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Objective; To determine the concentration of hydrogen peroxide, H2O2, in aqueous solution.

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Introduction

To determine the concentration of hydrogen peroxide, H2O2, in aqueous solution. In this practical examination I am provided with a '100-volume' hydrogen peroxide solution. Taking the '100-volume' into consideration I have to plan two experiments that would enable me to determine the exact concentration of H2O2, in mol dm-3. Titration: The first experiment I shall carry out will be a redox titration; between hydrogen peroxide and potassium manganate (VII). A titration will enable the reacting volumes of H2O2 and KMnO4 to be accurately determined. From this information and the stoichiometric ratio I will then be able to determine the concentration of H2O2. Prior to going into detail we must first understand what a'100-volume' solution is. By definition this means that 1cm3 of H2O2 will decompose to produce 100cm3 of O2 at STP. In simple terms it is just another way of indicating the strength of H2O2. 2H2O2 (aq) 2H2O(l) + O2(g) Equation 1. Consequently, we can understand that '100-volume' represents a very strong concentration of H2O2. Thus, before carrying out the titration the solution of H2O2 must be diluted. A reasonable dilution factor for this experiment is 100; hence from a 100-volume to a 1-volume solution. ...read more.

Middle

3. Set up a clamp, boss and stand in order to fix the burette on to it. 4. Place a white tile on the bottom of the stand (underneath the conical flask) in order to make the colour change easier to recognise. 5. Fill up the burette with 0.1 molar KMnO4 just above 0cm3, whilst having the tap closed. Record the morality in a data table. 6. Open the stopcock on the burette to allow any air bubbles to escape from the tip. Close the stopcock when the liquid level in the burette is 0cm3. Record the initial volume, remembering to always read from bottom of meniscus. 7. Start by opening the tap of the burette slightly and gently shaking the conical flask as the KMnO4 is poured in. 8. The KMnO4 is a purple colour, however as it reacts with the H2O2 it becomes colourless. The endpoint of the titration is when all the H2O2 has reacted and a further drop of KMnO4 causes the solution to remain pink/purple. This volume of KMnO4 added should be recorded. 9. Repeat the titration until the results only differ by 0.5cm3. The results obtained will be recorded in a table; below is a specimen: Titre 1 Titre 2 Titre 3 Molarity of KMnO4 0.1 0.1 0.1 Initial volume of KMnO4 solution (cm3) ...read more.

Conclusion

Attach a thread to the test tube; make sure it is secured tightly. 4. Place the test tube inside the conical flask using the attached thread; remember to keep part of the thread outside the conical flask. 5. Secure the bung, both to the conical flask and the gas syringe as illustrated in figure 1.0. Release the thread and measure the volume of gas collected. Repeat the experiment 3 times to get reliable results. Trail 1 Trail 2 Trail 3 Volume of O2 gas collected (cm3) 20.2 19.8 20.1 Mean volume of O2 gas collected (cm3) 20.03 20.03 20.03 6. Record the volume of gas collected in both reactions in a data table: Below is a specimen calculation: 20.03cm3= 0.02003dm3 number of moles of O2 = 0.02003/22.4 = 0.000894 3sf. Equation 1.0 states that H2O2 and O2 are in stoichiometric ratio of, 2:1 respectively. number of moles of H2O2 = 0.000894*2 = 0.00179 3sf. The volume of H2O2 used was 0.02dm3, therefore the concentration of H2O2 is: number of moles/ volume = concentration 0.00179/0.02= 0.0894 mol dm-3 As the solution used was diluted by a factor of 100; form 100 to 1 volume, the actual concentration of 100-volume H2O2 is: 0.0894 mol dm-3 * 100= 8.94 mol dm-3 ?? ?? ?? ?? ...read more.

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