Question

1. Why is not the pH at the equivalence point always equal to 7 in a neutralization titration? When would it be 7? (Hint: consider the strengths of the acids and bases) 2. What is the pH of the solution obtained by mixing 50.00 mL of 0.250M HCl and 50.00 mL of 0.500M NaOH? 3. What is the pH of a solution that is 0.20M in sodium acetate and 0.40M in acetic acid? (K, for acetic acid is 1.85 * 10.) 4. What is the pH of the solution obtained by mixing 50.00 mL of 0.1250M HOAc and 25.00 mL of 0.1000M NaOH?

I need help with questions 1-4 please. have not yet gone over pH in lecture yet, so I'm a little lost.
Thanks

Answer 1

1.Ans :-

At equivalence point pH is not always equal to 7, it depends upon the strength of acid and base as :

Case.1 :- Titration of weak acid and strong base (pH > 7):-

Results in the formation of a salt of weak acid and strong base due to which pH of the resulting solution will be greater than 7.

For example :-

CH₃COOH (weak acid) + NaOH (Strong base) ---------> CH₃COONa (Salt of weak acid and strong base) + H₂O

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Case.2 :- Titration of weak base and strong acid (pH < 7):-

Results in the formation of a salt of weak base and strong acid due to which pH of the resulting solution will be less than 7.

For example :-

NH₄OH (weak base) + HCl (Strong acid) ---------> NH₄Cl (Salt of weak base and strong acid) + H₂O

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Case.3 :- Titration of Strong acid and strong base (pH = 7):-

Results in the formation of a salt of strong acid and strong base i.e. neutral salt due to which pH of the resulting solution will be equal to 7.

For example :-

HCl (Strong acid) + NaOH (Strong base) ---------> NaCl (Salt of strong acid and strong base) + H₂O