Question
A sample of Co(NH) Cl, was analyzed by "precipitation titration" with silver nitrate solution: Co(NH3),C13 (aq) + 3 AgNo, (aq) Co(NH)6(N°3)3 (aq) + 3 AgCl (s) A standard solution of AgNO, was prepared by dissolving a weighed sample of AgNO, and disolv in water in an 0.0500 L volumetric flask. The AgNO, solution was placed in a buret and used to tit a weighed sample of Co(NH.),Cl, to the endpoint. Fill in the blanks below. Show your work in the space at the bottom of the page. 0.8114 g Mass of AgNO, in 0.0500 L of AgNO, solution Molarity of AgNO, solution Mass of sample of Co(NH3)Cl 0.1050 g Initial buret reading 0.89 mL 13.08 mL Final buret reading mL of AgNO, solution used in the titration Moles of AgNO, used in titration Moles of Co(NH,)Cl, present in sample Mass of Co(NHs),Cl, present in sample
Explanation / Answer
from equation,
1 mol Co(NH3)6Cl3 = 3 mol AgNO3
mass of Agno3 IN 0.5 L AgNO3 = 0.8114 g
molarity of Agno3 solution = (w/mwt)*(1/v in L)
= (0.8114/169.87)*(1/0.5) = 0.00955 M
volume(ml) of AgNo3 used = 13.08-0.89 = 12.19 ml
moles of AgNo3 used in titration = V*M/1000
= 12.19*0.00955/1000
= 0.0001164 mol
moles of Co(NH3)6Cl3 present in sample = 0.0001164*1/3 = 3.88*10^-5 mol
mass of Co(NH3)6Cl3 present in sample = n*Mwt
= 3.88*10^-5*267.48
= 0.0104 g