Name: Isabelle M. Escamis
CYS: BSES-2B
Group: 5 (De Peralta, Donadillo, Escamis)
Date:
Crs. Proff.
Lab. Rep.:
June1, 2022
Ma’am Corazon D. Sacdalan
9
EXPERIMENT NO. 9
DETERMINATION OF CHLORIDE ION BY MOHR METHOD
Introduction
As it was studied during previous laboratory experiments, we have known that titration is a
method of determining the concentration of an unknown component in a solution by adding known
amounts of a standard solution to the unknown. The unknown's concentration can then be determined
using the reaction's stoichiometry and the number of moles of standard solution required to reach the
"end point." In this experiment, the Mohr method is used where it is a titration technique that
determines the chloride ion content of a solution by titrating it with silver nitrate.
Objectives:
The main objective of this experiment is to learn how to titrate using the Mohr method to
determine the percentage of salt (NaCl) in the solution.
Apparatus/Materials:
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✓
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Digital balance
Micro pipette
Burette
Erlenmeyer flask
Volumetric flask
Wash bottle
✓
✓
✓
✓
✓
Graduated cylinder
0.1 N Sodium Chloride (NaCl)
0.1 N Silver Nitrate (AgNO3)
Potassium Chromate (K2CrO4)
Distilled water
Procedure:
5 g of potassium chromate crystal was dissolved in a volumetric flask filled with 100 mL
water and was mixed by shaking. After properly dissolving everything, the flask was covered with
aluminum foil to prevent direct light exposure before it was kept in a cool dark place. Then, 0.584 g
of NaCl was weighed and then transferred to a 100 mL volumetric flask which was filled up to the
mark before it was mixed well as the 0.1N NaCl solution. For the preparation of 0.1N AgNO3, 1.699
g silver nitrate crystal was weighed after that, was dissolved in 100 mL water, mixed well, and it is
then kept in an amber-colored container to avoid direct light exposure. We then took 10 mL of 0.1N
NaCl and poured it in an Erlenmeyer flask and added 1 mL of potassium chromate indicator. The
burette was washed with a small amount of silver nitrate before it was filled to the mark. We
continuously shake the flask after beginning titration. A reddish-brown precipitate formed shortly
after which indicates the endpoint of the titration. The volume of silver nitrate was then recorded, and
the normality of silver nitrate was calculated. After all that, 0.25 g of NaCl was weighed and placed in
a 250 mL Erlenmeyer flask where 50 mL of water is added and swirled until it was completely
dissolved. 1 mL of potassium chromate is added after that before the burette was filled with silver
nitrate up to the mark to start titration. While titrating, the flask was continuously mixed until the
reddish-brown precipitate was observed ending the titration before recording of the final burette
reading and finally the %NaCl was calculated.
Data and Results
Name: Isabelle M. Escamis
CYS: BSES-2B
Group: 5 (De Peralta, Donadillo, Escamis)
Date:
Crs. Proff.
Lab. Rep.:
June1, 2022
Ma’am Corazon D. Sacdalan
9
Group 5
A. Preparation of 0.1N NaCl (mass of NaCl=0.5854 g)
B. Standardization of 0.1 N AgNO3
Volume of AgNO3, mL
Vi
Trial
V2
Vused
N AgNO3
1
0.00
10.80
10.80
0.0927 N
2
10.80
21.55
10.75
0.09321 N
4
21.55
31.64
10.09
0.09931 N
Ave. N AgNO3
Computations:
0.0951 N
Name: Isabelle M. Escamis
CYS: BSES-2B
Group: 5 (De Peralta, Donadillo, Escamis)
Date:
Crs. Proff.
Lab. Rep.:
June1, 2022
Ma’am Corazon D. Sacdalan
9
Name: Isabelle M. Escamis
CYS: BSES-2B
Group: 5 (De Peralta, Donadillo, Escamis)
Date:
Crs. Proff.
Lab. Rep.:
June1, 2022
Ma’am Corazon D. Sacdalan
9
A. Determination of NaCl in unknown sample
Volume of AgNO3, mL
Vi
V2
Vused
Moles of NaCl
1
Mass
sample
0.2522 g
0.55
43.38
0.04283
2
0.2515 g
1.00
44.15
4
0.2529 g
0.00
43.45
Trial
% NaCl
4.073 x 10-3 mol
Mass
NaCl
0.2380g
0.04315
4.104 x 10-3 mol
0.2399g
95.39%
0.04345
4.132 x 10-3 mol
0.2415g
95.49%
Ave. % NaCl
Ave. Mass NaCl
94.37%
95.08%
0.2398g
Name: Isabelle M. Escamis
CYS: BSES-2B
Group: 5 (De Peralta, Donadillo, Escamis)
Date:
Crs. Proff.
Lab. Rep.:
June1, 2022
Ma’am Corazon D. Sacdalan
9
Name: Isabelle M. Escamis
CYS: BSES-2B
Group: 5 (De Peralta, Donadillo, Escamis)
Date:
Crs. Proff.
Lab. Rep.:
June1, 2022
Ma’am Corazon D. Sacdalan
9
Discussion
The well-known Mohr's method for chloride measurement, in which alkaline or alkaline earth
chlorides interact with silver nitrate with a few drops of potassium chromate solution as an indicator,
is a simple, direct, and accurate procedure.
As seen in our calculations, a given mass of sodium chloride, and three initial and three final
volumes of silver nitrate were the values used to successfully obtain the total volumes, and average
N of silver nitrate used which was 0.0951 N. The Mohr titration was obviously used to quantify the
amount of chloride in the material. Because chromate ion is the conjugate base of the weak chromic
acid, the titration was done at a pH between 7 and 10, and when the pH falls below 7, the chromate
ion is protonated, and the chromic acid form dominates the solution. As a result, the chromate ion
concentration in more acidic solutions is insufficient to create the precipitate at the equivalence
point. Brownish silver hydroxide occurs at pH levels above 10, masking the terminal point. By
saturating the analyte solution with sodium hydrogen carbonate, a sufficient pH was attained.
It is also apparent that the same temperatures were used throughout the experiment since the
silver chloride and silver chromate solubilities depend on temperature. So, all in all we are able to get
our own group’s correct values using the past given formulas for the needed measurements of
missing values.
Conclusion
This experiment employed Mohr titration to determine the amount of chloride in an unknown
sample. The sodium chloride's normality is 0.1002 N, which was then used to compute the silver
nitrate's normality over three trials, yielding an average of 0.0951 N.
It is known now that potassium chromate is one of numerous chromates used in the
manufacture of coatings and primers as anticorrosive agents. Because of its unique ability to react at
the metal coating interface to limit corrosion, particularly galvanic pair corrosion, chromates are
frequently utilized as corrosion and rust inhibitors. When distinct metallic parts are in touch, chromate
has the remarkable ability to actively block electron transport at both cathodic and anodic locations,
even at very low concentrations. Furthermore, because inhibitors dissolve in water and transfer to the
exposed surface, if the inhibitor's solubility is too high, it may be washed away, while if the solubility
is too low, the inhibitor's action will be reduced.
The following could be sources of error for this experiment: the pH of the solution should be
between 6.5 and 10. The end point cannot be reliably established if the solution is acidic; the reaction
with silver nitrate is not chloride specific. Interfering ions, such as bromide, can affect the titer value
if present in the chloride solution; chromate indicator color change (pale yellow to orange)
identification found to be difficult, especially when looking through a white precipitate; silver nitrate
solution is light sensitive, so it should not be left in the burette for too long without being protected
from ambient light.
Name: Isabelle M. Escamis
CYS: BSES-2B
Group: 5 (De Peralta, Donadillo, Escamis)
Date:
Crs. Proff.
Lab. Rep.:
June1, 2022
Ma’am Corazon D. Sacdalan
9
Application
Just like the life applications of the Mohr method in the previous titration experiments which
can be seen in the food, wine, pharmaceutical industries, water treatment industries, there is no doubt
that this analytical method is important to human survival. This is especially when all types of food
industries or businesses allows food processors and manufacturers to measure and calculate the
amount of a reactant in a sample food product. An example of this is the determination of the right
amount of salt content of a specific edible product that is safe for any type of consumer. Another is
the use of Mohr method to calculate and find out the measurements of the concentrations of vitamins
important for human health that could be put in food or medicine products. In terms of water industry,
it is also an important method since it can be used to determine the chloride ion concentration present
in many sources of water samples such as streams or rivers.
Name: Isabelle M. Escamis
CYS: BSES-2B
Group: 5 (De Peralta, Donadillo, Escamis)
Date:
Crs. Proff.
Lab. Rep.:
June1, 2022
Ma’am Corazon D. Sacdalan
9
References
Determination or assay of sodium chloride (NaCl) by titration_a complete procedure (Mohr's method)
https://youtu.be/gE7Z8DkfZ0A
Determination of salt (as NaCl) in Food & Other SAMPLES_A complete procedure (is 3507mohr's method)
https://youtu.be/spU6nkvg7wY