f.4 chem

1. Ionic equation: Cu2+(aq) + 2OH-(aq) → Cu(OH)2(s)
When excess ammonia solution is added, a complex ion is formed.
Cu(OH)2 (s) + 4NH3 (aq) → [Cu(NH3)4]2+ (aq) + 2OH- (aq)

Observations:
a. A pale blue gelatinous precipitate is formed.
b. The colour of the blue solution fades.
c. When excess ammonia solution is added, the precipite dissolves to form deep blue solution.


2. The answer is D.
For D, dirty green gelatinous precipitate should formed instead of reddish brown precipitate. It is because Fe(OH)2 is formed, the oxidation number of Fe is 2+, i.e. that is iron (II) ion, the colour is green but not brown. Fe3+ ion is brown in colour.
2OH- (aq) + Fe2+ (aq) → Fe(OH)2 (s)

For A, zinc hydroxide is formed and it is a white gelatinous precipitate, so it is correct.
For B, potassium hydroxide is formed, but it is soluble in water, so no observation can be seen. So it is correct.
For C, as above, copper (II) hydroxide is formed, it is blue precipitate, so it is correct.


3. All ions are soluble in water.
For compounds,
a. All group 1 compounds are soluble in water.
b. All nitrates are soluble in water.
c. All hydrogencarbonates are soluble in water.
d. All halides, except AgX and PbX2 (where X = Cl, Br or I) are soluble in water.
e. All sulphates except BaSO4 and PbSO4 (CaSO4 is only sparingly soluble).
f. Except group 1, all carbonates are insoluble.
g. Except group 1 and calcium, all hydroxide are insoluble.


4. NH3 is alkali, but it needs water to show its alkaline property, because water is required for NH3 to give OH- ion.
NH3 + H2O ←→ NH4OH

Mg(OH)2 is base, not alkali. As it is insoluble in water.
All alkalis are base, but not all the bases are alkalis.
Alkali refers to soluble base.

1.
Cu2+(aq) + 2(OH-)(aq) ---> Cu(OH)2(s)
in which the hydroxide ions come from ammonia SOLUTION.
The observation: pale blue precipitate is formed.

2.
The answer is A.
The white precipitate formed must be zinc hydroxide.

3.
Polar compounds are soluble in water while non-polar compounds are insoluble in water.
Most of ions are soluble in water.

The metal compound or ions of Ca2+, Mg2+, Al3+, Pb2+, Zn2+, Fe2+, Fe3+ are insoluble in alkali, forming precipitate.

4.
NH3 and Mg(OH)2 are alkali.

第二題ge 答案應該係"a"
第四題答案是 yes

我自問係化學高手...
但英文我一定唔識。
中文的話或者我可以幫到你!!