In this experiment you will prepare a co-ordination complex of Cu (II) and ammonia in Part A. In Part B, you will perform standardization titration of Na₂S₂O₃ solution to calculate its molarity. This titrant is used to estimate copper content of your complex. You will also perform blank reading for HCl solution in this subpart. This blank reading of HCl will be required to calculate ammonia content of the prepared complex.  In Part C of the experiment, you will be analyzing the complex synthesized by you for its copper and ammonia contents using titration technique.

PART A

Synthesis of the complex

You are supplied with 5.00 g of CuSO₄.5H₂O in a sample vial and cold NH₄OH solution. Carefully transfer the entire amount of Cu (II) sulphate in a 100 mL beaker. Using a measuring cylinder, add 15 mL of the given cold ammonia solution to the beaker. Keep the beaker in ice bath and do remember that the entire synthesis should be done in cold condition only.  Stir the mixture for 2-3 minutes, using a glass rod. To the same solution, add another 5 mL of the cold ammonia solution with stirring. To this solution, slowly add 20 mL of cold ethanol with constant stirring. The addition of entire ethanol content should be done in a dropwise manner. The product will be precipitated in the beaker and you have to take it for filtration. The filtration is done using a Buchner funnel and using suction. You should use cold ethanol solution (maximum 15 mL) for transferring and washing the precipitate on the Buchner funnel. The ethanol needed for washing purpose is kept near the filtration assembly.     The laboratory expert will guide you in this regard. After filtration, carefully take the product back to your table. Allow the product to dry for 30 to 40 minutes. At the end of this time interval, carefully transfer the product on the pre-weighed butter paper supplied to you. Take the product for weighing to the laboratory expert.

While the product is drying, perform the following titrations

1. Standardization of Na₂S₂O₃ solution
2. Blank titration for HCl solution

PART B

Standardization of supplied Na₂S₂O₃ solution

Transfer the content of one vial of KIO₃ (0.054g) and one vial of KI (0.500 g) in a 100 mL conical flask. Add 25 mL of distilled water and 1 mL of 1 M H₂SO₄ solution. At this stage the solution will be brown in colour. Immediately start titrating the solution with Na₂S₂O₃ solution till its colour changes to light yellow. At this point, add 1 mL of starch indicator. The reaction solution will be blue in colour. From this point, addition of Na₂S₂O₃ should be done gradually (drop wise) and with constant shaking.  At the end point, the solution will become colorless. Record your readings in the appropriate table provided in the answer sheet. Perform yet another titration in a similar manner. If the two readings are differing widely, then only take the third reading.

Blank titration for HCl

Take 20 mL of supplied HCl solution with the help of a burette. Add 30 mL of distilled water and 3 to 4 drops of methyl red indicator. Titrate the solution with standardized NaOH solution. Perform yet another titration in similar manner. If the two readings are differing widely, then only take the third reading.

PART C: Analysis of the prepared complex

Determination of the Cu content

For this titration, weigh 0.450 g of the prepared product in duplicate. The laboratory expert will help you in this regard.

1. Transfer 0.450g of weighed sample in a clean conical flask.
2. Add 50 mL of distilled water and add 2 M NaOH solution in drop wise manner until the sample solution becomes slightly turbid.
3. Then add 10 mL of 4 M acetic acid and 1 vial of solid KI powder. At this stage the solution will be brown in color.
4. Start titrating the solution against the standardized Na₂S₂O₃ solution till its color changes to light yellow. At this point, add 1 mL of starch indicator. The solution will be blue in colour. Continue the titration with shaking till the solution becomes colorless.
5. In a similar manner, perform the titration the other sample weighed by you. Enter your results in the answer sheet. If the two readings are differing widely, you should take one more reading. Record your readings

Determination of the ammonia content

For this titration, weigh 0.0850 g of the prepared product in duplicate. The laboratory expert will help you in this regard.

1. Transfer 0.0850g of the weighed sample to a clean conical flask.
2. Add 50 mL of distilled water and 20 mL of the supplied 0.1 M HCl solution (use burette to take HCl solution).
3. Add 4 drops of Alizarin Red S indicator and 4 drops of Bromocresol green indicators.
4. Titrate excess of HCl solution against the supplied NaOH solution until the solution changes to blue colour.
5. In similar manner, perform the titration with another sample weighed by you. Enter your results in the answer sheet. If the two readings are differing widely, you should take one more reading.
6. The blank titration for HCl is already done by you.