Burning Magnesium Ribbon: Identifying the Compound Formed

When a magnesium ribbon is heated in air, it undergoes a chemical reaction. Air is primarily composed of oxygen and nitrogen gases. Magnesium reacts with both of these components when heated to a high temperature, such as during burning.

Reaction with Oxygen

Magnesium reacts vigorously with oxygen in the air to form magnesium oxide. This is an exothermic reaction, releasing a significant amount of heat and light, which is characteristic of magnesium burning.

The balanced chemical equation for this reaction is:

$\text{2Mg(s)} + \text{O}_2\text{(g)} \rightarrow \text{2MgO(s)}$

Magnesium oxide ($\text{MgO}$) is a white solid.

Reaction with Nitrogen

Magnesium also reacts with nitrogen gas present in the air, especially at the high temperatures reached during burning, to form magnesium nitride.

The balanced chemical equation for this reaction is:

$\text{3Mg(s)} + \text{N}_2\text{(g)} \rightarrow \text{Mg}_3\text{N}_2\text{(s)}$

Magnesium nitride ($\text{Mg}_3\text{N}_2$) is a yellowish solid.

Products Formed

Therefore, when magnesium ribbon is burnt in air, the product is a mixture of magnesium oxide ($\text{MgO}$) and magnesium nitride ($\text{Mg}_3\text{N}_2$). Magnesium oxide is typically the primary product because oxygen is more reactive with magnesium than nitrogen under these conditions, and the concentration of oxygen in air (about 21%) is significant.

Analyzing the Options

Let's look at the given options:

1. Magnesium Nitrate: Magnesium nitrate ($\text{Mg(NO}_3)_2$) is a salt. It is not formed directly by burning magnesium in air.
2. Magnesium Carbonate: Magnesium carbonate ($\text{MgCO}_3$) can be formed from magnesium oxide or hydroxide reacting with carbon dioxide and water, but it is not a direct product of burning magnesium in dry air.
3. Magnesium Oxide: As explained, magnesium oxide ($\text{MgO}$) is a major product formed from the reaction of magnesium with oxygen in the air.
4. Magnesium Nitride: As explained, magnesium nitride ($\text{Mg}_3\text{N}_2$) is also formed from the reaction of magnesium with nitrogen in the air.

Among the options provided, both Magnesium Oxide and Magnesium Nitride are formed. However, Magnesium Oxide is usually considered the principal product due to the higher reactivity of magnesium with oxygen and oxygen's presence in air. Given the options, Magnesium Oxide is a correct compound formed during the process.

Conclusion

Based on the chemical reactions that occur when magnesium is burnt in air, Magnesium Oxide is a compound that is formed.

Revision Table: Key Concepts in Magnesium Burning

Additional Information: Properties of Products

The products formed when magnesium burns in air have distinct properties:

• Magnesium Oxide (MgO): It is a white solid with a high melting point. It is relatively insoluble in water, but it can react slowly with water to form magnesium hydroxide, $\text{Mg(OH)}_2$. It is a basic oxide.
• Magnesium Nitride (Mg$_3$N$_2$): It is a yellowish solid. Unlike MgO, magnesium nitride reacts readily with water to produce magnesium hydroxide and ammonia gas ($\text{NH}_3$). This reaction gives off a pungent smell of ammonia when the product mixture is treated with water.

The residue left after burning magnesium in air often contains both these compounds. Adding water to the residue can demonstrate the presence of magnesium nitride by the release of ammonia gas.