Ch. 17  equilibrium II               test     [100 points]                             AP Chem

 

For problems involving calculations, show your work in an organized manner, include any relevant equation (or formula and conversion factor(s)), put the proper units in your calculations / answer, and have the proper number of significant figures in your answer. 

 

Academic Honesty:   The answers on this test are my own and I am using only the allowed set of notes as described in the syllabus.  I have not discussed the test questions with anyone before or during the test nor have I seen the test questions prior to the exam.  If you violate any of the preceding items or do not sign, your semester grade is a F.

 

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  1.  Describe how a benzoic acid (C6H5COOH) / sodium benzoate (C6H5COONa) buffer works ?  [10 points]

2.  How many grams of sodium benzoate would need to be added to a 500.0 mL aqueous solution containing 1.0 mM benzoic acid, where the buffer’s pH = 4.4 ?  [15 points]

3. Sketch / label the acid – base titration curve involving 50.0 mL of  25.0 mM potassium hydroxide solution titrated by 75.0 mM nitric acid; justify / identify all values in the preceding curve.  [20 points]


4. What is the pH of a 50.0 mL of a 25.0 mM aqueous solution of lactic acid after the addition of 10.0 mL of 75.0 mM NaOH solution ?  [15 points]


5. What is the pH of a 50.0 mL of a 25.0 mM lactic acid / 35.0 mM sodium lactate after the addition of 10.0 mL of 75.0 mM NaOH solution ?  [15 points]


6. Identify / rationalize the first precipitate to be formed by the addition of sodium carbonate to an aqueous solution containing 1.0 mM barium nitrate and 0.5 mM calcium chloride.  [15 points]

 

 

7. Describe the “common ion effect” and its basis.  [10 points]