Kadir Alp Gunes Experiment 3: The Determination of Hydrogen Peroxideby Iodometric Titration  Abstract:Iodometry is a method of volumetric chemical analysis whereiodine reacts directly with organic and inorganic substances. For a purpose ofthis experiment, a redox titration was performed in order to determine hydrogenperoxide. Namely, potassium iodine was added into a flask containing sulphuricacid. Once dissolved, hydrogen peroxide was added gradually until the solutiondeveloped a brown colour.

Titration process began by adding thiosulpahte intothe flask, making it more of a yellow colour. Starch solution was added in orderto make the end point sharper causing the solution to develop black colour. Atthe end point, solution went colourless. Introduction:   Peroxide is a compound that has oxygen-oxygen single bondsand is a strong oxidizing agent.

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Its general formula is R2O2where R can either be an oxygen atom or 1st column metal. There aremany inorganic peroxides, ionic and covalent. Ionic peroxides contain alkalimetal ions, while one of the covalent peroxides’ representative is hydrogenperoxide.Hydrogen peroxide, H2O2, is a simple peroxide compound –corrosive, toxic liquid found as a main component in hair bleaches and is alsoused as antiseptic in chemical industries. In H2O2 the oxidation number of oxygenis -1, in oxides it is -2 and O2 gas is 0. An oxidation number is unstable.In this titration, the oxidation number of Hydrogen peroxide changes from -1 to0, meaing that it is the substance oxidized (reducing agent).

 Titrimetry is an analytical method where a certain solutionis treated with a reagent of a known concentration. This method is suitablewhen a number of moles of a reagent that reacts with undetermined substanceneeds to be obtained. The aim of the experiment is to determine the concentrationof a hydrogen peroxide solution by using iodometric titration.                   Materials and methods: The materials used in this experiment were  Materials used in thisexperiment were solutions; H2O2, sodium thiosulphate,sulphuric acid of concentration 1.25 mol/dm3, as well as a solutionof potassium iodide.  10.00 cm3 of sulphuric acid was added in 250 cm3conical flask. Exactly 1.

00 g of potassium iodide was weighed on a small plasticplate and was poured in flask. Flask was swirled gently until all of potassiumiodide can dissolve properly.  25.

00 cm3of hydrogen peroxide was added to the solution, when potassium iodide hasdissolved. The solution swirled constantly to mix it more effectively. Parafilmis used to cover up the top of the flask, the solution left for 15 minutes.Because of the presence of iodine, it turned dark black/orange. Sodiumthiosulphate poured into a burette. In order to remove bubbles sodiumthiosulphate is run through the burette once and is thoroughly checked forbubbles. A funnel put on the burette to get précises readings.

Initial volumewas noted down. Stopper valve was released and sodium thiosulphate passes intothe solution considering there were no colour changes in colour in the first phases.The stopper valve slowed downed as the colour of iodine solution change more toyellow. The flask was swirled during the titration process to increase the rateof titration.

When the solution converts to pale yellow a few drops of starchsolution is added as an indicator. The addition of thiosulphate continued untilthe iodine solution becomes colourless. The reading in the burette was observedand recorded. The experiment was repeated until there is three consistentresults.               Results: Table1: Titration results.   1 2 3 Initial volume (cm3) 0.00 0.

00 0.00 Final volume (cm3) 24.8 24.9 24.9 volume used (cm3) 24.8 24.

9 24.9   The experiment has been repeated three times to get aprecise result. It was required to get ± 0.1cm3 difference between the results as can be seen from Table 1.  The average volume used:­­­  The average volume iscalculated from table 1  Equation 1:                  H2O2+ 2H+ + 2I-  àI2 + 2H2OReactionof hydrogen peroxide with potassium iodine.

 From Equation 1 it can be said that 1 mole on Iodine (I2)can be created from 1 mole of hydrogen peroxide. This can be seen from theration of  H2O2 toI2.    Equation2:                    I2 + 2S2O32-à 2I- + S4O62Reactionof produce Iodine from Equation 1 react with Na2S2O3. The equation shows that it 1 mole of iodine gives 2 moles ofthiosulphate.    Titration 1.

 Volume used is 24.8  Z1 = 0.052 mole/L Titration 2. Volume used is 24.9 cm3  Z2 = 0.052 mole/L Titration 3.

 Volume used is 24.9 cm3   Z3 = 0.052 mole/L Moles of H2O2 for each titrationreaction can be calculated by knowing concentration of H2O2  in every reaction.Number of moles of thiosulhate =  Titration 1.  (25.

00 x 0.0519312) / 1000 = 1.29 x 10-3 moles Titration 2.

  (25.00 x 0.0521406) / 1000 = 1.30 x 10-3 moles  Titration 3.    (25.00 x 0.0521406) / 1000 = 1.

30 x 10-3 moles   The steps ofstandard deviation.   Standarddeviation is calculated using median.  Standarddeviation is calculated by subtracting the mean from each result, squaring thivalue, repeting this with each result and totalling the answers. There after wedivide the answer by the number of results taken minus one. Finally we squareroot the value.   (24.

80-24.87)2+ (24.90-24.

87)2 + (24.90-24.87)2 = 0.0067 0.0067/(3-1)= 0.

003  = 0.06  0.1  To calculate relative standard deviation:RSD (stand.

dev. x 100)/mean = (0.1 x 100)/24.87 = 0.40%                        Discussion and conclusion: The experiment was done in 3 attempts to get precise results 

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