Question

Carnallite on electrolysis gives: (a) \(\mathrm{Na}\) and \(\mathrm{CO}_{2}\) (b) \(\mathrm{Mg}\) and \(\mathrm{Cl}_{2}\) (c) \(\mathrm{Al}\) and \(\mathrm{Cl}_{2}\) (d) \(\mathrm{Ca}\) and \(\mathrm{Cl}_{2}\)

Short answer

(b) \( \mathrm{Mg} \) and \( \mathrm{Cl}_2 \).

Step-by-step solution

Understand the Composition of Carnallite

Carnallite is a mineral containing a mixed chloride and is a hydrous potassium magnesium chloride with the formula \( \text{KMgCl}_3 \cdot 6\text{H}_2\text{O} \). It primarily consists of potassium (\( \text{K} \)), magnesium (\( \text{Mg} \)), and chloride ions (\( \text{Cl}^- \)).

Determine the Products of Electrolysis

Electrolysis of molten carnallite leads to the decomposition of its ions. The electrolysis typically involves the breakdown of magnesium chloride and potassium chloride present in carnallite. During the electrolysis of magnesium chloride, magnesium (\( \text{Mg} \)) is deposited at the cathode, and chlorine gas (\( \text{Cl}_2 \)) is liberated at the anode.

Evaluate Given Options Against Electrolysis Products

Out of the given options, we need to identify which one corresponds with the products from the electrolysis of carnallite. The correct products from the electrolysis are magnesium (\( \text{Mg} \)) and chlorine gas (\( \text{Cl}_2 \)), which matches option (b).

Verification and Conclusion

By reviewing the process of electrolysis and the components of carnallite, it is evident that option (b) is indeed correct, as it corresponds to the generation of \( \text{Mg} \) at the cathode and \( \text{Cl}_2 \) at the anode.

Key concepts

Carnallite composition

Carnallite is an intriguing mineral that captures attention with its unique composition. It is primarily known as a hydrous potassium magnesium chloride. The chemical formula for carnallite is expressed as \( \text{KMgCl}_3 \cdot 6\text{H}_2\text{O} \), indicating that one unit of carnallite contains magnesium, potassium, and chloride ions along with water molecules. This formula allows it to serve as an important source of magnesium and potassium, both vital for various industrial applications. The mineral appears in nature as beautifully colored crystals, ranging from white to pinkish hues.

Understanding carnallite's composition is crucial because it lays the groundwork for predicting how it behaves during chemical processes like electrolysis. Knowing what elements and ions are present allows us to anticipate the products formed when these elements undergo specific reactions.

Electrolysis process

The process of electrolysis is an essential method used to decompose compounds using electricity. When it comes to carnallite, electrolysis involves passing an electric current through its molten form. This electric current causes the chemical bonds between the ions in carnallite to break, leading to the separation of its elements.

For effective electrolysis, the compound must be in a molten state to ensure the ions are free to move towards their respective electrodes. In the case of carnallite, breaking its ionic bonds requires sufficient energy to overcome the attractions between the ions. This energy is provided through the electrical current applied during the electrolysis process. The entire electrolysis setup requires a carefully controlled environment to achieve the desired chemical reactions, which include the suitable anode and cathode materials.

Products of electrolysis

Electrolysis of carnallite results in the formation of specific products, which are determined by the ions present in the mineral. When carnallite undergoes electrolysis, the primary products observed are magnesium metal and chlorine gas.

Here's a breakdown of what happens:

• At the cathode, magnesium ions (\( \text{Mg}^{2+} \)) gain electrons (a process called reduction) to form magnesium metal. This is represented by the equation: \( \text{Mg}^{2+} + 2e^- \rightarrow \text{Mg} \).
• At the anode, chloride ions (\( \text{Cl}^- \)) lose electrons (a process known as oxidation) to produce chlorine gas. This reaction can be shown as: \( 2\text{Cl}^- \rightarrow \text{Cl}_2 + 2e^- \).

These reactions highlight the fascinating transformation from simple ions in a liquid state to physically distinct products, with magnesium appearing as a solid metal and chlorine bubbling off as a gas.

Electrochemical reactions

The electrochemical reactions occurring during the electrolysis of carnallite are foundational concepts in understanding electrochemistry. In these reactions, ionic species undergo electron transfer at the electrodes, changing their oxidation states.

It’s important to understand the driving forces behind these reactions. The flow of electrons from an external power source creates potential differences that encourage the movement of ions to opposite electrodes.

• Reduction takes place at the cathode: Magnesium ions are reduced to magnesium metal. This is a gain of electrons process, emphasizing the notion of reduction.
• Oxidation occurs at the anode: Chloride ions release electrons, forming chlorine gas, displaying the principle of oxidation.

Understanding these electrochemical principles helps clarify why electrolysis can separate elements based on their electron affinities and robustly demonstrates the interaction between electrical energy and chemical change.