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I NEED TO DETERMINE THE CONCENTRATION OF HYDROGEN PEROXIDE IN THE SOLUTION. MY RESULTS ARE SHOWN IN THE BOXES AND TABLES BELOW. EXPERIMENT 3: THE DETERMINATION OF HYDROGEN PEROXIDE BY IODOMETRIC TITRATION. THEORY Titrimetry, or titrimetric analysis, is an example of a so-called classical method of analysis. Titrimetry is a convenient method of getting very small amounts of chemicals into a reaction because the method involves the use of dilute solutions of reactants. Hydrogen peroxide reacts with potassium iodide according to the reaction given below: H2O2 + 2H+ + 2I- = I2 + 2H2O (equation 1) Equation 1 shows that 1 mole of hydrogen peroxide gives 1 mole of iodine. Note: we have omitted the potassium ion, K+, from this reaction since it would occur on both sides of the equation and so it does not take part in the reaction. The iodine produced reacts with sodium thiosulphate, Na2S2O3, as shown in equation 2 below: I2 + 2S2O32- → 2I- + S4O62- (equation 2) Equation 2 shows that 1 mole of iodine reacts exactly with 2 moles of thiosulphate. Combining equations 1 and 2: 1 mole H2O2 gives 1 mole iodine AND 1 mole iodine reacts with 2 moles thiosulphate. This shows that 1 mole H2O2 is equivalent to 2 moles thiosulphate. This means that if we know how much (the number of moles) thiosulphate we need to react with the iodine, we can calculate how much hydrogen peroxide was in the solution we started with. Note the concentration of the sodium thiosulphate solution supplied: 0.1046 M. PROCEDURE Measure out 10 cm3 of 1.25 mol dm-3 sulphuric acid using a measuring cylinder and place it in a 250 cm3 conical flask. Add about 1 g of potassium iodide. There is NO NEED TO WEIGH THIS ACCURATELY, so just use a top pan balance. Swirl the flask in order to dissolve the potassium iodide in the sulphuric acid. FLASK 1: 1.06 g FLASK 2: 1.09 g FLASK 3: 1.09 g When the potassium iodide has all dissolved, use a pipette and measure out 25.00 cm3 of the hydrogen peroxide solution. Gradually add the hydrogen peroxide solution to the acidified potassium iodide solution with constant swirling. Use a cork, rubber bung, or parafilm to close the top of the conical flask and allow the mixture to stand for 15 minutes. The solution should become dark orange/brown because of the presence of iodine in solution. Pour sodium thiosulphate into a burette. Run some of this solution through the burette to remove any bubbles below the tap. Record the reading on the burette to the nearest 0.05 cm3 (NOTE: you will have to estimate the second decimal place). THERE IS NO NEED TO GET THE VOLUME TO EXACTLY 0.00 ON THE BURETTE. 0.00 Titrate the iodine solution in the conical flask with the sodium thiosulphate in the burette. You can add the thiosulphate fairly quickly in the early stages, but you will need to add the thiosulphate more slowly as the color of the iodine gets more and more yellow. When the iodine solution becomes straw-colored (pale yellow), add a few drops of starch solution. The iodine solution should now be much darker – almost black. Continue adding the thiosulphate solution until the iodine solution becomes colorless. Record the reading on the burette again to the nearest 0.05 cm3. The volume of thiosulphate required to react with the iodine solution is the difference between the final reading and the initial reading. Repeat steps 2 – 13 until you get THREE consistent results (i.e. where the volume used agrees to ± 0.1 cm3). RESULTS Titration 1 Initial volume (cm3): 0.00 Final volume (cm3): 26.6 Volume used (cm3): 26.6 Titration 2 Initial volume (cm3): 0.00 Final volume (cm3): 26.3 Volume used (cm3): 26.3 Titration 3 Initial volume (cm3): 0.00 Final volume (cm3): 26.4 Volume used (cm3): 26.4 CALCULATIONS Calculate the concentration of hydrogen peroxide in the solution provided. EVALUATION OF RESULTS If the concentration of the sodium thiosulphate provided is C and the volume of this solution required to react with all of the iodine is V: The number of moles of thiosulphate is CxV/1000. From equations 1 and 2: The number of moles of hydrogen peroxide = 0.5 x number of moles thiosulphate = 0.5 x CxV/1000. But we started with 25.00 cm3 of hydrogen peroxide solution of concentration, Z (the value we are trying to determine). The number of moles of hydrogen peroxide = half of the number of moles of thiosulphate used. Thus, we can balance the following equation if we know the concentration of sodium thiosulphate used (C) and the volume of sodium thiosulphate used in the titre (V): 25xZ/1000 = 0.5 x CxV/1000. So, as you know the concentration and volume of thiosulphate solution, you can now determine the concentration of hydrogen peroxide. QUESTIONS 1. Calculate a value for the concentration of the hydrogen peroxide solution for each of your titrations. 2. Calculate the mean, standard deviation, and relative standard deviation for your data. 3. Comment on your results.

THEORY
Titrimetry, or titrimetric analysis, is an example of a so-called classical method of analysis. Titrimetry is a convenient method of getting very small amounts of chemicals into a reaction because the method involves the use of dilute solutions of reactants.
Hydrogen peroxide reacts with potassium iodide according to the reaction given below:
H2O2 + 2H+ + 2I- = I2 + 2H2O (equation 1)
Equation 1 shows that 1 mole of hydrogen peroxide gives 1 mole of iodine.
Note: we have omitted the potassium ion, K+, from this reaction since it would occur on both sides of the equation and so it does not take part in the reaction.
The iodine produced reacts with sodium thiosulphate, Na2S2O3, as shown in equation 2 below:
I2 + 2S2O32- → 2I- + S4O62- (equation 2)
Equation 2 shows that 1 mole of iodine reacts exactly with 2 moles of thiosulphate.
Combining equations 1 and 2:
1 mole H2O2 gives 1 mole iodine AND 1 mole iodine reacts with 2 moles thiosulphate.
This shows that 1 mole H2O2 is equivalent to 2 moles thiosulphate.
This means that if we know how much (the number of moles) thiosulphate we need to react with the iodine, we can calculate how much hydrogen peroxide was in the solution we started with.
Note the concentration of the sodium thiosulphate solution supplied: 0.1046 M.

PROCEDURE
Measure out 10 cm3 of 1.25 mol dm-3 sulphuric acid using a measuring cylinder and place it in a 250 cm3 conical flask.
Add about 1 g of potassium iodide. There is NO NEED TO WEIGH THIS ACCURATELY, so just use a top pan balance. Swirl the flask in order to dissolve the potassium iodide in the sulphuric acid.
FLASK 1: 1.06 g
FLASK 2: 1.09 g
FLASK 3: 1.09 g
When the potassium iodide has all dissolved, use a pipette and measure out 25.00 cm3 of the hydrogen peroxide solution.
Gradually add the hydrogen peroxide solution to the acidified potassium iodide solution with constant swirling.
Use a cork, rubber bung, or parafilm to close the top of the conical flask and allow the mixture to stand for 15 minutes. The solution should become dark orange/brown because of the presence of iodine in solution.
Pour sodium thiosulphate into a burette. Run some of this solution through the burette to remove any bubbles below the tap.
Record the reading on the burette to the nearest 0.05 cm3 (NOTE: you will have to estimate the second decimal place). THERE IS NO NEED TO GET THE VOLUME TO EXACTLY 0.00 ON THE BURETTE.
0.00
Titrate the iodine solution in the conical flask with the sodium thiosulphate in the burette. You can add the thiosulphate fairly quickly in the early stages, but you will need to add the thiosulphate more slowly as the color of the iodine gets more and more yellow.
When the iodine solution becomes straw-colored (pale yellow), add a few drops of starch solution. The iodine solution should now be much darker – almost black.
Continue adding the thiosulphate solution until the iodine solution becomes colorless.
Record the reading on the burette again to the nearest 0.05 cm3.
The volume of thiosulphate required to react with the iodine solution is the difference between the final reading and the initial reading.
Repeat steps 2 – 13 until you get THREE consistent results (i.e. where the volume used agrees to ± 0.1 cm3).

RESULTS
Titration 1
Initial volume (cm3): 0.00
Final volume (cm3): 26.6
Volume used (cm3): 26.6

Titration 2
Initial volume (cm3): 0.00
Final volume (cm3): 26.3
Volume used (cm3): 26.3

Titration 3
Initial volume (cm3): 0.00
Final volume (cm3): 26.4
Volume used (cm3): 26.4

CALCULATIONS
Calculate the concentration of hydrogen peroxide in the solution provided.

EVALUATION OF RESULTS
If the concentration of the sodium thiosulphate provided is C and the volume of this solution required to react with all of the iodine is V:
The number of moles of thiosulphate is CxV/1000.
From equations 1 and 2:
The number of moles of hydrogen peroxide = 0.5 x number of moles thiosulphate = 0.5 x CxV/1000.
But we started with 25.00 cm3 of hydrogen peroxide solution of concentration, Z (the value we are trying to determine).
The number of moles of hydrogen peroxide = half of the number of moles of thiosulphate used.
Thus, we can balance the following equation if we know the concentration of sodium thiosulphate used (C) and the volume of sodium thiosulphate used in the titre (V):
25xZ/1000 = 0.5 x CxV/1000.
So, as you know the concentration and volume of thiosulphate solution, you can now determine the concentration of hydrogen peroxide.

QUESTIONS
1. Calculate a value for the concentration of the hydrogen peroxide solution for each of your titrations.
2. Calculate the mean, standard deviation, and relative standard deviation for your data.
3. Comment on your results.

Added by John M.

Chemistry: Structure and Properties

Nivaldo Tro 2nd Edition

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Solved by Expert Muhammad Ahsan

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- From 25·Z/1000 = 0.5·C·V/1000 → 25 Z = 0.5 C V → Z = (0.5 C V)/25 = (C·V)/50. Show more…

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I NEED TO DETERMINE THE CONCENTRATION OF HYDROGEN PEROXIDE IN THE SOLUTION. MY RESULTS ARE SHOWN IN THE BOXES AND TABLES BELOW. EXPERIMENT 3: THE DETERMINATION OF HYDROGEN PEROXIDE BY IODOMETRIC TITRATION. THEORY Titrimetry, or titrimetric analysis, is an example of a so-called classical method of analysis. Titrimetry is a convenient method of getting very small amounts of chemicals into a reaction because the method involves the use of dilute solutions of reactants. Hydrogen peroxide reacts with potassium iodide according to the reaction given below: H2O2 + 2H+ + 2I- = I2 + 2H2O (equation 1) Equation 1 shows that 1 mole of hydrogen peroxide gives 1 mole of iodine. Note: we have omitted the potassium ion, K+, from this reaction since it would occur on both sides of the equation and so it does not take part in the reaction. The iodine produced reacts with sodium thiosulphate, Na2S2O3, as shown in equation 2 below: I2 + 2S2O32- → 2I- + S4O62- (equation 2) Equation 2 shows that 1 mole of iodine reacts exactly with 2 moles of thiosulphate. Combining equations 1 and 2: 1 mole H2O2 gives 1 mole iodine AND 1 mole iodine reacts with 2 moles thiosulphate. This shows that 1 mole H2O2 is equivalent to 2 moles thiosulphate. This means that if we know how much (the number of moles) thiosulphate we need to react with the iodine, we can calculate how much hydrogen peroxide was in the solution we started with. Note the concentration of the sodium thiosulphate solution supplied: 0.1046 M. PROCEDURE Measure out 10 cm3 of 1.25 mol dm-3 sulphuric acid using a measuring cylinder and place it in a 250 cm3 conical flask. Add about 1 g of potassium iodide. There is NO NEED TO WEIGH THIS ACCURATELY, so just use a top pan balance. Swirl the flask in order to dissolve the potassium iodide in the sulphuric acid. FLASK 1: 1.06 g FLASK 2: 1.09 g FLASK 3: 1.09 g When the potassium iodide has all dissolved, use a pipette and measure out 25.00 cm3 of the hydrogen peroxide solution. Gradually add the hydrogen peroxide solution to the acidified potassium iodide solution with constant swirling. Use a cork, rubber bung, or parafilm to close the top of the conical flask and allow the mixture to stand for 15 minutes. The solution should become dark orange/brown because of the presence of iodine in solution. Pour sodium thiosulphate into a burette. Run some of this solution through the burette to remove any bubbles below the tap. Record the reading on the burette to the nearest 0.05 cm3 (NOTE: you will have to estimate the second decimal place). THERE IS NO NEED TO GET THE VOLUME TO EXACTLY 0.00 ON THE BURETTE. 0.00 Titrate the iodine solution in the conical flask with the sodium thiosulphate in the burette. You can add the thiosulphate fairly quickly in the early stages, but you will need to add the thiosulphate more slowly as the color of the iodine gets more and more yellow. When the iodine solution becomes straw-colored (pale yellow), add a few drops of starch solution. The iodine solution should now be much darker – almost black. Continue adding the thiosulphate solution until the iodine solution becomes colorless. Record the reading on the burette again to the nearest 0.05 cm3. The volume of thiosulphate required to react with the iodine solution is the difference between the final reading and the initial reading. Repeat steps 2 – 13 until you get THREE consistent results (i.e. where the volume used agrees to ± 0.1 cm3). RESULTS Titration 1 Initial volume (cm3): 0.00 Final volume (cm3): 26.6 Volume used (cm3): 26.6 Titration 2 Initial volume (cm3): 0.00 Final volume (cm3): 26.3 Volume used (cm3): 26.3 Titration 3 Initial volume (cm3): 0.00 Final volume (cm3): 26.4 Volume used (cm3): 26.4 CALCULATIONS Calculate the concentration of hydrogen peroxide in the solution provided. EVALUATION OF RESULTS If the concentration of the sodium thiosulphate provided is C and the volume of this solution required to react with all of the iodine is V: The number of moles of thiosulphate is CxV/1000. From equations 1 and 2: The number of moles of hydrogen peroxide = 0.5 x number of moles thiosulphate = 0.5 x CxV/1000. But we started with 25.00 cm3 of hydrogen peroxide solution of concentration, Z (the value we are trying to determine). The number of moles of hydrogen peroxide = half of the number of moles of thiosulphate used. Thus, we can balance the following equation if we know the concentration of sodium thiosulphate used (C) and the volume of sodium thiosulphate used in the titre (V): 25xZ/1000 = 0.5 x CxV/1000. So, as you know the concentration and volume of thiosulphate solution, you can now determine the concentration of hydrogen peroxide. QUESTIONS 1. Calculate a value for the concentration of the hydrogen peroxide solution for each of your titrations. 2. Calculate the mean, standard deviation, and relative standard deviation for your data. 3. Comment on your results.