WS8 - Chem 142 Name Worksheet 8 Weak Acids and Bases and...

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Chem 142 Summer 2011 Page 1 of 2 Name ________________________________________ Section ________________ Worksheet 8: Weak Acids and Bases and Salts 1. What is the pH of each of the following weak acid/base solutions? What is the percent dissociation of the acid/base? Step 1: Write balanced dissociation reactions for each the acid/base and water Step 2: Rank the species in order of strength (using the K a ) Step 3: Determine whether the water will contribute to the H + or OH - concentrations (base on K a values) Step 4: For the strongest acid/base, write the equilibrium expression and calculate the equilibrium concentrations (5% rule?) Step 5: If needed, repeat step 5 for the other species Step 6: For an acid – calculate pH from the [H + ]; for a base – calculate pOH or [H + ] from [OH - ], then find pH a. 0.500 M formic acid, HCOOH (K a = 1.77 x 10 -4 ) b. 0.200 M citric acid, C 6 H 10 O 8 or HCA (K a = 7.45 x 10 -4 ) c. 0.350 M methylamine, CH 3 NH 2 (K b = 4.38 x 10 -4 ) 2. What is the pH of each of the following weak acid mixtures, or polyprotic acids? What is the concentration of each anion (or conjugate
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