Define a catalyst. Are your observations consistent with the Mn complex being a

Question

Define a catalyst. Are your observations consistent with the Mn complex being a catalyst for a reaction of H2O2?

What is the significance of the amount of gas produced in the manometry experiment in terms of the definition of a catalyst and the stoichiometry of the H2O2 reaction?

experiment guide :Determine the “head space” volume of the manometer as follows: • Fill the 125 mL filter flask, with the side-arm sealed with parafilm, with water to the top of the flask. Determine the volume by pouring the water into a graduated cylinder. • Measure the inner diameter of the glass tube on the manometer, and its length (plus the length of the Tygon connecting tubing) to determine the volume of the tube. • Add these volumes to get the total volume, and subtract 50 mL for the solution to get the head space volume for the evolved gas. Rinse the filter flask with a little bit of ethanol or methanol to remove the residual water, and then with a small amount of methylene chloride to prepare it for the experiment. (NOTE: these solvents should NOT go down the drain!) Dissolve 10 µmol (7 mg) of [Mn(salpn)(µ-O)]2 in 50 mL of methylene chloride. Gravity filter the solution to remove any undissolved solids, and place the solution into a 125 mL filter flask with a clean stir bar. Seal the top of the flask with a rubber septum. Connect the flask side-arm to the manometer tube with the short length of Tygon tubing. Place a stir plate under the flask such that the connecting tubing is level. Stir the solution for a few minutes to equilibrate the solvent vapor pressure, then check the difference in Hg level so you can correct your final measurement for the partial pressure of solvent vapor. Bring 200 µL of 30% H2O2 up in about 0.75 mL of acetonitrile, and using a syringe and needle add it through the septum to the stirring Mn solution. Monitor the mercury level in the manometer until the level has not changed for at least 10 minutes, or for about an hour total, and record the difference in height between the Hg column exposed to the atmosphere and the column exposed to the sealed reaction mixture. [While you are monitoring the Hg level of the manometer, do the following experiment: In test tubes, dissolve a small amount of [Mn(salpn)(µ-O)]2 in several mL of methylene chloride. Make sure they are concentrated enough to see the color, but that no solid is present. Add a drop or two of 30% H2O2 and mix vigorously if two phases are observed. Note your observations.] Back to the manometry experiment… Note whether or not you observe a color change in the solution. Using the ideal gas law, calculate the molar amount of oxygen produced based on the difference in Hg height (1 atm = 760 mm Hg….remember to correct for vapor pressure) and the volume of the head space. Based on the stoichiometry of H2O2 vs. O2 in the balanced equation for the disproportionation of H2O2, determine the yield of this reaction relative to each the Mn2 complex and to H2O2.

Explanation / Answer

A catalyst is a substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change.

Hydrogen peroxide is unstable and slowly decomposes in the presence of base or a catalyst. At room temperature hydrogen peroxide decomposes very slowly. So the presence of a catalyst will cause its decomposition quicker.

2H2O2 O2 + 2H2O

The catalyst used is MnO2. If more catalyst will used the reaction rate will increased.This is because more catalyst will have surface area for the reaction to take place.When we used CuO or ZnO instead of MnO2 the reaction is slow when compare to MnO2.

A catalyst help a reaction go faster but do not ungo themselves any change in the reaction.The decomposition of H2O2 is slow so to enhance the process we use MnO2. When manganese dioxide is added to 2 moles of hydrogen peroxide, 1 mole of oxygen and 2 moles of water are formed. The manganese dioxide provides greater surface area for the decomposition to take place.

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