When a weak acid is titrated with a strong base, why should the pH at the equiva

Question

When a weak acid is titrated with a strong base, why should the pH at the equivalence point should be greater than 7? Write a reaction to illustrate your explanation. 1. In the following titrations, would you predict the pH to be greater than 7, less than 7 or equal to 7, at the equivalence point? Explain your answer and include balanced reactions to make your point. 2. a. HBr titrated with KOH b. NH3 titrated with HNO3. Calculate the pH at the following intervals during the titration of 50. mL of 0.100 M acetic acid (CH,COOH) with 0.200 NaOH: (K, value for acetic acid can be found in your textbook or lecture notes) 3. a. 0.00 mL NaOH added b. 5.0 mL NaOH added c. 25 mL NaOH added d. 40. mL NaOH added CEM-122 Acid Content of Aspirin By Potentiometric Titration

Explanation / Answer

Q1.

weak acid will form hydrolysis when no more base/acid is left

so

A- + H2O <-> HA + +OH-

HA is the weak acid in hydrolysys, and OH- is now left, pH will be higher than 7.

Q2

HBr + KOH = strong acid + storng base, p H= 7

NH3 = weak base, HNO3 storng acid

note that once all NH3 is reacted, NH4+ forms

this will form hydrolysis

NH4+ + H2O <- >H3O + NH3

H3O+ is aicidc, so pH < 7

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