The physical properties are insufficient to identify if a substance is metal or a nonmetal and so there is need to test chemical properties of metal and non-metal . Lets start with reaction of metals with oxygen.
Metal react with oxygen to form metal Oxide
Metal + Oxygen → Metal Oxide
4K + O2 → 2K2O
Reaction of metals with Oxygen: Highly reactive metals
- Highly reactive metals burn vigorously when reacts with oxygen forming metal oxide.
4Na + O2 → 2Na2O
4K + O2 → 2K2O -
Magnesium does not react with oxygen at room temperature but when heated it burns with bright light forming magnesium oxide.
2Mg + O2 → 2MgO -
Aluminium develops thin oxide layer on exposure to air. The layer protects the inner metal from further oxidation and thus prevent corrosion.
4Al + 3O2 →2Al2O3
Reaction of Metals with oxygen: Moderately reactive metals
- Zinc burns in air, only when strongly heated, forming zinc oxide.
2Zn + O2 → 2ZnO - Iron does not burn in air but iron filings when sprinkled in the flame burns vigorously.
3Fe + O2 → Fe3O4
Reaction of Metals with Oxygen: Least reactive metals
- Copper is a least reactive metal. Copper did not burn in air. On heating a black coloured copper oxide layer forms on the surface.
2Cu + O2 → 2CuO - Gold, Silver show very less reactivity towards oxygen.
Nature of Metal Oxides
- Basic Oxides: Most metal oxides dissolve in water to form alkalis. e.g. sodium oxide dissolve in water to form corresponding alkalies. This means that metal oxides are basic in nature.
Na2O (s) + H2O (l) → 2NaOH (aq) -
Amphoteric Oxides: Some metal oxide such as zinc oxide and aluminium oxide react with both acid and bases to produce salt and water hence these are called Amphoteric Oxides.
Here aluminium oxide shows ‘Basic’ nature on reaction with acids
Al2O3 + 6HCl → 2AlCl3 + 3H2O
Here aluminium oxide shows ‘acidic’ nature on reaction with bases
Al2O3 + 2NaOH → 2NaAlO2 + H2O
Anodising
- Aluminium if exposed to air forms thin oxide layer. This layer protect the metal from further corrosion. With anodising the thin oxide layer can be made thicker to help avoid corrosion.
- In this process a clean aluminium article is made the anode and is electrolysed with dilute sulphuric acid. When electric current is allowed to pass, hydrogen gas liberated at cathode and oxygen gas at anode. The oxygen gas at anode reacts with aluminium and forms a thick oxide layer. This process is called anodising.
This article is helpful for Class 10 Science
Keywords: Reaction of Metals with Oxygen, Anodising, Amphoteric Oxides, Metal Oxide
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