✔ 最佳答案
Metal + Acid:
All equations are correct.
K/Na + HCl/H2SO4:
An explosive reaction occurs.
(Don’t do such reactions in laboratory.)
Ca/Mg/Al/Zn/Fe + HCl/H2SO4
Colourless bubbles are formed, and the metal dissolves in the acid to form a colourless (for Ca/Mg/Al/Zn) or pale green (for Fe) solution.
Pb + HCl/H2SO4:
Colourless bubbles are formed.
The reaction stops soon after the reaction starts.
(A solid layer of PbCl2/PbSO4 is formed on the surface of the Pb metal. The solid layer separates the Pb metal and the acid, and this makes the reaction stop.)
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Metal + Water:
The equations are correct, except those of (Mg + cold H2O) and (Fe + steam).
K + cold water:
The potassium burns with a lilac flame, moves on the water, and finally dissolves to give a colourless solution.
(Since the potassium floats on water, it is difficult to see the bubbles formed.)
Na + cold water:
The sodium moves on water, may burn with a yellow flame, and finally dissolves to give a colourless solution.
(Since the sodium floats on water, it is difficult to see the bubbles formed.)
Ca + cold water
Colourless bubbles are formed, and the calcium dissolves.
(“Sinking” is not an important observation.)
Mg + cold water
Mg + 2H2O → Mg(OH)2 + H2
Cold water: Colourless bubbles are formed, and the reaction is extremely slow.
Mg/Al/Zn + steam
Mg + H2O → MgO + H2, etc.
A white solid is formed.
(Both H2O and H2 are gaseous. Therefore, no bubbles are observed.)
Fe + steam
3Fe + 4H2O → Fe3O4 + 4H2
A black solid is formed.
(Actually, the reaction is reversible.)
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