Chemical equation

conc.H2SO4 + NaCl + MnO4 點出 white fume?

When concentrated H2SO4 reacts with NaCl, a white fume of hydrogen chloride is formed. The reaction occurs because the concentrated H2SO4 is non-volatile and has a high boiling point.
H2SO4 + NaCl → NaHSO4 + HCl

When the mixture of concentrated H2SO4, NaCl and MnO2 (not MnO4) are heated, they react. Pale yellowish green gas of chlorine is formed instead.
3H2SO4 + 2NaCl + MnO2 → 2NaHSO4 + MnSO4 + Cl2 + 2H2O

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conc.H2SO4 + NaBr + MnO4 點出 red fume?

When the mixture of concentrated H2SO4, NaBr and MnO2 (not MnO4) are heated, they react. Reddish brown vapour of bromine is formed.
3H2SO4 + 2NaBr + MnO2 → 2NaHSO4 + MnSO4 + Br2 + 2H2O

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Heat KNO3 出乜 ?

Pale yellow potassium nitrite solid and colourless oxygen gas are formed.
2KNO3 → 2KNO2 + O2

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Heat Mg(NO3)2 出乜

White magnesium oxide solid, brown nitrogen dioxide gas and colourless oxygen gas are formed.
2Mg(NO3)2 → 2MgO + 4NO2 + O2

因為KNO3(aq)同Mg(NO3)2(aq)係離子化合物,所以熔點高,普通加熱只會將水蒸走,出左higher concentration的KNO3同Mg(NO3)2