analytical assignment #4

1.  Calculate the pPb2+ at each of the following points in the titration of 20.00 mL of 0.0200M Pb2+ by 0.010 M EDTA at pH 3.0 (log Kf for Pb-EDTA = 18.04):


(a) 0 mL, (b) Ve, (c) 10.0 mL, (d) 50.0 mL


2.  A 50 mL solution containing 0.10 M 1-Naphtoic acid (pKa = 3.70) and 0.15 M arsenic acid (pKa1 = 2.24; pKa2 = 6.96) is titrated with 0.20 M KOH.

(a)    How many end points will be observed?

(b)   What is the pH of the solution before adding any KOH?

(c)    Calculate the volume of KOH required to reach the first equivalence point.

(d)   Calculate the pH after the addition of 100 mL of KOH (assume that the OHcontribution from water autoprotolysis is negligible).


3.  Masking of Cu2+ can be achieved by reduction to Cu+.  A 25.00 mL aliquot of a solution containing Cu2+ and Ni2+ was treated with ascorbic acid at pH 3.0 to reduce the Cu2+ ions.  The pH was adjusted to 10.0 and 27.32 mL of 0.0565 M EDTA was required to reach a murexide end point.  In a parallel titration, 40.45 mL of 0.0565 M EDTA was required to reach the murexide end point in a 25.00 mL aliquot that was not treated with ascorbic acid.  What amounts of copper and nickel in ppt (mass/vol.) were in the original solution?