請幫手!!CE Chem MC 一條 (acid & alkali) 20pts!

The MC:

All metal hydroxides are basic, which can react with strong acid solutions to give salt and water.
Like other metal oxide, zinc oxide can react with strong acid solutions to give salt and water.
Zn(OH)2(s) + 2H+(aq) → Zn2+(aq) + 2OH-(aq)

Some metal hydroxides (e.g. zinc hydroxide, aluminium hydroxide and lead(II) hydroxide) have a property of weak acid to neutralize strong alkali solutions to forming salts.
Zn(OH)2(s) + 2OH-(aq) → [Zn(OH)2]2-(aq)
[Zn(OH)2]2- is named as zincate ion.

Since metal hydroxide can neutralize both strong acids and strong alkalis, it is known as an "amphoteric (雙性的) hydroxide".

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1.
Ca(s) + 2H2O(l) → Ca(OH)2(aq/s) + H2(g)

The Ca(OH)2 solid would not coat on the surface of Ca solid. The major reason is that the hydrogen bubbles would make the Ca(OH)2 solid detach from the unreacted Ca solid. Besides, some Ca(OH)2­ is dissolved in the solution.

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2.
Think in a way that you have studied in Physics:

No matter whether a salt bridge is installed or not, the two half-cells (linked together by the external circuit) build up a potential difference between them.

In the absence of a salt bridge, there is no current (no electron flow). A Current (electrons) flow(s) only when the circuit is complete.

2008-04-12 12:58:17 補充：
In the absence of a salt bridge, the circuit is incomplete (an open circuit).

zinc hydroxide can dissolve in sodium hydroxide or potassium
hydroxide to form [Zn(OH)4]2-, so it can react with acid and alkali
to form salt and water.
calcium granule is spherical structure but calcium hydroxide
is powder form. so the surface area of calcium hydroxide is
larger than that of calcium granule. so the reaction with
sulphuric acid is better in calcium hydroxide.
salt bridge can complete the circuit. so when the salt bridge is
broken. no charge can flow and so no electricity can be detected.