Consider the following titration curve which resulted from the titration of a we
ID: 706144 • Letter: C
Question
Consider the following titration curve which resulted from the titration of a weak monoprotic acid with a strong base. 21.(6) 14 12 10 0 20 40 60 80 Volume of base added (mL) (a) What volume of base must be added to reach the equivalence point? (b) What volume of base must be added to reach the half-equvalence point? (c) What is the value of the pko for eak acid? Extra-credit question.(5) Which of the following diagrams best represents an aqueous solution of NaF? The water molecules are not shown for clarity. Justify your reasoning with a balanced chemical equation.Explanation / Answer
Q21. (a) What volume of base must be added to reach the equivalence point? 30 mL
(b) What volume of base must be added to reach the half-equivalence point? 15 mL
(c) What is the value of the pKa for this weak acid? pKa = 5.0 (approx)
Explanation
Equivalence point is that point when moles of acid is equal to moles of base in the solution. This point is represented on the graph by a almost straight line indicating a very sharp rise in pH (in case of strong base as titrant). The middle point of this almost straight vertical line is taken as equivalence point and the corresponding value on x-axis is the equivalence volume.
Half equivalence point is reached when the volume of base added is exactly half of what was added at equivalence point. If the volume of base added at equilvalence point is equal to 30 mL, then half-equivalence point will be reached when (30 mL / 2) = 15 mL base has been added
pH at half equivalence point is equal to pKa