Preparation and Standardization of 0.1M Sodium Thiosulphate

1.0 OBJECTIVE 

To lay down the procedure for the Preparation and Standardization of 0.1M Sodium Thiosulphate 

2.0 SCOPE

This SOP is applicable to Operation, Maintenance and Calibration of Centrifuge , MAKE:REMI, MODEL: R-8C in company.

3.0 BACKGROUND 

NIL

4.0 RESPONSIBILITY

4.1 QC-Chemist 

4.2 Head-QC

5.0 PROCEDURE 

5.1 Preparation
Dissolve 25 g of sodium thiosulphate and 0.2 g of sodium carbonate in sufficient carbon dioxide-free water to produce 1000 ml.

5.2 Principle

The principle of standardization of sodium thiosulphate is based on redox iodometric titration with potassium iodate as primary standard. Potassium iodate a strong oxidizing agent is treated with excess potassium iodide in acidic media which liberates iodine which is back titrated with sodium thioslphate. Uniformity of reactions between iodine and sodium thiosulphate forms basis for utilizing the standard solution of iodine in the analysis of sodium thiosulphate and use of sodium thiosulphate in the analysis of iodine. Starch indicator is used as indicator showing disappearance of blue color.

5.3 Requirements

Apparatus : Burette, Volumetric flask, Pipette.

Reagents : 0.1 N sodium thiosulphate, Potassium iodate, Potassium iodide

5.4 Reagents

Preparation of 0.1N Potassium Iodate:

Weigh accurately about 356 mg of KIO3 and dissolve in 100 ml distilled water

Preparation of Starch indicator:

Take 1 gm of soluble starch and triturate with 5 ml of water and add it to 100 ml of boiling water containing 10 mg of mercuric iodide with continuous stirring

 5.5 Standardization

Take 10 ml of Potassium Iodate solution .Add 2 gm of Potassium Iodide and 5 ml of dilute H2SO4 ,keep it in dark for 10 minutes, add 2 to 3 drops of starch indicator and titrate with sodium thiosulphate using starch solution as indicator until the blue colour is disappeared.

N1V1=N2V2

N2= N1V1/V2

Note:

1) Re-standardise before use
2) Discard the solution after 30 days.
3) For storage and labeling follow the general procedure.

 or 

1.0 OBJECTIVE 

To lay down the procedure for the Preparation and Standardization of 0.1M Sodium Thiosulphate 

2.0 SCOPE

This SOP is applicable to Operation, Maintenance and Calibration of Centrifuge , MAKE:REMI, MODEL: R-8C in company.

3.0 BACKGROUND 

NIL

4.0 RESPONSIBILITY

4.1 QC-Chemist 

4.2 Head-QC

5.0 PROCEDURE 

5.1 Preparation: 
Dissolve 2.48gm of sodium thiosulphate pentahydrate in 100ml water swirl to dissolve.

5.2 Preparation of reagents for Standardization:

Preparation of 1% starch Solution: Dissolve 0.5gm of soluble starch in 50 ml of hot water and Filter.

15% potassium iodide solution: Dissolve 15gm of potassium iodide in 100 ml water swirl to dissolve completely. Store in dark place and use immediately.

Potassium dichromate: Dry potassium dichromate at 1100C for 30 minutes. After that take out  and cool for 10 minutes in desiccator.

5.3 Standardization:

Weigh accurately about 0.16 to 0.22g of potassium dichromate and transfer in to 500ml conical flask and add 25 ml of water swirl to dissolve. Then add 5 ml of Conc Hcl (37%), 20 ml of 15% Potassium iodide solution swirl the contents properly and wait for 5 minutes. Then add 100 ml of water into the flask.

Transfer 0.1M sodium thiosulphate solution into burette and titrate with potassium dichromate solution carry out the titration (with vigorous shaking) until yellow colour is completely disappeared. Now add 1% starch indicator Solution (vigorous shaking) until blue colour is completely disappeared (green colour may appear)

5.4 Calculation:

M=20.394xW/V

W= weight of Potassium dichromate

V= Volume of the sodium thiosulphate = Final burette reading – Initial Reading

M= Molarity of the sodium thiosulphate   

5.5 Example:

W=0.169gm

V=35.0-1.0 ml =34 ml

20.394x0.169/34 = 0.10137M



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