Why are Some Metals Stored in Kerosene Oil?

Certain metals are highly reactive and readily react with oxygen and moisture present in the air. This reaction can be quite vigorous, sometimes even catching fire. To prevent these reactive metals from coming into contact with air and moisture, they are stored in a medium that does not react with them, such as kerosene oil.

Reactivity of Common Metals

Metals vary greatly in their reactivity. Let's look at the reactivity of the metals given in the options:

• Sodium (Na): Sodium is an alkali metal and is highly reactive. It reacts vigorously with oxygen and water. This reaction produces heat, which can ignite the hydrogen gas produced, causing a fire.
• Copper (Cu): Copper is much less reactive than sodium. It reacts slowly with air and moisture over time, forming a greenish layer (patina), but it does not react violently or catch fire at room temperature.
• Gold (Au): Gold is a very unreactive metal. It is often called a noble metal because it does not react easily with air, water, acids, or bases under normal conditions.
• Platinum (Pt): Platinum is also a noble metal, similar to gold. It is very unreactive and resistant to corrosion and chemical attack.

Storing Sodium in Kerosene

Because of its high reactivity with air and moisture, Sodium must be stored in a way that prevents contact with these substances. Kerosene oil is a suitable medium for this purpose because it is an organic liquid that does not react with sodium. When sodium is submerged in kerosene, it is isolated from the oxygen and water vapor in the atmosphere, thus preventing its reaction and ensuring safe storage.

Copper, Gold, and Platinum, being far less reactive, do not require such protective storage and are typically stored openly or in standard containers.

Conclusion

Based on their reactivity, the metal that needs to be stored in kerosene oil to prevent reaction with air and moisture is Sodium.

Revision Table: Metal Storage and Reactivity

Understanding the reactivity series of metals helps explain their storage methods. Highly reactive metals are usually stored under oil or inert gases to prevent them from reacting with the environment.

Additional Information: Alkali Metals

Sodium belongs to the group of alkali metals (Group 1) in the periodic table. Other alkali metals like Lithium (Li) and Potassium (K) are also highly reactive. Lithium is slightly less reactive than sodium and can sometimes be stored in paraffin wax, while Potassium is more reactive than sodium and requires even more careful handling, often stored under mineral oil or in an inert atmosphere.

The reaction of sodium with water is represented by the equation:

\( \text{2Na(s)} + \text{2H}_2\text{O(l)} \rightarrow \text{2NaOH(aq)} + \text{H}_2\text{(g)} + \text{Heat} \)

The heat produced can ignite the hydrogen gas.