CHEM 122L
General Chemistry Laboratory
The Decomposition of Hydrogen Peroxide To learn about Avogadro's Hypothesis and the Ideal Gas Law.
To learn about gas phase Stoichiometry.
To learn about the chemistry of Peroxides.
In this laboratory exercise we will determine the percentage Hydrogen Peroxide present in a commercially available solution by measuring the volume of Oxygen gas liberated when the peroxide decomposes. Because the decomposition of dilute solutions of Hydrogen Peroxide is relatively slow, a Ferric Chloride catalyst will be used to increase the reaction rate so that the reaction goes to completion during the laboratory period.
In its pure form, Hydrogen Peroxide (H2O2) is a faintly bluish, syrupy liquid which boils at 150. 2 o C. It was first synthesized by the French chemist Louis Jaques Thenard in 1818 by acidification of Barium Peroxide (BaO2) with Nitric Acid (HNO3). This process was supplanted by an improved version in which the Barium Peroxide is initially treated with Hydrochloric Acid (HCl), followed by addition of Sulfuric Acid (H2SO4) to precipitate the Barium Ion (Ba 2+ ) as Barium Sulfate (BaSO4). This leaves a relatively pure aqueous solution of Hydrogen Peroxide:
BaO2(s) + 2 HCl(aq) H2O2(aq) + BaCl2(aq) (Eq. 1)
BaCl2(aq) + H2SO4(aq) BaSO4(s) + 2 HCl(aq) (Eq. 2)
When exposed to sunlight or metallic impurities, Hydrogen Peroxide rapidly decomposes to Oxygen gas:
2 H2O2(aq) 2 H2O(l) + O2(g) (Eq, 3)
This is a key reaction of Hydrogen Peroxide.
Commercially, dilute Hydrogen Peroxide solutions (3-30%) are used for bleaching (pulp, paper, straw, leather, hair, etc. ) and to treat wounds. Its value as an antiseptic is low, but the evolution of Oxygen when it comes into contact with clotted blood helps to loosen dirt and assists in cleansing a wound.
At higher concentrations (70-98%), the decomposition of the peroxide is accompanied by the evolution of enough heat to convert the Water to Steam. In this fashion, Hydrogen Peroxide is used as a monopropellant in rocket engines; the peroxide is passed over a Silver mesh which catalyzes the decomposition and the resulting gaseous H2O and O2 products are ejected through a P a g e | 2 nozzle at high velocity propelling the rocket forward. Concentrated Hydrogen Peroxide can also be used as an oxidant with organic compounds, such as kerosene, in a bipropellant rocket engine.
The German V2 Rocket of WWII used this design.
We will leverage the Hydrogen Peroxide decomposition reaction (Eq. 3) to determine the concentration of Hydrogen Peroxide in products typically sold in the supermarket. The reaction stoichiometry allows us to use the measured amount of Oxygen (#moles O2) produced as a result of the decomposition to determine the amount of peroxide (#moles H2O2) initially present in the solution:
# moles H2O2 = x # moles O2 (Eq. 4) The number of moles Oxygen produced (n) by this reaction can...
