<Experiment 1> burette with (add 10 mL of NEW hydrogen peroxide, 30 mL water and
ID: 872650 • Letter: #
Question
<Experiment 1>
burette with (add 10 mL of NEW hydrogen peroxide, 30 mL water and 2 mL of 6 M sulfuric acid)
the color was changed to purple when <18mL> of 0.2 M potassium permanganate is added.
<Exp 2>
burette with same thing with EXP1 but OLD hydrogen peroxide instead of NEW hydrogen peroxide
the color was changed to purple when <12.6mL> of 0.2 M potassium permanganate is added.
please do this as much as you can solve. it may not have enough records of this experiments. ( i just did as much as possible.)
Corse Titration Take a burette from the Containers shelf and place it on the workbench. Drag the potassium permanganate (KMnO4 solution from the Materials shelf to the top off of the burette. Fill the burette with 50 mL of 0.2 M potassium permanganate solution from the Materials shelf. Record this concentration in your Lab Notes. Take an Erlenmeyer flask from the Containers shelf and place it on the workbench. Add 10 mL of NEW hydrogen peroxide (H2O2) from the Materials shelf to the Erlenmeyer flask. Dilute the hydrogen peroxide with 30 mL of water from the Materials shelf. Add 2 mL of 6 M sulfuric acid (H2SO4to the Erlenmeyer flask. Drag the Erlenmeyer flask and drop it on the lower half of the burette. Titrate the hydrogen peroxide with the potassium permanganate (KMnO4 solution to the bright purple endpoint of excess permanganate (MnO4) ion. Be patient. As you learned in the Titration Tutorial, you should first do a rough titration by adding potassium permanganate (KMnO4 from the burette to the Erlenmeyer flask 2 mL at a time in order to quickly find the range in which the endpoint is reached. Record both the a) last volume where the solution was colorless and b) the first volume where the solution was suddenly bright purple. This gives you the range within which to do the fine titration. Discard the burette and Erlenmeyer flask in the recycling bin beneath the workbench. Remember to save your notes. Fine Titration Set-up the experiment as you did for the coarse titration: fill a burette with 50 mL of 0.2 M potassium permanganate, add 10 mL of NEW hydrogen peroxide. 30 mL water and 2 mL of 6 M sulfuric acid to an Erlenmeyer flask, connect the burette to the Erlenmeyer flask. Click and hold the black knob of the burette to quickly add enough potassium permanganate to just get into the range of the coarse titration but still have the solution in the flask appear colorless. This is near, but not yet at. the titration's endpoint. Add potassium permanganate (KMnO4 in small incremements. down to one drop at a time, until the addition of just one more drop causes the solution in the flask to turn bright purple. Record the final burette reading in your Lab Notes. Place the burette and Erlenmeyer flask in the recycling bin. Remember to save your notes. Repeat the fine titration once more, and record the results in your lab notes. If the results from the two fine titrations do not closely agree do a third fine titration to determine which of the first two was done incorrectly. Repeat the procedure in Experiment 1 (both the Coarse Titration and the Fine Titration) using OLD hydrogen peroxide (H2O2) in place of NEW hydrogen peroxide (H2O2). Are the results different? Given what you know about the stability of hydrogen peroxide (H2O2) do you expect them to be?Explanation / Answer
1. For new bottle of hydrogen peroxide:
a.) Volume of KMnO4 = 18 mL
b.) Volume of KMnO4 required to titrate 10 mL H2O2 =18 mL
c.) mole KMnO4 = Molarity x volume in liter
mole KMnO4 = 0.2 mol/L (0.018 L)
mole KMnO4 = 0.0036
d.) 2KMnO4 + 5H2O2 + 3H2SO4 --> 2MnSO4(aq) + K2SO4(aq) + 5O2 + 8H2O
mole H2O2 = 0.0036 mol KMnO4 x (5 mol H2O2/2 mol KMnO4)
mole H2O2 = 0.009
e.) mass of H2O2 = 0.009 mol (34.01 g/1 mol H2O2)
mass of H2O2 = 0.306 g
f.) % H2O2 = (0.306 g/30 g) x 100
% H2O2 = 1.02 %
2. For old bottle of hydrogen peroxide:
a.) Volume of KMnO4 = 12.6 mL
b.) Volume of KMnO4 required to titrate 10 mL H2O2 =12.6 mL
c.) mole KMnO4 = Molarity x volume in liter
mole KMnO4 = 0.2 mol/L (0.0126 L)
mole KMnO4 = 0.00252
d.) 2KMnO4 + 5H2O2 + 3H2SO4 --> 2MnSO4(aq) + K2SO4(aq) + 5O2 + 8H2O
mole H2O2 = 0.00252 mol KMnO4 x (5 mol H2O2/2 mol KMnO4)
mole H2O2 = 0.0063
e.) mass of H2O2 = 0.0063 mol (34.01 g/1 mol H2O2)
mass of H2O2 = 0.214 g
f.) % H2O2 = (0.214 g/30 g) x 100
% H2O2 = 0.714 %
3. The concentrations of new and old H2O2 are different. That of the old H2O2 is lower. It is highly expected because H2O2 readily decomposes with time. Hence the effective concentration reduces with time.
4. If the additives react with KMnO4, greater volume of permanganate will be used. This results in greater mole
of KMnO4 in the computation which will lead also to greater mole of H2O2. Hence the reported mass and percentage of H2O2 will be higher than the actual values. A positive error will be incurred.
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