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.

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

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