Slope and Buffer Index

This slope also measures the buffering power of the mixture, its resistance to change in pH. 

C is taken constant for this differentiation. From the definition of pH we can derive 

B is called the buffer index and expresses the slope as the increment 

This expresses only the left, derivative side of equation (7-2). Now invert and solve for the slope function s in pH units per milliliter 

Calculation of a slope follows three steps (1) Use the Kg expression to find the pH at the point desired. (2) Use equation (7-2) to find B at this point. (3) Use equation (7-3) to find s. 

---