The World of Metals and Non-metals - Effect of Air and Water on Other Metals

Reaction with Oxygen: Metals react with oxygen in the air to form metal oxides. These oxides are generally basic in nature. The general word equation is: $Metal + Oxygen \rightarrow Metal Oxide$.

Reactivity of Sodium and Potassium: Some metals like Sodium ($Na$) and Potassium ($K$) are highly reactive. they react so vigorously with oxygen and moisture in the air that they catch fire. Therefore, they are stored under kerosene.

Burning of Magnesium: When a Magnesium ($Mg$) ribbon is burnt in air, it reacts with oxygen to form a white powder called Magnesium Oxide ($MgO$). The reaction is: $2Mg + O_2 \rightarrow 2MgO$.

Rusting of Iron: Iron ($Fe$) reacts with oxygen and water (moisture) present in the air to form a reddish-brown flaky substance known as rust. Rust is hydrated iron oxide ($Fe_2O_3 \cdot xH_2O$).

Corrosion of Copper: When copper ($Cu$) objects are exposed to moist air for a long time, they develop a dull green coating. This green material is a mixture of Copper Hydroxide ($Cu(OH)_2$) and Copper Carbonate ($CuCO_3$).

Reaction with Water: Some metals react with water to produce metal hydroxides and hydrogen gas ($H_2$). For example, Sodium reacts violently with cold water: $2Na + 2H_2O \rightarrow 2NaOH + H_2 + \text{Heat}$.

Noble Metals: Metals like Gold ($Au$) and Platinum ($Pt$) do not react with air or water even at high temperatures, which is why they retain their luster for a long time.