chem ce07 paper2 問題..6條問題40分*

19. (not 18)
The answer is A.

A.
No brown colour is formed.
2Ca(OH)2 + 2Cl2 → CaCl2­ + Ca(OCl)2 + 2H2O
In aqueous solution, all products are colourless.

B.
The solution turns brown.
2I- + Cl2 → I2 + 2Cl-
I-(aq) is colourless (not brown), and I2(aq) is brown.

C.
The solution turns yellowish brown.
2Fe2+ + Cl2 → 2Fe3+ + 2Cl-
Fe2+(aq) is pale green, and Fe3+(aq) is yellowish brown.
(If Fe3+(aq) is dilute, the solution will be yellow.)

D.
The solution turns brown.
2Br- + Cl2 → Br2 + 2Cl-
Br-(aq) is colourless (not brown), and Br2(aq) is brown.


28.
Sulphur is a non-metal, which has simple molecular structure. Sulphur cannot conduct electricity in both solid and liquid states.


36.
H2(g) is a fuel, but O2 is NOT. O2 is not a fuel, because it cannot burn but it can support burning only. That means a fuel can burn in O2(g), but O2(g) does not burn.


38.
C is not a suitable method.
PbO(s) + H2SO4(aq) → PbSO4(s) + H2O(l)
PbSO4 formed is not soluble in water, and it will form a solid layer to cover the PbO reactant. Therefore, after a short period of time, the PbSO4 layer would separate the two reactants: PbO and H2SO4. Consequently, the reaction stops.

D is suitable, because only a precipitate of lead(II) sulphate is formed.
Pb2+(aq) + SO42-(aq) → PbSO4(s)
OR: Pb(NO3)2(aq) + H2SO4(aq) → PbSO4(s) + 2HNO3(aq)


43.
Ammonium nitrate is an ionic compound.
Almost all common cations are metal ions, but ammonium ion (NH4+) is an exception. Ammonium nitrate is ionic compound which contains NH4+ and NO3- ions.
=