Chapter Five · Organic chemistry · Chemistry. These are 10 questions from the Magmo3 bank on this lesson, from easy to hard. Solve each one, then open "Show answer and explanation". Magmo3 has 46 questions on this lesson, each with an explanation.
Esters are widely used in the food and perfume industries mainly because they:
Correct answer: (C) Have pleasant fruity odours
Explanation: Esters have characteristic sweet, fruity smells, so they are used as flavourings and in perfumes.
The reaction between ethanoic acid and methanol produces which ester?
Correct answer: (A) Methyl ethanoate
Explanation: The alcohol supplies the alkyl group (methyl) and the acid supplies the acyl group (ethanoate), giving methyl ethanoate.
What is the chemical name of Aspirin?
Correct answer: (C) Acetylsalicylic acid
Explanation: Aspirin is well-known as acetylsalicylic acid in the context of organic derivatives.
Which of the following describes the nature of ester odor as the molecular mass of the constituent alcohol and acid increases?
Correct answer: (A) The odor decreases, and the state changes toward a waxy solid.
Explanation: The odor of the ester decreases by the increase of the molecular mass of the alcohol and acid used, turning into a waxy solid.
Which statement correctly compares the acidic hydrolysis of an ester with its alkaline hydrolysis (heating with aqueous NaOH)?
Correct answer: (D) Acidic hydrolysis gives the carboxylic acid and the alcohol, while alkaline hydrolysis gives the salt of the acid and the alcohol
Explanation: Acid hydrolysis, catalysed by a dilute mineral acid, is the reverse of esterification and gives the carboxylic acid and the alcohol, e.g. acetic acid and ethanol. Alkaline hydrolysis (saponification) with aqueous NaOH gives the salt of the acid and the alcohol, e.g. sodium acetate and ethanol.
Three liquids are tested: A is neutral to litmus and turns acidified potassium dichromate from orange to green, B gives effervescence with sodium carbonate, and C has a pleasant fruity smell. Compounds A, B and C respectively are:
Correct answer: (B) A primary alcohol, a carboxylic acid, an ester
Explanation: A is a primary alcohol: alcohols are neutral to litmus and a primary alcohol is oxidised by acidified dichromate (orange to green), whereas a tertiary alcohol is not. B releases CO₂ from a carbonate, so it is a carboxylic acid, and C, with a pleasant fruity smell, is an ester.
What is the result of the ammonolysis of ethyl benzoate?
Correct answer: (A) Benzamide and ethanol.
Explanation: Ammonolysis of esters gives acid amide and the alcohol; specifically, ethyl benzoate reacts with ammonia to give benzamide and ethanol.
The carboxylic acid ethanoic acid is isomeric with which ester of the same molecular formula (C2H4O2)?
Correct answer: (B) Methyl methanoate
Explanation: Ethanoic acid (CH3COOH) and methyl methanoate (HCOOCH3) are isomers, both having the molecular formula C2H4O2.
What is the correct structural characteristic when comparing methyl acetate and methyl formate's classification tables?
Correct answer: (B) Both are classified as esters, but have different total numbers of carbon atoms.
Explanation: Both methyl acetate and methyl formate are listed under esters, differing in their alkyl and acid-derived carbon chain lengths.
Which of the following sets contains exclusively compounds classified as esters according to the provided text tables?
Correct answer: (D) Aspirin, CH3COOC6H5, C6H5COOCH3, Dacron
Explanation: Aspirin, CH3COOC6H5 (phenyl acetate), C6H5COOCH3 (methyl benzoate), and Dacron are all explicitly categorized or contain ester functional groups as per the tables.
The first 10 questions in every subject are free, each with an explanation.