化學高手請解答我一d無知ge chem問題!!!

答案係B.

1 is correct.

Zinc is more reactive than silver, so it can replace silver in AgNO3.
Zn + 2AgNO3 ---> 2Ag + Zn(NO3)2

But Zinc is less reactive than magnesium, so it cannot replace Mg in Mg(NO3)2.

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2 is incorrect.

There is no observable change.

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3 is correct.

AgNO3 + KCl ---> AgCl + KNO3
Mg(NO3)2 + 2KCl ---> MgCl2 + 2KNO3

AgCl is insoluble in water, so white ppt is formed.
MgCl2 is soluble in water, so no ppt is formed.

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Solution + solid 有時會係displacement reaction
好似呢條問題咁.
記熟書中的reactivity series 就可以了.

A metal will displace a less reactive metal from its solution.


圖片參考：http://image.tutorvista.com/content/metals-non-metals/metals-reactivity-series.jpeg


記Reaction with acid 既三條式.

Acid + metal ---> salt + hydrogen
Acid + metal oxide/ metal hydroxide ---> salt + water
Acid + metal carbonate/ metal hydrogencarbonate ---> salt + water + carbon dioxide

重有 reaction between metal ions and alkali ( NaOH, NH3 等 )
書都應該有.

重有ammonium cpd 同 alkali 既reaction
Ionic eq: NH4+ + OH- ---> NH3 + H2O

其實我都係記曬本教科書果D equations.
最緊要係識點樣用返出黎，所以做多D pp 係好既~
希望我可以幫到您啦 @_@

2011-04-15 18:11:43 補充：
多謝補充. ^^
nitrates / hydrogencarbonate - all soluble
halides - all are soluble except silver halides (AgCl, AgBr, AgI)
and lead (II) halides (PbCl2, PbBr2, PbI2)
Sulphates - all are soluble except - CaSO4, PbSO4, BaSO4
Carbonate - all are insoluble except - Li2CO,Na2CO3, K2CO3, (NH4)2CO3

Solubility of salts is also required to memorize.