Chemistry - Equilibrium

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You have an unknown concentration of ammonia. When you add 15.0mL of a 0.400 M HCl solution to 50.0mL of the ammonia solution, the pH of the solution becomes 8.75. What is the concentration of the original ammonia solution? [Kb (NH3) = 1.8 x 10^-5]

  • Chemistry - Equilibrium -

    Use the Henderson-Hasselbalch equation.
    15.0 mL x 0.400M = 6.0 millimols HCl
    50 mL x ?M NH3 = ??

    ...........NH3 + HCl ==> NH4^ + Cl^-
    ...........x.......0.......0
    add.............6.0.........
    change...-6.0..-6.0.......6.0
    equil....x-6.0...0.........6.0
    pH = pKa + log (base)/(acid)
    8.75 = 9.26 + log(x-6)/(6)
    Solve for x = millimols NH3
    M NH3 = millimols/50 mL

  • Chemistry - Equilibrium -

    .1132 M @ equilibrium

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