King Saud University
213 PHC
2nd Semester
College of Pharmacy
Final Exam
1429-1430
Pharm. Chem. Dept.
Dr. Mona Al-Shehri
Name:
No.
Q. 1
Mark ( √ ) for the correct statements and ( x ) for the false ones:
(
) Potassium dichromate is an example of a self indicator.
(
) In Volhard method the end point is detected by adding iron (III) as ferric
alum which forms a soluble red complex with the first excess of titrant.
(
) EDTA has two Ka values corresponding to the stepwise dissociation of the
four protons.
(
) The precipitation will not take place unless the product of [Ag +] and [Cl-]
exceeds the Ksp.
(
) Increasing the hydrogen ion concentration will favor formation of the CaY 4chelate.
(
) The standard hydrogen electrode is used to measure the potential of any
half reaction because it has a zero potential.
Q.2
What is the overall cell reaction and the cell potential for the two half-reactions?
Fe3+ + e = Fe2+ Eo = 0.77 V
Ti4+ + e = Ti3+
Eo = 0.15 V
Q.3
What is the electrode potential in a solution containing 0.5 M KBrO3 and 0.2 M Br2 at
pH 3?
BrO3- + 6H+ + 5e-
Q. 4
→ 1/2 Br2 + 3H2O
You are provided with a titration curve for 100 ml 0.1 M Cl-, Br-, and I- solutions
versus 0.1 M AgNO3.
a. Calculate the concentrations of Br-, and I- at the equivalence point.
b. The end point of I- is sharper than that of Cl- and Br--. Why?
Ksp
AgCl = 1 x 10-10
AgBr = 4 x 10-13
AgI = 1 x 10-16
Q. 5
Match each of the following statements (column B) with the appropriate
term (column A):
Column A
(
) Mohr method
Column B
a- The indicator reaction takes place
on the surface of the precipitate.
(
) Ammonia
b- A measured excess of AgNO3 is
added to precipitate the anions
and the excess Ag+ is determined
by back titration with standard
SCN- solution.
(
) Eriochrome Black T
c- Allows
charge
transfer
but
prevents mixing of solutions
(
) Chelating agent
d- The titrant is iodine and the
analyte is a reducing agent.
(
) Volhard method
e- Used when MnO4- titration of Fe2+
is performed in the presence of
Cl- ion.
(
) Salt bridge
f- Complexing agent with one pair
of unshared electrons.
(
) Iodimetry
g- Used for the titration of Mg2+
with EDTA.
(
) Adsorption indicator
h- The Cl- is titrated with standard
AgNO3 and K2CrO4 is added as the
indicator.
(
) Iodometry
(
) Zimmermann reagent
Q. 6
Give reasons:
a. We can titrate some metals (e.g. Fe3+) with EDTA in the presence of other
metals (e. g. Ca2+) at lower pH values.
b. The metal complexes formed with EDTA are often 1:1, regardless of the
charge on the metal ion.
c. In the titration of calcium with EDTA using Eriochrome Black T as indicator,
a small amount of magnesium salt is added to the calcium solution.