Additional Aspects of Aqueous Equilibria

Buffer Solutions solution that resists changes in pH upon addition of small amounts of strong acid or base consists of a mixture of a weak acid and its conjugate base it works b/c the weak acid can neutralize small amounts of strong base and the weak base can neutralize small amounts of strong acid

Common Ion Effect decreases the ionization of a weak electrolyte when a common ion is added to the solution Consider this: CH 3 COOH + H 2 O CH 3 COO - + H 3 O + – adding NaCH 3 COO to the solution will increase [CH 3 COO - ], causing the rxn to shift left, thus decreasing the ionization of acetic acid – resulting solution is a buffer containing a weak acid & a conjugate weak base

To make a buffer solution, what weak acid must be added to an amount of sodium phosphate? Write a chemical reaction and its corresponding equilibrium expression.

Understanding A/B reactions 1.SA + SB  NS + H 2 O – HCl + NaOH  H 2 O + NaCl – H + + OH -  H 2 O – sol’n is neutral b/c both the acid and base ions are neutral ions 2.SA + WB  WA + NC – HCl + NaCH 3 COO  NaCl + CH 3 COOH – H + + CH 3 COO -  CH 3 COOH – sol’n is slightly acidic 3.SB + WA  WB + NC – NaOH + CH 3 COOH  NaCH 3 COO + H 2 O – OH - + CH 3 COOH  CH 3 COO - + H 2 O – sol’n is slightly basic 4.WA + WB  does not measurably react

Write and balance complete and net ionic equations for the reaction of ammonia solution with nitric acid.

Calculating Buffer pH calculated the same as the pH of a weak acid sol’n - RICE: – What is the pH of an aqueous mixture containing 0.20 M acetic acid and 0.10 M sodium acetate?

If the sol’n contains: & the base is in excess, the resulting sol’n is a: & the acid is in excess, the resulting sol’n is a: & neither acid nor base is in excess, the resulting sol’n is a: SA + SBSBSAneutral SA + WBbufferSAWA WA + SBSBbufferWB WA + WBbuffer

Explain how nitric acid and sodium acetate can be used to make a buffer solution. Illustrate your answer using a chemical equation.

What is the pH of a solution made by mixing 1.0 L of 0.10 M HCl with 2.0 L of M NaOH

What is the pH is a sol’n made by mixing 0.11 M HCl with 3.0 L of M NaF?

What is the pH of a sol’n made by mixing 2.5 L of 0.20 M CH 3 COOH with 1.0 L of 0.30 M KCH 3 COO?