PO4- and HPO4-2 in a solution using the pH of the solution and Ka values of H3PO4.

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