Lecture 8 Titrations - II

Kjeldahl digestion Conc. H 2 SO 4 + catalyst All N  NH 4 + C  CO 2 HH2OHH2O >300 o C

NaOH+NH 3 NH 3 +H 2 O HCl or H 3 BO 3 NH 3 + H +  NH 4 + Excess of H + can be titrated with NaOH If HCl: If boric acid: B(OH) H +  H 3 BO 3 + H 2 O

Precipitation Titration AgNO 3 + NaCl  AgCl + NaNO 3 Ag + + Cl -  AgCl

AgCl  Ag + + Cl - K SP = [Ag + ][Cl - ] pX = - log 10 [X] pAg = - log 10 [Ag + ]

n- soluble AgCl Cl - Na + AgNO 3 NO 3 - AgCl Na + NO 3 - AgNO 3 Colloid equivalence point: coagulation no chloride ion left in solution, no further precipitation first drops In the middle

Equivalence point [Ag + ]=[Cl - ] 100.1% Ag % Ag + [Cl - ]=10 -4 M  [Ag + ]=1.8  M [Ag + ]=10 -4 M Acceptable end point Titration of NaCl with AgNO 3 C=0.1 M

I - + Ag +  AgI pAg= -log[Ag + ] K sp (AgI)=[Ag + ][I - ]=8.3  % Ag % Ag + Acceptable end point

Precipitation titration with silver electrode The change of V is proportional to pAg V(mV)

Ag Ind 2- Ag + I-I- I-I- I-I- I-I- _ _ _ _ _ _ _ _ Ind 2-

Precipitation Titrations: