Experiment Number: 05Name of the experiment:

Estimation of Copper contained in a supplied solution by Iodometric method.Course: Chem-114

Name:— Farhana AshrafRoll:— 0005004Group:— A1Partner’s Roll:—0005018 Department:— C.S.E.

Date of Performance:— 09-10-2001Date of Submission:— 30-10-2001

Objective:-The objective of this experiment is to estimate the amount

of copper contained in a supplied copper salt solution.The percentage of purity of CuSO4 .5H2O can be determined with the help of this experiment. Electric wires are mainly made of copper.So by determining the quantity of copper, the efficiency of the wire can be determined. The percentage of copper in any alloy can also be determined by this experiment.

Theory:- In this experiment, the amount of copper in a copper salt solution is determined. The reaction that occurs here is oxidation and reduction reaction as well as iodometric reaction. Titration involving iodine or dealing with iodine liberated in chemical reaction is called iodimetry and iodometry respectively. This reaction is iodometric because iodine is obtained from KI. The reaction takes place in two steps:

1. Cu2++ KI + H+ = I2 +…… 2. Na2S2O3 + I2 = Na2S4O6+ ……

In the 2nd Step of the reaction a specific indicator is used that is “Starch”- which has a significant effect on iodine.

Here, for the first part of the experiment ,the basis of the volumetric measurement is that one equivalent weight of an oxidizing agent will completely react with one equivalent weight of a reducing agent. To perform the second part of the experiment, we can follow the process discussed below:- 1000 ml (N) Na2S2O3 solution 1000 ml (N) iodine solution 1 equivalent weight of iodine 1 atomic weight of iodine As one atom of iodine is set free for each atom of copper,1000 ml (N) Na2S2O3 solution should be equivalent to one gram molecular weight that is 63.54 gram of copper. Therefore, 1 ml of (N) Na2S2O3 0.06354 gram of copper So, the weight of copper in the supplied solution may then be easily calculated using the above relation.

Apparatus:- 1.Conical flask , 2. Burette , 3. Pipette , 4.Volumetric flask, 5. Stand , 6. Funnel Chemicals:-

1. Na2S2O3 solution2. K2Cr2O7 solution3. KI solution4. NaHCO35. HCl solution (concentrated)

6. CuSO4 solution 7. CH3COOH solution 8. NH4CNS solution

9. Starch (Indicator)

Data :—

TABLE: 1Standardization of Na2S2O3 solution with standard K2Cr2O7 solution

No. of

obs.

Volume of

K2Cr2O7(ml)

Burette reading Volume of

Na2S2O3

(ml)

Average

(Volume of

Na2S2O3)

(ml)

Strengthof

Na2S2O3(N)

Initial(ml)

Final(ml)

1. 10 4.9 14.4 9.59.85 0.101

92. 10 15.0 24.8 9.83. 10 25.2 35.1 9.9

TABLE: 2Standardization of Na2S2O3 solution with standard copper salt(Cu2+)

solution

No. of obs.

Volume Of

Cu2+

Solution (ml)

Burette reading Volume of

Na2S2O3

(ml)

Average(Volume

of Na2S2O3)

(ml)

Initial

(ml)

Final

(ml)

1. 10 7.2 18.5 11.39.852. 10 19.0 29.2 10.2

3. 10 29.2 39.3 10.1

Calculation:- Here, SNa2S2O3 = 0.1047 N Again,

1000 ml 1.0N Na2S2O3 63.54 gm Cu2+ => 10.15 ml 0.1019N Na2S2O3 (63.54X10.15X0.1019)/1000 gm Cu2+

0.06572 gm Cu2+

Thus the amount of copper present per litre = ( 0.06572 X 100 ) gm = 6.572 gm

Result:- The amount of copper (in gm) present in the supplied CuSO4 solution (per litre) is = 6.572 gm.

Error:- Percentage of error = (known value ~observed value)X 100 ÷ known value = (6.572-6.5) X 100 / 6.5 = 1. 108%

Discussion:- The following causes can be assumed for the slight deviation of the result from the original one:1.While measuring the lower meniscus of the burette an error may be happened for the parallax error. 2.As the color change of the titration of Na2S2O3 with K2Cr2O7 is very confusing, the end point of the titration may not have been properly determined.