3.TO ESTIMATE THE THIOSULPHATE SOLUTION AND THE AMOUNT OF COPPER SULPHATE SOLUTION.

APPARATUS REQUIRED:

1. burette
2. beaker
3. watch glass
4. test tube
5. pipette
6. conical flask

CHEMICAL REQUIRED:

1. standard thiosulphate solution (NA2S2O3)
2. copper sulphate solution(CUSO4)
3. ammonium hydroxide
4. acetic acid
5. KI solution
6. starch

THEORY:

Titration:

               The technique to know the strength of given unknown solution with the help of known standard solution is called as titration.

Indicator:

                The chemical substance which indicates the completion of the chemical reaction by a sharp color change is known as indicator. eg. methyl orange

Normality:

                 The no. of gram equivalent weight of solute discovered to make one liter of solution is called normality.

When the excess of KI is added to salt solution at the pH about 5.5, iodine and CU iodide solution are produced in absence of light. The standard sodium thiosulphate using freshly prepared starch indicator is titrated in iodide dissolved KI.

Reaction involved:

2CUSO4 + 4KI → 2CuI2 =2K2SO4

I2 + 2NA2S2O3 → NA2S4O6 + 2NaI

PROCEDURE

  First of all, the given apparatus used for titration i.e. burette, pipette, conical flask were cleaned properly with water. Then, the burette was rinsed with sodium thiosulphate and was filled it up to zero mark point of CUSO4 solution. Then NH3 solution was added drop wise until the mixture appears slightly turbid and again acetic acid was added so that the turbidity disappeared. Then 1 gm of KI solution was added, shaked, and covered with watch glass. The solution was kept in dark place for five minutes. The wall of conical flask was cleaned with water and then titrated by using thiosulphate solution until straw yellow color was appeared. Then 2 ml of freshly prepared starch solution was added, dark blue color was obtained and thiosulphate solution was added , continued up to the blue color disappeared. Then burette reading was taken and titration was carried out till the concurrent reading occurred.

OBSERVATION TABLE:

S. N.	Volume    of CUSO4	initial	final	difference	Concurrent
1.	10 ml	0	9.2	9.2
2.	10 ml	9.2	18.4	9.2	9.2
3.	10 ml	18.4	27.4	9.2

CALCULATION:

Volume of KMNO4 (V1) = 9.2 ml                

 Strength of KMNO4 (N1) = 0.1 N

Volume of Mohr’s salt (V2) = 10 ml                      

Strength of Mohr’s salt (N2) =?

Then, N1V1 = N2V2

     Or, N2 = 9.2 ml×0.1                                                   

                      10 ml

                 =     0.092 N

 1000ml of 1N CUSO4 solution = 63.5g of Cu++

 9.2 ml of 0.113N Fe2+ solution = 63.5 × 0.092 × 9.2

                                                       1000

                                                    = 0.053gm of Cu++

And gm/liter = weight × 1000

                        Volume

                      = 0.053×1000

                                10

                       = 5.3 gm/liter

RESULT:

         From above observation, the amount of cu++ in given solution is 5.3 gm/liter.

CONCLUSION:

                            Hence, sodium thiosulphate was standardized and amount of copper can be determined by this standard solution.

PRECAUTION:

1. Reading should be noted carefully
2. Chemical should be used carefully.
3. Apparatus should be cleaned before and after use.