Understanding Metal Extraction Processes

The question asks about the process used to obtain highly reactive metals from their pure molten ore. Highly reactive metals, such as alkali metals (like Sodium, Potassium) and alkaline earth metals (like Calcium, Magnesium), are very difficult to reduce using common chemical reducing agents like carbon.

These metals have a high affinity for oxygen and other electronegative elements, forming very stable compounds (ores).

Analyzing the Options for Highly Reactive Metals

Let's look at the provided options and determine their suitability for extracting highly reactive metals from molten ore:

1. Calcination: This process involves heating carbonate or hydroxide ores in the absence of air to remove volatile substances like water and carbon dioxide, converting them into metal oxides. It does not directly yield the metal, and it's not applied to molten ores.
2. Electrolysis: This is a process where an electric current is passed through a molten ionic compound (like a molten metal ore or its molten salt). The metal ions migrate to the cathode (negative electrode) and gain electrons (reduction) to form the pure metal. This method is particularly effective for highly reactive metals because the powerful driving force of electrical energy can overcome the strong chemical bonds in their compounds. Since the ore is molten, the ions are free to move, allowing the electric current to pass through and facilitate the deposition of the pure metal at the cathode. Examples include the extraction of sodium from molten sodium chloride ($\text{NaCl}$) and aluminum from molten alumina ($\text{Al}_2\text{O}_3$) dissolved in cryolite.
3. Roasting: This process involves heating sulfide ores strongly in the presence of air to convert them into metal oxides. It is used for sulfide ores and does not yield the metal directly, nor is it applied to molten ores.
4. Reduction by an appropriate reducing agent: This method involves using a chemical substance (like carbon, carbon monoxide, or aluminum) to reduce a metal oxide or other compound to obtain the metal. While suitable for less reactive metals (e.g., iron from iron oxide using carbon), highly reactive metals are stronger reducing agents than typical reducing agents like carbon. Therefore, carbon cannot reduce the oxides of highly reactive metals. Electrolysis provides the necessary energy for reduction in these cases.

Why Electrolysis is Key for Highly Reactive Metals

Highly reactive metals are found in nature in stable combined states, usually as oxides, chlorides, or sulfates. Due to their high reactivity, they have strong affinities for oxygen and other non-metals. Reducing their compounds using common reducing agents like carbon is not feasible because these metals are more reactive than carbon. Electrolysis of their molten salts or oxides provides the electrical energy required to break these strong chemical bonds and obtain the pure metal at the cathode.

Electrolysis is carried out on the molten state of the ore or a suitable compound of the metal because in the molten state, the ions are mobile and can conduct electricity. Electrolysis of aqueous solutions is not suitable for highly reactive metals because water is reduced at the cathode instead of the metal ion.

Summary of Metal Extraction Methods

Based on this analysis, obtaining highly reactive metals from pure molten ore is achieved through Electrolysis.

Revision Table: Understanding Metal Extraction

Additional Information: Electrolytic Reduction

Electrolytic reduction is the primary method for extracting highly reactive metals because they are very electropositive and form stable compounds. During electrolysis of the molten compound:

• At the cathode (negative electrode): Metal ions gain electrons (reduction) and deposit as pure metal. $\text{M}^\text{n+} + \text{ne}^- \rightarrow \text{M}$
• At the anode (positive electrode): Anions lose electrons (oxidation). For example, if a chloride is electrolysed, chloride ions are oxidized to chlorine gas. $\text{2Cl}^- \rightarrow \text{Cl}_2 + \text{2e}^-$

The process requires significant electrical energy but is essential for obtaining these vital metals in their pure form.