Ch. 16 acid / base / pH / buffer                        test     [70 points]                   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. In regards to a buffer based on  ___ , illustrate / describe the basis of a buffer by writing the appropriate net ionic equation due to the addition of a (i) strong acid, HCl and (ii) strong base, KOH, to the buffer.  [20 points]

 

   a.  C6H5COOH (benzoic acid) and C6H5COONa (sodium benzoate)

i.

  

ii.

   b. CH3NH2 and CH3NH3Cl 

 

i.

  

ii.

 

 

 2.  What is the pH of an aqueous solution of ___ ?  [15 points]

 

   a.  25 mM HNO3, a strong acid  [5 points]  

 

   b.  75 mM NaOH, a strong base  [10 points]

 


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

 

 4. Based on an aqueous solution of a 75.0 mM weak base, CH3NH2, having a pH = 11.74, determine the value of it’s equilibrium constant, where the weak base reacts with water ?   [20 points]