Hydrogen peroxide is a very common chemical compound in the laboratory and have lot of uses in home and industrial scale. It is used as a disinfectant in the cleaning of injuries. In this tutorial, we will learn about preparation, reactions and other characteristics of hydrogen peroxide.
Boiling points of hydrogen peroxide and water are 1500C and 1000C respectively. We know both hydrogen peroxide and water are able to make hydrogen bonds.
Molecular masses of H2O2 and H2O are 34 and 18 respectively. Also hydrogen peroxide molecules have the ability to make more hydrogen bond than water molecules. Due to both greater molecular mass and number of hydrogen bonds, boiling point of hydrogen peroxide is higher than water.
Pure hydrogen peroxide is a weak acid dissociates as follow. It's Ka value is 1.55 * 10-12 mol dm-3 at 298K.
Hydrogen peroxide is stored in wax-lined glass or plastic vessels in the presence of stabilizers such as urea. Also it should be kept away from dust because dust can induces explosive decomposition.
In this section, you will learn how hydrogen peroxide is prepared. Chemical balanced equations are given with each method.
Alkali metals peroxides ( Na2O2, K2O2 ) will react with water and produce hydrogen peroxide and metal hydroxide.
Hydrogen peroxide can react in different ways.
Hydrogen peroxide decomposes into water and oxygen gas (O2) when temperature increases or exposing to the sunlight. This reaction can be catalyzed by minute traces of transition metal ions. In the presence of potassium iodide, MnO2 aqueous NaOH will also catalyze the decomposition of H2O2. Also decomposition of H2O2 is an oxidizing-reducing reaction.
Enthalpy change for the reaction is -196.0 kJ
But decomposition will slow down when acids are present. ( H2SO4 ).
This reaction is a disproportionation process. Two half reactions (oxidation and reduction) are occurred.
Hydrogen peroxide is reduced to water and other compound is oxidized.
Potassium iodide is oxidized to iodine and hydrogen peroxide is reduced to water. Also in the presence of excess potassium iodide produced iodine combines with iodide ion give red - brown I3-.
2KI + H2O2 + H2SO4 = I2 + 2H2O + K2SO4
2KI +I2O2 = KI3
PbS + 4H2O2 = PbSO4 + 4H2O
PbCO3 is a white inorganic compound. It is used as a pigment. But due to presence of H2S, PbCO3 is turned to black colour PbS. To take back the white colour, hydrogen peroxide is reacted with lead sulfide. Then lead sulfate, a white precipitate is given.
Ferrous ion ( iron(ii) ) is oxidized to ferric ion ( iron(iii) ) and H2O2 is reduced to water. Green colour of Fe2+ solution is changed to brown - yellow colour due to production of Fe3+.
2FeCl2+ + H2O2 + 3H2SO4 = Fe2(SO4)3 + 4HCl + 2H2O
Sulfurous acid is oxidized to sulfuric acid. So oxidation number of sulfur is increased from +4 to +6. As other product, water is given.
H2SO3 + H2O2 = H2SO4 + H2O
Sulfurous acid is a weak acid and sulfuric acid is a strong acid.
Hydrogen sulfide is oxidized to sulfur and hydrogen peroxide is reduced to water.
H2S + H2O2 = S + 2H2O
NaOH reacts with hydrogen peroxide and produce sodium hydroperoxide which is an acidic salt. With excess NaOH, hydrogen peroxide forms sodium peroxide which is a normal salt.
NaOH + H2O2 = NaHO2 + H2O
2NaOH + H2O2 = Na2O2 + 2H2O
Hydrogen peroxide can accept electrons in the alkaline medium and behave as an oxidizing agent.
Manganese sulfate is oxidized to manganese dioxide while hydrogen peroxide is reduced to water. Manganese dioxide is a red-brown precipitate.
MnSO4 + NaOH + H2O2 = MnO2 + Na2SO4 + H2O
NaNO2 + H2O2 = NaNO3 + H2O
Na2SO3 + H2O2 = Na2SO4 + H2O
Na3AsO3 + H2O2 = Na3AsO4 + H2O
Hydrogen peroxide can behave as a reducing agent in both acidic and basic mediums.
Acidified potassium permanganate is reduced to colourless manganese sulfate and hydrogen peroxide is oxidized to oxygen gas. Acidified potassium permanganate solution is purple colour.
2KMnO4 + 5H2O2 + 6H2SO4 = 2MnSO4 + 5O2 + K2SO4 + 8H2O
Acidified orange colour potassium dichromate solution is oxidized to green colour chromium salt while hydrogen peroxide is oxidized to oxygen gas.
K2Cr2O7 + 3H2O2 + 4H2SO4 = Cr2(SO4)3 + 3O2 + K2SO4 + 7H2O
In acidified medium, brown-black colour manganese dioxide is reduced to manganese sulfate. Oxygen is given by the oxidation of hydrogen peroxide.
MnO2 + H2O2 + H2SO4 = MnSO4 + O2 + 2H2O
Ozone is reduced to dioxygen molecule.
O3 + H2O2 + H2SO4 = 2O2 + 2H2O
Hypochlorous acid is reduced to chloride ion in acidic medium.
HOCl + H2O2 + H2SO4 = H3O+ + O2 + Cl-
Potassium permanganate is reduced to manganese dioxide while oxygen is oxidized to oxygen gas.
2KMnO4 + 3H2O2 = MnO2 + 3O2 + 2H2O + 2KOH
Ferric ions are reduced to ferrous ion by hydrogen peroxide which is oxidized to dioxygen molecule.
2FeCl3 + H2O2 + 2NaOH = 2FeCl2 + O2 + 2H2O + 2NaCl
When potassium ferrycyanide reacts with hydrogen peroxide in a alkaline medium, potassium ferrocyanide is given as the reduction product.
2K3[Fe(CN)6] + H2O2 + 2KOH = 2K4[Fe(CN)6] + O2 + 2H2O
Some metal oxides can be reduced to metal or higher oxidation state metal oxides can be reduced to lower oxidation state metal oxide.
Ag2O + H2O2 = 2Ag + O2 + H2O
PbO2 + H2O2 = PbO + O2 + H2O
HYdrogen peroxide can behave as an oxidzing agent or reducing agent. So, you have to remember how different compounds react with hydrogen peroxide.
Decomposition of hydrogen peroxide will increase by inorganic compounds such as aqueous KI, NaOH, solid MnO2.
If manganese dioxide is added to aqueous hydrogen peroxide, it accelarates the decomposition of hydrogen peroxide to water and oxygen gas.
If acidic manganese dioxide is used, hydrogen peroxide is oxidizzed to oxygen gas while manganese dioxide will be reduced to manganese +2 ion.
Hydrogen perioxide can behave as an oxidizing agent and reducing agent. So, hydrogen peroxide can react with many compounds.
Ferric chloride is reduced to ferrous cations by hydrogen peroxide.
There are different referencess for this reaction ad we will summarize them.
According to the The oxidation of ethanol by hydrogen peroxide. Part I. Catalysis by ferric ion research, ethanol is oxidized to acetaldehyde in the presence of Fe3+ catalyst. They have used boiling ethanol for this rection.
Acidified hydrogen peroxide and ethanol reaction be an explosive one. Concentration of hydrogen peroxide should be high. But higher concentrations of H2O2 are dengerous.
In acidic medium, permanganate ion is reduced to manganese +2 ion by H2O2.
In te basic medium, manganese +2 ion are oxidized to manganese dioxide (MnO2) by H2O2.
For which thing, you asked that temprature range?