Determine the pH of the solution.?

Determine the pH of the solution after the addition of 6.64 mL of 2.30 M hydrobromic

acid (HBr) to 507 mL of 0.631 M sodium hydrogen phosphate (Na2HPO4).

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  • 4 months ago

    Moles HPO42- = 0.507 L X 0.631 mol/L = 0.320 mol HPO42-

    Moles HBr added = 0.00664 L X 2.30 mol/L = 0.0153

    The added HBr protonates 0.0153 mol HPO42- forming 0.0153 mol H2PO4- and leaving 0.320 - 0.0153 = 0.3047 mol HPO42-

    The ionization of H2PO4- is:

    H2PO4- <--> HPO42- + H_

    Ka = [H+][HPO42-]/[H2PO4-] =6.23x10^-8

    6.23X10^-8 = [H+](0.0153) / (0.3047)

    [H+] = 1.24X10^-6

    pH = -log (1.24X10^-6) = 5.91

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