3 Instability: 2H,,=2H20+0 EAO20695H2O2176H2O EB°O20076HO2+0867OH left Disproportionation reaction Factors that affect decomposition of H2O2 Light or heat A Acid or base(In basic medium, the disproportionation reaction will be fast A Impurity: some ions of heavy metals: Mn2, Fe, Crt, Cu2* or their compounds will accelerate decomposition 3 Oxidizing /reducing properties A Oxidizing properties 2O2+2I+2H=l2+2H2O PbS+4 H202=PbSO4+4H2O 2Cr(OH)4+3H2O2 +20H=2CrO4+8H2O 2 Reducing properties 2MnO4+5H2O2+6H=2Mn+5021+8H2O Cl+ H202=2HCI+O 5H2O2+2HIO3=12+502↑+6H2O 5H2O2+12=2HIO3+4H2O Section Three Sulfur and main compounds of sulfur Oxidation number Type of compounds Example Sulfides, sulfoacid and the salts Na2S, AS2S3, Na2SnS3 Polysulfide Na2s? Simple substanc 第14页 2006-02-22第 14 页 2006-02-22 14 ○ 2 Instability: 2H2O2=2H2O+O2 EA θ O2 0.695 H2O2 1.76 H2O EB θ O2 -0.076 HO2 - +0.867 OH￾Eθ right>Eθ left →Disproportionation reaction Factors that affect decomposition of H2O2: △1 Light or heat △2 Acid or base (In basic medium, the disproportionation reaction will be fast) △3 Impurity: some ions of heavy metals: Mn2+, Fe3+, Cr3+, Cu2+ or their compounds will accelerate decomposition ○ 3 Oxidizing /reducing properties △1 Oxidizing properties H2O2 + 2I- + 2H+ = I2 + 2H2O PbS + 4 H2O2 = PbSO4 + 4H2O 2Cr(OH)4 - +3H2O2 +2OH- =2CrO4 2-+8H2O △2 Reducing properties 2MnO4 - +5H2O2+6H+ =2Mn2++5O2↑+8H2O Cl2 + H2O2 = 2HCl + O2 5H2O2 + 2HIO3 = I2 + 5O2↑ + 6H2O 5H2O2 + I2 = 2HIO3 + 4H2O ○ 4 Weak acid Section Three Sulfur and main compounds of sulfur Oxidation number Type of compounds Examples -2 Sulfides, sulfoacids and the salts Na2S, As2S3, Na2SnS3 -1 Polysulfide Na2S2 0 Simple substance S8