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11 May, 21:28

The ammonia/ammonium buffer system is used to optimize polymerase chain reactions (PCR) used in DNA studies. The equilibrium for this buffer can be written as NH4 + (aq) ? H + (aq) + NH3 (aq) Calculate the pH of a buffer that contains 0.045 M ammonium chloride and 0.095 M ammonia. The Ka of ammonium is 5.6*10?10. Express your answer using two decimal places.

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  1. 11 May, 21:54
    0
    The pH of the buffer system is 9.57

    Explanation:

    Step 1: Data given

    Molarity of NH4Cl = 0.045 M

    Molarity of NH3 = 0.095 M

    Ka of ammonium is 5.6*10^-10

    pKa = - log (5.6 * 10^-10) = 9.25

    Step 2: The balanced equation

    NH4 + (aq) ⇆ H + (aq) + NH3 (aq)

    Step 3: Calculate the pH of the buffer

    pH = pKa + log[NH3]/[NH4+]

    pH = 9.25 + log (0.095/0.045)

    pH = 9.57

    The pH of the buffer system is 9.57
  2. 11 May, 21:56
    0
    9.57

    Explanation:

    pH = pKa + log ([NH3]/[NH4CL])

    pKa = - logKa = - log (5.6*10^-10) = 9.25

    [NH3] = 0.095M

    [NH4CL] = 0.045M

    pH = 9.25 + log (0.095/0.045) = 9.25 + log2.11 = 9.25 + 0.32 = 9.57
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