P-Block Elements (VSAQs)

Chemistry-2 | 6. P-Block Elements – VSAQs:
Welcome to VSAQs in Chapter 6: P-Block Elements. This page features the important FAQs for Very Short Answer Questions. Answers are provided in simple English and follow the exam format. This approach helps in focusing on essential points and achieving top marks in your final exams.

VSAQ-1 : What is allotropy? Explain the different allotropic forms of phosphorus.

Allotropy refers to the ability of an element to exist in multiple structural forms, known as allotropes, in the same physical state under different conditions.

Phosphorus exhibits several allotropes, including

  1. White Phosphorus (P4): Highly reactive, waxy, and flammable.
  2. Red Phosphorus (P4): Less reactive, used in safety matches and flame retardants.
  3. Black Phosphorus: Stable, layered structure, significant in nanoelectronics.
  4. Violet Phosphorus: Forms under high pressures, less common.

These allotropes have distinct properties due to differences in atomic arrangement, illustrating the concept of allotropy in chemistry.

VSAQ-2 : Nitrogen molecule is highly stable. Why?

The nitrogen molecule (N2) is highly stable primarily due to its triple covalent bond (N≡N) between the two nitrogen atoms. This triple bond has a high bond dissociation energy, making it difficult to break. Additionally, nitrogen gas is chemically inert under normal conditions, meaning it does not readily react with other substances, further contributing to its stability.

VSAQ-3 : PH3 has lower boiling point than NH3. Why?

PH3 (phosphine) has a lower boiling point than NH3 (ammonia) primarily because PH₃ is a nonpolar molecule with weaker intermolecular forces, while NH₃ is a polar molecule with stronger intermolecular forces. The absence of permanent dipole-dipole interactions in PH3 results in lower boiling points compared to NH3, which exhibits hydrogen bonding and stronger dipole-dipole forces.

VSAQ-4 : NH3 forms hydrogen bonds but PH3 does not. Why?

NH3 (ammonia) forms hydrogen bonds, whereas PH3 (phosphine) does not due to differences in electronegativity. In ammonia, the significant electronegativity difference between nitrogen (N) and hydrogen (H) results in polar covalent bonds, creating partially positively charged hydrogen atoms and partially negatively charged nitrogen atoms. These polar characteristics allow ammonia to engage in hydrogen bonding by attracting the lone pairs of electrons on other nitrogen or oxygen atoms. In contrast, phosphine has a smaller electronegativity difference between phosphorus (P) and hydrogen, resulting in nonpolar covalent bonds and the absence of hydrogen bonding capabilities.

VSAQ-5 : What happens when white phosphorus is heated with conc. NaOH solution in an inert atmosphere of CO2?

When white phosphorus (P4) is heated with concentrated sodium hydroxide (NaOH) solution in an inert atmosphere of carbon dioxide (CO2), it undergoes the Hershberg reaction. The main product of this reaction is phosphine gas (PH3), along with the formation of sodium hypophosphite (Na2HPO4). Phosphine is a colorless, toxic gas with a garlic-like odor, and sodium hypophosphite is a stable, water-soluble compound. The presence of CO2 creates an inert environment, preventing oxidation and enhancing the yield of phosphine.

VSAQ-6 : What is tailing of mercury? How is it removed?

Tailing in the context of mercury refers to the residual mercury left in waste materials, such as soil or equipment, after mercury extraction or processing. To remove mercury tailing:

  1. Reprocessing: Mercury can be reprocessed from tailing materials through additional extraction methods.
  2. Isolation: Physical barriers or liners can isolate tailings to prevent mercury from leaching into the environment.

Proper management and containment of tailings are essential to prevent environmental contamination and health risks.

VSAQ-7 : SO2 can be used as an anti-chlor. Explain.

Sulfur dioxide (SO2) acts as an anti-chlorinating agent by reacting with excess chlorine (Cl2) or chloramines in water treatment processes. It reduces chlorine to form hydrochloric acid (HCl) and sulfuric acid (H2SO4), preventing the formation of harmful chlorinated byproducts and maintaining water quality. This helps ensure the safety of drinking water and environmental protection.

VSAQ-8 : Why is H2O a liquid while H2S is a gas?

H2O (water) is a liquid at room temperature due to the presence of strong hydrogen bonding, dipole-dipole interactions, and its relatively higher molecular mass (18.02 g/mol). These factors create cohesive forces that keep water molecules closely packed in the liquid state.

H2S (hydrogen sulfide), on the other hand, is a gas at room temperature because it primarily exhibits weaker London dispersion forces and has a lower molecular mass (34.08 g/mol). These weaker intermolecular forces allow H₂S molecules to remain separate in the gaseous state at normal conditions.

VSAQ-9 : What happens when Cl2 reacts with dry slaked lime?

When Cl2 (chlorine gas) reacts with dry slaked lime (calcium hydroxide, Ca(OH)2), it forms calcium chloride (CaCl2), calcium hypochlorite (Ca(ClO)2), and water (H2O). This reaction is significant in water treatment processes, as it helps neutralize excess chlorine, ensuring safe and disinfected water. Calcium chloride and calcium hypochlorite are common chemicals used in various industrial applications.

VSAQ-10 : Write the reactions of F2 and Cl2 with water.

Reaction of F2 (fluorine gas) with water (H2O): F2(g) + 2H2O(l) → 4HF(aq) + O2(g)

Reaction of Cl2 (chlorine gas) with water (H2O): Cl2(g) + H2O(l) ⇌ HCl(aq) + HClO(aq)

When fluorine gas (F₂) reacts with water, it forms hydrofluoric acid (HF) and oxygen gas (O2). Chlorine gas (Cl2) reacts with water to form hydrochloric acid (HCl) and hypochlorous acid (HClO) in an equilibrium reaction. These reactions involve the dissolution of halogen gases in water, leading to the formation of acidic products.

VSAQ-11 : How is chlorine manufactured by Deacon’s method?

Deacon’s method for the manufacturing of chlorine gas (Cl2) involves the oxidation of hydrogen chloride (HCl) gas using oxygen (O2) in the presence of a copper chloride (CuCl2) catalyst at elevated temperatures (typically 350°C to 450°C) and high pressures. The reaction is an equilibrium process, and the removal of chlorine gas as it forms helps maximize chlorine production. This method is crucial for large-scale industrial chlorine production, serving various applications across industries.

VSAQ-12 : List out the uses of neon.

Neon (Ne) is primarily used for its distinctive luminescent properties in applications such as:

  1. Neon Signs and Lighting: Neon gas is used to create colorful and eye-catching signs, decorative lighting, and advertising displays.
  2. Indicator Lamps: Neon lamps serve as indicator lights in electronic devices and control panels.

Additionally, neon finds applications in lasers, cryogenic refrigeration, high-voltage surge arresters, gas discharge tubes, and cryogenic research. Its unique properties make it valuable in specialized technologies and scientific research.

VSAQ-13 : Explain the structure of XeO3.

Xenon trioxide (XeO3) has a trigonal pyramidal molecular structure. In this arrangement, a central xenon (Xe) atom is bonded to three oxygen (O) atoms, forming a pyramid-like shape. Each oxygen atom forms a single covalent bond with xenon, and the molecule is polar due to the lone pairs of electrons on the oxygen atoms.

VSAQ-14 : In modern diving apparatus, a mixture of He and O2 is used – why?

A mixture of helium (He) and oxygen (O2), known as heliox, is used in modern diving apparatus for two primary reasons:

  1. Reduced Narcosis: Heliox reduces the risk of nitrogen narcosis, a condition that impairs judgment and cognitive functions during deep dives. By replacing nitrogen with helium, the narcotic effects are minimized, allowing for safer and more efficient deep-sea exploration.
  2. Lower Breathing Resistance: Helium has a lower density than nitrogen, leading to reduced gas density in the breathing mixture. This lower gas density results in decreased breathing resistance for divers, making it easier to breathe at greater depths and reducing the risk of overexertion.