The K a values for the TETRAPROTI C acid H4Y are as follows: K a1 = 1.0 x 10-2 K

Question

The Ka values for the TETRAPROTIC acid H4Y are as follows:

Ka1 = 1.0 x 10-2                                                               Ka3 = 7.0 x 10-7                                                

Ka2 = 2.0 x 10-3                                                              Ka4 = 6.0 x 10-11                

What is the value of Kb for the HY3- anion?       

a) 1.7 x 10-4                 

b) 1.0 x 10-12                 

c) 6.0 x 10-11                 

d) 1.4 x 10-8                 

e) 5.0 x 10-12                 

A 0.10 M solution of the compound CNOH has a pOH of 11.2. Which one of the following is the CORRECT equation for the ionization of this compound in water?

CNOH + H2O    ? H3O+ + CNO-  

Consider the following two solutions, each of which has a pH of 4.74:                   

             Solution R: 1.0 L of 0.100 M CH3COOH + 0.100 M CH3COONa

             Solution S: 1.0 L of 1.80 x 10-5 M HCl

If an identical “small” quantity of NaOH is added to each of these solutions, what will happen?

The pH of R will increase slightly; the pH of S will increase greatly.

The pH of R will decrease slightly; the pH of S will decrease greatly.

The pH of R will increase greatly; the pH of S will increase slightly.

The pH of R will decrease greatly; the pH of S will decrease slightly.

The pH of R will remain constant; the pH of S will increase greatly.

4. What mass of HBr should be present in 0.250 L of solution to obtain a solution with the pH value 1.75?                                                                                                             (6)

Molar Mass HBr = 80.91g/mol

Ephedrine, a central nervous system stimulant, is used in nasal sprays as a decongestant. This compound is a weak organic base:

     A 0.035 M solution of ephedrine has a pH of 11.33.

What are the equilibrium concentrations of C10H15ON, C10H15ONH+, and OH-?          

                                                                                                                                    (6)

      b) Calculate Kb for ephedrine.                                                                                    (2)

6. Determine the pair and mole ratio that you would use to prepare a liter of “carbonate buffer” at a pH of 6.08? You are provided with carbonic acid (H2CO3), sodium hydrogen carbonate (NaHCO3) and sodium carbonate (Na2CO3).                                  (4)

7. You need to prepare 100.0 mL of a pH = 4.00 buffer solution using 0.100 M benzoic acid and 0.140 M sodium benzoate. What volumes (in milliliters) of each solution should be mixed? (Benzoic acid Ka = 6.31 x 10-5)                                                                       (6)                             

Explanation / Answer

Question 1 )

answer )

For the acid H4Y, the dissociation for the HY3- anion is given as

HY^3- ------------------------------> Y^4- + H+

and the dissociation constant for it is given as :

Ka4 = 6.0 x 10-11

and we know that

Kw = 10^-14 = Ka * Kb

or

Kb = 10^-14 / Ka4

Kb = ( 10 x 10^-15 ) / ( 6.0 x 10-11)

Kb = 1.67 x 10^-15 x 10^11

or

Kb = 1.7 x 10-4   

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