Question

Calculate the theoretical number of mL of 0.200 M HCI needed to completely neutralize the weak base in the 25.0 mL of buffer. From your graph, determine how many mLo 0.200 MHCI were actually used to neutralize the base in the buffer. Compare this value to the calculated value. Did your buffer resist change in pH for the entire titration? Explain. Calculate how many moles of acid were added to reach the capacity of the buffer

Answer 1

Answer...

The first part of the question cannot be answered due to insufficient information. Here molarity (strangth) of the titer (taken in the conical flask) is not known. Therefore though the strength of titrant (0.2M) is given, that of titer is unknown.

Interpretation from the graph...

The neutralization point is indicated by the steepest (almost vertical) part of the plot. It is apparently 10.5 ml. of 0.2 MHCl.

No, the buffer is not effective during the entire titration procedure. In fact, the relative amount of acid and base should not differ much. A buffer is most effective when the concentrations of the acid and its conjugate base are approximately equal.

Buffer capacity is defined as the amount of strong acid or base in gm equivalents, should be added to 1000 ml of the solution so as to change its pH by one unit.

Here HCl is monobasic acid so it's molarity will be equal to its normality.

Hence, in 0.2M HCl no of gm equivalent is 0.2

From the graph it is apparent that volume of acid required to change pH by one (4.5 to3.5) is approximately 8 ml.

1000 ml of 0.2M contains 0.2 gm equivants

Therefore 8 ml contain 16x10^-5 eqts.

By simple calculation the number of gm. eqts necessary to change the pH of one liter of the buffer by one, the buffer capacity, comes to

64 x 10^-4. Hence the result.