CHEM CE問題2(已有答案, 只求解答) (20pt)

5. B

(1) No
NaNO3 is decomposed on heating to give NaNO2 and O2.
2NaNO3(s) → 2NaNO2(s) + O2(g)

(2) Yes
AgNO3 is decomposed on heating to give Ag, brown NO2 gas and O2.
2AgNO3(s) → 2Ag(s) + 2NO2(g) + O2(g)

(3) No
NH4NO3 is decomposed on heating to give colourless N2O gas and water vapour.
NH4NO3(s) → N2O(g) + 2H2O(g)

(4) Yes
Pb(NO3)2 is decomposed on heating to give PbO, brown NO2 gas and O2.
2Pb(NO2)2(s) → 2PbO(s) + 4NO2(g) + O2(g)


6. D

A. No
Aluminium sulphate solution gives white aluminum hydroxide precipitate.
Al3+(aq) + 3OH-(aq) → Al(OH)3(s)
Lead(II) ethanoate solution gives white lead(II) chloride solution.
Pb2+(aq) + 2Cl-(aq) → PbCl2(s)

B. No
Aluminium sulphate solution gives aluminium hydroxide precipitate which re-dissolves in excess sodium hydroxide solution.
Al3+(aq) + 3OH-(aq) → Al(OH)3(s)
Al(OH)3(s) + 2OH-(aq) → [Al(OH)4]‑(aq)
Lead(II) ethanoate solution gives lead(II) hydroxide precipitate which re-dissolves in excess sodium hydroxide solution.
Pb2+(aq) + 2OH-(aq) → Pb(OH)2(s)
Pb(OH)2(s) + 2OH-(aq) → [Pb(OH)4]2‑(aq)

C. No
Neither solution reacts with nitric acid.

D. Yes
Aluminium sulphate solution does not react with sodium chloride solution, but lead(II) ethanoate solution gives a white precipitate of lead(II) chloride with sodium chloride solution.
Pb2+(aq) + 2Cl-(aq) → PbCl2(s)


7. D

A. No
No reaction occurs.

B. No
No reaction occurs.

C. No
No reaction occurs.

D. Yes
A pale yellow precipitate would be produced.
S2­O32-(aq) + 2H+(aq) → H2O(l) + SO2(g) + S(s)


8. D

Each of the four methods can be used to prepare the corresponding substance.

D is the least suitable one. This is because nitrogen dioxide is highly toxic, but method D is too vigorous and the reaction can hardly be stopped when sufficient nitrogen dioxide is obtained. In laboratory, nitrogen dioxide is usually prepared by heating lead(II) nitrate (or a suitable metal nitrate).
2Pb(NO2)2(s) → 2PbO(s) + 4NO2(g) + O2(g)