Ch. 16 acid / base / pH / buffer                        test     [100 points]                 honors 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.

 

                                                                                                Signature:  ___________________

 

1.  In regards to a buffer, describe ___.  [20 points]

 

   a. its properties

 

   b. its composition

  

   c. its mechanism of action, i.e. basis of its action using the appropriate net ionic equation(s) with respect to your response in part b.

 

 

 2. What is the molar solubility of calcium carbonate in water ?  [10 points]

 

 

3.  What is the pH of __ ? [35 points] 

 

   a.  125 mL of 25 mM nitric acid

 

   b.  125 mL aqueous solution containing 1.0 g of sodium hydroxide, a strong base 

 

   c. aqueous mixture containing 25 mL of 55 mM hydrochloric acid and 75 mL of 95 mM nitric acid

 

 

   d. 75 mL of 25 mM benzoic acid, a weak acid

 

4. Sodium carbonate was added to a 75 mL aqueous solution containing 1.0 μM AgNO3, 10.0 μM FeCl2, and 0.1 mM CuBr2.  Assume that there is no change in the volume of the solution due to the addition of sodium carbonate; what is the first precipitate ?  last precipitate ?  justify / rationalize your response.  [20 points] 

 

5. Based on an aqueous solution of a 25.0 mM of a weak acid, C6H5COOH, having a pH = 2.91, what is the value of it’s equilibrium constant ?  [hint:  the weak acid reacts with water]     [15 points]