CHEMICAL PROPERTIES OF METALS

CHEMICAL PROPERTIES OF METALS AND NON METALS

Reaction of metal with air

Almost all metals combine with oxygen to form metal oxides.

Examples of reactions-

• Magnesium burns in air with a dazzling white flame.
• When copper is heated in air, it combines with oxygen to form copper (II) oxide, a black oxide.

•   Aluminium heated in air, it combines with oxygen to form aluminium oxide.

Important points of reaction of metal with air-

• all metals do not react with oxygen at the same rate.
• Different metals show different reactivities towards oxygen.
• Metals such as potassium and sodium react fast with open air and catch fire immediately.
• Hence, to prevent the accidental fires, they are kept immersed in kerosene oil.
• Iron does not burn on heating but iron filings burn rapidly when sprinkled in the flame of the burner.
•  Silver and gold do not react with oxygen even at high temperatures.

Oxides of metals

• Metal oxides are basic in nature.
• But some metal oxides, such as aluminium oxide, zinc oxide show both acidic as well as basic behavior.
• Such metal oxides which react with both acids as well as bases to produce salts and water are known as amphoteric oxides.

Example- Aluminium oxide reacts with both acid as well as base.

• Most metal oxides are insoluble in water but some of these dissolve in water to form alkalis.

For example– Sodium oxide and potassium oxide dissolve in water to produce sodium hydroxide and potassium hydroxide known as alkalis.

Note – The protective oxide layer at the surface of metal prevents them from further oxidation. Example– magnesium oxide

Reaction of metal with water

Metals react with water and produce a metal oxide and hydrogen gas.

• But all Metal oxides do not react with water.
• Metals like potassium and sodium react violently with cold water.
• The reaction is violent and exothermic and the evolved hydrogen gas immediately catches fire.

• The reaction of calcium with water is less violent.
• The heat evolved is not sufficient for the hydrogen to catch fire.
• Calcium metal floats on water due to formation of bubbles of hydrogen.

• Magnesium does not react with cold water.
• It reacts with hot water to form magnesium hydroxide and hydrogen.
• It also starts floating due to the bubbles of hydrogen gas sticking to its surface.
• Metals like aluminium, iron and zinc do not react either with cold or hot water.
• But they react with steam to form the metal oxide and hydrogen.

Note – Metals such as lead, copper, silver and gold do not react with water at any condition.

Reaction of metals with acids

• Metals react with acids to give a salt and hydrogen gas.

• Magnesium (Mg) and manganese (Mn) react with very dilute HNO3 to evolve H2 gas.

• The reactivity of metals with acid decreases in the order Mg > Al > Zn > Fe.
• Note-
• copper does not react with dilute HCl no bubble formation takes place.
• Hydrogen gas is not evolved when a metal reacts with nitric acid.
• It is because HNO3 is a strong oxidizing agent.
• It oxidizes the H2 produced to water and itself gets reduced to any of the nitrogen oxides (N2O, NO, NO2).

 REACTIVITY OF METALS

• Reactive metals can displace less reactive metals from their compounds in solution or molten form.

• Displacement reactions give better evidence about the reactivity of metals.
• Relative reactivity of metals is as shown below in table-