Tuesday, August 31, 2021

Conductometric titration of strong acid against strong base

Learn about the conductometric titration of strong acid vs strong base through a laboratory experiment or practical.

Aim:

To determine the strength of strong acid using a strong base by conductometry.

Requirements:

Glasswares: Burette, burette stand, conical flask, volumetric pipette, beaker, volumetric flask, funnel, glass rod, and wash bottle, etc.
Chemicals: LR grade sodium hydroxide (NaOH), hydrochloric acid (HCl), potassium hydrogen phthalate (KHP), anhydrous sodium carbonate (Na2CO3), phenolphthalein indicator, and methyl red or methyl indicator, etc.
Apparatus: Digital/analytical balance, and ultrasonicator, conductometer, and magnetic stirrer.

Principle:

The principle of conductometric titration is based on the fact that one of the ions is replaced by the other during the titration, and these two ions usually differ in ionic conductivity, causing the conductivity of the solution to change during the titration.

HCl directly titrates with NaOH to determine its strength, in which sodium hydroxide is a strong base while hydrochloric acid is a strong acid.

Preparation of reagents and solutions:

Preparation of 1 M hydrochloric acid solution:

Take 85.00 ml of hydrochloric acid (HCl) using a pipette, dilute in 1000 ml of distilled water in a volumetric flask, and properly mixing it.

Preparation and standardization of sodium hydroxide:

Click here to get the procedure of preparation and standardization of sodium hydroxide (1M) solution.

Titration procedure:

  • All glassware should be cleaned and dried according to standard laboratory procedures.
  • Before filling the burette for the titration, rinse it with distilled water and then pre-rinse it with a portion of the titrant solution. Pre-rinsing is required to make sure that all solution in the burette is the desired solution, not a contaminated or diluted solution.
  • Take the unknown stock solution of titrant in a clean and dry beaker then fill the burette using the funnel.
  • Remove air bubbles from the burette and adjust the reading to zero.
  • Switch ON the instrument and calibrate the conductivity meter with a standard solution. (Because potassium chloride (KCl) is soluble and stable, it is the most commonly used calibration solution for conductivity meters)
  • Once it is calibrated, rinse the platinum electrode with distilled water.
  • Take 50.00 ml of hydrochloric acid, pour it into a beaker.
  • Properly place the beaker on a stirrer and immerse both the platinum electrodes and set the burette properly on the beaker.
  • Note down the initial reading (conductance) of the sample i.e. millisiemens (mS) or micro-siemens (µS).
  • Turn on the stirrer and add 01.00 ml standardized NaOH solution from the burette at a time, properly record the readings.
  • Continue the titration process until the endpoint is reached.
  • The actual endpoint of the titration is indicated by a sharp increase in the conductivity of the sample.
  • Even after you've reached the endpoint, take a few more readings.
  • Plot the graph between conductivity (mho) vs volume of NaOH and calculate the strength of hydrochloric acid (HCl).

Calculations:

M1V1= M2V2
M2 = V1 M1 / V2

Where,
M1 is the molarity of sodium hydroxide
V1 is the volume of sodium hydroxide
M2 is the molarity of hydrochloric acid
V2 is the volume of hydrochloric acid

Result:

The strength of hydrochloric acid was found to be___M.


Commonly asked quetions on conductimetric titrations are as follows.

What happens when a strong acid is titrated with a strong base?
In the titration of a strong acid-strong base, the acid and base will react to form a neutral solution. The hydronium (H+) and hydroxide (OH-) ions will react to form water at the reaction's equivalence point, resulting in a pH of 07.00.

What is the best indicator for strong acid-strong base titration?
Phenolphthalein indicator is the best indicator for strong acid-strong base titration.

Which is the example conductometric titration of a weak base with a strong acid?
The titration of hydrochloric acid (HCL) in the form of strong acid and ammonium hydroxide (NH4OH) as the weak base is an example of conductometric titration of a strong acid with a weak base.
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Monday, August 30, 2021

Potentiometric titration of strong acid against strong base

Learn about the potentiometric titration of strong acid vs strong base through a laboratory experiment or practical.

Aim:

To determine the strength of strong acid using a strong base by potentiometry.

Requirements:

Glasswares: Burette, burette stand, conical flask, volumetric pipette, beaker, volumetric flask, funnel, glass rod, and wash bottle, etc.
Chemicals: LR grade sodium hydroxide (NaOH), sulphuric acid (H2SO4), potassium hydrogen phthalate (KHP), anhydrous sodium carbonate (Na2CO3), and phenolphthalein indicator, etc.
Apparatus: Digital/analytical balance, and ultrasonicator, potentiometer, and magnetic stirrer.

Principle:

In principle, determining the pH of a solution is easy since it is based on measuring the potential of a hydrogen electrode immersed in the sample solution.

Potentiometry is a type of electrochemical measurement. A strong acid is H2So4, while a strong base is NaOH. H2So4is directly titrated with sodium hydroxide to determine its strength. There is no indicator is required since the endpoint of the reaction can be detected by a sharp change in potential across the electrodes.
potentiometric titration of strong acid vs strong base

Preparation of reagents and solutions:

Click here to get the procedure of preparation and standardization of 01 M sodium hydroxide.
Click here to get the procedure of preparation and standardization of 01 M sulphuric acid solution.

Titration procedure:

  • All glassware should be cleaned and dried according to standard laboratory procedures.
  • Before filling the burette for the titration, rinse it with distilled water and then pre-rinse it with a portion of the titrant solution. Pre-rinsing is required to make sure that all solution in the burette is the desired solution, not a contaminated or diluted solution.
  • Take the unknown stock solution of titrant in a clean and dry beaker then fill the burette using the funnel.
  • Remove air bubbles from the burette and adjust the reading to zero.
  • Switch ON the potentiometer and calibrate the electrodes with pH 04.00, 07.00, and 09.20 standard buffer solutions.
  • Once it is calibrated, rinse the electrode with distilled water.
  • Take 50.00 ml of sulphuric acid, pour it to a beaker
  • Properly place the beaker on a stirrer and immerse both the electrodes and set the burette properly on the beaker.
  • Note down the initial reading of the sample i.e. e.m.f. in millivolts (mV).
  • Turn on the stirrer and add 01.00 ml standardized NaOH solution from the burette at a time, properly record the readings in mV.
  • Continue the titration process until the endpoint is reached.
  • The actual endpoint of the titration is indicated by a sharp increase in e.m.f.
  • Even after you've reached the endpoint, take a few more readings.
  • Plot the graph and calculate the strength of sulphuric acid.

Calculations:

M1V1= M2V2
M2 = V1 M1 / V2

Where,
M1 is the molarity of sodium hydroxide
V1 is the volume of sodium hydroxide
M2 is the molarity of sulphuric acid
V2 is the volume of sulphuric acid

Result:

The strength of sulphuric acid was found to be___ by plotting the normal 1st and 2nd derivative curves.


Commonly asked question on acid-base titration are as follows.

What is potentiometric acid-base titration?
The potentiometric titration technique is similar to the direct titration of a redox reaction. It's a useful method for characterizing an acid. Instead of using an indicator, the potential across the analyte, which is usually an electrolyte solution, is measured.

Which indicator can be used in the titration of strong acid and strong base?
Phenolphthalein indicator is most commonly used in the titration of strong acid and strong base which is one of the most suitable indicators for acid-base titration.

Which is the example titration of a strong acid with a strong base?
The titration of hydrochloric acid (HCL) in the form of strong acid and sodium hydroxide (NaOH) as the strong base is an example of titration of a strong acid with a strong base.


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Assay of sodium chloride

Learn about the assay of sodium chloride through a laboratory experiment or practical.

Aim:

To determine the percentage purity of given sample of sodium chloride using standard 0.1 N AgNO3 (Volhard’s method).

Requirements:

Glasswares: Burette, burette stand, conical flask, volumetric pipette, beaker, volumetric flask, funnel, glass rod, and wash bottle, etc.
Chemicals: LR grade silver nitrate (AgNO3), sodium chloride (NaCl), and potassium chromate (K2CrO4), etc.
Apparatus: Digital/analytical balance, and Ultrasonicator.

This practical is divided into two parts.
A. Preparation and standardization of silver nitrate (0.1 M)
B. To perform the assay of sodium chloride

Principle of assay of sodium chloride:

We already mentioned the principle of assay of sodium chloride in previous article (click here to visit).

Preparation and standardization of silver nitrate (0.1 M):

Click here to get the procedure of preparation and standardization of 0.1 M silver nitrate solution.

Preparation of sodium chloride solution (Sample):

Take 01 gm of sodium chloride and dissolve in 50 ml of distilled water in a volumetric flask, and properly mixing it. Once it has completely dissolved, make up the volume to 100 ml.

Titration procedure:

  • All glassware should be cleaned and dried according to standard laboratory procedures.
  • Before filling the burette for the titration, rinse it with distilled water and then pre-rinse it with a portion of the titrant solution. Pre-rinsing is required to make sure that all solution in the burette is the desired solution, not a contaminated or diluted solution.
  • Take the unknown stock solution of titrant in a clean and dry beaker then fill the burette using the funnel.
  • Remove air bubbles from the burette and adjust the reading to zero.
  • Take 10.00 ml of prepared sample solution of sodium chloride and pour it into a conical flask.
  • Add 2-3 drops of potassium chromate solution as an indicator.
  • Titrate the sample solution with silver nitrate solution until the endpoint is reached.
  • The actual endpoint of the titration is indicated by a brick red color at the end of the reaction.
  • To get accurate results, repeat the titration three times.
  • Properly record the readings of the burette.
  • Take their mean and calculate the molarity of the silver nitrate solution.

Observation table:

Sr. No.

Content in conical flask

Burette reading

Volume of titrant used (ml)

Initial

Final

1

 

 

 

 

2

 

 

 

3

 

 

 

 

Mean:

Calculations:

V x E x AM x 100 / W x RM

Where,
V is a volume of silver nitrate used
E is an equivalent factor
AM is an actual molarity
RM is a required molarity
W is the weight of the sample
For 1 ml of 0.1 M silver nitrate, the equivalent factor of PHP is 0.005845

Result:

The percentage purity of the sodium chloride (NaCl) sample was found to be_____.


Commonly asked questions on titration are as follows.

Which method is used for assay analysis of sodium chloride?
Assay analysis of sodium chloride is performed using the argentometric titration which is a type of titration involving the silver (I) ion, generally used to determine the amount of chloride present in the sample solution.

Which indicator is used in the assay of sodium chloride?
Assay of silver nitrate is based on the precipitation titration in which potassium chromate solution is used as an indicator that produces a brick red color at the end of the reaction.

Which titrant is used for the assay of sodium chloride?
The titrant in the sodium chloride assay is silver nitrate, which determines the chloride ion concentration. The precipitate of silver chloride is produced in the solution when silver nitrate is slowly.
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Sunday, August 29, 2021

Preparation and standardization of 0.1 M silver nitrate

    Learn about the preparation and standardization of silver nitrate through a laboratory experiment or practical.

Aim:

To prepare and standardize 0.1 M AgNO3 using sodium chloride as primary standard (Mohr’s method).

Requirements:

Glasswares: Burette, burette stand, conical flask, volumetric pipette, beaker, volumetric flask, funnel, glass rod, and wash bottle, etc.
Chemicals: LR grade silver nitrate (AgNO3), sodium chloride (NaCl), and potassium chromate (K2CrO4), etc.
Apparatus: Digital/analytical balance, and Ultrasonicator.

Principle:

Prepare and standardize silver nitrate-based on argentometric titration. When silver nitrate is directly titrated against sodium chloride, it forms a white precipitate AgNO3 with NaCl. When all of the NaCl has been consumed, it reacts with K2CrO4 and the endpoint is detected as a brick red color due to the formation of silver chromate and potassium nitrate.
The following is the reaction that is involved in this titration.
preparation and standardization of silver nitrate

The molecular weight of silver nitrate (AgNO3) is 169.87 g/mol.

Preparation of 0.1 M silver nitrate:

Take 16.99 gm of silver nitrate using a pipette, dissolve in 500 ml of distilled water in a volumetric flask, and properly mixing it. Once it has completely dissolved, make up the volume to 1000 ml.

Preparation of 0.1 M sodium chloride:

Take 05.84 gm of previously dried sodium chloride and dissolve in 500 ml of distilled water in a volumetric flask, and properly mixing it. Once it has completely dissolved, make up the volume to 1000 ml.

Preparation of 5% w/v potassium chromate solution:

Take 05.00 gm of potassium chromate and dissolve in 70 ml of distilled water in a volumetric flask, and properly mixing it. Once it has completely dissolved, make up the volume to 100 ml.

Titration procedure:

  • All glassware should be cleaned and dried according to standard laboratory procedures.
  • Before filling the burette for the titration, rinse it with distilled water and then pre-rinse it with a portion of the titrant solution. Pre-rinsing is required to make sure that all solution in the burette is the desired solution, not a contaminated or diluted solution.
  • Take the unknown stock solution of titrant in a clean and dry beaker then fill the burette using the funnel.
  • Remove air bubbles from the burette and adjust the reading to zero.
  • Take 25.00 ml of prepared solution of sodium chloride and pour it into a conical flask.
  • Add 2-4 drops of potassium chromate solution as an indicator.
  • Titrate the sample solution with silver nitrate solution until the endpoint is reached.
  • The actual endpoint of the titration is indicated by a brick red color at the end of the reaction.
  • To get accurate results, repeat the titration three times.
  • Properly record the readings of the burette.
  • Take their mean and calculate the molarity of the silver nitrate solution.


Observation table:


Sr. No.

Content in conical flask

Burette reading

Volume of titrant used (ml)

Initial

Final

1

 

 

 

 

2

 

 

 

3

 

 

 

 

Mean:


Calculations:

M1 V1= M2 V2,
M2 = V1 M1 / V2

Where,
M2 is the molarity of silver nitrate.
V1 is a volume of sodium chloride solution used
M1 is molarity of sodium chloride solution
V2 is a volume of silver nitrate used

Result:

The strength of the prepared silver nitrate solution was found to be_____M.


Commonly asked questions on titration are as follows.

Which indicator is used in the standardization of silver nitrate?
Standardization of silver nitrate is based on the argentometric titration in which potassium chromate solution is used as an indicator that produces a brick red color at the end of the reaction.

Why do we standardize the AgNO3 solution?
Standardization of a prepared silver nitrate solution is performed to determine its exact molarity.

Why should standard silver nitrate be protected from light?
Silver nitrate is protected from light due to it is extremely light-sensitive. This means that when the chemical is exposed to light, it will react. As a result, if this is exposed to direct sunlight or other bright light, it will begin to hydrolyze.
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Saturday, August 28, 2021

Assay of sodium benzoate

Learn about the assay of sodium benzoate through a laboratory experiment or practical.

Aim:

To determine the percentage purity of sodium benzoate using standard 0.1 N perchloric acid (non-aqueous titration).

Requirements:

Glasswares: Burette, burette stand, conical flask, volumetric pipette, beaker, volumetric flask, funnel, glass rod, and wash bottle, etc.
Chemicals: LR grade sodium benzoate (C7H5O2Na), glacial acetic acid (CH3COOH), potassium hydrogen phthalate (KHP), acetic anhydride (C4H6O3), 1-naphtholbenzein and crystal violet, etc.
Apparatus: Digital/analytical balance, and Ultrasonicator.

Principle of assay of sodium benzoate:

Sodium benzoate is a preservative that comes in the form of a white granular or crystalline powder. The base sodium benzoate is dissolved in glacial acetic acid that increases the strength of weak base sodium benzoate. Acetic acid acts as a base during the titration with strong acid, allowing an accurate endpoint to be determined. As an indication, the 1-naphtholbenzein solution is used to detect the endpoint of the reaction.

This practical is divided into two parts:
A: Preparation and standardization of perchloric acid (0.1M).
B: To perform the assay of sodium benzoate.

Preparation and standardization of 0.1 M perchloric acid:

Click here to get the procedure to prepare and standardize perchloric acid (0.1M).

Preparation of 1-naphtholbenzein indicator solution:

Take 200 mg of 1-naphtholbenzein and dissolve in 50 ml of anhydrous glacial acetic acid in a volumetric flask, and properly mixing it. Once it has completely dissolved, make up the volume to 100 ml.

Titration procedure:

  • All glassware should be cleaned and dried according to standard laboratory procedures.
  • Before filling the burette for the titration, rinse it with distilled water and then pre-rinse it with a portion of the titrant solution. Pre-rinsing is required to make sure that all solution in the burette is the desired solution, not a contaminated or diluted solution.
  • Note: Since it is a non-aqueous titration, it needs to be extra careful during the cleaning and drying of glassware. Glassware is required to be clean with acetone and dried for purpose.
  • Take the unknown stock solution of titrant in a clean and dry beaker then fill the burette using the funnel.
  • Remove air bubbles from the burette and adjust the reading to zero.
  • Take 0.25 gm of sodium benzoate and pour it into a conical flask.
  • Add 20.00 ml anhydrous glacial acetic acid, sonicate to dissolve, and if required warm it at 50°C.
  • Then add 2 drops of 1-naphtholbenzein indicator solution.
  • Titrate the sample solution with the perchloric acid solution until the endpoint is reached.
  • The actual endpoint of the titration is indicated by a change of violet color to emerald green.
  • To get accurate results, repeat the titration three times.
  • Properly record the readings of the burette.
  • Take their mean and calculate the percentage purity of sodium benzoate.
  • For the blank determination, repeat the titration as directed above but without the sodium benzoate (B).

Observation table:

A.     For titration of sample

Sr. No.

Content in conical flask

Burette reading

Volume of titrant used (ml)

Initial

Final

1

 

 

 

 

2

 

 

 

3

 

 

 

 

Mean:

  

B.     For titration of blank

Sr. No.

Content in conical flask

Burette reading

Volume of titrant used (ml)

Initial

Final

1

 

 

 

 


Calculations:

% purity of sodium benzoate = V x E x AM x 100 / W x RM
Where,
V is the volume of perchloric acid solution used
V= A-B
A is a volume of perchloric acid solution used in titration with sodium benzoate
B is a volume of perchloric acid solution used in titration without sodium benzoate
E is an equivalent factor
AM is actual molarity
RM is a required molarity
W is the weight of the sample
For 0.1 M perchloric acid solution, the equivalent factor of PHP is 0.01441.

Result:

The percentage purity of sodium benzoate was found to be_____M.


Commonly asked questions on titration are as follows.

Sodium benzoate can be estimated by which titration?
Sodium benzoate can be estimated by the non-aqueous titration method in which it is dissolved in anhydrous glacial acetic acid, which increases the strength of sodium benzoate, a weak basic.

Which indicator is used in sodium benzoate assay?
1-naphtholbenzein indicator solution is used in sodium benzoate assay which produces emerald green at the endpoint or equivalence point.

Which titrant used in the assay of sodium benzoate?
The perchloric acid solution is used as a titrant in the assay of sodium benzoate by non-aqueous titration.
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Preparation and standardization of 0.1M perchloric acid

Learn about the preparation and standardization of perchloric acid through a laboratory experiment or practical.

Aim:

To prepare and standardize 0.1 M perchloric acid using potassium hydrogen phthalate as primary standard. 

Requirements:

Glasswares: Burette, burette stand, conical flask, volumetric pipette, beaker, volumetric flask, funnel, glass rod, and wash bottle, etc.

Chemicals: LR grade glacial acetic acid (CH3COOH), perchloric (HClO4), potassium hydrogen phthalate (KHP), acetic anhydride (C4H6O3), and crystal violet, etc.
Apparatus: Digital/analytical balance, and Ultrasonicator.

Principle:

It is a type of non-aqueous titration in which water is removed by the reaction with the acetic anhydride.
preparation and standardization of perchloric acid

The endpoint of reaction is determined by titrating a known amount of potassium hydrogen phthalate with perchloric acid in glacial acetic acid, in which crystal violet solution is used as an indicator.

The molecular weight of perchloric acid (HClO4) is 100.46 g/mol.

Preparation of crystal violet indicator solution:

Take 54 mg of crystal violet and dissolve in 50 ml of anhydrous glacial acetic acid in a volumetric flask, and properly mixing it. Once it has completely dissolved, make up the volume to 100 ml.

Preparation of 0.1 M perchloric acid:

Take 08.50 ml of perchloric acid using a pipette in a volumetric flask, mix with 500 ml anhydrous glacial acetic acid and 25.00 ml of acetic anhydride. Allow to cool at room temperature and make up the volume to 1000 ml with anhydrous glacial acetic acid.

Let allows the mixture to stand for one day and determining the water content. If it exceeds 0.5 percent, add extra acetic anhydride and let it stand again. The amount of water in the solution must be between 0.2 and 0.5 %.

Titration procedure:

  • All glassware should be cleaned and dried according to standard laboratory procedures.
  • Before filling the burette for the titration, rinse it with distilled water and then pre-rinse it with a portion of the titrant solution. Pre-rinsing is required to make sure that all solution in the burette is the desired solution, not a contaminated or diluted solution.
  • Note: Since it is a non-aqueous titration, it needs to be extra careful during the cleaning and drying of glassware. Glassware is required to be clean with acetone and dried for purpose.
  • Take the unknown stock solution of titrant in a clean and dry beaker then fill the burette using the funnel.
  • Remove air bubbles from the burette and adjust the reading to zero.
  • Take 0.35 gm of previously heated (120°C for 2 hours) KHP and pour it into a conical flask.
  • Add 50.00 ml anhydrous glacial acetic acid.
  • Then add 2 drops of crystal violet indicator solution
  • Titrate the sample solution with the perchloric acid solution until the endpoint is reached.
  • The actual endpoint of the titration is indicated by a change of violet color to emerald green.
  • To get accurate results, repeat the titration three times.
  • Properly record the readings of the burette.
  • Take their mean and calculate the molarity of a perchloric acid solution.
  • For the blank determination, repeat the titration as directed above but without the potassium hydrogen phthalate (B).

Observation table:

A.     For titration of sample

Sr. No.

Content in conical flask

Burette reading

Volume of titrant used (ml)

Initial

Final

1

 

 

 

 

2

 

 

 

3

 

 

 

 

Mean:

 

 B.     For titration of blank

Sr. No.

Content in conical flask

Burette reading

Volume of titrant used (ml)

Initial

Final

1

 

 

 

 

Calculations:

Molarity of perchloric acid = W x RM / V x E
Where,
W is a weight of KHP
E is an equivalent factor of KHP
RM is a required molarity
V is the volume of perchloric acid solution used
V= A-B
A is the volume of perchloric acid solution used in titration with KHP
B is the volume of perchloric acid solution used in titration without KHP
For 0.1 M perchloric acid solution, the equivalent factor of PHP is 0.020422.

Result:

The strength of the prepared perchloric acid solution was found to be_____M.


Commonly asked questions on titration are as follows.

Which indicator is used in the standardization of perchloric acid solution?
Crystal violet is used as an indicator in the standardization of perchloric acid solution which produces emerald green at the endpoint or equivalence point.

Why do we standardize perchloric acid solution?
Standardization of a prepared perchloric acid solution is performed to determine its exact molarity.

What type of titration is the standardization of perchloric acid?
Standardization of perchloric acid is a type of non-aqueous titration.
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