Dioxygen gas is usually obtained in the laboratory by the thermal decomposition ofA. `KNO_(3)`B. `KMnO_(3)`C. `KCIO_(3)`D. `(NH_(4))_(2)Cr_(2)O_(7)`

Dioxygen gas is usually obtained in the laboratory by the thermal deco

1.	Dioxygen gas is usually obtained in the laboratory by the thermal decomposition ofA. `KNO_(3)`B. `KMnO_(3)`C. `KCIO_(3)`D. `(NH_(4))_(2)Cr_(2)O_(7)`
Answer» Correct Answer - 3 The usual laboratery method consisting in heating of a mixture of potassium chlorate and maganese oxide in the ratio of `1:4KClO_(3)` evolves oxygen at `375^(@)C` but at this temperature. it melts and get converted into potassium `4KClO_(3)rarr3KClO_(4)+KCl` `KClO_(4)overset(650^(@)C)rarrKCl+2O_(2)` When `MnO_(2)` is added ,`KClO_(3)` starts giving `O_(2)` at ` 250^(@)C` thus, `MnO_(2)` acts as a catayst. `2KClO_(3)underset(heat)overset(MnO_(2))rarr2KCl+3O_(2)` `MnO_(2)` used for this purpose should be completely free from carbon as `KClO_(3)` and `C` mixture is expolsive in nature. The mixture should be first hated gently and then strongly when it is ensured that there is no vigorous reaction.`2KNO_(3)overset(Delta)rarr2KNO_(2)+O_(2)` `2KMnO_(4)overset(Delta)rarrK_(2)MnO_(4)+MnO_(2)+O_(2)` `(NH_(4))_(2)Cr_(2)O_(7)overset(Delta)rarrCr_(2)O_(3)+H_(2)O+N_(2)` `4K_(2)Cr_(2)O_(7)overset(Delta)rarr4K_(2)CrO_(4)+2Cr_(2)O_(3)+3O_(2)`

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