Question

a) Use this plot to estimate the volume of NaOH required to reach the equivalence point of each titration curve.

b) Estimate the original concentration of weak acid in solution before strong base was added.

c) Find the midpoint pH for each of the trials using half the volume of NaOH required to reach the equivalence point for that trial. Check if this pH is at the most flat part of the titration curve. This is the pKa of the weak acid.

Α' Α- 29 General $ % 9140 Conditional Format as Formatting Table Styles Cell Styles - Delete- Format Alignment Number 15 Cells NO Titration #2 V (ml) pH 2.6 3.1 2.91 3.06 in a wo 3.87 pH vs Volume of Base (mL) NES ph 10 Volume of NaOH (ml) oo 4.72 5.03 55 5.78 12.5 127 13 131 5.92 10.83 11 28

Take the first row of data for the initial pH of the weak acid.

Answer 1

* In an acid -base titration, the floutin curre reflects the strenghts of the conspending acid and base. * If one reagent is a meak acid @ base and the Other is a stong acid @ base, the titration curve is incgular, and the pH shifts less with small additions of titraht near the CA equivalence print. & The pH changes very slowly and gradually. this indicates the formation of a bulter system as the formation of a butter system at the titration appruches. the equivalence point. & At the equivalence point & beyond the came is typical strong acid & string bare curre.

* The initial pH of the solution at the begining of the titration is approximately that of the weak acid in water. At the equivalence point, all of the meals acid is neutralised & connected to its conjugale base. However the pit at the equivalence point does not equal to 7 This is due to the productim of conjugate base during the titrahin. the resulting solution is slightly basic. (1) Equivalence point is the noof moles of t ta no of moles of on. -- after equivalence point Eurulenience punt Bethe entralence punt volume of titrant wlume required bet equivalence point i Approsimately the wlume of TAVSD NaOH is 13 mL

& the original concentration of weak acid can be calculated by taking the pH value of the heat acid. -) The initial pH of the solution at the begining of the tilation is approximately that of the weat acid in water. ". The initial pH of the acid is a 2.91 as per the table ginn. We know that at pH = -log (A1) 2.912 - log (41) . (Hi] = 1.23x103 in Concentralm of weak acid is 1.23x

o the volume required reach the equivalence point is 13mL of NaOH. Halt the volume means G.SmL. The pH value at the 6.5ml is approximately 4.26. As per the graph this value is at the most flat part of the titration curre. i. PH2 4.26 is the pla of the wak acid.