Problem 103 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is correct? (a) sodium reduces \(\mathrm{CO}_{2}\) to carbon (b) in the Castner's process of sodium extraction, \(\mathrm{NaCl}\) is used as an electrolyte (c) magnalium is an alloy of \(\mathrm{Mg}\) and \(\mathrm{Zn}\) (d) \(\mathrm{Mg}\) reacts with cold water and liberate hydrogen gas

Step-by-Step Solution

Answer

Only option (b) is correct; \(\mathrm{NaCl}\) is used as an electrolyte in the Castner's process.

Step 1: Understanding the Sodium Reaction

Option (a) suggests that sodium reduces \(\mathrm{CO}_{2}\) to carbon. In reality, sodium does not reduce \(\mathrm{CO}_{2}\) directly to carbon under standard conditions. This option is incorrect as it depicts an uncommon reaction for sodium.

Step 2: Analyzing the Castner's Process

Option (b) refers to the Castner's process of sodium extraction. In this process, \(\mathrm{NaCl}\) is indeed used as an electrolyte for the electrolysis to obtain sodium. Thus, this statement is correct.

Step 3: Evaluating Magnalium's Composition

Option (c) claims that magnalium is an alloy of \(\mathrm{Mg}\) and \(\mathrm{Zn}\). However, magnalium is actually an alloy of magnesium (\(\mathrm{Mg}\)) and aluminum (\(\mathrm{Al}\)), not zinc (\(\mathrm{Zn}\)). Therefore, this statement is incorrect.

Step 4: Investigating Magnesium's Reaction with Water

Option (d) asserts that \(\mathrm{Mg}\) reacts with cold water to liberate hydrogen gas. In reality, magnesium reacts very slowly with cold water, if at all, to produce any significant amount of hydrogen gas. Magnesium typically reacts with steam rather than cold water, making this statement incorrect.

Key Concepts

Electrolysis Process

Electrolysis is a fascinating chemical process that utilizes electricity to cause a non-spontaneous chemical reaction. Imagine the need to break apart a compound into its elements, like splitting water into hydrogen and oxygen gases. To achieve this, an electric current is passed through an electrolyte—a substance that conducts electricity when dissolved in water or melted. For example, the electrolysis of sodium chloride (\(\mathrm{NaCl}\)) is critical in extracting sodium metal. In the Castner's process, molten \(\mathrm{NaCl}\) acts as the electrolyte. Inside an electrolytic cell, an electrical current breaks down the compound into sodium and chlorine gas.

• During electrolysis, anode and cathode are used where oxidation and reduction occur, respectively.
• For \(\mathrm{NaCl}\), sodium ions travel to the cathode to gain electrons and form sodium metal.
• Meanwhile, chlorine ions move to the anode where they lose electrons and release chlorine gas.

By understanding this process, we grasp how elements are extracted and how electrical energy can drive chemical transformations.

Chemical Reactions

Chemical reactions are pivotal in changing substances into different ones by breaking and forming bonds. When elements and compounds interact, they undergo transformations that alter their structures and properties. These reactions can be simple swaps or complex rearrangements, and they come in various types such as synthesis, decomposition, and combustion. Take, for instance, the interaction of magnesium (\(\mathrm{Mg}\)) with water.

• Magnesium typically reacts with steam rather than cold water.
• In its reaction with steam, magnesium forms magnesium oxide (\(\mathrm{MgO}\)) and hydrogen gas (\(\mathrm{H_2}\)).
• This reaction showcases a typical oxidation-reduction process, releasing energy in the form of hydrogen gas.

Understanding these fundamental principles offers insights into how much of the materials around us are formed and transformed. These reactions are at the heart of countless daily processes, from cooking food to powering vehicles.

Alloy Composition

Alloys are mixtures of metals, or metals with other elements, designed to enhance specific qualities such as strength, durability, or resistance to corrosion. Magnalium is a noteworthy example, often mistakenly thought to contain zinc (\(\mathrm{Zn}\)). However, it is actually composed of magnesium (\(\mathrm{Mg}\)) and aluminum (\(\mathrm{Al}\)). This alloy combines the lightness of magnesium with the strength of aluminum, making it highly valuable in various applications.

• Alloys like magnalium are lighter and more resistant to corrosion compared to pure metals.
• This composition is beneficial in fields like aerospace, where reduced weight and high strength are crucial.
• Alloys typically have enhanced properties that pure metals would not possess alone.

Understanding alloy composition allows us to appreciate the meticulous design choices in various engineering and industrial applications, where the right combination of elements leads to superior performance and functionality.