40. Titration of weak acids and bases

Question 1

If acetic acid is titrated with the strong base NaOH, what will we find?

Answer 1

• dissociation is not complete in the weak acid solution
• dissociation is 100% in the NaOH solution (strong base)

Question 2

What happen when a strong base is added to a weak acid solution during titration?

Answer 2

OH- deriving from the strong base react with protons from the dissociation of the weak acid,
=> reducing the H+ concentration
=> the addition of a strong base shifts the reaction to the right, favoring the deprotonation of the weak acid
=> weak acid ionizes completely (= equivalent point)

Question 3

Write the general equation if we had dissolved sodium acetate in water?

Answer 3

Na+ + CH3COO- + H2O Na+ + CH3COOH + OH-

CH3COO- + H2O CH3COOH + OH-

Question 4

if a weak acid and a strong base are mixed in stoichiometric amounts, will the pH be basic or acidic?

Answer 4

the pH of the solution will be basic at the equivalency point

Question 5

A weak acid and a strong base are mixed in stoichiometric amounts
=> which pH indicator is used? Properties?

Answer 5

an indicator changing color at alkaline pH is used as an indicator, e.g. phenophthalein.

Question 6

Titration of acetic acid (CH3COOH) solution of unknown concentration

What are the 2 solutions and pH indicator used in this titration?

Answer 6

• CH3COOH solution of unknown concentration
• 0,1 N NaOH as titrating solution
• phenolphtalein as pH indicator

Question 7

What is Phenolphthalein? What does it do?

Answer 7

Phenophthalein is colorless at neutral and acidic pH and red in alkaline media.