NAME: ALVIN LIM WEA SHYANGSTUDENT ID:1402916EXPERIMENT:6DATE OF EXPERIMENT:17/6/2015DATE OF SUBMISSION:30/6/2015LECTURER: DR. SIM YOKE LENGPRACTICAL GROUP:P3GROUP MEMBER:LIM TZE CHIN, MYRON WONG A/L MANOKARAN

Title: Standardization of sodium thiosulphate (Na2S2O3) solution by potassium iodate (KIO3).

Objective: To standardize sodium thiosulphate (Na2S2O3) solution by potassium iodate (KIO3).

Material: -Approximately 0.1M sodium thiosulphate -0.167M potassium iodate-1M sulphuric acid -Starch indicator-Volumetric flask 100ml-Pipette 10mlProcedure:Preparation of 0.167M of potassium iodate solution1. 10ml of the stock solution of potassium iodate was pipette into a volumetric flask of 100ml.2. Distilled water was then carefully added to the volumetric flask until the graduation mark was reached.3. The flask was stopper and shaken well.

Titration1. 25 of potassium iodide was pipette into a conical flask.2. About 1g of potassium iodide was then added to the conical flask.3. With about 15 of diluted sulphuric acid was added to acidified the solution.4. Sodium thiosulphate was then added from the burette, until the colour of the solution is orange.5. Then a few drops of starch 9ndicator was added to the solution and the titration was continued until the blue colour of indicator was discharged.6. The titration was repeated twice.

Results:Titration number123

Initial volume of burette(0.000.209.20

Final volume of burette(25.9026.2034.30

Total volume of Na2S2O3 used (25.9026.0025.10

Average volume of Na2S2O3 required for titration = 25.70Calculations:1. a) Molarity of Na2S2O3

No. of mol of = KIO3 = 4.175xmol

KIO3 + 5 KI + 3 H2SO4 _ 3 K2SO4 + 3 H2O + 3 I2

From the equation above 1 mole of KIO3 produce 3 mole of I2

4.175xmol of KIO3 will produce X mole of I2

No. of mol of I2 = (4.175x (3) =1.253mol

I2 + 2 Na2S2O3 = Na2S4O6 + 2NaI

From the equation above 1 mole of I2 react with 2 mole of Na2S2O3

1.253 of I2 reacts with X mole of Na2S2O3

No. of mole of Na2S2O3 =( 1.2532) =2.506molAverage volume of Na2S2O3 required for titration = 25.70 =0.0257

Molarity of Na2S2O3 = 2.5060.0257 =0.09751mol/

b) Concentration of hydrated salt No. of mol = 2.506molof Na2S2O3

Relative molecular mass of Na2S2O3 =158g/mol

Mass of = (2.506158)Na2S2O3= 0.3959g

Concentration of = 0.3959hydrated salt (25.70/1000) =15.41g/

2. Relative molecular mass of Na2S2O3 =158g/mol Relative molecular mass of XH2O = 248-158 =90g/molX= 90/18 =5 mole3.Iodometry , also known asiodometric titration, is a method ofvolumetricchemical analysis, aredox titrationwhere the appearance or disappearance of elementaryiodine indicates the end point of the experiment. Iodimetry is the determination of the amount of iodine in a compound or of the amount consumed in a reaction by titrating with a standard solution. The correct definition of this experiment is iodometry.

4.No ,because starch indicator can be destroyed in the presence of excess triiodide in the experiment and that is why after the amount of the triiodide in the experiment has decrease almost at the end of the experiment then the starch indicator will be added to indicate the presence of iodine.

Discussion :

The purpose of the experiment is to standardized by potassium iodate by first diluting the potassium iodate solution with distilled water in a volumetric flask and pipette it into a conical flask and further titrate with sodium thiosulphate solution.

From the experiment the result that have been obtained for the first titration is 25.90 of sodium thiosulphate solution was used. For the second titration the volume of sodium thiosulphate solution that was used was 26.00. Lastly for the third titration the volume of sodium thiosulphate solution that was used was 25.10. The average amount of sodium thiosulphate solution that was used was 25.70.

During titration the solution turn to orange and at that moment starch indicator was added and the solution turned dark blue. At the end of the titration the solution turns colourless. This was because iodide solutions are colourless and the amount of sodium thiosulphate solution used was recorded.

Precaution steps that has to be taken when performing the experiment is to wear gloves all the time. This is because we are handling with concentrated chemical solution. Second precaution steps is to wear lab coat in the lab as we do not want any spill of chemical to our body. Third when taking down the measurement form the apparatus like measuring cylinder, pipette and burette, make the eye is on the same level as the meniscus. Fourth precaution step is repeating the titration three times to get an average reading of the volume of sodium thiosulphate solution used. Last precaution step is to read the lab manual before performing the experiment to avoid uncertainties .

Conclusion:The average volume of sodium thiosulphate solution(Na2S2O3 ) that was required for the titration is 25.70.

Reference:Burns, R. (2003).Fundamentals of chemistry. Upper Saddle River: Pearson Education International.Lim, Y. and Yip, K. (2005).Physical chemistry. Petaling Jaya: Pearson Malaysia.