Topic content:
In recent years, the consumption demand of potassium permanganate in the field of drinking water and industrial sewage treatment has increased rapidly. The laboratory can use manganese dioxide as the main raw material to prepare potassium permanganate. Part of the process is as follows:
(1) The reason why iron crucible is used instead of porcelain crucible in step ① is (expressed by chemical equation) ________________________________________.
(2) The chemical equation of KOH, KClO3 and MnO2 eutectic reaction to produce dark green K2MnO4 is ________________________________________.
(3) Step ④ CO2 can make MnO42 react to generate MnO4 and MnO2. Then when K2MnO4 completely reacts, the percentage of conversion to KMnO4 is about ________ (accurate to 0.1%).
(4) The purpose of step ⑤ hot filtration is ______________________________________.
(5) Step ⑥ Heat and concentrate until there are fine crystals on the liquid surface, stop heating, cool crystallization, ________, wash and dry. During drying, the temperature should not be too high, because ____________________________________.
Best answer:
(1)SiO2+2KOH=K2SiO3+H2O
(2)6KOH+KClO3+3MnO2KCl+3K2MnO4+3H2O
(3)66.7 %
(4) Reduce the loss during filtration (or prevent the loss due to KMnO4 precipitation during cooling)
(5) If the filtration temperature is too high, KMnO4 will decompose
Answer analysis:
In the process, MnO2 is first converted into K2MnO4, and K2MnO4 undergoes its own redox reaction to generate KMnO4. (1) In step ①, the iron crucible is used instead of the porcelain crucible because the SiO2 contained in the latter will react with KOH at high temperature: SiO2+2KOH=K2SiO3+H2O.
(2) When KOH, KClO3 and MnO2 are melted together, MnO2 is oxidized to K2MnO4, KClO3 is reduced to KCl, and the chemical equation is 6KOH+KClO3+3MnO2KCl+3K2MnO4+3H2O.
(3) In step ④, CO2 can make MnO42 react. According to the conservation of gain and loss of electrons, the ratio of the amount of material that generates MnO4 - and MnO2 is 2:1, so when K2MnO4 completely reacts, the percentage of conversion to KMnO4 is about 66.7%.
(4) The purpose of step ⑤ hot filtration is to prevent KMnO4 precipitation and loss during cooling.
(5) During drying, the temperature should not be too high, otherwise KMnO4 will decompose.
Test core:
Introduction to balancing: The chemical reaction equation strictly abides by the law of conservation of mass. After writing the chemical reaction equation and writing the reactants and products, the number of atoms on the left and right sides is often not equal, which does not meet the law of conservation of mass, which needs to be solved by balancing.