AP Chem Need Help Urgent (Titration)

Question

1. Answer all parts of the following question:

a) The graph below shows the titration curves of a 1 M solution of a weak acid with strong base and 1 M solution of a strong acid with the same base. Which curve is which?

b) Suppose you have four color indicators to choose from to detect the equivalence point of the titration reaction represented by the red curve in the graph above. The pKa values of the four indicators are 3.3, 5.0, 7.0, and 9.0. Which indicator would be the best one to choose?

c) Estimate the pKa of the weak acid in the graph above.

d) Why does a solution of a weak base and its conjugate acid control the pH better than a solution of the weak base alone?

Here is the image link : https://imgur.com/a/JBuMRU6

Answer 1

a) the weak acid with strong base is the red line. Weak acids will have a higher pH compared to strong acids when there is no base present. This means that the blue line is the strong acid with strong base

b) you will need an indicator that is near the equivalence point for this particular weak acid. The equivalence point occurs at around pH 9 (which is shown in the graph as a dramatic increase of pH indicating the equivalence point has been reached). Choose indicator with a pKa of 9.

c) The pKa of a weak acid can be determined by the graph. It is the y value of the graph at the half equivalence volume. This means that the pKa is around 6.

d) A weak base and its conjugate acid is a buffer which is known to control pH within a certain range. The weak base reacts with acid and the conjugate acid reacts with base to stabilize the pH.