Experiment Number: 05

Experiment Number: 05

Name of the experiment:

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

Name: Farhana Ashraf

Roll: 0005004

Group: A1

Partners Roll:0005018

Department: C.S.E.

Date of Performance: 09-10-2001

Date of Submission: 30-10-2001

Objective:

The objective of this experiment is to determine the strength of

CuSO4 .5H2O and thus to determine the amount of copper in a supplied copper salt solution. This reaction also helps to study about Iodometric Reaction and about oxidation and reduction theory. The percentage of purity of CuSO4 .5H2O can also be determined with the help of this experiment.

As electric wires are made of copper, by determining the quantity of copper, the efficiency of the wire can also 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 with iodine or dealing with iodine liberated in chemical reaction is called Iodimetric and Iodometric titration respectively. This reaction is iodometric because iodine is got 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 characteristic 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

Since 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. FunnelName of the chemicals used:

1. Na2S2O3 solution

2. K2Cr2O7 solution

3. KI solution

4. NaHCO3

5. HCl solution (concentrated)

6. Distilled water

7. CuSO4 solution

8. CH3COOH solution

9. NH4CNS solution

10. Starch (Indicator)Data:

TABLE: 1

(Standardization of Sodium Thiosulphate solution with standard potassium Dichromate Solution)

Number of Obser-

-vationVolume of

K2Cr2O7mlBurette readingVolume of Na2S2O3mlAverageVolume of NaS2O3MlStrength

Of

Na2S2O3N

Initial

Reading

mlFinal

Reading

ml

01107.116.79.69.550.1047

021016.726.29.5

TABLE: 2(Standardization of Sodium Thiosulphate solution with standard potassium Dichromate Solution)

Number of Obser-

-vationVolume OfCu2+SolutionmlBurette readingVolume of Na2S2O3mlAverageVolume of NaS2O3MlStrength

Of

Cu2+ SolutionN

Initial

Reading

mlFinal

Reading

ml

011029.2399.89.70.10157

02103948.79.7

031028.237.89.6

Calculation:

from Vred X Sred = Vox X Sox

Here,

VK2Cr2O7 = 10 ml

SK2Cr2O7 = 0.1 N

VNa2S2O3 = 9.55 ml (average)

SNa2S2O3 = 0.1047 N

Again,

1 ml (1.0N) Na2SO3 = 0.06354 gm cu2+ (10 ml)

=> 9.7 ml = 0.616338 gm cu2+ (10 ml)

=> 0.1047 N = 0.0645305(10 ml) Thus the amount of copper present per litre

= ( 0.0645305 X 100 ) gm

= 6.45305 gmResult:

The amount of copper (in gm) present in the supplied CuSO4 solution (per litre) is : Wcu = 6.45305 gm.

Percentage of error:

Percentage of error = (known value observed value) X 100 known value

Known amount of copper = 6.4 gm

Observed amount of copper = 6.45305 gm

Percentage of error = -0.82%

Discussion:

The following may be the possible cause of error :

1) There might have been a little mistake in determining the end point of titration.