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 187 questions on this lesson, each with an explanation.
The first four members of the alkane series are gases at room temperature. Which alkane is the first member of the series that exists as a liquid at room temperature?
Correct answer: (D) Pentane
Explanation: Alkanes from C5 (pentane) up to about C17 are liquids at room temperature.
All the following hydrocarbons decolourise bromine water, EXCEPT:
Correct answer: (A) Ethane
Explanation: Ethane is a saturated alkane with no multiple bond, so it does not add bromine and cannot decolourise bromine water.
Catalytic hydration of the simplest alkyne (ethyne) gives:
Correct answer: (B) Ethanal
Explanation: Water adds across the triple bond of ethyne to form ethanal (acetaldehyde).
When ethene is passed into potassium permanganate solution in an alkaline medium (Baeyer's reaction), the observation and the organic product are, respectively:
Correct answer: (D) The purple colour is discharged, and ethylene glycol is formed
Explanation: In Baeyer's reaction alkaline potassium permanganate oxidises ethene to ethylene glycol and its purple colour is discharged; this is a test for the double bond.
When propane (C3H8) undergoes mono-substitution with chlorine (replacing only one hydrogen atom), how many isomeric monochloropropane products are possible?
Correct answer: (B) 2
Explanation: Chlorine can replace a hydrogen on a terminal carbon (1-chloropropane) or on the middle carbon (2-chloropropane), giving two isomers.
Two compounds are described as structural isomers when they share the same molecular formula but differ in structure. Which of the following pairs are structural isomers of each other?
Correct answer: (D) Butane and 2-methylpropane
Explanation: n-Butane and 2-methylpropane both have the molecular formula C4H10 but different structures, so they are structural isomers.
Which of the following statements about alkanes (paraffins) is chemically accurate?
Correct answer: (C) They contain only strong sigma bonds, making them relatively inactive.
Explanation: Alkanes contain single sigma bonds which are strong and difficult to break, leading to chemical inactivity, and they differ by a methylene (-CH2) group, not methyl.
During the catalytic hydration of ethene, ethyl hydrogen sulphate is first formed at 80°C, and then it undergoes hydrolysis at what temperature to give ethyl alcohol?
Correct answer: (C) 110°C
Explanation: The textbook equation shows the hydrolysis of ethyl hydrogen sulphate occurs at 110°C with delta: CH3 - CH2 - OSO3H + H2O at 110°C -> CH3 - CH2 - OH + H2SO4.
The complete combustion of 0.05 mol of a gaseous alkane produced 4.4 g of carbon dioxide. Which of the following is the molecular formula of the alkane? (C=12, O=16)
Correct answer: (D) C2H6
Explanation: 4.4 g CO2 = 0.1 mol, so n = 0.1/0.05 = 2, giving the alkane C2H6 (ethane).
Which of the following physical and chemical properties is correct regarding most organic compounds compared to inorganic compounds?
Correct answer: (A) Organic compounds are mostly insoluble in water, inflammable, and have low boiling points
Explanation: Organic compounds have low melting points, low boiling points, are mostly insoluble in water but soluble in organic solvents, are inflammable, and most have a characteristic odour.
The first 10 questions in every subject are free, each with an explanation.