Learn about the preparation and standardization of 0.1 N iodine solution through a laboratory experiment or practical.
Aim:
To prepare and standardize 0.1 N iodine solution using 0.1 N sodium thiosulphate as secondary standard (Iodimetry).
Requirements:
Glasswares: Burette, burette stand, conical flask, volumetric pipette, beaker, volumetric flask, funnel, glass rod, and wash bottle, etc.
Chemicals: Analytical grade iodine (I), potassium iodide (KI), hydrochloric acid (HCl), sodium thiosulphate (Na2S2O3), mercuric iodide (HgI2), sodium carbonate (Na2CO3), arsenic trioxide (As2O3), methyl orange solution, and starch solution, etc.
Preparation of starch solution:
Mix 01.00 gm soluble starch with 10.00 ml distilled water, then add this solution to 100ml boiling water containing 10.00 mg mercuric iodide.
Preparation of 0.1 N iodine solution:
Take 14.00 gm of iodine and dissolve in a solution of 36.00 gm of potassium iodide in 100ml of water. Add 2-3 drops of hydrochloric acid, then dilute to 1000 ml in an amber-colored volumetric flask.
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.
- Weigh 0.15 gm of arsenic trioxide that has been dried for 1 hour at 105°C.
- Dissolve in 20 ml of 1N NaOH solution, heating it if necessary.
- Dilute it with 40.00 ml of water and add 2 drops of methyl orange solution.
- Add diluted HCl drop by drop until the yellow color turns pink, and then add 02.00 gm of sodium carbonate.
- Dissolve it in 50.00 ml of water and add 03.00 ml of prepared starch solution.
- Titrate the solution with 0.1N iodine solution until the endpoint.
- A permanent blue color indicates the endpoint of the titration.
- To get accurate results, repeat the titration three times.
- Properly record the readings of the burette.
- Take their mean and calculate the normality of the iodine solution.
Observation table:
Sr. No. | Content in conical flask | Burette reading | Volume of titrant used (ml) | |
Initial | Final | |||
1 | | | | |
2 | | | | |
3 | | | | |
| Mean: | |||
Each ml of 0.1 N Iodine solution ≡ 0.00496 grams of Arsenic Trioxide
Calculations:
I= W / 0.0496 x V
Where,
I is the normality of iodine solution,
W is grams of As2O3 used,
V is required iodine solution in ml
Result:
The strength of the prepared iodine solution was found to be_____N.
Frequently Asked Questions (FAQ):
What is the molarity of 0.1N iodine?
The molarity of 0.1N iodine is 0.05M. It is also used topically as a disinfectant and antibacterial agent.
Why do we use sodium carbonate in the standardization of iodine?
Under acidic pH conditions, thiosulfate becomes unstable, the sodium carbonate solution is alkaline, and the abundance of hydroxide anions prevents thiosulfate from encountering the positive charges that would trigger its decomposition. Hence sodium carbonate in standardization of iodine.
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