Chemical Properties
Burning Metal in Air/O2
M + O --> MO
Almost all metals combine with O2 to form metal oxides
2Cu + O2 --> 2Cu(II)O Black oxide
4Al +3 O2 --> 2Al2O3
Metal form basic oxides & non metals form acidic oxides
They react with acids & bases to form salt & water
But some metal oxides are both acidic & basic & are called Amphoteric oxides
Eg: Al2O3 & ZnO
Al2O3 + 6HCl --> 2AlCl3 + 3H2O
Al2O3 + 2NaOH --> 2NaAlO2 + H2O (sodium aluminate)
Solubility of MO in water
Most MO are insoluble in water
Some MO - K, Na dissolve in water to form alkalies
Na2O + H2O --> 2NaOH (aq)
K2O + H2O --> 2KOH (aq)
Alkali is a water soluble base
Difference in Reactivity with O2
K, Na react vigorously with air & catch fire when kept in the open
Hence to prevent accidental fires they are kept immersed in kerosene oil
At ordinary temperatures, Mg, Al, Zn, Pb etc are covered with a thin layer of oxide - this protective oxide layer prevents further oxidation
Iron does not burn on heating but iron filings catch fire when sprinkled in a flame
Silver & gold do not react with O2 even at high temperatures
Copper does not burn but the hot metal gets coated with black Cu(II)O
Reaction of Metal with Water
M + H2O --> MO + H2
Metals dissolve in water to form metal oxide & H2
If the MO is soluble in water it form MOH/metal hydroxide
MO + H2O --> M(OH)
K, Na reacts violently with cold water
The reaction is so violent & exothermic that the evolved H2 catches fire
Ca reacts with cold water less violently - heat evolved is not enough for H2 to catch fire
2K + H2O --> 2KOH(aq) + H2 + heat
Ca+ H2O --> Ca(OH)2(aq) + H2 + less heat
2Na + H2O --> 2NaOH(aq) + H2 + heat
Mg reacts with hot water to form Mg(OH)2 + H2
Ca starts floating as the evolved H2 sticks to the surface of the metal
Mg also starts floating as the evolved H2 sticks to the surface of the metal
Mg does not react with cold water
Al, Fe, Zn do not react with cold or hot water
They react with steam to form MO & H2
2Al + 3H2O --> Al2O3 + 3H2
3Fe + 4H2O --> Fe3O4 + 4H2
Pb, Cu, Ag, Au do not react with water at all