Hydrocarbons MCQ Quiz - Objective Question with Answer for Hydrocarbons - Download Free PDF

The correct answer is CₙH₂ₙ.

Key Points

• Alkenes are hydrocarbons that contain a carbon-carbon double bond (C=C).
• The general formula for alkenes is CₙH₂ₙ, where n is the number of carbon atoms.
• Alkenes are unsaturated hydrocarbons because they have fewer hydrogen atoms than alkanes with the same number of carbon atoms.
• Examples of alkenes include ethene (C₂H₄), propene (C₃H₆), and butene (C₄H₈).
• Alkenes undergo addition reactions due to the presence of the double bond, making them more reactive than alkanes.

Additional Information

• Alkanes
  • Alkanes are saturated hydrocarbons with single bonds between carbon atoms.
  • The general formula for alkanes is CₙH₂ₙ₊₂.
• Alkynes
  • Alkynes are unsaturated hydrocarbons with at least one carbon-carbon triple bond (C≡C).
  • The general formula for alkynes is CₙH₂ₙ₋₂.
• Aromatic Hydrocarbons
  • Aromatic hydrocarbons, also known as arenes, contain a conjugated ring of alternating double and single bonds, such as benzene.
  • Benzene (C₆H₆) is the simplest aromatic hydrocarbon.

The correct answer is They are highly stable and inert..

Key Points

• Alkenes are a class of hydrocarbons characterized by the presence of at least one carbon-carbon double bond.
• They are unsaturated hydrocarbons, meaning they contain fewer hydrogen atoms than their alkane counterparts.
• Alkenes can undergo addition reactions, where atoms or groups are added to the carbon atoms involved in the double bond.
• They are not highly stable and inert; in fact, the double bond makes them quite reactive.

Additional Information

• Hydrocarbons: Compounds composed entirely of hydrogen and carbon. Alkenes belong to this category and are specifically unsaturated hydrocarbons.
• Double Bond: A chemical bond where two pairs of electrons are shared between two atoms. In alkenes, this occurs between carbon atoms.
• Addition Reactions: Chemical reactions where atoms are added to a molecule. Alkenes commonly participate in these due to their double bonds.
• Reactivity: Alkenes are more reactive than alkanes due to the presence of the double bond, which is a site for chemical reactions.
• Examples of Alkenes: Ethene (C2H4), Propene (C3H6), and Butene (C4H8) are common examples of alkenes.

The correct option is Alkynes.

Key Points

• The 'sp' hybridization is present in alkynes.
• Alkynes contain triple bonds.
• The C-C bonds overlap to form a sigma bond.
• One 's' and one 'p' orbital of carbon atom overlap and form an 'sp' hybrid orbital in alkynes.
• Thus it shows a linear shape and geometry.

Additional Information Alkanes

• Alkanes contain 'sp³' hybridization.
• It shows a tetrahedral shape and geometry.

Alkenes

• Alkenes contain 'sp2'  hybridization.
• It shows a trigonal planar shape and geometry.

Cycloalkanes

• Cycloalkanes contain single bonds.
• They have 'sp3' hybridization.
• Thus it shows tetrahedral shape and geometry.

The correct answer is Alkyne.

Key Points

• A hydrocarbon in which two carbon atoms are joined by a triple bond is called an Alkyne.
• A hydrocarbon is an organic compound consisting entirely of hydrogen and carbon.

Important Points

• Alkane
  • These are organic compounds that consist entirely of single-bonded carbon and hydrogen atoms and lack any other functional groups.
  • General Formula- C_nH_2n+2
  • They are the principal constituent of gasoline and lubricating oils and are extensively employed in organic chemistry.
•  Alkene
  • These are a class of hydrocarbons unsaturated compounds with at least one carbon-to-carbon double bond.
  • General Formula-C_nH_2n
  • Alkenes are more reactive than alkanes due to the presence of the double bond.
  • They are used in the synthesis of alcohols, plastics, lacquers, detergents, and fuels as starting materials.
• Alkyne
  • These are organic molecules made of the functional group carbon-carbon triple bonds.
  • Chemical Formula-C_nH_2n−2
  • Alkynes are commonly used to artificially ripe fruits.

The correct answer is Methane.

Key Points

• Methane (CH4)
  • It is the simplest hydrocarbon consisting of one carbon atom and four hydrogen atoms and the simplest hydrocarbon, is the most abundant hydrocarbon pollutant.
  • It is a powerful greenhouse gas.
  • Major natural sources of methane include emissions from wetlands, and oceans and from the digestive processes of termites.
  • Methane is more than 25 times as potent as carbon dioxide at trapping heat in the atmosphere.

Additional Information

• Butane is a gaseous component (at room temperature and atmospheric pressure) of the Alkane group having the chemical formula is C4H10.
• It is a colourless, highly flammable, and easily liquefied gas.
• In the abundance of oxygen, it forms Carbon dioxide, but if limited oxygen is available, then it forms Carbon Monoxide.

2C4H10 + 13O2 → 8CO2 + 10H2O                   (oxygen in plenty)

2C4H10 + 9O2 → 8CO + 10H2O                      (oxygen is limited)

• Uses –
  • Gasoline blending
  • Fuel gas
  • Fragrance extraction solvent
  • Feedstock for the manufacture of ethylene and butadiene
  • Ingredient for synthetic rubber
  • Isobutane to enhance the Octane number of gasoline in refineries.
• A propane molecule has three carbon atoms and eight hydrogen bonds and has the formula C3H8. 
• Propane is a colourless, easily liquefied, gaseous hydrocarbon (compound of carbon and hydrogen) and the third member of the paraffin series following methane and ethane.
• Propane is produced as a by-product of two other processes, natural gas processing and petroleum refining.
• It is separated in large quantities from natural gas, light crude oil, and oil-refinery gases and is commercially available as liquefied propane or as a major constituent of liquefied petroleum gas (LPG).
• Uses: 
  • It is used in LPG, also used as biofuel in buses and taxis and it is also the main gas in blowtorches and for hot air balloons.
  • Propane gas has become a popular choice for barbecues and portable stoves because its low boiling point makes it vaporize as soon as it is released from its pressurized container.
• The chemical formula of Ethane is C2H6.
• It is a colourless, odourless gas at normal temperature and pressure.
• It is extracted from natural gas on an industrial scale and is a petrochemical by-product of petroleum refining.
• Michael Faraday first synthesized it in 1834, using the electrolysis of a solution of potassium acetate.

The correct answer is option 3, i.e. C3H8.

• The molecular formula of propane is C3H8.
• Alkanes are acyclic hydrocarbons in which carbon-carbon atoms have a single bond between them, i.e. they are saturated hydrocarbons.
• The general formula for alkanes is C_nH_2n+2, where 'n' is the number of carbon atoms.
• Propane is the third member of the alkane family with 3 carbon atom. If we put the number of carbon and hydrogen atoms present in propane in the above-mentioned formula, we will find that it holds true.
• CH₄ is Methane, the first member of the alkane family.
• C₄H₁₀ is Butane, the fourth in the line of alkanes.
• C₂H₆ is Ethane, the second member of the alkane family.
• The lower alkanes from C₁ to C₄ are gases, from C₅ to C₁₆ are liquids and beyond that are solids.

The correct answer is Alkene.

• A hydrocarbon in which two carbon atoms are joined by a double bond is called an Alkene.
• A hydrocarbon is an organic compound consisting entirely of hydrogen and carbon.

Important Points

• Alkane
  • These are organic compounds that consist entirely of single-bonded carbon and hydrogen atoms and lack any other functional groups.
  • General Formula- C_nH_2n+2
  • They are the principal constituent of gasoline and lubricating oils and are extensively employed in organic chemistry.
•  Alkene
  • These are a class of hydrocarbons unsaturated compounds with at least one carbon-to-carbon double bond.
  • General Formula-C_nH_2n
  • Alkenes are more reactive than alkanes due to the presence of the double bond.
  • They are used in the synthesis of alcohols, plastics, lacquers, detergents, and fuels as starting materials.
• Alkyne
  • These are organic molecules made of the functional group carbon-carbon triple bonds.
  • Chemical Formula-C_nH_2n−2
  • Alkynes are commonly used to artificially ripe fruits.

Explanation:

• Liquefied petroleum gas (LPG) mainly consists of propane and butane.
• It is odorless that's why Ethyl Mercaptan is added to it so there may be a smell if LPG leaks from its storage container.

The correct answer is Option 4, i.e Carbon.

• Carbon can form a large number of chemical compounds, at least 10 million in number.
• It also has the highest sublimation point among all the elements.
• It is the 15th most abundant element on Earth’s Crust.
• Graphite, Diamond, Fullerenes are some of the allotropes of Carbon.

Explanation:

• Liquefied petroleum gas (LPG) mainly consists of propane and butane.
• Ethyl Mercaptan (CH3CH2SH) is an organic sulphur compound. It has a distinct smell that is used to detect the leakage of otherwise odourless LPG cooking gas.

The correct answer is 5.

• C₆​H_14​ is hexane. It has 5 structural isomers like n-hexane, 2-methyl pentane, 3-methyl pentane, 2,2-dimethyl butane, 2,3-dimethyl butane.

Important Points

• Compounds with different physical properties were found to have the same elemental composition and molecular weight. Such compounds were called isomers.
• The below table shows the number of constitutional isomers for each of the acyclic alkanes C_nH_2n+2, where n=1-10.
• If the number of carbon atoms increases, the number of possible constitutional isomers increases rapidly.

Option 2 is the correct answer: Bitumen is used for the construction of roads.

• Bitumen is a mixture of 500-700 organic compounds (hydrocarbons) in which also contain small proportions of Nitrogen, Sulphur and Oxygen.
• It is a byproduct obtained during the distillation of petroleum.
• It is used in the construction of roads mainly as a binder, it binds the construction material together and provides strength to roads.
• The melting point of bitumen is high enough that it does not get melted in harsh weather conditions and much low that it can be melted at the construction site.
• Using bitumen instead of Tar decreases the cost of construction.

Coke:

• It is a fuel having high carbon content formed by heating the bituminous coal in the absence of air.
• Uses:
  • Used in the Blast Furnace to reduce ferric oxide to Iron.
  • Used to prepare Syngas (carbon monoxide and hydrogen) and Producer gas (carbon monoxide + hydrogen + nitrogen). 

Paraffin:

• Paraffin is a hydrocarbon obtained from Petroleum during its dewaxing process.
• Paraffin wax is used as fuel in candles and gives out fumes when burnt.
• Paraffin oil is used as a pediatric laxative and also as a fuel (kerosene).

Naphthalene:

• Naphthalene is an aromatic organic compound with the Chemical formula C₁₀H₈.
• The structure of Naphthalene is like two benzene rings fused together.
• It is a major component of Coal tar.

The correct answer is Hydrogen.

Explanation:

• Combustion is a chemical reaction that produces heat when a substance reacts with oxygen.
• Combustible refers to a substance that can be burned. It is also known as a fuel. The fuel can be either solid, liquid, or gas.
• The amount of heat energy produced by the complete combustion of one kilogram of fuel is referred to as its calorific value.
• The calorific value of a fuel is expressed in kilojoule per kilogram (kJ/kg).
• Hydrogen has the highest caloric value and is highly combustible. Minor contact with a burning agent can result in a blast.

Calorific Values of Fuels

Hence, Hydrogen has highest calorific value.

The correct answer is Hexene.

Key Points

• In chemistry, aromaticity is a property of cyclic, planar structures with a ring of resonance bonds that gives increased stability compared to other geometric or connective arrangements with the same set of atoms.
• These molecules are very stable and do not break apart quickly to react with other substances.
• 1-Hexene is an organic compound with the formula C₆H₁₂. It is not an aromatic compound.
• It is an alkene that is classified in industry as higher olefin and an alpha-olefin, the latter term meaning that the double bond is located at the alpha position, endowing the compound with higher reactivity and thus useful chemical properties. 
  • Formula- C₆H₁₂
  • Boiling point- 63.85 °C
  • Density- 673 kg/m³
• Benzene is an aromatic compound, as the C-C bonds formed in the ring are not exactly single or double, rather they are of intermediate length.
  • Aromatic compounds are divided into two categories: benzenoids (one containing benzene ring) and non-benzenoids (those not containing benzene ring), provided they follow the Huckel rule.
• Naphthalene is an organic compound with the formula C₁₀H₈. It is the simplest polycyclic aromatic hydrocarbon and is a white crystalline solid with a characteristic odor that is detectable at concentrations as low as 0.08 ppm by mass. 
  • Formula- C₁₀H₈
  • Melting point- 80.26 °C
  • Boiling point- 218 °C
  • Density- 1.14 g/cm³
  • Classification- Hydrocarbon, Polycyclic aromatic hydrocarbon, Organic compound
• Anthracene is a solid polycyclic aromatic hydrocarbon of formula C₁₄H₁₀, it consists of 3 fused benzene rings.
  • It is a component of coal tar. It is used in the production of the red dye alizarin and other dyes.
  • Anthracene is colourless but exhibits a blue fluorescence under ultraviolet radiation.
    • Formula- C₁₄H₁₀
    • Boiling point- 340 °C
    • Density- 1.25 g/cm³
    • Classifications- Polycyclic aromatic hydrocarbon

The correct answer is option 4 i.e C4H6

• Butyne is a member of the alkyne series which has a general formula C_nH_2n-2.
• They are unsaturated hydrocarbons having a triple bond between two carbon atoms in them.
• Out of the three bonds, two are pi and one is sigma.

Characteristics of Butyne - 

• It is a highly inflammable gas. 
• Its chemical formula is C₄H₆, which has 4 carbon and one alkyne. 
• The two isomers of Butyne are - 1-Butyne and 2-Butyne.