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.
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 |
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|
|
|
2 |
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|
| |
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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