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XI CHEMISTRY NEW CHAPTER-09: HYDROCARBONS _ A&R TEST ITEMS
XI CHEMISTRY NEW CHAPTER-09: HYDROCARBONS _ A&R TEST ITEMS
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Spread the Happiness. Assertion and Reason Statements Feedback: 9008271516XI_CHEMISTRY_NEW_CHAPTER-09: HYDROCARBONS _ A&R TEST ITEMS
# Correct Assertion Correct Reason
9.1 Classification
1 Hydrocarbons are energy sources. Combustion reactions release usable energy from hydrocarbons.
"Hydrocarbon" refers to hydrogen and carbon By definition, hydrocarbons contain only hydrogen and carbon
2
compounds only. atoms.
Fractional distillation separates petroleum fuels. Different boiling points of fuel components allow for separation
3
during fractional distillation.
Destructive distillation of coal yields coal gas. High-temperature breakdown (decomposition) of coal molecules
4
produces coal gas.
Compression yields CNG from natural gas. Increased pressure through compression makes natural gas more
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manageable for storage and transportation.
Hydrocarbon type (saturated vs. unsaturated) The presence of double or triple bonds in unsaturated
6 impacts combustion pollution. hydrocarbons influences completeness of combustion, affecting
pollutant levels.
Hydrocarbons are versatile starting materials. Unique carbon structures of hydrocarbons enable their
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modification to create various complex molecules.
9.2 ALKANES; 9.2.1 Nomenclature and Isomerism; 9.2.2 Preparation
Alkanes are saturated hydrocarbons. Alkanes contain only single C-C bonds and have the maximum
8 number of hydrogen atoms bonded to each carbon, lacking the π-
bonds of alkenes & alkynes.
Methane (CH4) is the first alkane. The general formula (CnH2n+2) predicts CH4 for n = 1, reflecting its
9
structure with one carbon and four hydrogens.
CnH2n+2 is the general formula for alkanes. This formula accurately predicts the hydrogen count for alkanes to
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satisfy carbon valences with single bonds.
Alkanes exhibit tetrahedral geometry. Sp3 hybridization of carbon orbitals promotes a tetrahedral
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arrangement for efficient bond overlap.
C-C and C-H bond lengths differ in alkanes. Sp3 hybridization leads to slightly longer C-C bonds (154 pm) due to
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larger orbital size compared to C-H bonds (112 pm).
Sp3 orbitals form strong σ bonds between C-C and C- Head-on overlap of sp3 orbitals from carbon and 1s orbitals of
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H. hydrogen enables strong sigma bond formation.
Higher alkanes (˃ 3 C atoms) can have isomers. Branching in carbon chains creates various spatial arrangements
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(isomers) for the same molecular formula.
Structural isomers have the same formula but differ Isomers arise due to variations in the order of atoms or chain
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in atomic arrangement. connections despite having the same total number of atoms.
Alkanes are relatively unreactive under normal Strong and stable σ bonds from sp3 hybridization and the absence
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conditions. of functional groups make alkanes less reactive.
Carbon classification (primary, etc.) is based on This classification reflects the bonding environment of each carbon
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attached carbons. atom (number of carbon neighbors).
Alkyl groups (CnH2n+1) are derived from alkanes. Removing one hydrogen from an alkane yields an alkyl group with a
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general formula for forming new bonds.
IUPAC nomenclature is used for clear alkane naming. This systematic approach ensures unambiguous identification of
19 alkane structures based on chain length, branching, and substituent
locations.
Petroleum and natural gas are primary alkane These fossil fuels contain abundant long-chain hydrocarbon
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sources. molecules, with alkanes as a major constituent.
Hydrogenation converts unsaturated hydrocarbons Addition of hydrogen across double or triple bonds in unsaturated
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to alkanes. molecules (alkenes/alkynes) forms saturated alkanes.
Alkanes can be prepared from various methods. Several methods exist for alkane synthesis, including reduction of
22 alkyl halides, Wurtz reaction, decarboxylation, and Kolbe's
electrolytic method.
Alkanes can have linear or branched chains. The carbon skeleton of alkanes can be linear (straight chain) or
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branched.
Carbon classification defines bonding environment. Primary (1°), secondary (2°), tertiary (3°), and quaternary (4°)
24 classifications distinguish carbon atoms based on the number of
attached carbon neighbors (1, 2, 3, or 4 respectively).
Longest carbon chain is used for IUPAC naming. The longest continuous carbon chain is chosen as the base for
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alkane naming in the IUPAC system.
Substituent locations and names are incorporated in IUPAC nomenclature includes the location and identity of any
26
IUPAC nomenclature. substituent groups present on the alkane chain.
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, Spread the Happiness. Assertion and Reason Statements Feedback: 9008271516
XI_CHEMISTRY_NEW_CHAPTER-09: HYDROCARBONS _ A&R TEST ITEMS
# Correct Assertion Correct Reason
Structure can be determined from a molecule's The IUPAC name provides a systematic blueprint for constructing
27
IUPAC name. the molecule's structure.
9.2.3 Properties; 9.2.4 Conformations (of Alkanes)
Alkanes are non-polar molecules. Covalent C-C and C-H bonds with minimal electronegativity
28 difference result in symmetrical electron distribution and minimal
polarity.
Weak van der Waals forces exist between alkane Non-polar nature of alkanes leads to weak attractive forces
29
molecules. between molecules.
Alkanes are insoluble in water. Non-polar alkanes are not attracted to polar water molecules and
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cannot form hydrogen bonds.
Greasy substances, like those used in dry cleaning, "Like dissolves like" - non-polar substances are attracted to other
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are non-polar and hydrophobic. non-polar substances and repel polar water molecules.
Boiling points of alkanes increase with increasing Stronger intermolecular van der Waals forces exist between larger
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molecular mass. alkane molecules.
Branched-chain alkanes have lower boiling points Weaker intermolecular forces are present in branched-chain
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than straight-chain alkanes. alkanes due to their less compact shapes.
Alkanes are generally unreactive towards acids, Strong and stable σ-bonds due to sp3 hybridization and the absence
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bases, oxidizing, and reducing agents. of functional groups make them inert.
Combustion of alkanes yields carbon dioxide and Alkanes react completely with oxygen, breaking C-C and C-H bonds
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water with the release of heat. and forming CO2 and H2O molecules with energy release.
Incomplete combustion of alkanes results in the Insufficient oxygen during alkane combustion limits complete
36
formation of carbon black. oxidation, forming carbon particles (soot or carbon black).
Alkanes can undergo isomerization to form branched- Specific catalysts promote rearrangement of carbon skeletons in
37 chain alkanes in the presence of specific catalysts. alkanes, leading to branched-chain isomers.
Aromatization of higher alkanes at high temperature Extreme conditions break and rearrange carbon-carbon bonds in
38 and pressure yields benzene and its derivatives. alkanes to form a stable aromatic ring structure like benzene.
Methane reacts with steam in the presence of a At high temperatures, steam can react with methane in the
39 nickel catalyst to produce carbon monoxide and presence of a nickel catalyst to form CO and H2 molecules.
hydrogen.
Pyrolysis of higher alkanes at high temperatures When subjected to high temperatures without oxygen, higher
40 leads to decomposition into smaller alkanes and alkanes break down into smaller molecules, including shorter
alkenes. alkanes and alkenes with double carbon bonds.
Ethane molecules exist in various conformations due The single carbon-carbon bond in ethane allows free rotation,
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to rotation around the C-C single bond. resulting in different spatial arrangements of the atoms.
Staggered conformation of ethane is more stable The eclipsed conformation experiences torsional strain due to
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than the eclipsed conformation. repulsion between electron clouds of adjacent hydrogen atoms.
Rotation around the C-C bond in ethane is almost The energy barrier for rotation around the C-C bond in ethane is
43 free for practical purposes. small enough to be overcome by thermal energy at room
temperature.
9.3 Alkenes; 9.3.1 Structure of Double Bond; 9.3.2 Nomenclature; 9.3.3 Isomerism; 9.3.4 Preparation; 9.3.5 Properties
Alkenes: unsaturated hydrocarbons with at least one Double bond limits hydrogen attachment, creating unsaturation.
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double bond.
Alkene general formula (CnH2n) reflects double bond. Formula accounts for fewer hydrogens due to the double bond.
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"Olefins" term reflects alkene oil-forming properties. Historical link between double bond and oily liquids.
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Alkene double bond: one strong sigma (σ) and one Unique bonding influences reactivity due to the weaker pi bond.
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weaker pi (π) bond.
IUPAC alkene naming: longest chain with double Systematic naming based on structure and double bond position.
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bond, "-ane" to "-ene".
Alkenes exhibit both structural and geometrical Different arrangements (structural) and spatial configurations
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isomerism. (geometrical) due to restricted rotation.
Alkene preparation methods strategically create Dehydration, dehydrohalogenation, and other methods target
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double bonds. double bond formation.
Pi bond in alkenes makes them susceptible to Electron-rich pi bond attracts electron-deficient electrophiles for
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electrophiles. addition reactions.
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