Problem 50 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is incorrect? (a) \(\mathrm{Mg}\) bums in air releasing dazaling light rich in uv rays (b) \(\mathrm{CaCl}_{2} 6 \mathrm{H}_{2} \mathrm{O}\) when mixed with ice gives a freering mixture (c) \(\mathrm{Mg}\) cannot form complexes (d) Be can form complexes due to its very small sipe

Step-by-Step Solution

Answer

The incorrect statement is (c) \(\mathrm{Mg}\) cannot form complexes.

Step 1: Analyze Statement (a)

Statement (a) states that magnesium (\(\mathrm{Mg}\)) burns in air releasing dazzling light rich in UV rays. This statement is generally correct as magnesium does burn in air producing a bright, white light and also emits UV radiation in the process.

Step 2: Evaluate Statement (b)

Statement (b) indicates that \(\mathrm{CaCl}_{2} \cdot 6 \mathrm{H}_{2} \mathrm{O}\) mixed with ice yields a freezing mixture. This is true because calcium chloride when mixed with ice can lower the mixture’s temperature below 0°C, thus is used as a freezing mixture.

Step 3: Check Statement (c)

Statement (c) asserts that magnesium cannot form complexes. This statement is incorrect as magnesium, although not known for extensive complex formation, can form complexes under certain conditions with certain ligands.

Step 4: Assess Statement (d)

Statement (d) claims that beryllium (Be) can form complexes due to its very small size. This is correct because beryllium has a high charge density which favors the formation of complexes, especially with ligands that can accept small, highly charged ions.

Key Concepts

Complex Formation

Complex formation in chemistry involves the combination of central metal atoms or ions with ligands, which are molecules or ions capable of donating electron pairs. This results in a coordination complex, where the metal ion is at the center surrounded by these ligands.
Complexes are critical in various biological systems and industrial applications. Different metals have varying abilities to form complexes based on their size, charge, and electron configuration.

• Some common ligands include water, ammonia, chloride ions, and organic molecules such as ethylenediamine.
• The stability of a complex depends on factors including the charge and size of the central ion and the nature of the ligands.

Understanding complex formation helps in fields such as synthetic chemistry, where designing new compounds requires manipulating these interactions effectively.

Magnesium Complexes

Although magnesium is not widely known for forming complexes, it does have the capacity to do so under certain conditions.
Magnesium is an alkaline earth metal with a +2 oxidation state, which allows it to form bonds with various ligands. In biological systems, magnesium plays a key role, often complexed with molecules like chlorophyll in plants.

• Ligands such as nitrogenous bases like ATP and nucleotides often form complexes with magnesium.
• Environmental conditions, like pH and the presence of other ions, can influence complex formation with magnesium.

Because of these properties, magnesium complexes find applications in chemistry and biology, including catalysis and metabolic processes.

Beryllium Chemistry

Beryllium, being one of the lightest metals, has unique chemical properties. It can form complexes relatively easily due to its small size and the high charge density it possesses.
This small atomic radius allows beryllium to interact closely with ligands, creating stable complexes.

• Beryllium complexes are often characterized by their coordination number, which typically ranges from 4 to 6.
• Common ligands include fluoride ions, oxalates, and other oxygen-donating molecules.

Understanding beryllium's chemistry is important in areas like materials science and nuclear applications, where its resistance to heat and lightweight make it valuable.

Freezing Mixture

A freezing mixture is a combination of substances that results in a drop in temperature when mixed. Calcium chloride (CaCl_2 ) mixed with ice is a classic example.
When added to ice, calcium chloride dissolves exothermically, lowering the system's freezing point below 0°C. This is commonly used in applications requiring lower temperatures than what ice alone can achieve.

• Freezing mixtures are useful for maintaining cold temperatures for food preservation during transportation.
• They are also used in laboratory settings for experiments that require a stable, cold environment.

These mixtures are significant in industries where processes at reduced temperatures are crucial, showing the interplay of chemistry and practical applications.