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201. Which reactant is commonly used for the laboratory preparation of pure Carbon Monoxide (${CO}$)?
ⓐ. Heating calcium carbonate (${CaCO}_3$)
ⓑ. Reacting carbon with steam
ⓒ. Heating oxalic acid (${H}_2{C}_2{O}_4$) with concentrated ${H}_2{SO}_4$
ⓓ. Heating formic acid (${HCOOH}$) with concentrated ${H}_2{SO}_4$
Correct Answer: Heating formic acid (${HCOOH}$) with concentrated ${H}_2{SO}_4$
Explanation: Pure Carbon Monoxide gas is conveniently prepared in the laboratory by dehydrating formic acid (${HCOOH}$) using hot, concentrated sulfuric acid (${H}_2{SO}_4$) as a powerful dehydrating agent.
$${HCOOH} \xrightarrow{{conc.} \\, {H}_2{SO}_4} {CO}({g}) + {H}_2{O}$$
202. For industrial-scale production, Carbon Monoxide is typically prepared along with Hydrogen, forming a mixture known as water gas. Which reaction produces water gas?
ⓐ. Heating carbon with excess air
ⓑ. Passing steam over hot coke ($\sim 1000 \, ^{\circ}{C}$)
ⓒ. Heating a mixture of ${CO}_2$ and ${H}_2$
ⓓ. Electrolysis of water
Correct Answer: Passing steam over hot coke ($\sim 1000 \, ^{\circ}{C}$)
Explanation: Water gas (or synthesis gas) is a crucial industrial mixture of ${CO}$ and ${H}_2$. It is produced by passing steam (${H}_2{O}$) over red-hot coke (carbon) at temperatures around $1000 \, ^{\circ}{C}$:
$${C}({s}) + {H}_2{O}({g}) \xrightarrow{1000 \, ^{\circ}{C}} {CO}({g}) + {H}_2({g})$$
203. Carbon Monoxide is a fatal poison because it binds strongly to which component of the blood?
ⓐ. Iron ions in ferritin
ⓑ. Globin protein in plasma
ⓒ. Iron ions in the heme group of hemoglobin (${Hb}$)
ⓓ. Calcium ions in the blood platelets
Correct Answer: Iron ions in the heme group of hemoglobin (${Hb}$)
Explanation: ${CO}$ binds to the iron atom in the heme group of hemoglobin to form carboxyhemoglobin (${COHb}$). The affinity of ${CO}$ for hemoglobin is about 200-300 times greater than that of oxygen, effectively preventing the hemoglobin from transporting oxygen to body tissues.
204. Which statement correctly describes the bonding present in the Carbon Monoxide (${CO}$) molecule?
ⓐ. Two $\sigma$ bonds and one $\pi$ bond.
ⓑ. One coordinate covalent bond, two $\sigma$ bonds, and one $\pi$ bond.
ⓒ. Two $\sigma$ bonds and one coordinate covalent bond.
ⓓ. One $\sigma$ bond and two $\pi$ bonds.
Correct Answer: One $\sigma$ bond and two $\pi$ bonds.
Explanation: The Carbon Monoxide molecule has a strong triple bond (${C} \equiv {O}$). This bond consists of one $\sigma$ bond and two $\pi$ bonds. Additionally, one of the three shared pairs often originates from a coordinate covalent bond (from ${O}$ to ${C}$), but structurally, it’s described as one $\sigma$ and two $\pi$ bonds.
205. Carbon Monoxide acts as a powerful reducing agent, especially at high temperatures. Which reaction illustrates ${CO}$ reducing a metal oxide?
ⓐ. $2{CO} + {O}_2 \rightarrow 2{CO}_2$
ⓑ. ${CO} + {H}_2{O} \rightleftharpoons {CO}_2 + {H}_2$
ⓒ. ${Fe}_2{O}_3 + 3{CO} \rightarrow 2{Fe} + 3{CO}_2$
ⓓ. ${CO} + 2{H}_2 \rightarrow {CH}_3{OH}$
Correct Answer: ${Fe}_2{O}_3 + 3{CO} \rightarrow 2{Fe} + 3{CO}_2$
Explanation: ${CO}$ is a primary reducing agent in metallurgical processes like the blast furnace. It reduces metal oxides (like ${Fe}_2{O}_3$) to their elemental metals, while ${CO}$ itself is oxidized to ${CO}_2$.
206. Carbon Monoxide is a neutral gas, meaning it does not react with acids or bases. Which physical property is also characteristic of ${CO}$?
ⓐ. Sweet smelling, green color, highly soluble in water.
ⓑ. Colorless, odorless, sparingly soluble in water.
ⓒ. Pungent smelling, colorless, highly soluble in water.
ⓓ. Yellowish gas, odorless, insoluble in water.
Correct Answer: Colorless, odorless, sparingly soluble in water.
Explanation: ${CO}$ is known as the “silent killer” because it is a colorless, odorless, and tasteless gas. It is only sparingly soluble in water, further making it hard to detect its presence in the air.
207. Carbon Monoxide is classified as a Lewis base because:
ⓐ. It can donate a lone pair of electrons from the carbon atom to a metal.
ⓑ. It readily accepts electrons to stabilize its empty $p$ orbital.
ⓒ. It forms a stable acidic solution in water.
ⓓ. It accepts a proton (${H}^+$) easily.
Correct Answer: It can donate a lone pair of electrons from the carbon atom to a metal.
Explanation: Although ${CO}$ is mostly non-polar, the carbon atom has a lone pair of electrons (due to the coordinate bond structure). ${CO}$ uses this lone pair to form metal carbonyls (e.g., ${Ni}({CO})_4$) by donating the pair to the vacant ${d}$-orbitals of transition metals, acting as a $\sigma$-donor Lewis base.
208. The reaction of Carbon Monoxide with water vapor at high temperatures in the presence of a catalyst is known as the Water Gas Shift reaction. What are the products of this reversible reaction?
ⓐ. ${CO}_2$ and ${H}_2$
ⓑ. ${CH}_4$ and ${O}_2$
ⓒ. ${HCOOH}$
ⓓ. ${C}$ and ${H}_2{O}_2$
Correct Answer: ${CO}_2$ and ${H}_2$
Explanation: The Water Gas Shift reaction is used industrially to increase the hydrogen content of synthesis gas (${CO} + {H}_2$). It involves the oxidation of ${CO}$ to ${CO}_2$ by steam:
$${CO}({g}) + {H}_2{O}({g}) \rightleftharpoons {CO}_2({g}) + {H}_2({g})$$
209. Carbon Monoxide is a major air pollutant primarily produced by:
ⓐ. Volcanic eruptions and geothermal vents.
ⓑ. Incomplete combustion of carbon-containing fuels.
ⓒ. Photosynthesis by marine algae.
ⓓ. Decomposition of ozone in the upper atmosphere.
Correct Answer: Incomplete combustion of carbon-containing fuels.
Explanation: ${CO}$ is formed when there is insufficient oxygen available for the complete combustion of carbon or carbon compounds (e.g., in car engines or faulty furnaces). Instead of forming ${CO}_2$, ${CO}$ is produced:
$$2{C} + {O}_2 \rightarrow 2{CO}$$
210. What is the standard and most effective first-aid treatment for severe Carbon Monoxide poisoning?
ⓐ. Administering a strong oxidizing agent intravenously.
ⓑ. Hemodialysis to filter the blood.
ⓒ. Administering ${CO}_2$ gas to induce rapid breathing.
ⓓ. Administering pure oxygen or carboxygen (5\\% ${CO}_2$ in ${O}_2$).
Correct Answer: Administering pure oxygen or carboxygen (5\\% ${CO}_2$ in ${O}_2$).
Explanation: The treatment involves replacing the ${CO}$ bound to hemoglobin with oxygen. Administering pure oxygen or hyperbaric oxygen increases the partial pressure of ${O}_2$ drastically, speeding up the dissociation of ${CO}$ from hemoglobin and effectively decreasing the half-life of carboxyhemoglobin.
211. Which of the following is the standard laboratory method for preparing Carbon Dioxide (${CO}_2$) gas?
ⓐ. Heating sodium bicarbonate (${NaHCO}_3$) strongly.
ⓑ. Passing steam over hot coke ($\sim 1000 \, ^{\circ}{C}$).
ⓒ. Reacting formic acid (${HCOOH}$) with concentrated sulfuric acid.
ⓓ. Reacting calcium carbonate (${CaCO}_3$) with dilute hydrochloric acid (${HCl}$).
Correct Answer: Reacting calcium carbonate (${CaCO}_3$) with dilute hydrochloric acid (${HCl}$).
Explanation: The reaction of an inexpensive carbonate, like marble chips (${CaCO}_3$), with a dilute acid (${HCl}$) is the conventional and most efficient method for laboratory ${CO}_2$ preparation.
212. The Carbon Dioxide molecule has a linear shape. What is the hybridization of the central carbon atom in ${CO}_2$ and the bond angle, respectively?
ⓐ. $sp^3$, $109.5^{\circ}$
ⓑ. $sp^2$, $120^{\circ}$
ⓒ. $sp$, $120^{\circ}$
ⓓ. $sp$, $180^{\circ}$
Correct Answer: $sp$, $180^{\circ}$
Explanation: The carbon atom forms two double bonds with the two oxygen atoms (${O}={C}={O}$), leading to $sp$ hybridization and a linear molecular geometry with a $\mathbf{180^{\circ}}$ bond angle.
213. Carbon Dioxide is classified as an acidic oxide. Which of the following chemical reactions demonstrates this property?
ⓐ. ${CO}_2 \rightarrow {C} + {O}_2$
ⓑ. ${CO}_2 + 2{H}_2 \rightarrow {CH}_4 + {O}_2$
ⓒ. ${CO}_2 + {H}_2{O} \rightleftharpoons {H}_2{CO}_3$
ⓓ. ${CO}_2 + 2{Mg} \rightarrow {C} + 2{MgO}$
Correct Answer: ${CO}_2 + {H}_2{O} \rightleftharpoons {H}_2{CO}_3$
Explanation: An acidic oxide is one that reacts with water to form an acid. ${CO}_2$ reacts with water to form the weak carbonic acid (${H}_2{CO}_3$).
214. The greenhouse effect is caused by certain gases in the atmosphere absorbing and re-emitting which type of radiation emitted from the Earth’s surface?
ⓐ. Ultraviolet (UV) radiation
ⓑ. Infrared (IR) radiation
ⓒ. Microwave radiation
ⓓ. Visible light
Correct Answer: Infrared (IR) radiation
Explanation: The Earth re-radiates heat as long-wavelength infrared radiation. Greenhouse gases like ${CO}_2$ are highly efficient at absorbing this IR radiation and re-emitting it, which traps heat in the lower atmosphere.
215. Which property of Carbon Dioxide makes it an effective agent in fire extinguishers?
ⓐ. It is non-combustible and significantly denser than air, displacing oxygen from the burning material.
ⓑ. It reacts chemically with the fuel, rendering it inert.
ⓒ. It is lighter than air, allowing it to easily blanket the flame.
ⓓ. It is highly soluble in water, allowing for easy distribution.
Correct Answer: It is non-combustible and significantly denser than air, displacing oxygen from the burning material.
Explanation: ${CO}_2$ is non-flammable and sinks/settles over the fire due to its high density (${CO}_2$ is $\sim 1.5$ times denser than air), effectively cutting off the oxygen supply.
216. Solid Carbon Dioxide, known as ‘dry ice,’ has a significant advantage over ordinary ice for cooling due to which unique physical process?
ⓐ. Melting directly into a cold liquid at $0^{\circ}{C}$.
ⓑ. Its low thermal conductivity, making it an excellent insulator.
ⓒ. Sublimation (transition directly from solid to gas) without forming a liquid residue.
ⓓ. Its extremely low density, allowing it to float on top of liquids.
Correct Answer: Sublimation (transition directly from solid to gas) without forming a liquid residue.
Explanation: Dry ice passes directly from the solid to the gaseous state at atmospheric pressure, ensuring that as it cools, it leaves no messy liquid residue, making it ideal for shipping and refrigeration.
217. In the process of photosynthesis, Carbon Dioxide is utilized by plants. What is the primary chemical product of this process?
ⓐ. Water (${H}_2{O}$)
ⓑ. Glucose (${C}_6{H}_{12}{O}_6$)
ⓒ. Oxygen (${O}_2$)
ⓓ. Chlorophyll
Correct Answer: Glucose (${C}_6{H}_{12}{O}_6$)
Explanation: Photosynthesis uses ${CO}_2$ and water (${H}_2{O}$) in the presence of sunlight and chlorophyll to produce energy-storing carbohydrates, primarily glucose (${C}_6{H}_{12}{O}_6$), with oxygen as a byproduct.
218. The largest sink for anthropogenic ${CO}_2$ is currently the world’s oceans. What is the chemical consequence of the ocean absorbing large amounts of ${CO}_2$?
ⓐ. Ocean thermal expansion and sea level rise.
ⓑ. Increased dissolved oxygen levels, promoting marine life.
ⓒ. Ocean acidification, or a decrease in ocean ${pH}$.
ⓓ. Increased precipitation and localized flooding.
Correct Answer: Ocean acidification, or a decrease in ocean ${pH}$.
Explanation: When ${CO}_2$ dissolves in water, it forms carbonic acid (${H}_2{CO}_3$), which dissociates and releases hydrogen ions (${H}^+$), thereby lowering the ${pH}$ of the seawater (making it more acidic).
219. Industrial production of ${CO}_2$ is often a major byproduct of which large-scale chemical process involving calcium carbonate (${CaCO}_3$)?
ⓐ. The manufacturing of cement (decomposition of limestone).
ⓑ. The Contact process (sulfuric acid synthesis).
ⓒ. The Hall-Héroult process (aluminum production).
ⓓ. The Haber process (ammonia synthesis).
Correct Answer: The manufacturing of cement (decomposition of limestone).
Explanation: In cement production, limestone (${CaCO}_3$) is heated strongly (calcined) to produce lime (${CaO}$) and large quantities of ${CO}_2$ as an unavoidable byproduct, making it a major industrial source of the gas.
220. Which statement correctly describes a key difference between ${CO}_2$ and its homologue ${SiO}_2$ (silica)?
ⓐ. Both form discrete, linear molecules that sublime at high temperatures.
ⓑ. ${CO}_2$ is a polar molecule, while ${SiO}_2$ is non-polar.
ⓒ. ${CO}_2$ is a gas due to strong ${C}-{O}$ single bonds; ${SiO}_2$ is a solid due to ${Si}={O}$ double bonds.
ⓓ. ${CO}_2$ is a discrete molecule formed by ${C}={O}$ double bonds; ${SiO}_2$ is a giant network formed by ${Si}-{O}$ single bonds.
Correct Answer: ${CO}_2$ is a discrete molecule formed by ${C}={O}$ double bonds; ${SiO}_2$ is a giant network formed by ${Si}-{O}$ single bonds.
Explanation: Carbon forms stable ${p}\pi – {p}\pi$ double bonds leading to the discrete molecular gas ${CO}_2$. Silicon cannot form stable double bonds and prefers four strong ${Si}-{O}$ single bonds in a giant tetrahedral network structure, resulting in the high-melting solid ${SiO}_2$.
221. Silicones are synthetic organosilicon polymers characterized by which repeating structural unit?
ⓐ. $(-{Si}-{C}-)_n$
ⓑ. $(-{C}-{O}-{C}-)_n$
ⓒ. $(-{R}_2{Si}-{O}-)_n$
ⓓ. $(-{Si}-{Cl}-)_n$
Correct Answer: $(-{R}_2{Si}-{O}-)_n$
Explanation: Silicones are polymers containing a silicon-oxygen backbone (${Si}-{O}-{Si}$), with organic groups (${R}$, such as methyl or phenyl) attached directly to the silicon atoms.
222. The starting material (monomer) used for the preparation of linear chain silicones is typically:
ⓐ. ${SiCl}_4$ (Silicon tetrachloride)
ⓑ. ${R}_2{SiCl}_2$ (Dialkyldichlorosilane)
ⓒ. ${R}_3{SiCl}$ (Trialkylchlorosilane)
ⓓ. ${RSiCl}_3$ (Alkyltrichlorosilane)
Correct Answer: ${R}_2{SiCl}_2$ (Dialkyldichlorosilane)
Explanation: ${R}_2{SiCl}_2$ is a difunctional monomer. Upon hydrolysis, it forms a diol (${R}_2{Si}({OH})_2$), which then undergoes condensation to link up at two points, forming the extended linear chain structure $(-{R}_2{Si}-{O}-)_n$.
223. The polymerization reaction used to convert the hydrolyzed monomers (${R}_2{Si}({OH})_2$) into long-chain silicone polymers is known as:
ⓐ. Addition polymerization
ⓑ. Ionic polymerization
ⓒ. Condensation polymerization
ⓓ. Free-radical polymerization
Correct Answer: Condensation polymerization
Explanation: The silanols (${R}_2{Si}({OH})_2$) react with each other by eliminating a small molecule, usually water, to form the ${Si}-{O}-{Si}$ linkage. This release of a small molecule classifies the reaction as condensation polymerization.
224. Which exceptional property of silicones makes them widely used as waterproofing materials and sealants?
ⓐ. High electrical conductivity
ⓑ. Chemical reactivity
ⓒ. Hydrophobicity (water repellency)
ⓓ. Low thermal stability
Correct Answer: Hydrophobicity (water repellency)
Explanation: The organic alkyl groups (${R}$) attached to the silicon atoms are non-polar and project outward, covering the polar ${Si}-{O}-{Si}$ backbone. This surface layer of organic groups repels water strongly, making silicones excellent waterproofing agents.
225. To produce a highly rigid, three-dimensional (cross-linked) silicone polymer rather than a linear chain, which monomer must be incorporated along with ${R}_2{SiCl}_2$?
ⓐ. ${RSiCl}_3$ (Alkyltrichlorosilane)
ⓑ. ${SiCl}_4$
ⓒ. ${R}_3{SiCl}$
ⓓ. ${R}_4{Si}$
Correct Answer: ${RSiCl}_3$ (Alkyltrichlorosilane)
Explanation: The ${RSiCl}_3$ monomer is trifunctional, meaning it can form three ${Si}-{O}$ linkages after hydrolysis. This extra point of attachment allows the polymer chains to link together and form a stable, rigid, three-dimensional network.
226. Silicones are noted for their high thermal stability compared to most carbon-based organic polymers. This is attributed to the strength of the:
ⓐ. ${C}-{Si}$ bond
ⓑ. ${R}-{R}$ van der Waals forces
ⓒ. ${C}-{C}$ bond
ⓓ. ${Si}-{O}$ bond
Correct Answer: ${Si}-{O}$ bond
Explanation: The ${Si}-{O}$ bond is significantly stronger (approx. $452 \, {kJ} \, {mol}^{-1}$) than the ${C}-{C}$ bond (approx. $348 \, {kJ} \, {mol}^{-1}$), giving the silicone backbone exceptional resistance to heat and chemical degradation.
227. Silicones in the form of oils and greases are widely used as lubricants, especially for specialized equipment. This application is due to their stability in which two extreme conditions?
ⓐ. Wide temperature range and chemical inertness
ⓑ. High humidity and high conductivity
ⓒ. High pressure and low acidity
ⓓ. Extreme ${pH}$ and low density
Correct Answer: Wide temperature range and chemical inertness
Explanation: Silicone oils maintain their viscosity and lubricating properties across a very wide temperature range (they don’t thin out when hot or thicken excessively when cold) and are chemically inert, meaning they do not react with materials they are lubricating.
228. If the only monomer used in the preparation process is ${R}_3{SiCl}$ (Trialkylchlorosilane), what type of product will be formed?
ⓐ. A low molecular weight dimer or trimer that acts as a chain terminator.
ⓑ. A long, linear silicone chain.
ⓒ. A highly cross-linked thermoset plastic.
ⓓ. A cyclic silicone elastomer.
Correct Answer: A low molecular weight dimer or trimer that acts as a chain terminator.
Explanation: The ${R}_3{SiCl}$ monomer is monofunctional (it forms only one ${Si}-{O}$ bond). It can only attach to the end of a growing chain, capping it off and preventing further polymerization. It is therefore used as a chain terminator.
229. Which application of silicones makes direct use of their property as an electrical insulator?
ⓐ. Cosmetic implants
ⓑ. Water-repellent sprays for clothing
ⓒ. Mold release agents
ⓓ. Encapsulation of electronic components
Correct Answer: Encapsulation of electronic components
Explanation: Silicones are excellent electrical insulators due to the absence of free electrons or mobile ions. They are widely used to encapsulate sensitive electronic parts (potting) to protect them from moisture, heat, and electrical interference.
230. Silicones can exist in various physical forms, ranging from viscous liquids (oils) to rubbery solids (elastomers) and hard resins. The final form of the silicone material is primarily determined by:
ⓐ. The type of organic group (${R}$) attached.
ⓑ. The degree of cross-linking and the chain length.
ⓒ. The temperature at which the final product is cured.
ⓓ. The solvent used during the hydrolysis step.
Correct Answer: The degree of cross-linking and the chain length.
Explanation: The chain length dictates viscosity (longer chain = more viscous oil). The degree of cross-linking determines rigidity (no cross-linking = liquid/oil; slight cross-linking = rubber/elastomer; extensive cross-linking = hard resin).
231. What is the fundamental building block of all silicate minerals?
ⓐ. A linear ${Si}-{O}$ chain.
ⓑ. A planar ${Si}_3{O}_9$ ring.
ⓒ. A silicon atom bonded to four oxygen atoms in a tetrahedral arrangement (${SiO}_4^{4-}$ unit).
ⓓ. A silicon atom bonded to six oxygen atoms in an octahedral arrangement (${SiO}_6^{2-}$ unit).
Correct Answer: A silicon atom bonded to four oxygen atoms in a tetrahedral arrangement (${SiO}_4^{4-}$ unit).
Explanation: All silicates are constructed from the silicon tetrahedron, where a silicon atom is covalently bonded to four oxygen atoms at the corners of a tetrahedron, giving the base unit a $4-$ charge (${SiO}_4^{4-}$).
232. Orthosilicates (or Nesosilicates) are characterized by which structural feature?
ⓐ. Linear chains where tetrahedra share two oxygen atoms each.
ⓑ. Double chains connected by metal ions.
ⓒ. Isolated ${SiO}_4^{4-}$ tetrahedral units with no shared oxygen atoms.
ⓓ. Sheets where tetrahedra share three oxygen atoms each.
Correct Answer: Isolated ${SiO}_4^{4-}$ tetrahedral units with no shared oxygen atoms.
Explanation: Orthosilicates (from Greek nesos, meaning island) contain discrete, isolated ${SiO}_4^{4-}$ units. The tetrahedra are held together only by surrounding metal cations, not by covalent ${Si}-{O}-{Si}$ bonds.
233. The Pyrosilicate (or Sorosilicate) structure is formed when two ${SiO}_4^{4-}$ tetrahedra share how many oxygen atom(s) at one corner?
ⓐ. Zero
ⓑ. One
ⓒ. Two
ⓓ. Three
Correct Answer: One
Explanation: Pyrosilicates (from Greek soros, meaning heap) are formed by the corner sharing of one oxygen atom between two tetrahedra, resulting in a single ${Si}_2{O}_7^{6-}$ ion.
234. What is the general anion formula for a Cyclic Silicate (or Cyclosilicate), such as the ion found in the mineral beryl?
ⓐ. $({SiO}_3^{2-})_n$
ⓑ. $({SiO}_4^{4-})_n$
ⓒ. $({Si}_2{O}_7^{6-})_n$
ⓓ. $({SiO}_3^{2-})_n$ or $({Si}_{n}{O}_{3n})^{2n-}$
Correct Answer: $({SiO}_3^{2-})_n$ or $({Si}_{n}{O}_{3n})^{2n-}$
Explanation: Cyclic silicates are formed when each tetrahedron shares two oxygen atoms with its neighbors, forming a closed ring (e.g., ${Si}_3{O}_9^{6-}$ or ${Si}_6{O}_{18}^{12-}$). The empirical ratio is ${SiO}_3^{2-}$, giving the general formula $({SiO}_3^{2-})_n$.
235. In single-chain silicates (Pyroxenes), how many oxygen atoms does each silicon tetrahedron share with other tetrahedra?
ⓐ. One
ⓑ. Two
ⓒ. Three
ⓓ. Four
Correct Answer: Two
Explanation: Single-chain silicates are formed by continuous chains where each ${SiO}_4$ tetrahedron shares two of its oxygen atoms (one on each side) with neighboring tetrahedra. This gives the chain a repeating unit ratio of ${SiO}_3^{2-}$.
236. The group of silicates known as Amphiboles (e.g., hornblende) are classified as which type of silicate structure?
ⓐ. Double-chain silicates
ⓑ. Single-chain silicates
ⓒ. Orthosilicates
ⓓ. Sheet silicates
Correct Answer: Double-chain silicates
Explanation: Amphiboles are double-chain silicates. Their structure is formed by two single chains linked together periodically by sharing oxygen atoms, resulting in a formula that alternates between sharing two and three oxygen atoms per ${SiO}_4$ unit.
237. Clay minerals and Micas are excellent examples of which type of silicate structure?
ⓐ. Phyllosilicates (Sheet silicates)
ⓑ. Tectosilicates
ⓒ. Inosilicates (Chain silicates)
ⓓ. Sorosilicates (Pyrosilicates)
Correct Answer: Phyllosilicates (Sheet silicates)
Explanation: Phyllosilicates (from Greek phyllon, meaning leaf) are formed when each ${SiO}_4$ tetrahedron shares three oxygen atoms with its neighbors, creating flat, extended, two-dimensional sheets that are often easily cleavable, as seen in mica.
238. In a Sheet Silicate (Phyllosilicate), what is the resulting formula for the silicate anion?
ⓐ. ${SiO}_4^{4-}$
ⓑ. ${Si}_2{O}_7^{6-}$
ⓒ. $({SiO}_3^{2-})_n$
ⓓ. $({Si}_2{O}_5^{2-})_n$
Correct Answer: $({Si}_2{O}_5^{2-})_n$
Explanation: Since three of the four oxygen atoms are shared by adjacent tetrahedra, the general anion ratio becomes ${Si}_2{O}_5^{2-}$.
239. In the class of silicates known as Tectosilicates (Framework Silicates), what fraction of the oxygen atoms are shared by each ${SiO}_4$ tetrahedron with its neighbors?
ⓐ. $\frac{1}{2}$
ⓑ. $\frac{3}{4}$
ⓒ. $\frac{1}{4}$
ⓓ. All four
Correct Answer: All four
Explanation: Tectosilicates (from Greek tectos, meaning structure or framework), like quartz, are formed when every ${SiO}_4$ tetrahedron shares all four of its oxygen atoms with neighboring tetrahedra. This results in a neutral, three-dimensional framework with the empirical formula ${SiO}_2$.
240. Quartz is the most common example of a Tectosilicate. If aluminum (${Al}^{3+}$) replaces some of the silicon (${Si}^{4+}$) atoms in a Tectosilicate framework, what is the chemical consequence?
ⓐ. The structure becomes more stable and rigid.
ⓑ. The framework develops a negative charge, requiring the inclusion of metal cations.
ⓒ. The mineral changes from colorless to black.
ⓓ. The crystal lattice transitions from tetrahedral to octahedral symmetry.
Correct Answer: The framework develops a negative charge, requiring the inclusion of metal cations.
Explanation: Replacing ${Si}^{4+}$ with ${Al}^{3+}$ creates a charge imbalance (a negative charge on the framework). This charge must be balanced by the incorporation of metal cations (like ${Na}^+$ or ${K}^+$) into the structural voids, which is how feldspars and zeolites (aluminosilicates) are formed.
241. Zeolites are a class of microporous, crystalline materials. Chemically, they are classified as:
ⓐ. Simple ${SiO}_2$ Tectosilicates.
ⓑ. Hydrated Aluminosilicates.
ⓒ. Pure Carbon Allotropes.
ⓓ. High molecular weight organosilicon polymers.
Correct Answer: Hydrated Aluminosilicates.
Explanation: Zeolites are framework silicates where some ${Si}^{4+}$ ions in the ${SiO}_2$ structure are replaced by ${Al}^{3+}$ ions, forming a negative framework balanced by exchangeable metal cations and incorporating water molecules, thus making them hydrated aluminosilicates.
242. What is the key structural feature of zeolites that allows for their selective uses in separation and catalysis?
ⓐ. A non-porous, rigid, tetrahedral crystal lattice.
ⓑ. Strong interlayer van der Waals forces.
ⓒ. A porous, cage-like framework with a uniform, fixed pore size.
ⓓ. The ability to form ${Si}={O}$ double bonds.
Correct Answer: A porous, cage-like framework with a uniform, fixed pore size.
Explanation: Zeolites possess a three-dimensional framework that creates interconnected channels, cavities, and pores of very precise and uniform molecular dimensions. This allows them to act as molecular sieves.
243. In the zeolite structure, the substitution of ${Si}^{4+}$ by ${Al}^{3+}$ introduces a net negative charge on the framework. This charge is balanced by the presence of:
ⓐ. Covalently bonded ${H}^+$ ions.
ⓑ. Free, delocalized electrons.
ⓒ. Covalently bonded ${Cl}^-$ ions.
ⓓ. Exchangeable metal cations (e.g., ${Na}^+$, ${K}^+$).
Correct Answer: Exchangeable metal cations (e.g., ${Na}^+$, ${K}^+$).
Explanation: Since ${Al}^{3+}$ has one less positive charge than ${Si}^{4+}$, every ${Al}$ atom introduced creates a fixed negative charge. This charge is neutralized by easily exchangeable cations residing within the zeolite cages.
244. The use of zeolites as catalysts is primarily based on the principle of ‘shape-selective catalysis’. This means the catalytic reaction is dependent on:
ⓐ. The type of metal cation balancing the charge.
ⓑ. The reactants/products having a specific shape and size to fit the pores/cages.
ⓒ. The presence of strong ${Si}={O}$ double bonds.
ⓓ. The magnetic properties of the zeolite framework.
Correct Answer: The reactants/products having a specific shape and size to fit the pores/cages.
Explanation: Shape-selective catalysis occurs because only molecules of a certain size and geometry can enter the pores to reach the active sites, and only products small enough can exit the pores. The reaction is dictated by the dimensions of the molecular sieve.
245. The major industrial use of zeolites is in the petrochemical industry for the process of:
ⓐ. Synthesis of ${H}_2{SO}_4$.
ⓑ. Production of plasticizers.
ⓒ. Cracking and isomerization of hydrocarbons.
ⓓ. Synthesis of ammonia (Haber process).
Correct Answer: Cracking and isomerization of hydrocarbons.
Explanation: Zeolites are highly effective solid acid catalysts (Brønsted acid sites are formed when ${H}^+$ replaces metal cations) used for breaking down large, heavy petroleum molecules (cracking) and rearranging their structures (isomerization) to produce gasoline and other lighter, more valuable fuels.
246. What property of zeolites makes them widely used in water softening and detergent formulations?
ⓐ. Cation exchange capacity.
ⓑ. Their high density.
ⓒ. Their resistance to high temperatures.
ⓓ. Their optical transparency.
Correct Answer: Cation exchange capacity.
Explanation: Zeolites (typically ${Na}$-zeolites) can exchange their readily available ${Na}^+$ ions for the ‘hardness’ ions in water, specifically ${Ca}^{2+}$ and ${Mg}^{2+}$. This process effectively softens the water by removing the polyvalent metal ions.
247. The general formula for a natural zeolite can be represented as:
ⓐ. ${Si}_x {C}_y {O}_z$
ⓑ. $({R}_2{SiO})_n$
ⓒ. ${M}_{x/n} [({AlO}_2)_x ({SiO}_2)_y] \cdot {zH}_2{O}$
ⓓ. ${M}_{x/n} [({CO}_3)_x ({SiO}_2)_y] \cdot {zH}_2{O}$
Correct Answer: ${M}_{x/n} [({AlO}_2)_x ({SiO}_2)_y] \cdot {zH}_2{O}$
Explanation: The formula represents: ${M}$ (metal cation of valence $n$), the ${AlO}_2$ and ${SiO}_2$ units that make up the framework, and ${zH}_2{O}$ representing the included water molecules. The ratio of ${Si}$ to ${Al}$ ($\frac{y}{x}$) determines the properties.
248. The ${Si}/{Al}$ ratio in a zeolite affects its properties. A higher ${Si}/{Al}$ ratio (e.g., $5:1$ vs. $1:1$):
ⓐ. Increases its hydrophilicity (affinity for water).
ⓑ. Decreases the number of negative charge sites, resulting in lower ion-exchange capacity.
ⓒ. Increases its basicity (tendency to accept protons).
ⓓ. Makes the zeolite framework less stable and more prone to decomposition.
Correct Answer: Decreases the number of negative charge sites, resulting in lower ion-exchange capacity.
Explanation: Since each ${Al}$ atom introduces one negative charge, a lower ${Al}$ content (higher ${Si}/{Al}$ ratio) means fewer charge sites that need to be balanced by exchangeable cations, thus lowering the ion-exchange capacity. Higher ${Si}/{Al}$ ratio also generally increases hydrophobicity.
249. Zeolites are used as sorbents (adsorbents) for gases. Their effectiveness as sorbents is due to their large:
ⓐ. Internal surface area.
ⓑ. Thermal conductivity.
ⓒ. Total mass.
ⓓ. Density.
Correct Answer: Internal surface area.
Explanation: Due to their highly porous structure, zeolites possess an enormous internal surface area (hundreds of square meters per gram) where gas molecules can be physically trapped or adsorbed, making them excellent drying agents and purifiers.
250. The ${ZSM}-5$ zeolite, a key catalyst in the “Methanol-to-Gasoline” (${MTG}$) process, is an example of a synthetic zeolite. This process demonstrates the zeolite’s ability to selectively convert:
ⓐ. Water gas (${CO}+{H}_2$) into methanol.
ⓑ. ${CO}_2$ into long-chain fatty acids.
ⓒ. Small oxygenated hydrocarbons (methanol) into longer, branched hydrocarbons (gasoline).
ⓓ. ${NO}_x$ emissions into harmless nitrogen gas.
Correct Answer: Small oxygenated hydrocarbons (methanol) into longer, branched hydrocarbons (gasoline).
Explanation: The ${MTG}$ process uses the acidic, shape-selective properties of ${ZSM}-5$ to catalyze the dehydration, coupling, and cyclization of methanol, selectively producing a high-octane gasoline product.
251. The reaction ${Fe}_2{O}_3 + 3{CO} \xrightarrow{{heat}} 2{Fe} + 3{CO}_2$ is a fundamental process in metallurgy. What type of reaction is best exemplified by this equation?
ⓐ. Combination reaction
ⓑ. Decomposition reaction
ⓒ. Neutralization reaction
ⓓ. Redox (Reduction-Oxidation) reaction
Correct Answer: Redox (Reduction-Oxidation) reaction
Explanation: In this reaction, Carbon Monoxide (${CO}$) is oxidized (oxidation state of ${C}$ changes from $+2$ to $+4$) and acts as the reducing agent, while Iron (${Fe}$) in ${Fe}_2{O}_3$ is reduced (oxidation state changes from $+3$ to $0$) and acts as the oxidizing agent.
252. The industrial preparation of water gas (${CO} + {H}_2$) from coke (${C}$) and steam (${H}_2{O}$): ${C}({s}) + {H}_2{O}({g}) \xrightarrow{1000 \, ^{\circ}{C}} {CO}({g}) + {H}_2({g})$ is an example of a reaction that is highly:
ⓐ. Exothermic
ⓑ. Endothermic
ⓒ. Spontaneous at low temperatures
ⓓ. Acid-base neutralization
Correct Answer: Endothermic
Explanation: This reaction requires a large input of heat to proceed ($\sim 1000 \, ^{\circ}{C}$), as energy is needed to break the strong bonds in steam and in the carbon lattice. The reaction is therefore highly endothermic (absorbs heat).
253. The reaction ${SiCl}_4 + 2{H}_2{O} \rightarrow {SiO}_2 + 4{HCl}$ (or the formation of silanol intermediates) is a critical step in the synthesis of silicone polymers. What type of reaction is this?
ⓐ. Dehydration
ⓑ. Addition
ⓒ. Thermal Decomposition
ⓓ. Hydrolysis
Correct Answer: Hydrolysis
Explanation: Hydrolysis is a reaction where water acts as a reactant to break a chemical bond. Here, the ${Si}-{Cl}$ bonds are broken by the ${H}_2{O}$ molecule, resulting in the formation of ${Si}-{OH}$ bonds (silanols) and ${HCl}$.
254. When Carbon Dioxide is passed through an aqueous solution of sodium hydroxide (${NaOH}$), the reaction ${CO}_2 + 2{NaOH} \rightarrow {Na}_2{CO}_3 + {H}_2{O}$ occurs. This reaction demonstrates the acidic nature of ${CO}_2$ and is an example of which reaction type?
ⓐ. Decomposition
ⓑ. Condensation
ⓒ. Acid-Base (Neutralization)
ⓓ. Precipitation
Correct Answer: Acid-Base (Neutralization)
Explanation: ${CO}_2$ is an acidic oxide (it forms carbonic acid in water). It reacts with the strong base ${NaOH}$ to form a salt (${Na}_2{CO}_3$) and water, which is the definition of a neutralization reaction.
255. The decomposition of limestone: ${CaCO}_3({s}) \xrightarrow{1000 \, ^{\circ}{C}} {CaO}({s}) + {CO}_2({g})$ is used for the industrial production of lime. This reaction is classified as:
ⓐ. Displacement reaction
ⓑ. Thermal Decomposition
ⓒ. Redox reaction
ⓓ. Polymerization
Correct Answer: Thermal Decomposition
Explanation: Thermal decomposition is a reaction in which a single compound breaks down into two or more simpler substances when heated. This specific reaction is also called calcination.
256. In the Water Gas Shift reaction: ${CO}({g}) + {H}_2{O}({g}) \rightleftharpoons {CO}_2({g}) + {H}_2({g})$, how does the oxidation state of Carbon change?
ⓐ. From $+2$ to $+4$
ⓑ. From $0$ to $+4$
ⓒ. From $+2$ to $0$
ⓓ. Remains $+2$
Correct Answer: From $+2$ to $+4$
Explanation: Carbon Monoxide (${C}^{+2}$) acts as a reducing agent, being oxidized to Carbon Dioxide (${C}^{+4}$). The oxidation state of carbon increases from $+2$ in ${CO}$ to $+4$ in ${CO}_2$.
257. The reaction used to prepare Calcium Carbide (${CaC}_2$) from quicklime and coke: ${CaO} + 3{C} \xrightarrow{2000 \, ^{\circ}{C}} {CaC}_2 + {CO}$ requires extremely high temperatures. This is fundamentally a reaction where ${C}$ acts as a:
ⓐ. Catalyst
ⓑ. Reducing Agent
ⓒ. Oxidizing Agent
ⓓ. Amphoteric reagent
Correct Answer: Reducing Agent
Explanation: Carbon (${C}$) is oxidized to ${CO}$ (oxidation state changes from $0$ to $+2$), while Calcium in ${CaO}$ is reduced. Carbon, therefore, functions as the reducing agent.
258. Carbon Monoxide reacts with heated powdered nickel metal (${Ni}$) to form ${Ni}({CO})_4$ (nickel tetracarbonyl). This specific reaction is classified as a:
ⓐ. Redox reaction (Oxidation state change)
ⓑ. Precipitation reaction
ⓒ. Coordination/Complex formation reaction
ⓓ. Hydrolysis
Correct Answer: Coordination/Complex formation reaction
Explanation: Carbon Monoxide acts as a neutral Lewis base ligand, donating a lone pair of electrons to the nickel atom to form a coordinate covalent bond. This results in the formation of a metal carbonyl complex, ${Ni}({CO})_4$.
259. A fundamental reaction in the synthesis of elemental silicon involves the reduction of silica: ${SiO}_2({s}) + 2{C}({s}) \xrightarrow{high \, heat} {Si}({l}) + 2{CO}({g})$. In this reaction, the ${SiO}_2$ is:
ⓐ. Reduced
ⓑ. Neutralized
ⓒ. Polymerized
ⓓ. Hydrolyzed
Correct Answer: Reduced
Explanation: Silicon in ${SiO}_2$ changes its oxidation state from $+4$ to $0$ in elemental ${Si}$. This gain of electrons signifies that the ${SiO}_2$ is being reduced, while the carbon is oxidized.
260. Which reaction type is used to prepare the monomer ${R}_2{SiCl}_2$ (dialkyldichlorosilane) from elemental silicon and alkyl halide (${RCl}$) in the presence of copper powder as a catalyst (Rochow Process)?
ⓐ. Condensation reaction
ⓑ. Polymerization
ⓒ. Direct synthesis/Nucleophilic substitution
ⓓ. Thermal decomposition
Correct Answer: Direct synthesis/Nucleophilic substitution
Explanation: The industrial preparation of the intermediate chlorosilane monomers involves the direct reaction of elemental silicon with an alkyl halide (like ${CH}_3{Cl}$) at high temperature with a copper catalyst. This reaction is often termed ‘direct synthesis’ and proceeds via nucleophilic substitution/rearrangement mechanisms.
261. Carbon Monoxide (${CO}$) is stable at room temperature but can undergo disproportionation at higher temperatures ($500 \, ^{\circ}{C}$). Which equation correctly represents the products of this disproportionation reaction?
ⓐ. $2{CO} \rightarrow {C} + {CO}_2$
ⓑ. ${CO} + {H}_2{O} \rightarrow {CO}_2 + {H}_2$ (Water Gas Shift)
ⓒ. $2{CO} \rightarrow {C}_2{O}_2$ (Dicarbon dioxide)
ⓓ. $2{CO} + {O}_2 \rightarrow 2{CO}_2$
Correct Answer: $2{CO} \rightarrow {C} + {CO}_2$
Explanation: In a disproportionation reaction, a single species is simultaneously oxidized and reduced. Here, carbon in ${CO}$ (${C}^{+2}$) is oxidized to ${CO}_2$ (${C}^{+4}$) and reduced to elemental carbon (${C}^0$).
262. Why does Silicon tetrachloride (${SiCl}_4$) readily undergo hydrolysis when exposed to moisture, while Carbon tetrachloride (${CCl}_4$) is generally stable towards hydrolysis?
ⓐ. ${Si}-{Cl}$ bond is weaker than the ${C}-{Cl}$ bond.
ⓑ. ${CCl}_4$ is non-polar, preventing reaction with polar ${H}_2{O}$.
ⓒ. Silicon has vacant ${d}$-orbitals available to accommodate the lone pair from the oxygen atom of water.
ⓓ. ${SiCl}_4$ has a smaller size than ${CCl}_4$, allowing easier attack.
Correct Answer: Silicon has vacant ${d}$-orbitals available to accommodate the lone pair from the oxygen atom of water.
Explanation: The key difference lies in the mechanism. The initial step of hydrolysis requires the attacking nucleophile (${H}_2{O}$) to form an intermediate complex. ${Si}$ can expand its coordination shell beyond four by utilizing its vacant $3{d}$ orbitals, which ${C}$ lacks (having only $2{s}$ and $2{p}$ orbitals).
263. The addition of lead (II) chloride (${PbCl}_2$) to an aqueous solution containing a mild oxidizing agent (like ${Cl}_2$ water) results in the formation of lead (IV) chloride (${PbCl}_4$). This difference in stability between the $+2$ and $+4$ oxidation states is best explained by:
ⓐ. The metallic character increasing down the group.
ⓑ. The Inert Pair Effect.
ⓒ. High lattice energy of ${PbCl}_4$.
ⓓ. Relativistic effects on the valence electrons.
Correct Answer: The Inert Pair Effect.
Explanation: For the heavier elements of Group 14 (especially ${Pb}$), the reluctance of the ${ns}^2$ electrons to participate in bonding (the Inert Pair Effect) stabilizes the lower oxidation state (${Pb}^{2+}$) much more than the higher one (${Pb}^{4+}$). This makes ${Pb}^{4+}$ a strong oxidizing agent that is easily reduced to ${Pb}^{2+}$.
264. The formation of ${SiC}$ (Silicon Carbide, Carborundum) from ${SiO}_2$ (sand) and ${C}$ (coke) at $\sim 2000 \, ^{\circ}{C}$ represents which type of high-temperature synthesis reaction?
ⓐ. Dehydration
ⓑ. Fusion
ⓒ. Carbothermal Reduction
ⓓ. Metathesis
Correct Answer: Carbothermal Reduction
Explanation: Carbothermal reduction is a high-temperature industrial process where a metal oxide (here, ${SiO}_2$) is reduced to the element or carbide by elemental carbon (coke). The overall reaction is ${SiO}_2 + 3{C} \xrightarrow{heat} {SiC} + 2{CO}$.
265. The reaction used in the synthesis of silicone polymers, where $-{Si}-{OH}$ groups react to form $-{Si}-{O}-{Si}-$ bonds while eliminating water (${H}_2{O}$), is an example of:
ⓐ. Addition polymerization
ⓑ. Free-radical coupling
ⓒ. Hydrolysis
ⓓ. Condensation reaction
Correct Answer: Condensation reaction
Explanation: A condensation reaction is characterized by the coupling of two molecules to form a larger one, with the simultaneous release of a small molecule, in this case, water.
266. Carbon can be used to reduce almost all metal oxides at high temperatures. However, carbon reduction is ineffective for reducing Aluminum Oxide (${Al}_2{O}_3$) under similar conditions. This is because:
ⓐ. Aluminum has a much higher affinity for oxygen (more negative $\Delta G$ of formation).
ⓑ. Carbon is oxidized to ${CO}_2$ instead of ${CO}$.
ⓒ. ${Al}_2{O}_3$ is a strong acid.
ⓓ. ${Al}_2{O}_3$ is volatile at high temperatures.
Correct Answer: Aluminum has a much higher affinity for oxygen (more negative $\Delta G$ of formation).
Explanation: The thermodynamic stability of the metal oxide is key. The Gibbs free energy of formation ($\Delta G_f$) for ${Al}_2{O}_3$ is much more negative than that of ${CO}$ or ${CO}_2$. This means ${Al}_2{O}_3$ is much more stable than the carbon oxides, making the reduction by carbon thermodynamically unfavorable.
267. When water is added to calcium carbide (${CaC}_2$), the products are calcium hydroxide (${Ca}({OH})_2$) and acetylene gas (${C}_2{H}_2$). This reaction is specifically classified as:
ⓐ. Oxidation
ⓑ. Neutralization
ⓒ. Displacement of ${Ca}$
ⓓ. Hydrolysis of a salt
Correct Answer: Hydrolysis of a salt
Explanation: ${CaC}_2$ is a salt of a strong base (${Ca}({OH})_2$) and a very weak acid (${C}_2{H}_2$). The carbide anion (${C}_2^{2-}$) reacts with water, acting as a strong base, to form the parent acid (${C}_2{H}_2$) and ${OH}^-$.
268. The chemical equation ${SiO}_2 + 4{HF} \rightarrow {SiF}_4 + 2{H}_2{O}$ describes the etching of glass (silica). In this reaction, the role of ${HF}$ is unique because:
ⓐ. It acts as a strong reducing agent.
ⓑ. It forms a volatile compound with ${SiO}_2$.
ⓒ. It is the only common acid that reacts with ${SiO}_2$ due to the high affinity of ${Si}$ for ${F}$.
ⓓ. It acts as a catalyst by lowering the activation energy.
Correct Answer: It is the only common acid that reacts with ${SiO}_2$ due to the high affinity of ${Si}$ for ${F}$.
Explanation: ${SiO}_2$ is highly unreactive toward most acids (${HCl}, {HNO}_3$). The reaction with ${HF}$ occurs because the formation of the ${Si}-{F}$ bond is extremely exothermic, providing the thermodynamic driving force to break the highly stable ${Si}-{O}$ framework.
269. Tin (II) salts (${Sn}^{2+}$) are often used in volumetric analysis because they can easily act as a reducing agent. This is primarily because ${Sn}^{2+}$ can easily be converted to:
ⓐ. ${Sn}^{0}$
ⓑ. ${Sn}^{4+}$
ⓒ. ${SnH}_4$
ⓓ. ${SnO}$
Correct Answer: ${Sn}^{4+}$
Explanation: Tin, being a p-block element, exhibits both the $+2$ and $+4$ oxidation states. ${Sn}^{2+}$ is easily oxidized to the more stable ${Sn}^{4+}$ state (the higher oxidation state is more stable for lighter Group 14 elements), making it an effective reducing agent.
270. When highly purified ${Si}$ is treated with concentrated aqueous ${NaOH}$ solution, the products are sodium silicate (${Na}_2{SiO}_3$) and hydrogen gas (${H}_2$). This reaction classifies ${Si}$ as a substance that is:
ⓐ. A strong Lewis acid
ⓑ. A selective oxidizing agent
ⓒ. Amphoteric
ⓓ. Purely metallic
Correct Answer: Amphoteric
Explanation: Silicon is an amphoteric element. While it is chemically inert toward most acids, it readily reacts with strong bases (${NaOH}$) to release hydrogen gas and form a soluble salt (sodium silicate, ${Na}_2{SiO}_3$).
271. In the Group 14 elements, the dioxide (${MO}_2$) is generally more stable than the monoxide (${MO}$). However, for Tin, the stability of the oxides is reversed at very high temperatures. Which statement accurately describes the thermal stability of tin oxides?
ⓐ. ${SnO}$ is the only stable oxide at all temperatures due to its ionic character.
ⓑ. ${SnO}_2$ (${Sn}^{4+}$) is the more thermodynamically stable oxide at standard temperature, but ${SnO}$ (${Sn}^{2+}$) is favored above $1000 \, ^{\circ}{C}$.
ⓒ. ${SnO}$ (${Sn}^{2+}$) is the more thermodynamically stable oxide at all temperatures due to the ${ns}^2$ electrons participating in bonding.
ⓓ. ${SnO}_2$ decomposes readily into ${Sn}$ and ${O}_2$ without forming ${SnO}$.
Correct Answer: ${SnO}_2$ (${Sn}^{4+}$) is the more thermodynamically stable oxide at standard temperature, but ${SnO}$ (${Sn}^{2+}$) is favored above $1000 \, ^{\circ}{C}$.
Explanation: While $\mathbf{{SnO}_2}$ is the most stable form under normal conditions, the increasing stability of the lower oxidation state (${Sn}^{2+}$) due to the Inert Pair Effect means that at very high temperatures, the $\mathbf{+2}$ state (${SnO}$) becomes the favored product upon reduction or decomposition.
272. Although ${SiO}_2$ is highly unreactive, it is attacked by concentrated hot sodium hydroxide (${NaOH}$). The products of this reaction are:
ⓐ. ${Na}_2{SiO}_3 + {H}_2{O}$
ⓑ. ${Na}_2{Si}_2{O}_5 + {H}_2$
ⓒ. ${Na}_2{SiF}_6 + {H}_2{O}$
ⓓ. ${Na}_4{SiO}_4 + {O}_2$
Correct Answer: ${Na}_2{SiO}_3 + {H}_2{O}$
Explanation: Silicon Dioxide (${SiO}_2$) acts as an acidic oxide. It reacts with the strong base ${NaOH}$ to form a soluble salt, sodium silicate (${Na}_2{SiO}_3$), and water:
$${SiO}_2 + 2{NaOH} \xrightarrow{{heat}} {Na}_2{SiO}_3 + {H}_2{O}$$
273. The classic qualitative test for the presence of ${CO}_2$ gas involves bubbling the gas through limewater (aqueous ${Ca}({OH})_2$). The initial observation that confirms the presence of ${CO}_2$ is:
ⓐ. The solution turns blue due to the formation of ${Ca}({OH})_2$.
ⓑ. The solution turns acidic due to the formation of carbonic acid.
ⓒ. The solution turns milky due to the precipitation of ${CaCO}_3$.
ⓓ. ${O}_2$ gas is released, causing effervescence.
Correct Answer: The solution turns milky due to the precipitation of ${CaCO}_3$.
Explanation: ${CO}_2$ reacts with calcium hydroxide to form insoluble calcium carbonate, which is observed as a white precipitate (milkiness).
$${Ca}({OH})_2({aq}) + {CO}_2({g}) \rightarrow {CaCO}_3({s}) + {H}_2{O}({l})$$
274. The reaction of elemental Silicon (${Si}$) with aqueous ${NaOH}$ produces ${H}_2$ gas, but ${Si}$ is unreactive toward dilute ${HCl}$. This contrasting reactivity implies that ${Si}$ is a substance with which characteristic chemical property?
ⓐ. Electrophilic
ⓑ. Hydrophilic
ⓒ. Tectosilicate
ⓓ. Amphoteric
Correct Answer: Amphoteric
Explanation: ${Si}$ does not react with acids (except ${HF}$) but reacts with strong bases (${NaOH}$). A substance that reacts only with one extreme (like a base) or both (acid and base) is classified as amphoteric or tending toward amphoterism.
275. When Carbon is heated with concentrated nitric acid (${HNO}_3$), the products are ${CO}_2$, ${NO}_2$, and ${H}_2{O}$. In this reaction, the ${HNO}_3$ acts as:
ⓐ. An acidic catalyst
ⓑ. A reducing agent
ⓒ. A strong oxidizing agent
ⓓ. A dehydrating agent
Correct Answer: A strong oxidizing agent
Explanation: Carbon (${C}^0$) is oxidized to ${CO}_2$ (${C}^{+4}$). This means the ${HNO}_3$ must be the reactant undergoing reduction (the oxidizing agent). Nitrogen in ${HNO}_3$ (${N}^{+5}$) is reduced to ${NO}_2$ (${N}^{+4}$).
276. The major source of high-purity Carbon Monoxide (${CO}$) for specific industrial chemical syntheses (like the preparation of metal carbonyls) is through the dehydration of which acid using concentrated sulfuric acid?
ⓐ. Carbonic acid (${H}_2{CO}_3$)
ⓑ. Acetic acid (${CH}_3{COOH}$)
ⓒ. Oxalic acid (${H}_2{C}_2{O}_4$)
ⓓ. Formic acid (${HCOOH}$)
Correct Answer: Formic acid (${HCOOH}$)
Explanation: The reaction is: ${HCOOH} \xrightarrow{{conc.} \, {H}_2{SO}_4} \mathbf{{CO}} + {H}_2{O}$. Concentrated ${H}_2{SO}_4$ acts as a powerful dehydrating agent, selectively removing water from formic acid.
277. Unlike ${CCl}_4$, the hydrolysis of ${SiCl}_4$ proceeds rapidly. If ${GeCl}_4$ (Germanium tetrachloride) were subjected to the same conditions, what would be the expected relative rate of hydrolysis compared to ${SiCl}_4$?
ⓐ. Much slower, due to increased steric hindrance.
ⓑ. Similar or faster, due to the larger size and increasing polarity of the ${Ge}-{Cl}$ bond.
ⓒ. Only occurs at very high temperatures.
ⓓ. The reaction would be explosive due to the instability of ${GeCl}_4$.
Correct Answer: Similar or faster, due to the larger size and increasing polarity of the ${Ge}-{Cl}$ bond.
Explanation: Like ${Si}$, ${Ge}$ has vacant ${d}$-orbitals, allowing ${H}_2{O}$ to attack. As we move down Group 14, the central atom’s size increases, and the electropositivity increases, making the ${M}-{Cl}$ bond more polar and thus more susceptible to nucleophilic attack by water.
Welcome to Class 11 Chemistry MCQs – Chapter 11: The p-Block Elements (Part 3). This is the final section of this chapter containing 77 advanced-level MCQs for your complete revision. The focus here is on anomalous behavior of boron and carbon, catenation, oxidation states, and practical compounds used in metallurgy and electronics.
Go through the questions carefully, mark ❤️ Favourites for revision, and note down key reactions in the Workspace below each question. These final MCQs are perfect for quick exam revision and concept strengthening before your Boards or JEE/NEET exams.
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