Problem 23 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Both lithium and magnesium display several similar properties due to the diagonal relationship; however, the one which is incorrect is : (a) Both form basic carbonates (b) Both form soluble bicarbonates (c) Both form nitrides (d) Nitrates of both Li and Mg yield \(\mathrm{NO}_{2}\) and \(\mathrm{O}_{2}\) on heating

Step-by-Step Solution

Answer

The incorrect statement is (b): Both form soluble bicarbonates.

Step 1: Understanding Diagonal Relationships

The diagonal relationship in the periodic table refers to the phenomenon where elements in different groups but in adjacent periods show similar properties. Here, we are comparing the properties of lithium (Li) and magnesium (Mg).

Step 2: Evaluating Option (a)

Both lithium and magnesium form basic carbonates. Lithium carbonate (Li2CO3) and magnesium carbonate (MgCO3) are basic in nature. This statement is true.

Step 3: Evaluating Option (b)

Magnesium bicarbonate is not stable as a solid under normal conditions, forming only in aqueous solution, whereas lithium forms no stable solid bicarbonate at all. Thus, this statement is incorrect.

Step 4: Evaluating Option (c)

Both lithium and magnesium form nitrides. Lithium forms lithium nitride (Li3N) and magnesium forms magnesium nitride (Mg3N2). This statement is true.

Step 5: Evaluating Option (d)

Both lithium nitrate (LiNO3) and magnesium nitrate (Mg(NO3)2) decompose upon heating to give nitrogen dioxide (NO2) and oxygen (O2), among other products. This statement is true.

Key Concepts

Properties of Lithium

Lithium, the lightest metal, holds a unique spot in the periodic table. As an alkali metal, it is well-known for its distinct reactivity and least density among all the solid elements. Here's what makes lithium interesting:

• Color and Softness: Lithium is a shiny, silver-white metal that is very soft, so soft that it can be cut with a knife.
• Alkali Metal Characteristics: As the lightest alkali metal, lithium exhibits high reactivity, especially with water, to form lithium hydroxide (\[\text{LiOH}\]) and hydrogen gas.
• Low Density: It is the least dense of all metals, which is why it can float on water if the reaction is not immediately violent.

Lithium's unique properties contribute to its diagonal relationship with magnesium, displaying similarities in their chemical behavior.

Properties of Magnesium

Magnesium, a group two element, is often praised for its role in biological systems and its chemical properties. It's the eighth-most abundant element in the Earth's crust. Here's a closer look at magnesium:

• Color and Structure: Magnesium is a shiny gray metal. It's quite strong for a light metal and has good corrosion resistance.
• Reactivity: Although less reactive than alkali metals, magnesium burns with a bright white flame when heated in air, forming magnesium oxide (\[\text{MgO}\]).
• Role in Biology: It's crucial in biology, helping to compose the structure of chlorophyll, which plants need for photosynthesis.

These properties help it parallel the chemical behavior of lithium, demonstrating the diagonal relationship that exists between them.

Chemical Reactions and Stability

Chemical reactions can tell us a lot about the stability and reactivity of elements. In the context of lithium and magnesium, their reactions demonstrate some fascinating behaviors:

• Nitride Formation: Both lithium and magnesium can form nitrides. Lithium forms lithium nitride (\[\text{Li}_3\text{N}\]), while magnesium forms magnesium nitride (\[\text{Mg}_3\text{N}_2\]). These compounds form when the metals react with nitrogen gas at elevated temperatures.
• Carbonate Formation: Both elements form carbonates that are basic. Lithium carbonate (\[\text{Li}_2\text{CO}_3\]) and magnesium carbonate (\[\text{MgCO}_3\]) feature prominently in chemistry due to their basic properties.
• Nitrate Decomposition: One unique reaction is the decomposition of lithium nitrate (\[\text{LiNO}_3\]) and magnesium nitrate (\[\text{Mg(NO}_3)_2\]). Upon heating, they both release nitrogen dioxide (\[\text{NO}_2\]) and oxygen (\[\text{O}_2\]), showcasing their similar thermal instability.

Understanding these reactions provides insights into why lithium and magnesium often behave similarly, thanks to their diagonal relationship on the periodic table.