Procedure

(I) Standardization of Na₂S₂O₃(hypo):

1. Take a clean and dry conical flask.
2. Take 10 ml CuSO₄ in a clean dry conical flask with the help of pipette.
3. Add 5 ml of KI solution to the above flask, dark yellowish brown solution is obtained.
4. Titrate this solution against hypo till the solution became light yellow.
5. In the above solution, add 1-2 drops of starch (Blue colored iodo starch complex is formed.)
6. Titrate again the above solution against hypo to get milky white endpoint.
7. Repeat the above procedure to get concordant reading.

II) Titration of unknown CuSO₄ with hypo :

Repeat the above procedure with unknown CuSO4 in place of known CuSO4.

Safety Precautions:

1. Use distilled water throughout the experiment.
2. Volume of starch indicator should be same in all the titrations.
3. Indicator should be prepared freshly.
4. End point of the titrations should be carefully observed.

Clean-Up:

1. Dispose of waste solutions properly.
2. Clean and return all glassware to its designated place.