Buffers and Titration

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					                                       Chem 1A
                                   Buffers/Titration

   1.   Which of the following are buffer solutions? What is the approximate pH of the
        solutions that are buffers.
            a. HClO3/NaClO4
            b. H2S/NaHS
            c. K2HPO4/K3PO4
   2.   What is the equilibrium constant for the mixture of HClO2 with NH3? What is the
        strongest acid and base in the equilibrium mixture?
   3.   What is the pH at the equivalence point for the following titrations?
            a. NaOH with HBr                    pH = 7 pH > 7 pH < 7
            b. HCl with NaCH3COO                pH = 7 pH > 7 pH < 7
            c. KOH with HCN                     pH = 7 pH > 7 pH < 7
   4.   Which of the following 50 mL solutions can absorb the most acid without changing
        the pH?
            a. 0.4 M HF and 0.5 M NaF
            b. O.6 M HF and 0.7 M NaF
   5.   Calculate the pH of the following.
            a. 0.2 M HN3/0.2 M NaN3
            b. 0.2 M HN3/0.1 M NaN3
            c. 30 mL of 0.1 M HN3/ 40 mL of 0.2 M NaN3
            d. 25 mL of 0.1 M HCl /25 mL of 0.2 M KNO2
            e. 50 mL of 0.1 M HCl /25 mL of 0.2 M KNO2
            f. 60 mL of 0.1 M HCl/25 mL of 0.2 M KNO2
            g. 40 mL of 0.25 M KOH/40 mL of 0.5 M HClO
            h. 80 mL of 0.25 M KOH/40 mL of 0.5 M HClO
            i. 100 mL of 0.25 M KOH/40 mL of 0.5 M HClO
            j. 20 mL of 0.1 M HCl is added to 100 mL of the solution in 5a.
            k. 20 mL of 0.1 M NaOH is added to 100 mL of the solution in 5a.



Problem solving advice:
   1. For buffers always write the acid equilibrium and use Ka to solve for H + (x)
   2. For neutralization reactions:
           a. Write the net ionic reaction
           b. Reaction goes 100% to completion so work in mols or mmols
           c. After reaction is complete ask what’s left in solution
                     i. Buffer – convert mols or mmols into M then write the acid
                        equilibrium and use Ka to solve for H+ (x)
                    ii. Excess H+ - convert mols or mmols to M to find the pH
                   iii. Excess OH- - convert mols or mmols to M to find the pOH
                   iv. Only conjugate acid - convert mols or mmols into M then write the
                        acid equilibrium and use Ka to solve for H+ (x)
                    v. Only conjugate base - convert mols or mmols into M then write the
                        base equilibrium and use Kb to solve for OH- (x)

				
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posted:11/30/2011
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