Practical Analytical Chemistry
First Year
Medical Laboratory Science, University of Raparin
2022 – 2023
Experiment (1)
Standardization of hydrochloric acid by a standard solution of
.sodium carbonate (0.2N)
Lecturer: Salah Kamal Omer
Salah.kamal15@uor.edu.krd
Introduction:
• Standardization is the process of determining the exact
concentration of a solution by titration against standard solution.
• Titration is the process of adding a standard solution of known
concentration (titrant) to a solution of the analyte (titrand) until
the point at which the reaction is believed to be complete.
• Standard Solution is a reagent of a known concentration which is
prepared from primary standard substance.
Titrant
Titrand
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Introduction:
• Primary Standard substance is a reagent having the following
properties:
1. Extremely pure
2. Stable
3. Non hygroscopic
4. Has a high molecular weight
Some primary standards
dichromate, oxalic acid etc.
Primary standard
substance
3
Dissolution
are sodium
carbonate,
Primary standard
solution
Secondary
standard solution
potassium
Non-standard
solution
Standardization
Introduction:
• Indicator is a chemical substance that having different colour in
acids and bases. Indicators are used to give an observable physical
change (end point) at or near the equivalence point during the
titration.
• Equivalence Point is the point at which the amount of added
titrant is chemically equivalent to the amount of analyte in a
sample.
•
End point is the point at which color change occurs due to a pH
change.
• End point occurs only once in a titration while a titration can have
multiple equivalence point.
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The aim of this experiment:
• In this experiment, a standard solution of sodium
carbonate is used to determine the exact concentration of a
hydrochloric acid solution (standardization). Methyl orange
indicator is used.
• Hydrochloric acid HCl is unstable? So it is necessary to
standardize its solutions so as to know the exact
concentration.
Chemicals and tools:
• Burette
• Conical flask
• Beaker
• pipette
• Sodium carbonate solution Na2CO3 (standard).
• HCl solution of unknown normality.
5 • Methyl orange indicator.
Procedure:
1. Prepare 100ml solution of 0.2N Na2CO3.
2. Add the base solution to the burette.
3. Transfer 10 ml of the HCl solution with a pipette to a conical flask
then add one to two drops of methyl orange to this solution (red
to pink color).
4. Add the Na2CO3 (standard solution) from the burette gradually
with continuous stirring of the solution in the conical flask.
Continue the addition of the base till the color of the solution
passes from red to yellow.
5. Calculate the concentration of the HCl solution.
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Calculations:
Suppose that the volume of HCl is V1 and its normality is N1 while V2
is the volume taken from sodium carbonate (Na2CO3) and N2 is its
normality.
Sodium carbonate reacts with hydrochloric acid according to the
following equation:
Na2CO3 + 2HCl → 2NaCl + CO2 + H2O
(N1 x V1) HCl = (N2 x V2) Na2CO3
N1HCl = =
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N