Question

Explain why there is a steep slope in a section of the titration curve and explain how it can be used in calculations ?

Answer 1

The slope of your titration curve represents the change in pH with respect to the volume of strong base (or acid) titrated into the other. The amount of change produced by each unit of volume is not the same every time. Say you have 0.005 moles of hydrogen cation in 1 liter of solution, or a 0.005 M solution, yielding a pH of ~2.30.

You then add 1 mL of a solution containing 0.00005 moles of hydroxide anion. The hydrogen ion concentration is now (0.005 - 0.00005 mol)/(1 + .001 L) = or ~0.004945 mol/L, yielding a pH of ~2.31 for a change in pH of of ~0.01.

Each time you add another volume unit of base you are decreasing the numerator (subtracting more from the initial concentration) and increasing the denominator (adding more to the initial volume). Mathematically, doing either of these will give you a smaller number. As the hydrogen ion concentration decreases, the pH (-log10(H+)) increases, and it will increase by more with each addition because the effect is magnified. Each drop (or milliliter or gallon or any unit of volume) further decreases the numerator and increases the denominator