A Buffer in Action

For illustration, we choose a widely used buffer called tris.  

BH Cr is dissolved in water, it dissociates completely to and Cl . To find the pH of a known mixture of B and BH, simply plug their concentrations into the Henderson-Hasselbalch equation. 

Don t panic over significant figures in pH. For consistency, we are almost always going to express pH to the 0.01 place. 

Assuming that what we mixed stays in the same form, we insert the concentrations into the Henderson-Hasselbalch equation to find the pH  

Test Yourself Find the pH if we had mixed 4.67 g of tris with 12.43 g of tris hydrochloride. (Answer 7.76 makes sense—more acid and less base give a lower pH.) 

---

Fig. 16.1 A buffer in action, (a) When a drop of 2.0 mol dm hydrochloric acid is added a water, the pH falls drastically, (b) There is no change in pH when an acid is added to the buffer solution.

---