Chemistry 534

Homework: DISSOCIATION OF WEAK ACIDS AND BASES

 

  1. A student adds some HCl (aq) to water and finds the resulting pH of the solution of 3.50. What is the concentration of [OH-1]aq? (Remember, Kw = 1.0 x 10-14)

 

 

 

  1. At 25 0C, HF(aq) dissociates and reaches an equilibrium. The Ka of the solution is 4.7 x 10-4. What is the concentration of H+1(aq) in the solution when initial concentration of HF(aq) is 2.0 M? Solve with and without the assumption that [HF]i = [HF]f

 

 

 

  1. A 0.011 M solution of hydrocyanic acid, HCN dissociates in solution. The concentration of H+1 (aq) at equilibrium is 5.8 x 10-3 M. What is the Ka of this solution? Can you apply 5% Rule? Explain.

 

 

 

  1. In 80.0 mL solution, 0.25 mol of boric acid, H3BO3 dissociates into 3.4 x 10-4 mol of H2BO3-1 (aq). What is the Ka and pH of this solution?

 

 

 

  1. The acid dissociation constant of NH4+1 is 5.6 x 10-10. When a 0.100 M solution of NH4+1 dissociates and reaches equilibrium. What is the concentration of H+1(aq) and pOH of the solution?

 

NH4+1(aq)      ßà      NH3 (aq)      +       H+1(aq)

 

 

 

  1. The initial concentration and pH of NH4OH(aq) is 0.12 M and 10.0 respectively. What is the base dissociation constant, Kb of NH4OH?

 

 

 

  1. Codeine is a derivative of morphine that is used as an analgesic, narcotic, or antitussive. It was once commonly used in cough syrups but it is now available only by prescription because of its addictive properties. The molecular mass of codeine is 300.0 g/mol, and the pKb is 6.05. Calculate the pH of a 10.0 mL solution containing 5.0 mg codeine. (Remember pKb = -log Kb and mg = 10-3 g)

 

Codeine (aq)       +          H2O (l)      ßà     CodeineH+1 (aq)     +         OH-1 (aq)