Quantitative Analysis chemistry

 

For a pH 10 buffer containing ammonia (pKb=4.756) and ammonium at total concentration of 1.0 M, calculate the fraction of Zn2+ in the un-complexed form ([Zn2+]). 

Assume that the Zn concentration is 0.00100 M calculate the pZn2+ at 2, 4, 5, 8, 9.9, 10, 10.5 mL when 100 mL of this zinc solution is titrated with a standardized 0.0100M EDTA solution. (2, 5, 8, 9.9, 10, 10.5 mL). Hint: There is a large difference in the total ammonia concentration and the Zinc concentration so make a sensible approximation

Zn2++NH3​⇌ZnNH32+​  ,  βn1​=102.21  

Zn2++2NH3​⇌Zn(NH3​)22+​  ,  βn2​=104.50  

Zn2++3NH3​⇌Zn(NH3​)32+​  ,  βn3​=106,86  

Zn2++4NH3​⇌Zn(NH3​)42+​  ,  βn4​=108.88  

Zn2++H2​O⇌ZnOH+  ,  βh1​=10−8.997  

Zn2++2H2​O⇌Zn(OH)2​  ,  βh2​=10−16.894  

Zn2++3H2​O⇌Zn(OH)3−​  ,  βh3​=10−28.391  

Zn2++4H2​O⇌Zn(OH)42−​  ,  βh4​=10−41.118