High School Chemistry: Bleached Substances Exam Sites! Don't be confused!
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Today I want to share with you: the types of bleached substances, and a few questions worth thinking about. Commonly used bleaching agents are activated carbon, chlorine water, Na2O2, O3, H2O2, SO2, HClO, NaClO, Ca(ClO)2 (active ingredient of bleaching powder), etc., but their bleaching principle is easy to confuse, here is a summary, for the reference of students.
➤ A few questions worth thinking about bleaching
1. Is the following fading phenomenon the bleaching of SO2?
(1) SO2 fades the orange bromine water
(2) SO2 fades the purple KMnO4 acidic solution
(3) SO2 fades the red phthalides
Analysis: The above fading phenomenon is not caused by the bleaching of SO2.
(1) (2) The reason for fading is the reductivity of SO2. Redox reactions occur separately
SO2+Br2+2H2O= H2SO4+2HBr
5SO2+2KMnO4+2H2O=K2SO4+2MnSO4+ 2H2SO4
(3) The reason for fading is that SO2 is dissolved in H2O to form H2SO3, and H2SO3 is an acid that can make red phthalides colorless.
2. What phenomena do chlorine water and SO2 cause purple litmus respectively?
Analysis: HClO in chlorine water first turns the purple litmus red, and then fades the red because of its strong oxidation.
SO2 is dissolved in H2O to form H2SO3, an acid that can make purple litmus red. H2SO3, on the other hand, does not have strong oxidation, so the red color does not fade.
3. Can the bleaching effect be enhanced after SO2 and Cl2 are mixed?
Resolution: No. Because so2 and Cl2 mix will undergo a redox reaction
SO2+ Cl2+2H2O= H2SO4+2HCl
Neither the products H2SO4 nor HCl have a bleaching effect, so the bleaching effect is weakened. When n(SO2): n(Cl2) = 1:1, the bleaching effect is completely lost.
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