1. consider an aqueous solution that is 0.310M in the salt, potassium benzoate,

Question

1. consider an aqueous solution that is 0.310M in the salt, potassium benzoate, K+ c6h5coo-. ka for benzoic acid , c6h5cooh is 6.5x10^-5

a. what is the initial concentration of the k+ cation and the benzoate anion, c6h5coo- upon dissolution but before any hydrolysis takes place.

b. do either or both the anion and cation of this salt undergo hydrolysis? write the equation for the relevant hydrolysis reaction(s) of this salt.

c. is this salt an acidic, basic, or neutral salt?

d. determine the equilibrium concentrations of all of the equilibrium species in the aqueous solution of 0.310M potassium benzoate.

e. what is the pH of this solution?

2. enough solid ammonium bromide, nh4Br, is dissolved in water to make a solution which is 0.015M in NH4+ ion. What is the pH of this solution if the Pka of NH4+ is 9.25?

3. A buffer solution is prepared by mixing equal volumes of 0.25M methylammine, ch3nh2(aq) with 0.35M methylammoniumchloride, ch3nh3cl. kb for methylamine is 3.7x10^-4. What is the pH of this buffer?

Explanation / Answer

2) NH4+(aq) -----> NH3 (aq) + H+(aq) , [H+] ={A-] = x , [NH4+] = 0.015-x

Ka = 10^ -9.25 = [H+][NH3]/[NH4+] = x^2/(0.015-x) ,

x = 2.9 x 10^ -6 = [H+] , pH = -log(2.9 x10^ -6) = 5.537

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