2nd Year NotesChemistry class 12th

2nd Year CHEMISTRY CHAPTER 03 (Group IIIA and IVA Elements

2nd Year CHEMISTRY CHAPTER 03 Group IIIA and IVA Elements Question And Answer

Short And Simple Question And Answer

Q1: What is boric acid? Give its uses.

Ans: Boric acid (H3BO3) is a white lustrous crystalline solid with a soft, soapy touch. It is slightly soluble in cold water but fairly soluble in hot water. Boric acid is formed when water is added to metaboric acid (HBO2).

Uses:

1. Used in medicines as an antiseptic.

2. Employed in pottery as a glaze.

3. Utilized in the candle industry for stiffening wicks.

Q2: Why carbon behaves differently from other members of its group?

Ans: Carbon behaves differently from other members of its group due to:

1. Non-Metallic Nature: Carbon and silicon are non-metals, whereas other family members are metalloids or metals.

2. Self-Linkage Property: Carbon exhibits catenation, forming long chains, while other family members lack this property.

Q3: How weathering phenomenon converts potassium feldspar into clay?

Ans: The Earth’s crust contains aluminum silicates in the form of rocks, such as potassium feldspar. Weathering processes like rain, storms, and freezing lead to the disintegration of these silicate-rich rocks. Water and carbon dioxide play a crucial role in the chemical reactions that transform potassium feldspar into potassium carbonate, sand, and clay.

The reaction for the weathering of potassium feldspar is represented as follows:

K2O.Al2O3.6SiO2 + H2CO3 + H2O → K2CO3 + 4SiO2 + Al2O3.(SiO2)2.2H2O

This reaction illustrates the breakdown of potassium feldspar into potassium carbonate, sand (SiO2), and a hydrated form of aluminum oxide (Al2O3).(SiO2)2.2H2O, which represents clay.

Q4: Give uses of lead sub oxide?

Ans: Lead Sub Oxide (Pb2O): Uses

  1. Pigment: Lead sub oxide is employed as a pigment in various applications.

2. Lead Storage Battery: It is utilized in the manufacturing process of lead storage batteries.

Q5: Show that H3BO3 is a monobasic acid?

Ans: Boric acid, H3BO3, is a monobasic acid.

It reacts with water, releasing H⁺ ions and forming borate ions (B(OH)₄)⁻, accepting only one H⁺ ion in the process. This characteristic demonstrates its monobasic nature.

Q6: How Al finds its uses in metallurgy and photoflash bulbs?

Ans: Aluminum (Al): Metallurgical and Photoflash Uses

Metallurgy:
Aluminum, due to its high reactivity, is employed in metallurgy for extracting chromium and manganese from their oxides. The reduction reactions involve aluminum reacting with the metal oxides.

  1. Chromium Extraction:
    [Cr_2O_3 + 2Al \rightarrow 2Cr + Al_2O_3]
  2. Manganese Extraction:
    [3Mn_3O_4 + 8Al \rightarrow 9Mn + 4Al_2O_3]

Photoflash Bulbs:
1. Aluminum is utilized in photoflash bulbs, where it is incorporated as a thin filament or foil. In these bulbs, aluminum, when ignited by electricity, reacts with oxygen to produce a brilliant flash.

2. This dual utility showcases aluminum’s reactivity in both metallurgical processes and applications requiring intense light emission, like photoflash bulbs.

Q7: Why CO2 is a gas while SiO2 is a solid at room temperature?

Ans; CO2 (Carbon Dioxide):
At room temperature, CO2 exists in a gaseous state. The carbon atom forms double bonds with two oxygen atoms ((O=C=O)), resulting in the creation of a small, independent, and stable gaseous molecule. Due to this linear structure, CO2 experiences very weak intermolecular forces of attraction, allowing it to be in a gaseous state at room temperature.

SiO2 (Silicon Dioxide):
In contrast, SiO2 (Silicon Dioxide) is a solid at room temperature. Silicon atoms, being larger than carbon atoms, are surrounded by more oxygen neighbors. Silicon forms a single bond with each of the four oxygen atoms, arranged at tetrahedral angles. This structure leads to the formation of a large and stable solid crystal.

The difference in molecular structures and bonding patterns accounts for the distinct physical states of CO2 and SiO2 at room temperature.

Q8: Borate glazes are better than silicate glazes. Explain?

Ans: Borate Glazes vs. Silicate Glazes

Borate Glazes:

  • Used in pottery.
  • More fusible than silicate glazes.
  • Possess a higher coefficient of expansion.

Explanation:
Borate glazes, employed in pottery, exhibit superior qualities compared to silicate glazes. They are more fusible, meaning they melt more readily. Additionally, borate glazes have a higher coefficient of expansion, indicating their ability to accommodate temperature changes without cracking or compromising their integrity. This makes borate glazes a preferred choice over silicate glazes in pottery applications.

Q9: Write two principle uses of Borax? OR Write four uses of Borax?

Two Principal Uses of Borax:

  1. Softening Water: Borax is utilized in water softening processes.

2. Metallurgical Operations: Borax plays a role in various metallurgical activities.

Four Uses of Borax:

  1. Softening Water: Borax is employed to soften water.

2. Metallurgical Operations: Used in metallurgy.

3. Making Washing Powders: Included in the production of washing powders.

4. Leather Industry: Utilized for tinning and dyeing in the leather industry.

Q10: How Boron differs from members of its family?

  1. Nonmetallic Nature: Boron is nonmetallic, whereas other family members are metallic.

2. Electron Count: It has less than 4 electrons in the outermost shell.

3. Ionic Compounds: Boron forms ionic compounds with sulfates, a trait distinct from other family members.

Q11: Write down formulas of Bauxite and corundum?

Ans: Formulas of Minerals:

  1. Bauxite: Al2O3.2H2O

2. Corundum: Al2O3

Q12: What is chemistry of Borax bead test?

Chemistry of Borax Bead Test:
When borax is fused, it decomposes into sodium metaborate and boric anhydride:
Na_2B_4O_7 longrightarrow 2NaBO_2 + B_2O_3

The metallic oxide from the substance being tested combines with (B_2O_3) to form colored metallic borates. For example, with cupric oxide (CuO), the beads are colored blue in the oxidizing flame:
CuO + B_2O_3 longrightarrow Cu(BO_2)_2

Q13: How will you convert boric acid into borax and vice versa?
Ans: when boric acid is neutralized by soda ash borax is formed.
4H3BO3 + Na2CO3 →Na2B4O7 + 6H2O + CO2
Aqueous solution of borax reacts with HCl or H2SO4 to form boric acid.
Na2B4O7 + 2HCl +5H2O ⟶ 2NaCl + 4H3BO3

Q14: Write four uses of sodium silicate?

Uses of Sodium Silicate:

  1. Soap Industry: Used as a filler for soap.

2. Textile Industry: Employed as a fireproofing agent.

3. Furniture Polish: Used in furniture polishing.

4. Chemical Garden: Utilized in the preparation of chemical gardens.

Q15Write the reactions of boric acid with i. Ethyl alcohol ii. NaOH?

Ans: Reactions of Boric Acid:*

i. With NaOH:
2NaOH + 4H_3BO_3 Na_2B_4O_7 + 7H_2O

ii. With Ethyl Alcohol (C2H5OH):
H_3BO_3 + 3C_2H_5OH C_2H_5_3BO_3 + 3H_2O

Q16: What is meant by chemical garden?

Ans: Chemical Garden:

A chemical garden is formed by adding crystals of a water-soluble, colored salt (e.g., nickel chloride, ferrous sulfate, copper sulfate, or cobalt nitrate) to solutions of sodium silicate (Na2SiO3Na2​SiO3​). This results in the growth of a visually striking, plant-like structure.

Q17: Give the formulae of four boric acids?

Ans: Boric Acids and Formulas:

  1. Orthoboric Acid: H_3BO_3

2. Metaboric Acid: HBO_2

3. Tetraboric Acid: H_2B_4O_7

4. Pyroboric Acid: H_6B_4O_9

Q18: What is the action of heat on orthoboric acid?

Ans: Heat Action on Orthoboric Acid:

Heating orthoboric acid at around 100°C leads to the loss of a water molecule, forming metaboric acid. Further heating to approximately 140°C results in the formation of tetra boric acid.

Q19: Why aqueous solution of borax is alkaline?

Ans: Alkalinity of Borax Solution:

Borax dissolves in water, forming ions such as Na2B4O7, Na+, and B4O7^2-. The hydrolysis of B4O7^2- ions produces hydroxyl ions (OH-), making the solution alkaline.

[B4O7^{2-} + 7H2O \longrightarrow 4H3BO3 + 2OH^-]

This results in the formation of a highly ionized strong alkali (NaOH), contributing to the overall alkalinity of the borax solution. Conversely, boric acid (H3BO3) ionizes to a lesser extent as it is a weak acid.

Q20: Explain structure of CO2?

Ans: Structure of CO2:

Carbon dioxide (CO2) adopts a linear molecular structure in the gaseous state, represented as O=C=O. The observed carbon-oxygen (C=O) bond length is 115 picometers (pm). In its solid form, CO2 exhibits a face-centered cubic structure. Due to its linear arrangement, the molecule has a dipole moment of zero.

Q21: How aqueous solution of Borax is alkaline?

Ans: Explanation:

When Borax (Na2B4O7) dissolves in water, it ionizes to form Na+ ions and the tetrahydroxyborate ion (B4O7^2-). The hydrolysis of the tetrahydroxyborate ions generates hydroxyl ions (OH-) in the solution, making it alkaline.

B4O7^2- + 7H2O → 4H3BO3 + 2OH-

This results in the formation of a strong alkali (NaOH), which is highly ionized. In contrast, boric acid (H3BO3) ionizes to a lesser extent as it is a weak acid. The overall effect is that the solution of borax is alkaline.

Q22: Give two similarities between carbon and silicon?

Ans: Similarities between Carbon and Silicon:

  1. Non-Metals in Group IVA:

Both carbon and silicon belong to Group IVA in the periodic table.

Carbon is known for its ability to form long carbon chains, while silicon forms long chains of alternating silicon and oxygen atoms.

  1. Formation of Acidic Oxides:

Both carbon and silicon exhibit the property of forming acidic oxides.

The oxides produced by carbon and silicon are capable of reacting with water to form acids.

Q23:Why Liquid Silicones are Preferred over Ordinary Organic Lubricants?

Ans: Liquid silicones are preferred over ordinary organic lubricants due to their minimal change in viscosity with temperature fluctuations. When the temperature decreases from 100°C to 0°C, petroleum oils used as lubricants experience a 100-fold increase in viscosity. In contrast, silicon oils undergo less than a 4-fold increase in viscosity over the same temperature change. This property makes silicones more temperature-stable, hence the preference over ordinary organic lubricants.

Q24:Write down chemical formulae of colemanite and bauxite?

Ans:1. Colemanite: Ca2B6O11

2. Bauxite: Al2O3.2H2O

Q25: Write any four uses of Aluminum?

Ans: 1. Excellent Heat and Electricity Conductor

2. Non-Toxic Material for Food and Brewing Equipments

3. Alloy Formation

4. Construction of Petrol and Milk Storage Tanks

Q26. What is vitreous silica? Give its two uses.

Ans: Vitreous silica, or silica glass, is a rigid, under-cooled liquid formed by melting crystalline silica (such as opal or quartz) at high temperatures. It lacks a regular crystal pattern and solidifies without crystallizing readily.

Uses of Vitreous Silica:

  1. Envelope for Mercury Vapor Lamps

2. Windows for Space Vehicl27.

Q27: Write two reactions for the preparation of Borax?

27. Preparation of Borax:

From Colemanite with Sodium Carbonate:
Ca2B_6O11 + 2Na_2CO_3Na_2B_4O_7 + 2NaBO_2 + 2CaCO_3 After filtration to remove CaCO_3 cooling the filtrate yields borax crystals.

Using Sodium Metaborate with Carbon Dioxide:
4NaBO_2 + CO_2Na_2B_4O_7 + 6H_2O + CO_2Define semiconductor.

Q28: Define semiconductor. Write its properties?

Ans: Semiconductor Definition: A semiconductor is a substance that exhibits varying resistance to electric current at different temperatures, examples include Silicon, Germanium, Lead sulphide, Gallium arsenide, etc.

Properties:

Conductivity:

Semiconductors can conduct electricity.

Temperature Sensitivity:

Their resistance decreases with an increase in temperature.

Light Sensitivity:

Semiconductors are sensitive to light.

Electron Mobility:

Electrons in semiconductors do not conduct electric current as effectively as those in good conductors like metals.

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