Critical Thinking Questions: Organic Chemistry - Hydrocarbons

Type I

Q1: During an experiment, a student adds sodium metal to a compound known to contain only carbon, hydrogen, and oxygen. The reaction produces a colourless gas that ignites with a pop sound. What functional group does the original compound most likely contain?
(a) Aldehyde
(b) Carboxylic acid
(c) Ether
(d) Ketone

Q2: A hydrocarbon 'Y' is found to decolourise bromine water, indicating the presence of a carbon-carbon double bond. What is the general formula for the simplest type of Y?
(a) C₆H₁₂O₂
(b) C₆H₁₂O₂
(c) C₆H₁₂O₂
(d) C₆H₁₂O₂

Q3: During a lab experiment, ethane reacts with chlorine gas in diffused sunlight to produce a series of chlorinated hydrocarbons. Which of the following products is NOT expected to be formed during this reaction?
(a) C₂H₃Cl (chloroethane)
(b) C₂H₄Cl₂ (dichloroethane)
(c) C₂H₃Cl₃ (trichloroethane)
(d) C₂H₂Cl₄ (tetrachloroethane)

Q4: An organic compound is treated with aqueous potassium hydroxide and ethanol under hot conditions. The reaction produces potassium chloride and water as by-products. What kind of reaction is this, and what is the organic reactant?
(a) Substitution reaction, Chloroethane
(b) Elimination reaction, Chloroethane
(c) Addition reaction, Ethylene
(d) Oxidation reaction, Ethanol

Q5: A chemist treats an alkyne with an acidic potassium permanganate solution and observes the purple colour fading. What is the most likely outcome of this reaction?
(a) Formation of a diol.
(b) Formation of an oxalic acid.
(c) Formation of an alkene.
(d) No reaction takes place.

Q6: During an experiment, a student adds a small piece of sodium metal to a sample of an alcohol, R-OH, and observes the evolution of a gas. Which of the following gases is most likely being evolved?
(a) Oxygen
(b) Hydrogen
(c) Carbon dioxide
(d) Nitrogen

Q7: A chemist performs an oxidation reaction on an alcohol using potassium dichromate and observes the formation of a new compound with a fruity smell. Considering the starting material is a primary alcohol, what is the likely identity of the new compound?
(a) An aldehyde
(b) A ketone
(c) A carboxylic acid
(d) An ester

Q8: During a laboratory experiment, a student adds sodium carbonate to a solution of an unknown carboxylic acid. The student observes brisk effervescence. Which of the following compounds could the unknown acid be?
(a) Methanoic acid
(b) Ethanoic acid
(c) Propanoic acid
(d) Butanoic acid

Type I

Q9: During the esterification reaction of a carboxylic acid, what is the expected outcome when ethanoic acid reacts with ethanol in the presence of concentrated sulphuric acid?
A. Formation of ethyl ethanoate and water
B. Release of carbon dioxide gas
C. Formation of sodium ethanoate
D. Production of ethyl hydrogen sulphate
(a) only A
(b) only B
(c) A and C
(d) B and C

Q10: Which of the following properties is not associated with pure ethanoic acid?
A. It has a boiling point of 118°C.
B. It is a hygroscopic liquid with a specific gravity of 1.08 at 0°C.
C. It forms acetic anhydride on heating with phosphorus pentoxide.
D. It is insoluble in water, alcohol, and ether.
(a) only A
(b) only D
(c) B and C
(d) A and D

Q11: When ethyl alcohol is left open in the air, it tends to taste like vinegar after a few days due to a chemical reaction. Which of the following scenarios best explains this change?
A. The alcohol undergoes dehydration to form ether.
B. The alcohol reacts with oxygen to form acetic acid.
C. The alcohol participates in a substitution reaction to form haloalkanes.
D. The alcohol is reduced to form an aldehyde.
(a) only A
(b) only B
(c) A and D
(d) B and C

Q12: If a reaction takes place between an alcohol and acetic acid in the presence of concentrated sulphuric acid, which of the following compounds is most likely to be formed?
A. An aldehyde
B. A carboxylic acid
C. An ester
D. An ether
(a) only A
​​​​(b) only C
(c) B and D
(d) A and D

Q13: What is the expected outcome when ethyne reacts with bromine in carbon tetrachloride?
A. The bromine's brown colour persists indicating no reaction.
B. The brown colour of bromine solution gets decolourised forming an addition product.
C. Ethyne gas is collected via downward displacement of bromine.
D. The reaction produces hydrobromic acid and ethene gas.
(a) only A
(b) only B
(c) B and C
(d) A and C

Q14: What is the result of the halogenation of ethene with bromine in CCl₄ solution?
A. 1,2-dibromoethane
B. 1-bromoethane
C. Ethyl bromide
D. Bromoethanol
(a) only A
(b) only B
(c) only C
(d) only D

Q15: Considering the isomerism of alkanes, which of the following is true about butane (C₄H₁₀)?
A. It can form only one isomer.
B. It can form two different isomers.
C. It has isomers with the same molecular but different structural formulas.
D. It has isomers that are cyclic compounds.
(a) only A
(b) only B
(c) B and C
(d) A and D