CHEM CE 程度

唔係所有organic compounds都係flammable嫁咩? 點解第1個唔係既?

In organic compounds, C atoms are less combustible than H atoms. If an organic compound does not contain H, then it is usually non-flammable.

Actually, bromochlorodifluoromethane (short name: BCF) is a fire extinguisher. You may see its short name BCF (used as fire extinguisher) in MTR stations.

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conc. sulphuric acid 同 1 種chemical react 係咪一定會出SO2

No.
SO2 is formed only from some redox reactions when concentrated sulphuric acid acts as an oxidizing agent.

For example, consider the reaction between sugar cube and conc. sulphuric acid. Since conc. sulphuric acid acts as a dehydrating agent but not an oxidizing agent, no SO2 is formed.
C12H22O11 → 12C + 11H2O

Even in some redox reactions using conc. sulphuric acid, no SO­2 is formed. For example, in the redox reaction between hydrogen iodide and conc. sulphuric acid, H2S is formed instead of SO2.
H2SO4 + 8HI → H2S + 4H2O + 4I2

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conc. nitric acid 同 1 種chemical react 係咪一定會出NO2

No.
NO2 is formed only from redox reactions when concentrated nitric acid acts as an oxidizing agent.

For example, consider the reaction between sodium carbonate and conc. nitric acid. Since conc. nitric acid acts as an acid, but not an oxidizing agent, no NO2 is formed.
2HNO3 + Na2CO3 → 2NaNO3 + H2O + CO2