Two bases, B and D, each approxiately 0.10 M in concentration, are titrated sepa
ID: 509127 • Letter: T
Question
Two bases, B and D, each approxiately 0.10 M in concentration, are titrated separately with a strong acid, hydrochloric acid (HCl). At the equivalence point of the B titration, pH= 5.8; at the equivalence point of the D titration, pH=5.0.
a) write the conjugate acids of B and D.
b) What reaction explains the fact that the pH at the equivalence point of the base B and HCl titration is lower than 7? Write the raction equation.
c) What reaction explains the fact that the pH at the equivalence point of the base D and HCl titration is lower than 7? Write the raction equation.
d) Which conjugate acid, the conjugate acid of B or the conjugate acid of D, is the stronger acid? Defend your aswer.
e) Which of the two bases, B or D, is the stronger base? Defend your answer.
Please explain the best you can and show all calculations.
Explanation / Answer
Ans. #A. B-OH(aq) + HCl(aq) ------> B+(aq) + Cl-(aq) + H2O(aq) ; B+ is conjugate acid
D-OH(aq) + HCl(aq) ------> D+(aq) + Cl-(aq) + H2O(aq) ; D+ is conjugate acid
#B. B-OH(aq) + HCl(aq) ------> B+(aq) + Cl-(aq) + H2O(aq)
The conjugate acid, B+ further reacts with H2O to produce H3O+ as shown below-
B+ + H2O -----------> BOH + H3O+
The formation of hydronium ion lowers the pH below 7.0 making it acidic.
#C. D-OH(aq) + HCl(aq) ------> D+(aq) + Cl-(aq) + H2O(aq)
The conjugate acid, D+ further reacts with H2O to produce H3O+ as shown below-
D+ + H2O -----------> DOH + H3O+
The formation of hydronium ion lowers the pH below 7.0 making it acidic.
#D. A stronger conjugate acid accepts OH- with greater affinity.
Thus, D+ is a stronger conjugate acid than B+.
#E. The base of a weaker conjugate acid is stronger than the base of a stronger conjugate acid. Thus, B is a stronger base.
Alternatively, the stronger is the base, the equivalence pH is closer to 7.0 when titrated with a string acid. So, B (equivalence pH is closer to 7.0 than that of D’s) is stronger base than D.