0.
1 N Silver Nitrate VS Preparation and Standardization
Experiment no. 1
Preparation and Standardization
0.1 Silver Nitrate (AgNO3) VS
I. Principle Involved
Direct titration using Fajans’ Method of Volumetric Precipitation is employed in the
standardization of 0.1 N silver nitrate VS, in which 0.1 N silver nitrate serves as the titrant while
sodium chloride acts as the primary standard. The reaction involves the precipitation of silver
chloride with eosin y TS acting as the indicator. The endpoint is signaled by the precipitate’s
change in color from white to pink. This change in color is most apparent at pH 2.0 and is best
seen in diffuse light condition.
II. Procedure (USP 30, p. 821)
Dissolve about 17.5 g of silver nitrate in 1000 mL of water and standardize the solution
as follows:
Transfer about 100 mg, accurately weighed, of reagent-grade sodium chloride,
previously dried at 110◦ for 2 hours, to a 150 mL beaker, dissolve in 5 mL water and add 5 mL of
acetic acid, 50 mL of methanol and about 0.5 mL of eosin y TS. Stir, preferably with a magnetic
stirrer, and titrate with the silver nitrate solution.
N=
III. Official Requirement
Not applicable.
IV. Clean up Procedure
After the standardization, decant the liquid from the reaction flask. The liquid can be
disposed into the sink. The silver chloride precipitate can be disposed to the metal wastes bottle.
V. Reasons for Important Steps
1. Titration must be done in a dim environment to prevent photocatalytic degradation of silver
chloride. This is due to the reducing effect of light on silver chloride, producing free silver
which in turn causes a purplish color on the precipitate. (Knevel and Digangi, 1977, 132)
2. Sodium chloride has a purity of 99.9 – 100.0 percent and may be used as a primary standard.
(Jeffery, et al., 1989, 349)
3. Sodium chloride is very slightly hygroscopic, therefore, it is necessary to dry the finely
powdered solid at 110◦ for 2 hours prior to dissolution to correct for absorbed moisture.
(Jeffery, et al., 1989, 349) (Knevel and Digangi, 1977, 15)
4. The Fajans’ method uses an adsorption indicator whose color when adsorbed to the
precipitate is different from that when it is in solution. Before the endpoint, the precipitate
of AgCl has a negative surface charge due to the adsorption of excess Cl -. The anionic
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0.1 N Silver Nitrate VS Preparation and Standardization
indicator, eosin y, is repelled by the precipitate and remains in the solution where it has a
greenish yellow color. After the end point, the precipitate has a positive surface charge due
to the adsorption of excess Ag+. The anionic indicator now adsorbs to the precipitate’s
surface where its color is pink. This change in color signals the endpoint. (Harvey, 2000, 354)
5. Acetic Acid is added to the solution to prevent a premature endpoint by suppressing the
ionization of eosin, thus, avoiding the displacement of Cl -. in the primary adsorbed layer.
(Jeffery, et al., 1989, 347) The color change is also sharpest in acetic acid solution. (Knevel
and Digangi, 1977. 131)
6. Alcohol, in this case methanol, is added to help keep the precipitated silver chloride in a
colloidal state and thus give sharpness to the color change which occurs in the precipitate
surface. (Knevel and Digangi, 1977, 139)
7. Slow addition of the titrant should be employed with constant stirring to produce a
precipitate with larger particles. (Knevel and Digangi, 1977, 132) In using adsorption
indicators, the precipitate formed should remain highly dispersed, allowing for maximum
surface area of adsorption. (Christian, 2004, 351)
VI. Chemical Equations
AgNO3 + NaCl → AgCl↓ + NaNO3 (Svehla, 1996, 191)
Factor: 1
Explanation: 1 mole of AgNO3 is needed to react with 1 mole of NaCl to form AgCl
VII. Computations
Preparation:
N = MF
0.1 N = M (1)
M = 0.1 mol/liter
Standardization:
Weight of 1◦ std (g) = NT x VT x
Weight of 1◦ std (g) = x 0.03 L x = 0.17532 g NaCl
*Weigh 175-176 mg
VIII. References
CHRISTIAN, G.D., 2004. Analytical Chemistry. 6th edition. New York: John Wiley and Sons, Inc.,
238, 352
HARVEY, D., 2000. Modern Analytical Chemistry. New York: McGraw-Hill Companies, Inc., 354
JEFFERY, G.H., BASSETT, J., MENDHAM, J., DENNEY, R.C., 1989. Vogel’s Textbook of Quantitative
Chemical Analysis. 5th edition. UK: Longman Scientific and Technical, 347, 349
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0.1 N Silver Nitrate VS Preparation and Standardization
KNEVEL, A.M., DIGANGI, F.E., 1977. Jenkins’ Quantitative Pharmaceutical Chemistry. 7th edition.
New York: McGraw-Hill Book Company, 131-132, 130
SVEHLA, G., 1996. Vogel’s Qualitative Inorganic Analysis. 7th edition. England: Longman Group
Ltd., 191
UNITED STATES PHARMACOPOEIAL CONVENTION, INC., 2007. United States Pharmacopoeia 30th
Revision and the National Formulary 25th edition. USP Convention, Rockville, Maryland, 821
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