Daily Olympiad: Science - Organic Chemistry [20260717]

Solution

Correct: B

The longest carbon chain contains 4 carbon atoms, making it a derivative of butane. There is a methyl group (CH3) attached to the second carbon atom when numbering from the end closest to the branch. Thus, the IUPAC name is 2-Methylbutane.

Solution

Correct: C

Saturated hydrocarbons (alkanes) contain only carbon-carbon single bonds. Due to the saturation, they are relatively unreactive and primarily undergo substitution reactions, where one atom or group is replaced by another. Addition reactions are characteristic of unsaturated hydrocarbons.

Solution

Correct: B

Alkenes are unsaturated hydrocarbons containing one carbon-carbon double bond. Their general formula is CnH2n, where 'n' represents the number of carbon atoms.

Solution

Correct: C

Catenation is the unique property of carbon atoms to link with other carbon atoms through covalent bonds to form long chains, branched chains, or cyclic structures. This property is responsible for the vast number of organic compounds.

Solution

Correct: D

Ethanol is an alcohol. The characteristic functional group of alcohols is the hydroxyl group (-OH) attached to an alkyl group.

Solution

Correct: C

Dehydration is a type of elimination reaction where a small molecule (in this case, water) is removed from a larger molecule. From ethanol (CH3CH2OH), H2O is eliminated to form ethene (CH2=CH2).

Solution

Correct: B

Ethene is an unsaturated hydrocarbon (alkene) and will decolorize reddish-brown bromine water due to an addition reaction. Ethane is a saturated hydrocarbon (alkane) and will not react with bromine water under normal conditions, so it will not decolorize it. This is a common test for unsaturation.

Solution

Correct: C

Complete combustion of any hydrocarbon in the presence of sufficient oxygen always produces carbon dioxide (CO2) and water (H2O). For example, CH4 + 2O2 → CO2 + 2H2O.

Solution

Correct: B

For C4H10, two structural isomers are possible: n-butane (a straight chain alkane) and 2-methylpropane (also known as isobutane, a branched-chain alkane).

Solution

Correct: C

Ammoniacal cuprous chloride solution is a test for terminal alkynes (alkynes with a triple bond at the end of the chain, having an acidic hydrogen). Ethyne (acetylene) is a terminal alkyne and will form a red precipitate of cuprous acetylide. Other options are an alkane, an alkene, and another alkane, none of which react with this reagent.

Solution

Correct: B

This is an esterification reaction. Ethanoic acid (a carboxylic acid) reacts with ethanol (an alcohol) in the presence of concentrated H2SO4 (as a dehydrating agent and catalyst) to form an ester, ethyl ethanoate, and water. CH3COOH + CH3CH2OH → CH3COOCH2CH3 + H2O.

Solution

Correct: D

CH3COOH is a carboxylic acid with two carbon atoms. The prefix 'eth-' indicates two carbon atoms, and the '-oic acid' suffix indicates a carboxylic acid. Thus, its IUPAC name is Ethanoic acid (common name: Acetic acid).

Solution

Correct: C

Polyethylene is an addition polymer. Its monomer unit is ethene (ethylene). Many ethene molecules (monomers) link together to form the long polymer chain of polyethylene.

Solution

Correct: D

Isomerism requires a sufficient number of carbon atoms to allow for different arrangements. Methane, ethane, and propane have only one possible structural arrangement. Butane (C4H10) is the simplest alkane that exhibits structural isomerism (n-butane and 2-methylpropane).

Solution

Correct: D

The unique combination of carbon's tetravalency (ability to form four bonds) and its strong tendency for catenation (forming long chains, branches, and rings with other carbon atoms) allows for an immense variety of stable carbon compounds, leading to millions of known organic compounds.

Solution

Correct: B

In ethene (CH2=CH2), each carbon atom forms one double bond and two single bonds. To accommodate this, each carbon atom undergoes sp2 hybridization, resulting in a trigonal planar geometry around each carbon.

Solution

Correct: C

Alkanes are saturated hydrocarbons and primarily undergo substitution reactions. In the presence of UV light, chlorine atoms substitute hydrogen atoms on the alkane, forming alkyl halides and hydrogen chloride. For example, CH4 + Cl2 → CH3Cl + HCl.

Solution

Correct: B

HCOOH is a carboxylic acid with one carbon atom. The prefix 'meth-' indicates one carbon atom, and the '-oic acid' suffix indicates a carboxylic acid. Thus, its IUPAC name is Methanoic acid (common name: Formic acid).

Solution

Correct: C

The conversion of an alkene (containing a C=C double bond) to an alkane (containing only C-C single bonds) requires the addition of hydrogen across the double bond. This process is called hydrogenation, which is a type of addition reaction, usually carried out in the presence of a catalyst like Ni, Pt, or Pd.

Solution

Correct: B

In a homologous series, successive members differ by a -CH2 group (e.g., methane CH4, ethane C2H6). They have the same general formula, similar chemical properties, and a gradual change in physical properties.