Daily Olympiad: Science - Carbon Compounds [20260709]

Solution

Correct: D

Carbon's unique ability to form bonds with other carbon atoms, leading to long chains, branched chains, and rings, is called catenation. Its tetravalency (ability to form four stable covalent bonds) allows these chains/rings to be stable and also allows carbon to bond with various other elements, contributing significantly to the vast number of carbon compounds. Both properties are crucial for the diversity of organic compounds.

Solution

Correct: B

Alkenes are unsaturated hydrocarbons containing at least one carbon-carbon double bond. Their general molecular formula is CnH2n, where 'n' is the number of carbon atoms. CnH2n+2 is for alkanes, CnH2n-2 is for alkynes, and CnH2n+1OH is for alcohols.

Solution

Correct: B

Butane (C4H10) has two structural isomers: 1. n-butane (straight chain: CH3-CH2-CH2-CH3) and 2. Isobutane (2-methylpropane, a branched chain: CH3-CH(CH3)-CH3). These two compounds have the same molecular formula but different structural arrangements of atoms.

Solution

Correct: C

A) -OH is the hydroxyl group, characteristic of alcohols. B) -COOH is the carboxyl group, characteristic of carboxylic acids. C) -CHO is the formyl group, characteristic of aldehydes, where the carbon atom is double-bonded to oxygen and single-bonded to hydrogen. D) -CO- is the carbonyl group, which, when located between two alkyl groups, characterizes ketones.

Solution

Correct: D

A homologous series is a series of organic compounds in which all members have the same functional group and similar chemical properties (not identical, but similar due to the same functional group). They differ by a -CH2 unit, have the same general formula, and show a gradual change in physical properties as molecular mass increases. Statement D is incorrect because having different functional groups would mean they are not part of the same homologous series and would lead to different chemical properties.

Solution

Correct: B

Unsaturated hydrocarbons (alkenes and alkynes) contain carbon-carbon double or triple bonds. These bonds are reactive and can 'open up' to accommodate additional atoms or groups, forming a saturated compound. This type of reaction is called an addition reaction. Saturated hydrocarbons (alkanes) primarily undergo substitution reactions. Combustion is a general reaction for most organic compounds, and esterification is a specific reaction between an alcohol and a carboxylic acid.

Solution

Correct: B

This is an esterification reaction. Ethanol (an alcohol) reacts with ethanoic acid (a carboxylic acid) in the presence of an acid catalyst (concentrated H2SO4) to form an ester and water. The ester formed is ethyl ethanoate (CH3COOCH2CH3), which has a characteristic fruity smell.

Solution

Correct: C

Saponification is the process of making soap. It involves the alkaline hydrolysis of an ester (typically a triglyceride, which is a fat or oil) to produce a soap (a salt of a long-chain fatty acid) and glycerol. Esterification is the formation of an ester, hydrogenation is adding hydrogen to unsaturated compounds, and polymerization is forming large molecules from monomers.

Solution

Correct: D

A) Ethanoic acid (acetic acid) is a weak acid, not a strong one. B) It reacts with sodium carbonate to produce carbon dioxide gas (not hydrogen gas), a common test for acids (2CH3COOH + Na2CO3 → 2CH3COONa + H2O + CO2). C) It has a characteristic vinegar smell, not similar to chloroform. D) Dilute ethanoic acid (5-8% solution) is known as vinegar and is widely used as a food preservative.

Solution

Correct: C

Denatured alcohol is ethanol that has been made unfit for human consumption by adding small amounts of poisonous substances (like methanol, pyridine, or other toxic chemicals) or foul-smelling/tasting agents. This is done to avoid the heavy excise duty levied on alcoholic beverages, allowing it to be used for industrial purposes at a lower cost.

Solution

Correct: B

Hard water contains dissolved salts of calcium and magnesium. Soaps (sodium or potassium salts of long-chain fatty acids) react with these metal ions to form insoluble precipitates called scum, which reduces their cleansing action. Detergents (sodium salts of long-chain benzene sulphonic acids or alkyl hydrogen sulphates) do not form insoluble precipitates with calcium and magnesium ions and thus work effectively in hard water.

Solution

Correct: C

Unsaturated compounds contain carbon-carbon double or triple bonds. A) Propane (C3H8) is an alkane, saturated. B) Butane (C4H10) is an alkane, saturated. C) Ethene (C2H4) is an alkene, containing a carbon-carbon double bond, hence unsaturated. D) Methane (CH4) is an alkane, saturated.

Solution

Correct: B

Alkaline potassium permanganate (KMnO4) is a strong oxidizing agent. It oxidizes alcohols to carboxylic acids. Ethanol (CH3CH2OH) upon oxidation first forms ethanal (CH3CHO) and then further oxidizes to ethanoic acid (CH3COOH). Since alkaline KMnO4 is a strong oxidizing agent, the reaction proceeds to the carboxylic acid stage.

Solution

Correct: B

The compound CH3-CO-CH3 has three carbon atoms and a ketone functional group (-CO-) in the middle. The IUPAC naming conventions: 'Prop-' indicates three carbon atoms, '-an-' indicates single bonds between carbon atoms in the main chain, and '-one' is the suffix for a ketone. Thus, its IUPAC name is Propanone (common name: acetone). Propanal has an aldehyde group, Propanoic acid has a carboxylic acid group, and Ethanal has two carbon atoms.

Solution

Correct: C

Let's check the molecular formulas for each option: A) Methanol is CH3OH, which is C1H4O. B) Ethanoic acid is CH3COOH, which is C2H4O2. C) Ethanol is CH3CH2OH, which is C2H6O. D) Diethyl ether is CH3CH2OCH2CH3, which is C4H10O. Therefore, ethanol is the correct compound. (Note: Dimethyl ether also has the formula C2H6O, making it an isomer of ethanol, but ethanol is typically the primary example taught at this level among the given choices.)

Solution

Correct: C

A) Diamond is an excellent electrical insulator and has a rigid 3D tetrahedral structure. B) Fullerene (e.g., C60) has a spherical cage-like structure and is a semiconductor. C) Graphite is a good conductor of electricity due to the presence of delocalized electrons in its layered hexagonal structure. The layers can slide over each other, making it soft and a good lubricant. D) Charcoal is an amorphous form of carbon and is a poor conductor of electricity.

Solution

Correct: B

Ethane (C2H6) has the structure CH3-CH3. Each carbon atom forms 3 covalent bonds with hydrogen atoms and 1 covalent bond with the other carbon atom. So, there are 3 C-H bonds on the first carbon, 3 C-H bonds on the second carbon, and 1 C-C bond between the two carbons. Total covalent bonds = 6 (C-H) + 1 (C-C) = 7 covalent bonds.

Solution

Correct: A

The general formula CnH2n can represent either an alkene (with one double bond) or a cycloalkane (a cyclic saturated hydrocarbon). A) Cyclohexane is C6H12, which fits the CnH2n formula (n=6). B) Benzene is C6H6, which does not fit CnH2n. C) Ethane is C2H6, which is CnH2n+2 (an alkane). D) Propyne is C3H4, which is CnH2n-2 (an alkyne). Therefore, Cyclohexane is the correct option.

Solution

Correct: C

Polythene (or polyethylene) is a polymer formed by the polymerization of ethene (ethylene) monomers. The double bond in ethene breaks, and many ethene units join together to form a long chain polymer. Methane and Ethane are saturated hydrocarbons and do not easily polymerize to form polythene. Propene is the monomer for polypropylene.

Solution

Correct: A

A) Alkanes are saturated hydrocarbons containing only strong C-C and C-H single bonds. These bonds are nonpolar and stable, making alkanes relatively unreactive. They primarily undergo substitution reactions under harsh conditions (e.g., UV light for halogenation) and combustion. B) Alkenes contain a C=C double bond, which is a site of high electron density and is reactive towards addition reactions. C) Alkynes contain a C≡C triple bond, which is even more reactive than double bonds towards addition reactions. D) Aromatic hydrocarbons (like benzene) have a stable delocalized pi-electron system, which makes them less prone to addition reactions than typical alkenes, but they readily undergo electrophilic substitution reactions. Among the options, alkanes are generally considered the least reactive.