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
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.
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
5.2 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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