Free Chemistry of Hydrocarbons MCQs with Answers

• A. their carbon to hydrogen bonds are strong and almost non polar, offering nothing for a nucleophile or electrophile to attack
• B. they contain a double bond
• C. they are ionic compounds
• D. they have very high molar masses

Explanation: Carbon and hydrogen have similar electronegativities, so the bonds carry almost no dipole and there is no region of high or low electron…

• A. sp
• B. sp2
• C. sp3
• D. unhybridised p

Explanation: Four sigma bonds require four equivalent orbitals, so one s and three p orbitals mix to give four sp3 hybrids pointing to the corners of a…

• A. nucleophilic substitution
• B. electrophilic addition
• C. free radical substitution
• D. elimination

Explanation: Ultraviolet light splits the chlorine molecule homolytically into two radicals, which then abstract hydrogen from methane and set up a…

• A. the reaction of a chlorine radical with methane
• B. the combination of two methyl radicals
• C. the reaction of a methyl radical with chlorine
• D. the homolytic splitting of a chlorine molecule into two chlorine radicals by ultraviolet light

Explanation: Initiation is the step that creates radicals where there were none, and only the chlorine to chlorine bond is weak enough to be broken by…

• A. Free radical substitution
• B. Electrophilic addition
• C. Nucleophilic substitution
• D. Electrophilic substitution

Explanation: The exposed pi electrons of the double bond attract electrophiles, which add across the bond and convert an unsaturated compound into a…

• A. sodium metal
• B. silver nitrate solution
• C. bromine water, which is decolourised by the alkene
• D. limewater

Explanation: The orange colour of bromine water disappears as bromine adds across the double bond to form a colourless dibromo compound, and an alkane…

• A. 1-bromopropane
• B. 2-bromopropane
• C. 1,2-dibromopropane
• D. propan-2-ol

Explanation: The hydrogen adds to the carbon that already carries more hydrogens, so the bromine ends up on the middle carbon.

• A. sp3 and 109.5 degrees
• B. sp and 180 degrees
• C. sp2 and 120 degrees
• D. sp2 and 109.5 degrees

Explanation: Each carbon forms three sigma bonds using sp2 hybrids arranged in a plane at 120 degrees, and the remaining unhybridised p orbitals…

• A. one sigma and two pi bonds between the carbon atoms, with sp hybridisation
• B. two sigma bonds between the carbon atoms
• C. only sigma bonds
• D. three pi bonds between the carbon atoms

Explanation: A triple bond is always one sigma bond plus two pi bonds, formed from two unhybridised p orbitals on each sp hybridised carbon, and the…

• A. calcium carbonate
• B. calcium oxide
• C. calcium hydroxide
• D. calcium carbide

Explanation: Calcium carbide reacts vigorously with water to give ethyne and calcium hydroxide, which was once used in carbide lamps and is still the…

• A. the triple bond adds silver
• B. the hydrogen attached to the triply bonded carbon is weakly acidic and is replaced by silver
• C. silver catalyses polymerisation
• D. alkynes are strong bases

Explanation: The sp hybridised carbon holds its bonding electrons closer, so the attached hydrogen is slightly acidic and can be replaced by a metal to…

• A. the molecular formula C6H6
• B. the ring shape of the molecule
• C. why benzene resists addition reactions and has all its carbon to carbon bonds of equal length
• D. why benzene contains only carbon and hydrogen

Explanation: Alternating single and double bonds would predict two different bond lengths and the ready addition reactions of an alkene, but experiment…

• A. preserves the stable delocalised pi system
• B. produces a smaller molecule
• C. requires no catalyst
• D. is always exothermic

Explanation: Addition would destroy the aromatic sextet and lose the large resonance stabilisation, whereas replacing a hydrogen leaves the delocalised…

• A. dilute nitric acid alone at room temperature
• B. a mixture of concentrated nitric and concentrated sulphuric acids at about 50 to 60 degrees Celsius
• C. sodium nitrate solution
• D. nitrogen dioxide gas in sunlight

Explanation: Sulphuric acid protonates nitric acid so that it loses water and generates the nitronium ion, which is the actual electrophile attacking…

• A. CnH2n
• B. CnH2n-2
• C. CnH2n+2
• D. CnH2n+1

Explanation: Every carbon in a saturated open chain carries the maximum hydrogen, giving two per carbon plus two extra for the ends of the chain, so…

• A. the covalent bonds within the molecules become stronger
• B. the molecules become more polar
• C. hydrogen bonding develops between longer chains
• D. the larger surface area increases the dispersion forces between molecules

Explanation: Longer chains touch each other over a greater area, so the temporary induced dipole attractions between molecules add up to more, and more…

• A. produce shorter, more useful alkanes and alkenes for fuel and plastics
• B. remove sulphur from crude oil
• C. convert alkenes into alkanes
• D. increase the molar mass of the products

Explanation: Fractional distillation yields more of the heavy fractions than the market wants and too little petrol, so cracking breaks the long chains…

• A. ethane
• B. ethanoic acid
• C. ethanol
• D. ethanal

Explanation: Ethene adds sulphuric acid to give ethyl hydrogen sulphate, and hydrolysing that with water releases ethanol and regenerates the acid…

• A. dehydration
• B. hydrogenation
• C. hydrolysis
• D. halogenation

Explanation: Hydrogen adds across the double bond to give the corresponding alkane, and this is the process used to convert liquid vegetable oils into…

• A. has a pleasant smell
• B. contains only carbon and hydrogen
• C. reacts readily by addition
• D. is planar, cyclic and has a delocalised system of six pi electrons obeying Huckel's rule

Explanation: Aromaticity in the modern sense requires a planar cyclic conjugated system containing 4n plus 2 pi electrons, which for benzene means six…