In today

1
CH 103 PERCENT HYDROGEN PEROXIDE

• In todays experiment you will be given a
  solution that has an unknown concentration of
  hydrogen peroxide (H2O2).
• You will measure this concentration by
  determining the volume of oxygen (O2(g)) produced
  from the catalytic decomposition of H2O2(aq).
• What is a catalyst?
• A catalyst speeds up a chemical reaction. It is
  recycled during the reaction. It is not
  permanently created. And it is not permanently
  consumed.
• In todays experiment yeast will be the catalyst.

2
A REVIEW OF LEWIS STRUCTURES

• What is the Lewis structure for hydrogen peroxide
  (H2O2)?
• What is the Lewis structure for hydroxide ion
  (OH-)?
• Does hydroxyl radical ( ) have a
  complete octet?
• No therefore, it is very reactive.
• Similarly, hydroperoxyl radical (
  ) does not have a complete octet and is very
  reactive.
• What is the Lewis structure for oxygen (O2)?
• What is the Lewis structure for water (H2O)?

3
THE CATALYTIC DECOMPOSITION OF H2O2

• The reaction mechanism for the catalytic
  decomposition of H2O2 has 5 steps. Use your
  Lewis structures to account for every valence
  electron in this mechanism.
• Is the catalyst recycled?
• Yes, it either losses or gains an electron in
  each of the first 4 steps. Therefore, the
  catalyst is not permanently changed.
• Do the highly reactive hydroxyl radicals (
  ) cancel?
• Yes. Radicals often have an incomplete octet
  therefore, they are too reactive to form stable
  products.
• Do the highly reactive hydroperoxyl radicals (
  ) cancel?
• Yes.
• What is the net reaction?

4
EXPERIMENTAL APPARATUS

• The rubber tubing connecting Flask B with Beaker
  D must be filled with water.
• The water level in Flask B must come to just
  below the short inlet tube.
• The volume of O2(g) produced by the catalytic
  decomposition of H2O2 equals the volume of water
  collected in Beaker D.

5
THE IDEAL GAS LAW

• The Ideal Gas Law will be used to convert this
  volume of O2(g) to moles of O2(g).

6
THE IDEAL GAS LAW

• The pressure of an ideal gas is 745 mm Hg (745
  Torr). Its temperature is 45 C. And its volume
  is 514 mL. Calculate the moles of this gas.
• Convert the pressure to atmospheres.
• Convert the temperature to Kelvin.
• Convert the volume to liters.
• Calculate the moles of ideal gas.

7
DALTONS LAW OF PARTIAL PRESSURES

• Daltons Law of Partial Pressures says that the
  total pressure (Ptotal) exerted by a mixture of
  gases in a container equals the sum of individual
  pressures for each gas.
• Ptotal PA PB PC
• John Dalton

8
DALTONS LAW OF PARTIAL PRESSURES

• In todays experiment the total press (Ptotal) in
  flask B equals the pressure of oxygen (PO2) plus
  the pressure of water vapor (PH2O). This Ptotal
  also equals the barometric pressure (Pbar).
• Ptotal Pbar PO2 PH2O
• PO2 Pbar PH2O
• The decomposition of a H2O2 solution displaces
  315 mL of water at 14 C. The vapor pressure of
  water at 14 C is 12.0 mm Hg or 12.0 Torr. The
  atmospheric pressure is 746 mm Hg or 746 Torr.
• What is the pressure of O2(g)?
• PO2 Pbar PH2O 746 mm Hg 12.0 mm Hg 734
  mm Hg
• How many moles of O2(g) was produced?

9
SAFETY

• Give at least 1 safety concern for the following
  procedures that will be used in todays
  experiment.
• Using H2O2.
• This is an irritant. Wear your goggles at all
  times. Immediately clean all spills. If you do
  get H2O2 in your eye, immediately flush with
  water.
• Using glassware.
• Glass can easily break and form shards. Wear
  your goggles at all times.
• Your laboratory manual has an extensive list of
  safety procedures. Read and understand this
  section.
• Ask your instructor if you ever have any
  questions about safety.

10
SOURCES

• McMurry, J., R.C. Fay. 2004. Chemistry, 4th ed.
  Upper Saddle River, NJ Prentice Hall.
• Park, J.L. 2004. ChemTeam Photo Gallery Menu.
  Available http//dbhs.wvusd.k12.ca.us/webdocs/Gal
  lery/GalleryMenu.html accessed 16 November
  2006.
• Petrucci, R.H. 1985. General Chemistry Principles
  and Modern Applications, 4th ed. New York, NY
  Macmillan Publishing Company.
• Schumb, W.C., C.N Satterfield, R.L. Wentworth.
  1955. Hydrogen Peroxide. New York, NY Reinhold
  Publishing Corporation.