Learn about the preparation and standardization of 0.1 M sodium thiosulphate through a laboratory experiment or practical.
Aim:
To prepare and standardize 0.1 M sodium thiosulphate solution using potassium iodate as primary standard.
Reference: Indian Pharmacopoeia (IP) 2014; Volume-1, Page No. 316
Principle:
The principle of sodium thiosulphate standardization is based on redox titration utilizing the iodometric method in which potassium bromate is used as the oxidizing agent.
The 250 ml primary standard solution is prepared by a precisely weighed amount of the potassium bromate is dissolved in its water. To this 50 ml is carefully measured and 20.00 gm of potassium iodide (KI) and 30.00 ml of 2M hydrochloric acid (HCl) are added. Titrate the liberated iodine with sodium thiosulphate solution, until the blue color disappears, using starch solution as an indicator.
The molecular weight of sodium thiosulphate (Na2S2O3) is 248 g/mol.
How to prepare sodium thiosulphate solution (0.1M):
Take 25.00 gm of sodium thiosulphate and 0.20 gm sodium carbonate 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.
Procedure for standardization of 0.1M sodium thiosulphate solution:
- Weighed correctly 0.2 gm of potassium bromate (KBrO3) and dissolve in 100 ml of distilled water in a volumetric flask, once it has completely dissolved, make up the volume to 250 ml with distilled water.
- Take 50 ml of this solution and pour it into a conical flask.
- Add 02.00 gm of potassium iodide (KI) and 3 ml of 2M HCl and titrate with sodium thiosulphate solution using starch solution as an indicator until the blue color disappears.
- Equivalent factor: 0.02784 gm of KBrO3 per ml of 0.1M Na2S2O3.
Observation table:
|
Sr. No. |
Content
in conical flask |
Burette
reading |
Volume
of titrant used (ml) |
|
|
Initial |
Final |
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1 |
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|
|
|
|
2 |
|
|
|
|
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3 |
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|
|
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Mean: |
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Calculation:
Molarity of sodium thiosulphate = Weight taken of KBrO3 x molarity required / titration volume x equivalent factor.
Note:
Calculate how much potassium bromate is contained in the volume pipetted out based on the actual weight of the sample taken.
Commonly asked questions on titration are as follows.
Which primary standard is used for the standardization of sodium thiosulphate?
Potassium bromate is used as a primary standard is used for the standardization of sodium thiosulphate.
How will you prepare 0.1 M sodium periodate?
Take 21.4 g of sodium periodate (NaIO4) and dissolve in 1000 ml of distilled water in a volumetric flask, and properly mixing it
Why do we perform standardization of sodium thiosulphate solution?
We do standardization to determine the exact molarity or normalcy of the prepared sodium thiosulphate solution, which is important for calculations in titration or assay.
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