What is the pH of the buffer used in the reactions?

• A. 5.0
• B. 7.0
• C. 8.0
• D. 6.5

Answer: (B)

Buffers keep the pH steady during reactions by using a weak acid and its conjugate base to soak up added H+ or OH-. In this setup, the buffer is chosen to sit near neutral, around pH 7.0, to keep the reaction environment and the molecules involved in optimal conditions. Because many enzymes and reaction steps work best near neutral pH, the buffer is set there so small amounts of acid or base don’t push the pH far from this point.

The Henderson–Hasselbalch idea helps explain why pH 7.0 is attainable and stable: when the buffer’s acid and conjugate base are present in roughly equal amounts and the pKa is near 7, the pH remains around 7 even if a bit of acid or base is added. Phosphate buffers commonly used in such experiments have a pKa near 7, making pH 7.0 a natural, stable choice.

So the pH of the buffer used in the reactions is 7.0. Values like 5.0 or 8.0 would push the environment too acidic or too basic for the intended reaction conditions, and 6.5 would be slightly acidic, not matching the neutral conditions this setup aims for.