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Iodometric Titration: Principle, Example, Advantages, and How Does it Work

Wednesday, April 20, 2022

Identification test for boric acid

Learn the identification test for boric acid through a laboratory experiment or practical.

Aim:

To perform an identification test for boric acid.

Reference: Indian Pharmacopoeia (IP)

Requirements:

Glasswares and miscellaneous:

Test tube, measuring cylinder, pipette, glass rod, volumetric flask, beaker, dropper, rubber stopper, test tube stand, test tube holder, balance, etc.

Chemicals:

Boric acid (H3BO3), methanol (CH3OH), sulphuric acid (H2SO4), etc.

Theory of identification test for boric acid:

Identification tests are used to determine the drug's quality so that it can be used safely. Boric acid is often used as an antiseptic, insecticide, flame retardant, neutron absorber, or chemical precursor to other chemical compounds. It is also used as a dusting powder.

It's a crystalline powder that's colorless or white, odorless, and has some bitter taste. It is sparingly soluble in water and ethanol, and freely soluble in boiling water, ethanol, and glycerin.

Procedure of identification tests for boric acid:

With gentle warming, dissolve 0.1 gm of boric acid in 05 ml of methyl alcohol containing a few drops of H2SO4. Perform the flame test by igniting the solution. The flame has a green border because of the formation of methyl bromate.
Taker 03 gm of boric acid and dissolve it in 90 ml of boiling water and cool. The solution is faintly acidic.

Observation table:

Sr.

Identification test

Observation

Inference

Dissolve 0.1 gm by warming+05 ml methanol+4-5 drops of H2SO4.

Flame test: Ignite the solution

Green flame

Boric acid:

Present/Absent

03 gm of sample+90 ml of water (boiling) and cool

Acid solution

Boric acid:

Present/Absent

Result:

The given sample is identified as boric acid.

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Identification test for barium sulphate

Learn the identification tests for barium sulphate through a laboratory experiment or practical.

Aim:

To perform an identification test for barium sulphate.

Reference: Indian Pharmacopoeia (IP) 2010

Requirements:

Glasswares and miscellaneous:

Test tube, measuring cylinder, pipette, glass rod, volumetric flask, beaker, dropper, rubber stopper, test tube stand, test tube holder, litmus paper, balance, etc.

Chemicals:

Barium sulphate (BaSO4), barium chloride (BaCl2), sodium carbonate (Na2CO3), lead acetate (Pb (C2H3O2)2), sulphuric acid (H2SO4), and hydrochloric acid (HCl), etc.

Theory of identification test for barium sulfate:

This identification of BaSO4 is usually based on the reactions of ions and cations present in the sample, by which we can determine the quality of the drug. Barium sulfate/sulphate is an inorganic compound. It is a crystalline white solid that is odorless. In water, organic solvents, and dilute acid and alkali solutions, it is insoluble.

Procedure:

For five minutes, boil 0.2 g BaSO4 in a 50% Na2CO3 solution. The salt is not soluble. By fusing it with anhydrous sodium carbonate or anhydrous potassium carbonate, it is converted into a less soluble salt. Filter the resulting mass after treating it with hot water. Perform barium tests on the residue collected on filter paper and for sulphate in filtrate collected after filtration.

BaSO3 + Na2CO3 → Na2SO4 + BaCO3

Identification tests for barium ion:

Dissolve a portion of the residue in HCl and perform a flame test. The presence of barium ions is indicated by the yellowish-green color of the flame.
Wash off the remaining residue with a small amount of water continuously. Wash off the other part of the residue with a small amount of water continuously. Add 5 mL of dilute hydrochloric acid to the residue and filter. To the filtrate, add 0.3 ml of dil. HCl. A white barium sulfate precipitate is formed, which is insoluble in nitric acid (HNO3).

Identification tests for sulphate ion:

To a portion of the filtrate, add 01 ml of barium chloride solution. A white precipitate formed from the formation of barium sulfate.
To 01 ml of filtrate, add 01 ml of lead acetate solution. A white precipitate formed from the formation of barium sulfate lead sulphate. Ammonium acetate solution and sodium hydroxide dissolve the precipitate.

Result:

The given sample is identified as barium sulphate.

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Tuesday, April 19, 2022

Identification test of ammonium chloride

Learn the identification tests for ammonium chloride through a laboratory experiment or practical.

Aim:

To perform an identification test for ammonium chloride.

Reference: Indian Pharmacopoeia (IP) 2010

Requirements:

Glasswares and miscellaneous:

Test tube, measuring cylinder, pipette, glass rod, volumetric flask, beaker, dropper, rubber stopper, test tube stand, test tube holder, litmus paper, balance, etc.

Chemicals:

Ammonium chloride (NH4Cl), sodium hydroxide (NaOH), sodium cobalt nitrate (CoN6Na3O12), light magnesium oxide (MgO), silver nitrate (AgNO3), ammonia solution, potassium dichromate(K2Cr2O7), diphenylcarbazide (C13H14N4O), hydrochloric acid (HCl), nitric acid (HNO3), sulphuric acid (H2SO4), and methyl red solution, etc.

Theory of identification test for ammonium chloride:

The purpose of identification tests is to determine the quality of a drug so that it can be used safely. This identification of NH4Cl is usually based on the reactions of ions and cations present in the sample, by which we can determine the quality of the drug.

Ammonium chloride comes in the form of colorless, or white crystalline powder, odorless, with a saline flavor. It is used as a diuretic, expectorant, and systemic acidifier. It is slightly soluble in ethanol and easily soluble in water.

Procedure:

Identification tests for ammonium ion:

Heat a small amount of NH4Cl in a solution of sodium hydroxide.
Add 3-4 drops of sodium cobalt nitrate (10% w/v) to the ammonium chloride solution.
A yellow precipitate of ammonium cobalt nitrate is formed.
To the solution of ammonium chloride, add 0.2 gm of light magnesium oxide. Pass a flow of air through the mixture and direct the gas which is evolved just below the surface of the mixture of 01.00 ml of HCl (0.1 M) and 0.05 ml of methyl red solution. The solution color changes to yellow.

Identification tests for chloride ion:

Add 01.00 ml of dilute HNO3 solution to a 03.00 ml solution of ammonium chloride.
Then add a few drops of silver nitrate solution, resulting in a white silver nitrate precipitate.
When dilute ammonia is added, the precipitate dissolves due to the formation of a complex. (NH4CI + AgNO3 → AgCI+ NHNO3)
In a test tube, add 0.2 gm potassium dichromate and 01 ml sulphuric acid with a little amount of ammonium chloride. Cover the mouth of the test tube with a filter-paper strip soaked with 0.1 mL of diphenylcarbazide solution. The color of the paper changes to a violet-red color.

Result:

The given sample is identified as ammonium chloride.

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Monday, April 18, 2022

Assay of calcium lactate

Learn about the assay of calcium lactate through a laboratory experiment or practical.

Aim:

To perform an assay of a given sample of calcium lactate.

Requirements:

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

Chemicals: Calcium lactate (C6H10CaO6), calcium chloride (CaCl2), EDTA (C10H16N2O8), magnesium sulphate (MgSO4), ammonium chloride (NH4Cl), ammonia (NH3), and eriochrome black-T (C20H12N3O7SNa ) etc.

Apparatus: Digital/analytical balance, pH meter.

Theory of assay of calcium lactate:

The calcium lactate is a white crystalline salt (granules or powder) with formula C6H10CaO, it is odorless or with a slight but not unpleasant odor. It has 218.2 g/mol. molecular weight, and is soluble in water, very soluble in methanol, and insoluble in ethanol. Calcium lactate is a specific antacid that is also used to treat calcium deficiency.

This titration (assay) is an example of complexometric titration. Complexometric titration is a reaction in which a metal ion is converted into a stable complex ion by the addition of a reagent or ligand. Eriochrome Black-T is used as an indicator, which produces a blue endpoint, is used as an indicator.

Reaction involved in the assay of calcium lactate is as follows.

Preparation of 0.05 M disodium edetate solution:

Take 18.60 gm of disodium edetate and dissolve in 800 ml of distilled water in a volumetric flask, and properly mix it. Once it has completely dissolved, make up the volume to 1000 ml with water.

Preparation of 0.05 M calcium chloride solution:

Take 14.70 gm of calcium chloride and dissolve in 800 ml of distilled water in a volumetric flask, and properly mix it. Once it has completely dissolved, make up the volume to 1000 ml with water.

Preparation of ammonia buffer (pH 10):

Take 05.40 gm of ammonium chloride and dissolve in 20 ml of distilled water in a volumetric flask, add 35 ml of 10 M ammonia and properly mix it. Once it has completely dissolved, make up the volume to 100 ml with water.

Preparation of 0.05 M magnesium sulphate solution:

Take 12.50 gm of magnesium sulphate and dissolve in 800 ml of distilled water in a volumetric flask, and properly mix it. Once it has completely dissolved, make up the volume to 1000 ml with water.

Procedure:

Standardization of EDTA solution:

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 ml of 0.5 M calcium chloride solution and pour it into a conical.
Add 2-3 drops of Eriochrome Black-T indicator and properly mix it.
Titrate the sample solution with 0.05M EDTA until the endpoint is reached. The actual endpoint of the titration is indicated by a change in color from red to blue.
Properly record the readings of the burette.
To get accurate results, repeat the titration three times.
Take their mean and calculate the molarity of 0.05M EDTA solution.

Procedure for assay of calcium lactate:

Accurately weigh 00.3 gm of calcium lactate and pour into a conical and add 50.00 ml of distilled water to dissolve it.
Add 5.0 ml of 0.05 of magnesium sulphate and 10.00 ml of strong ammonia solution.
Add 2-3 drops of Eriochrome Black-T indicator.
Titrate the sample solution with 0.05M EDTA until the endpoint is reached.
Properly record the readings of the burette.
Subtract the volume of magnesium sulphate solution added from the volume of 0.05 M disodium edetate needed.
To get accurate results, repeat the titration three times.
Take their mean and calculate the percentage purity of calcium lactate.

Observation table:

Sr. No.	Content in conical flask	Burette reading		Volume of titrant used (ml)
Sr. No.	Content in conical flask	Initial	Final	Volume of titrant used (ml)
1
2
3
				Mean:

Calculations:

Percentage purity of C6H10CaO6= V x E x AM X 100 / W x RM

Where,

V is a volume of EDTA used

E is an equivalent factor

AM is an actual molarity

RM is a required molarity

W is the weight of the sample

Each mL of 0.05M disodium edetate is equivalent to 0.001091 gm of C6H10CaO6.

Result:

The percentage purity of the given sample calcium lactate was found to be_____.

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Saturday, April 16, 2022

Assay of borax

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

Aim:

To determine the percentage purity (assay) of borax in a given sample using standard 0.5N HCl

Requirements:

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

Chemicals: Borax, hydrochloric acid (HCl), sodium carbonate (Na2CO3), methyl red indicator, etc.

Apparatus: Digital/analytical balance.

Theory of assay of borax:

Borax has a molecular weight of 381.4 g/mol and is sodium tetraborate decahydrate Na2B4O7.10H2O. It comes in a crystalline powder or a glassy crystal that’s colorless. Since borax is alkaline in nature, it can be titrated with a standard solution of an acid. On titration with HCl, it converted to boric acid and sodium chloride (NaCl).

The indicator must be carefully chosen so that it is not affected by liberated boric acid to obtain the correct endpoint of the titration. The methyl red indicator, which is employed in the assay of borax, which changes from yellow to pink, is more suitable for this requirement. It is an acid-base titration.

The reaction involved in the assay of borax is as follows:

Preparation of 0.5 M hydrochloric acid solution:

Take 42.50 ml of HCl using a pipette, dilute it with 1000 ml of distilled water in a volumetric flask, and properly mix it.

Preparation of 0.5 M sodium carbonate solution:

Take 52.95 gm of anhydrous sodium carbonate and dissolve it in 500 ml of distilled water in a volumetric flask, and properly mix it. Once it has completely dissolved, make up the volume to 1000 ml.

Procedure:

Standardization of 0.5 M hydrochloric acid solution:

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 ml of 0.5 M sodium carbonate solution and pour it into a conical.
Add 2-3 drops of methyl red indicator.
Titrate the sample solution with HCl until the endpoint is reached. The actual endpoint of the titration is indicated by the appearance of red color.
Properly record the readings of the burette.
To get accurate results, repeat the titration three times.
Take their mean and calculate the molarity of 0.5M HCl.

Procedure for the assay of borax:

Accurately weigh 03.00 gm of borax and pour into a conical and add 75.00 ml of distilled water.
Add 2-3 drops of methyl red indicator.
Titrate the sample solution with 0.5 M HCl until the endpoint is reached.
Properly record the readings of the burette.
To get accurate results, repeat the titration three times.
Take their mean and calculate the percentage purity of borax.

Observation table:

Sr. No.	Content in conical flask	Burette reading		Volume of titrant used (ml)
Sr. No.	Content in conical flask	Initial	Final	Volume of titrant used (ml)
1
2
3
				Mean:

Calculations:

Percentage purity of Na2B4O7.10H2O = V x E x AM X 100 / W x RM

Where,

V is a volume of HCl used

E is an equivalent factor

AM is an actual molarity

RM is a required molarity

W is the weight of the sample

Each mL of 0.5M hydrochloric acid is equivalent to 0.09535 gm of borax.

Result:

The percentage purity of the given sample borax was found to be_____.

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Iodometric Titration: Principle, Example, Advantages, and How Does it Work

Why do we standardize a solution?

Titration, often referred to as titrimetry, is a volumetric analysis used to measure the analyte concentration in a sample solution. In which the two steps performed are called standardization and titration.

Standardization is the process of calculating the exact concentration of the prepared solution. Titration is the process of calculating an unknown sample concentration. Standardization is often done in the form of titrations.

It consists of a burette filled with titrant and a pipette that is used to pour the titrand into the conical flask where the reaction takes place.

Until the reaction is complete, i.e., the chemical equivalence point or endpoint, a titrant of a known concentration is applied. To indicate the endpoint, a chemical compound called an indicator is used.

Why do we standardize a solution?

It is required to standardize the solution/reagent before starting an experiment since it allows us to obtain accurate measurements during the experiment; On the other hand, the exact concentration of the solution may differ.

You can also reduce the deviation of instrumental and random human errors by standardizing the solution.

As a result, it's necessary to standardize and measure the actual concentration right at the start of the titration.

Example of standardization in chemistry:

Standardization of sodium hydroxide (NaOH) using potassium hydrogen phthalate (C8H5KO4) or oxalic acid dihydrate (C2H2O4). In which KHP/oxalic acid solution is used as a primary standard.

If you prepare the 0.1N NaOH solution, however, its actual concentration is not actual 0.1N therefore we need to standardize it to determine its exact concentration.

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Friday, April 15, 2022

How and where should NaOH solution be stored?

Sodium hydroxide also known as caustic soda belongs to the category of inorganic compounds is highly soluble in water. It is a corrosive white crystalline solid that freely absorbs moisture from air until dissolved. Its molecular formula is NaOH, molar mass is 39.997 g/mol, and density is 2.13 g/cm³.

In industrial, NaOH is a commonly used as strong base. It is used to make sodium salts and detergents, as well as for pH control and organic synthesis. It is usually handled in bulk as an aqueous solution because solutions are cheap and easy to handle.

Table of Contents:

How to store sodium hydroxide?
What happens when NaOH is left in an open container?
Where should NaOH solution be stored?
Why standardized NaOH should be kept in a stoppered bottle?
Why is a plastic bottle generally preferred to a glass bottle to store NaOH?
How long can you store NaOH solution?
Can we store NaOH in aluminum container?
Why does glass not react with acid?

How to store sodium hydroxide?

Most sodium hydroxide is packaged in plastic containers which is made from high-density polyethylene (HDPE). To avoid water and/or CO2 adsorption, solid form of NaOH should be stored in airtight containers with limited atmospheric exposure. When not in use, make sure the container is tightly sealed and airtight. When not in use, make sure the container is tightly sealed and airtight.

What happens when NaOH is left in an open container?

Sodium hydroxide pellets absorb water from the air so rapidly that they melt if exposed in the open, hence it need to be covered.

Where should NaOH solution be stored?

Plastic containers should be used to store sodium hydroxide stock solutions, glass containers should be avoided. To avoid the formation of carbonate in volumetric NaOH solutions, they should be kept away from air.

Why standardized NaOH should be kept in a stoppered bottle?

When atmospheric carbon dioxide comes into contact with the stored NaOH, it reacts to form carbonic acid, therefore, the base concentration decreases. To avoid contact with ambient carbon dioxide, NaOH should be stored in a closed bottle.

Why is a plastic bottle generally preferred to a glass bottle to store NaOH?

The fact that Na2CO3 is also a component of glass is one reason for this. As a result, the Sodium carbonate formed in the air by the reaction of NaOH and CO2 can initiate crystallization on the Na2CO3 in the glass, thus creating a bonding between stopper and bottle.

The given reaction is that NaOH reacts with CO2 to form Na2CO3, and if a glass stopper is used, it will be tightly stuck. By the reaction

2NaOH (aq) + CO2 (g) -> Na2CO3(s) + H2O (l).

There are Teflon sleeves for standardized conical glass stoppers as well as conical plastic stoppers, which prevent this.

How long can you store NaOH solution?

When stored correctly in a dark, cool environment, sodium hydroxide solution has a shelf life of approximately 30 days.

Can we store NaOH in aluminum container?

NaOH cannot be stored in a vessel made with aluminum (Al) or zinc (Zn), because hydrogen gas is produced (redox reaction occurs) when sodium hydroxide reacts with aluminum from sodium metalluminate. In the reaction between sodium hydroxide and metals, hydrogen atoms undergo reduction.

Why does glass not react with acid?

Because glass has a very robust and stable atomic structure, it is unaffected by acid. Due to its strong chemical bonds, the most common material in glass, silicon dioxide, is a particularly non-reactive substance, making glass very resistant to most acids. Glass is resistant to most acids, however is susceptible to attack by alkaline substances, particularly the concentration of OH- ions which gives a pH greater than 09.00.

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Iodometric Titration: Principle, Example, Advantages, and How Does it Work