What is the change in pH after addition of 10.0 mL of 1.0 M aqueous sodium hydroxide to 90.0 mL of an aqueous 1.0 M NH₃/1.0 M NH₄⁺ buffer? (K_b for ammonia is 1.8 × 10^-5) A)1.0 pH unit B)0.1 pH unit C)0.01 pH unit D)0.001 pH unit E)zero

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Quizplus · Accepted Answer

The buffer system in question is an ammonia/ammonium chloride (NH3/NH4Cl) buffer. The addition of a strong base (NaOH) to this buffer system will slightly shift the equilibrium towards the production of more NH3, but due to the buffering capacity, the change in pH will be minimal. The Henderson-Hasselbalch equation can be used to calculate the exact change, but without doing the calculations, it's known that buffers are designed to resist changes in pH, so the change will be small, but not zero, making 0.1 pH unit a reasonable estimate.

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