Preparation of a Standard Acid Solution
Content
PREPARATION OF A STANDARD ACID SOLUTION
Name: Eghan Kojo
Index N o : 6138811
Experiment N 0 : A 2.2.3
Graduate Assistant: Judith Odei
Date: 2 n d April, 2013
AIMS
1. To be able to prepare standard solutions.
2. To determine the strength of a given solution of Hydrochloric acid (HCl).
3. To analyze errors that occurs during standardization experiments.
INTRODUCTION
In analytical chemistry, a standard solution is a solution containing a precisely known concentration of
an element or a substance i.e., a known weight of solute is dissolved to make a specific volume. It is prepared
using a standard substance, such as a primary standard. Standard solutions are used to determine the
concentrations of other substances, such as solutions in titrations. The concentrations of standard solutions are
normally expressed in units of moles per litre (mol/L, often abbreviated to M for molarity), moles per cubic
decimetre (mol/dm3), kilomoles per cubic metre (kmol/m3) or in terms related to those used in particular
titrations (such as titres).
Standardization is doing a titration to work out the exact concentration of the solution you want to use to
determine the concentration of an unknown solution. To do a titration you must to know the exact number of
moles of one of the reagents (titrant) you are using so that you can then determine the number of moles of the
unknown reagent.
A simple standard is obtained by the dilution of a single element or a substance in a soluble solvent with which
it reacts. A solution of acid can be standardized by titrating it against a solution of alkali of known
concentration. Once this has been calculated, it can in turn be used as a standard solution to find the
concentration of a solution of alkali.
Standard solutions are also commonly used to determine the concentration of an analyte species. By
comparing the absorbance of the sample solution at a specific wavelength to a series of standard solutions at
differing known concentrations of the analyte species, the concentration of the sample solution can be found via
Beer's Law. Any form of spectroscopy can be used in this way so long as the analyte species has substantial
absorbance in the spectra. The standard solution is a reference guide to discover the molarity of unknown
species. Titration methods can be used to acquire the concentration of a standard solution. These involve using
equipment such as a burette.
Good standardizing reagents should have the following characteristics: They should have a
high degree of purity. They should be stable and unaffected by the atmosphere, i.e. they should not be
efflorescent or deliquescent, for easy weighing.
The process used to determine the concentration of a solution with very high accuracy is called standardizing a
solution. To standardize an unknown solution, you react that solution with another solution whose concentration
is already known very accurately.
In a standardization experiment, the solution being standardized is compared to a known
standard. This known standard can be either a solution that is already a standard solution or an accurately
weighed solid material. The accuracy of standardization depends on the glassware and quality of the reagent
used to prepare the standard. Reagents used as standards are divided into primary reagent and secondary
reagent. A primary reagent can be used to prepare a standard containing an accurately known amount of analyte.
A primary reagent must have a known stoichiometry, a known purity (or assay) and be stable during a long term
storage both in solid and solution form. The purity of a secondary reagent in a solid form or the concentration of
a standard prepared from a secondary reagent must be determined relative to a primary reagent
There are commercially available acids as concentrated solutions. Two of these acids widely used in the
preparation of standard solutions of acids are hydrochloric acid and sulphuric acid. Concentered hydrochloric
acid is about 10.5 - 12M and sulphuric acid is about 18M. From these concentrated solutions, solutions of any
desired approximate concentration can be prepared. If a solution of an exact concentration is required, a solution
of an approximate concentration is first prepared by diluting appropriate volume of the concentrated acid with
distilled water and this is standardized against some alkaline substance such as anhydrous sodium carbonate.
For example, to standardize the hydrochloric acid solution we made up in a preceding lab, we might very
carefully measure a known quantity of that solution (called an aliquot) and neutralize that aliquot with a
solution of sodium carbonate whose concentration is already known very accurately. Adding a few drops of an
indicator, such as phenolphthalein or methyl orange, to the solution provides a visual indication (a color change)
when an equivalence point is reached, when just enough of the standard solution has been added to the
unknown solution to neutralize it exactly. By determining how much of the sodium carbonate solution is
required to neutralize the hydrochloric acid, we can calculate a very accurate value for the concentration of the
hydrochloric acid. This procedure is called titration.
CHEMICALS
1.
2.
3.
4.
Anhydrous sodium carbonate
Methyl orange indicator
Concentrated hydrochloric acid
Distilled water
APPARATUS
1.
2.
3.
4.
1000ml volumetric flask
250ml conical flask
Funnel
Burette
5. Measuring cylinder
6. Electronic balance
PROCEDURE
1. 0.1M hydrochloric acid was prepared
Specific gravity = 1.18g/ml
Percentage purity = 36.5%
Molar mass of HCl = 36.5g/mol
density x precentage purity x 10
concentration=
Molar mass
concentration=
1.18 x 36.5 x 10
36.5
concentration
= 11.8mol/dm3
Final concentration = 0.1M
Final volume = 250ml
Initial concentration = 11.8M
Initial volume = x
0.1 x 250
x=
11.8
x=2.12 ml
2. 2.12ml of the stock solution was measured and diluted to 250ml in a volumetric flask.
3. 0.2g of sodium carbonate were weighed into a 250ml conical flask and dissolved in 100ml of distilled
water and top up to the mark
4. Methyl orange indicator was added and titrated against the prepared acid solution.
5. Two more titrations were done
TABLE OF RESULTS
Colour change = Yellow to orange
Indicator used = Methyl orange
Burette reading/ml
Final reading/ml
Initial reading/ml
Titre value/ml
1
44.50
0.00
44.50
44.50+44.40+ 44.30
Average titre=
3
2
44.40
0.00
44.40
3
44.30
0.00
44.30
Average titre=44.40 ml
CALCULATIONS
The reaction equation of the reaction that occurred between Na2CO3 and HCl is
Na2CO3 + 2HCl
2NaCl + CO2 + H2O
from the above reaction equation
n(Na2CO3) =1
n(HCl)
2
this implies that n(HCl)= 2×n(Na2CO3)
n(Na2CO3)= m/M = 0.2g/106gmol-1= 1.8868×10-3mol
hence n(HCl) = 2×1.8868×10-3= 3.7736×10-3mol
for 44.50ml
[HCl]= 3.7736×10-3mol = 0.0848M
44.50 ×10-3L
for 44.40ml
[HCl]= 3.7736×10-3mol = 0.0850M
44.40×10-3L
for 44.30ml
[HCl]= 3.7736×10-3mol = 0.0852M
44.30×10-3L
mean concentration=
0.0848+ 0.0850+0.0852
3
mean concentration=0.085 M
DISCUSSION
In this experiment a standard 0.1M HCl solution was prepared by diluting a stock solution of the HCl. A
stock solution is a solution from which a dilute solution can be prepared. The prepared solution was
standardized with sodium carbonate pellets which is hygroscopic which absorb water from the surroundings but
do not dissolve. Na2CO3 is 99% pure thus, only the 99% of Na2CO3 would give the accurate concentration of
HCl. That is only 85% of the expected concentration would be determined hence the concentration of HCl after
the experiment is 0.085M which is 85% of the expected concentration. So the 85% of the expected
concentration which is less than the expected concentration of 100% can be due to some errors occurring during
the measurement of the solution also the sodium carbonate might have absorb some water from the
surroundings.
PRECAUTIONS
1. The electronic balance was calibrated before use.
2. Accurate volume measurements were ensured.
3. Sodium carbonate was used for the standardization because it is 99% pure.
SOURCES OF ERROR
1. Since Na2CO3 is hygroscopic, it could have absorbed water molecules from the atmosphere during
weighing thereby increasing the weight.
CONCLUSION
The concentration of HCl after the preparation was found to be 0.085M which is 85% of the expected
concentration. Also, the concentration of the analyte was found to depend on the purity of the standard solution
used.
REFERENCES
1. Freiser, Henry; Nancollas, George H (1987). Compendium of Analytical Nomenclature: Definitive Rules
1987. Oxford: Blackwell Scientific Publications. p. 48
2. Skoog, Douglas A., Donald M. West and F. James Holler. (1995) "Fundamentals of Analytical Chemistry
8th ed." Harcourt Brace College Publishers.
3. Sawyer, C.N. & P.L. McCarty (1978) Chemistry for Environmental Engineers, McGraw Hill Publ,. pp.
65-69, 284-285, 454-462.
Name: Eghan Kojo
Index N o : 6138811
Experiment N 0 : A 2.2.3
Graduate Assistant: Judith Odei
Date: 2 n d April, 2013
AIMS
1. To be able to prepare standard solutions.
2. To determine the strength of a given solution of Hydrochloric acid (HCl).
3. To analyze errors that occurs during standardization experiments.
INTRODUCTION
In analytical chemistry, a standard solution is a solution containing a precisely known concentration of
an element or a substance i.e., a known weight of solute is dissolved to make a specific volume. It is prepared
using a standard substance, such as a primary standard. Standard solutions are used to determine the
concentrations of other substances, such as solutions in titrations. The concentrations of standard solutions are
normally expressed in units of moles per litre (mol/L, often abbreviated to M for molarity), moles per cubic
decimetre (mol/dm3), kilomoles per cubic metre (kmol/m3) or in terms related to those used in particular
titrations (such as titres).
Standardization is doing a titration to work out the exact concentration of the solution you want to use to
determine the concentration of an unknown solution. To do a titration you must to know the exact number of
moles of one of the reagents (titrant) you are using so that you can then determine the number of moles of the
unknown reagent.
A simple standard is obtained by the dilution of a single element or a substance in a soluble solvent with which
it reacts. A solution of acid can be standardized by titrating it against a solution of alkali of known
concentration. Once this has been calculated, it can in turn be used as a standard solution to find the
concentration of a solution of alkali.
Standard solutions are also commonly used to determine the concentration of an analyte species. By
comparing the absorbance of the sample solution at a specific wavelength to a series of standard solutions at
differing known concentrations of the analyte species, the concentration of the sample solution can be found via
Beer's Law. Any form of spectroscopy can be used in this way so long as the analyte species has substantial
absorbance in the spectra. The standard solution is a reference guide to discover the molarity of unknown
species. Titration methods can be used to acquire the concentration of a standard solution. These involve using
equipment such as a burette.
Good standardizing reagents should have the following characteristics: They should have a
high degree of purity. They should be stable and unaffected by the atmosphere, i.e. they should not be
efflorescent or deliquescent, for easy weighing.
The process used to determine the concentration of a solution with very high accuracy is called standardizing a
solution. To standardize an unknown solution, you react that solution with another solution whose concentration
is already known very accurately.
In a standardization experiment, the solution being standardized is compared to a known
standard. This known standard can be either a solution that is already a standard solution or an accurately
weighed solid material. The accuracy of standardization depends on the glassware and quality of the reagent
used to prepare the standard. Reagents used as standards are divided into primary reagent and secondary
reagent. A primary reagent can be used to prepare a standard containing an accurately known amount of analyte.
A primary reagent must have a known stoichiometry, a known purity (or assay) and be stable during a long term
storage both in solid and solution form. The purity of a secondary reagent in a solid form or the concentration of
a standard prepared from a secondary reagent must be determined relative to a primary reagent
There are commercially available acids as concentrated solutions. Two of these acids widely used in the
preparation of standard solutions of acids are hydrochloric acid and sulphuric acid. Concentered hydrochloric
acid is about 10.5 - 12M and sulphuric acid is about 18M. From these concentrated solutions, solutions of any
desired approximate concentration can be prepared. If a solution of an exact concentration is required, a solution
of an approximate concentration is first prepared by diluting appropriate volume of the concentrated acid with
distilled water and this is standardized against some alkaline substance such as anhydrous sodium carbonate.
For example, to standardize the hydrochloric acid solution we made up in a preceding lab, we might very
carefully measure a known quantity of that solution (called an aliquot) and neutralize that aliquot with a
solution of sodium carbonate whose concentration is already known very accurately. Adding a few drops of an
indicator, such as phenolphthalein or methyl orange, to the solution provides a visual indication (a color change)
when an equivalence point is reached, when just enough of the standard solution has been added to the
unknown solution to neutralize it exactly. By determining how much of the sodium carbonate solution is
required to neutralize the hydrochloric acid, we can calculate a very accurate value for the concentration of the
hydrochloric acid. This procedure is called titration.
CHEMICALS
1.
2.
3.
4.
Anhydrous sodium carbonate
Methyl orange indicator
Concentrated hydrochloric acid
Distilled water
APPARATUS
1.
2.
3.
4.
1000ml volumetric flask
250ml conical flask
Funnel
Burette
5. Measuring cylinder
6. Electronic balance
PROCEDURE
1. 0.1M hydrochloric acid was prepared
Specific gravity = 1.18g/ml
Percentage purity = 36.5%
Molar mass of HCl = 36.5g/mol
density x precentage purity x 10
concentration=
Molar mass
concentration=
1.18 x 36.5 x 10
36.5
concentration
= 11.8mol/dm3
Final concentration = 0.1M
Final volume = 250ml
Initial concentration = 11.8M
Initial volume = x
0.1 x 250
x=
11.8
x=2.12 ml
2. 2.12ml of the stock solution was measured and diluted to 250ml in a volumetric flask.
3. 0.2g of sodium carbonate were weighed into a 250ml conical flask and dissolved in 100ml of distilled
water and top up to the mark
4. Methyl orange indicator was added and titrated against the prepared acid solution.
5. Two more titrations were done
TABLE OF RESULTS
Colour change = Yellow to orange
Indicator used = Methyl orange
Burette reading/ml
Final reading/ml
Initial reading/ml
Titre value/ml
1
44.50
0.00
44.50
44.50+44.40+ 44.30
Average titre=
3
2
44.40
0.00
44.40
3
44.30
0.00
44.30
Average titre=44.40 ml
CALCULATIONS
The reaction equation of the reaction that occurred between Na2CO3 and HCl is
Na2CO3 + 2HCl
2NaCl + CO2 + H2O
from the above reaction equation
n(Na2CO3) =1
n(HCl)
2
this implies that n(HCl)= 2×n(Na2CO3)
n(Na2CO3)= m/M = 0.2g/106gmol-1= 1.8868×10-3mol
hence n(HCl) = 2×1.8868×10-3= 3.7736×10-3mol
for 44.50ml
[HCl]= 3.7736×10-3mol = 0.0848M
44.50 ×10-3L
for 44.40ml
[HCl]= 3.7736×10-3mol = 0.0850M
44.40×10-3L
for 44.30ml
[HCl]= 3.7736×10-3mol = 0.0852M
44.30×10-3L
mean concentration=
0.0848+ 0.0850+0.0852
3
mean concentration=0.085 M
DISCUSSION
In this experiment a standard 0.1M HCl solution was prepared by diluting a stock solution of the HCl. A
stock solution is a solution from which a dilute solution can be prepared. The prepared solution was
standardized with sodium carbonate pellets which is hygroscopic which absorb water from the surroundings but
do not dissolve. Na2CO3 is 99% pure thus, only the 99% of Na2CO3 would give the accurate concentration of
HCl. That is only 85% of the expected concentration would be determined hence the concentration of HCl after
the experiment is 0.085M which is 85% of the expected concentration. So the 85% of the expected
concentration which is less than the expected concentration of 100% can be due to some errors occurring during
the measurement of the solution also the sodium carbonate might have absorb some water from the
surroundings.
PRECAUTIONS
1. The electronic balance was calibrated before use.
2. Accurate volume measurements were ensured.
3. Sodium carbonate was used for the standardization because it is 99% pure.
SOURCES OF ERROR
1. Since Na2CO3 is hygroscopic, it could have absorbed water molecules from the atmosphere during
weighing thereby increasing the weight.
CONCLUSION
The concentration of HCl after the preparation was found to be 0.085M which is 85% of the expected
concentration. Also, the concentration of the analyte was found to depend on the purity of the standard solution
used.
REFERENCES
1. Freiser, Henry; Nancollas, George H (1987). Compendium of Analytical Nomenclature: Definitive Rules
1987. Oxford: Blackwell Scientific Publications. p. 48
2. Skoog, Douglas A., Donald M. West and F. James Holler. (1995) "Fundamentals of Analytical Chemistry
8th ed." Harcourt Brace College Publishers.
3. Sawyer, C.N. & P.L. McCarty (1978) Chemistry for Environmental Engineers, McGraw Hill Publ,. pp.
65-69, 284-285, 454-462.
