Chemistry 21    Acids and Bases

    A. The Concepts

1. Which is the stronger acid, nicotinic acid (Ka = 1.4 x10-3) or acetylsalicylic acid
                   (Ka = 3.3 x 10 –3)
.   (Consider the acidity of the H in bold.)

                                             

  2. Which is a stronger acid, pyruvic acid (pKa = 2.49) or lactic acid (pKa = 3.86)?
(Can you reason out why? Consider the acidity of the H in bold.)

                  

                                              3.Will the following reaction at equilibrium favor reactants or products?
                                                                     pKa of ethene = 44 and pKa of NH3 = 36 Calculate Keq.

      

                                 4. Consider the structure of ethane and acetone and determine which is a stronger acid, ethane or acetone.|
                         Consider a) possible inductive effects  The O atom causes some electron inductive withdrawal and   
                        b)  resonance effects. The conjugate base of acetone is more stable because there are more resonance
                            contributors.

                    ethane                                      acetone   

              B. The Math

 

     1. Do the problems (1 – 12) of “Special Topic I, pH, pKa, and Buffers” on page 45 in the “Study Guide and Solutions Manual”  
        that accompanies the Bruice text. Problems worked out in subsequent pages.

     2.Find the pH of 250 mL of 1.20M formic acid. (formic acid pKa=3.75)  The structure of formic acid is shown.   
       (Consider the acidity of the H in bold.)    1.83 

   

 formic acid

      3. What % of the formic acid is deprotonated in the solution described in question 2? 1.2%

      4. With Lewis structures, illustrate the reaction that takes place between formic acid and NaOH.
          (Use arrows to show where electrons go.)  

                         

      5. Find the pH of the solution described in question 2 after 3.0 mL of 10M NaOH has been added.
           2.85

      6. What % of the formic acid is deprotonated in the solution described in question 5?  
                       11.2%
 

      7. How many mL of 10M NaOH need to be added to the solution described question 2 to bring it to pH of 3.75?
in                    14.6 mL

      8. Consider the reaction between formic acid and HCl:

    formic acid + HCl                      Cl

 



At what pH is 1.0 % of the formic acid in the protonated form?  -4.51

(The pKa for the protonated form of formic acid =  -6.5)