Question

Calculate the pH at the equivalence point in titrating 0.100 M solutions of each of the following with 0.080 M NaOH:

(a) HBr (aq), (b) HClO2 (aq), (c) Benzoic acid (C6H5CO2H).

Answer 1

At the equivalence point of titration, a strong acid like HBr with a strong base will have a pH of 7.00, while weak acids like HClO2 and Benzoic acid will result in a pH above 7, whose exact values depend on their specific Ka values.

To calculate the pH at the equivalence point in titrating 0.100 M solutions with 0.080 M NaOH, we must consider the type of acid being titrated:

• For HBr, a strong acid, the resulting solution will be neutral at the equivalence point, and the pH will be 7.00.
• Titrating HClO2, a weak acid, will result in a slightly basic solution due to the formation of its conjugate base, ClO2-, and so the pH will be greater than 7.
• For Benzoic acid, another weak acid, the solution will also be slightly basic at the equivalence point, with the pH determined by the hydrolysis of the benzoate anion.

The exact pH values for the weak acids can be determined using the Henderson-Hasselbalch equation or by considering the hydrolysis of the conjugate base formed. The pH for weak acids will typically be located above 7 but the actual value will depend on the specific acid dissociation constant (Ka) of the acid.

Answer 2

(a) 7.0 (b) 7.30 (c) 8.42

Step-by-step explanation:

(a) HBr is a strong acid and NaOH is also a very strong base, hence, the solution will be neutral give a pH of 7.0

(b) HClO3

ClO2- + H20 <=> HClO2- + OH-

ClO2- = 0.1*0.08/0.18 = 0.044M

Kb=Kw/Ka=1.0 x 10^-14/1.1 x 10^-2=9.09x10^-13

[OH-] = 2.0 x 10^-7M

p[OH] = 6.7

pH = 7.3

(c) C6H5COOH

C6H5COO- + H20 <=> C6H5COOH + OH-

[C6H5COO-] = 0.1 * 0.80/0.180 = 0.44

Kb=Kw/Ka=1.0 x 10^-14/6.3 x 10-²=1.59x10^-10

[OH] = 1.59x10-10/0.44 = 2.69x10-6

pOH = 5.58

pH = 8.42