Question
Ethene and propene are both members of the same homologous series. Which statements explain why ethene and propene have similar chemical properties?
1 They are both hydrocarbons.
2 They are both made by cracking.
3 They have the same functional group.
A. 1 and 2 B. 1 and 3 C. 2 only D. 3 only
▶️Answer/Explanation
Ans:
D
Both ethene and propene are both members of the alkene group. Hence, they have the same functional group. So, ethene and propene have similar chemical properties.
Question
Increasing the number of atoms in one molecule of a hydrocarbon increases the amount of
energy released when it burns.
What is the correct order?
▶️Answer/Explanation
Ans:D
Methane CH4 has 4 atoms,
Ethene, C2H4 has 6 atoms and
Ethane, C2H6 has 9 atoms.
As increasing the number of atoms in one molecule of a hydrocarbon increases the amount of energy released when it burns, hence methane releases least energy and ethane releases the maximum energy.
Question
Which statement about alkenes is correct?
A Alkenes are saturated hydrocarbons.
B Alkenes can be made by cracking other hydrocarbon compounds.
C Alkenes change bromine water from colourless to brown.
D Alkene molecules contain double bonds between carbon atoms and hydrogen atoms.
▶️Answer/Explanation
Ans:B
Cracking of alkanes can produce alkenes. Cracking is a process used to break down larger hydrocarbon molecules, including alkanes, into smaller molecules, which can include alkenes.
During the cracking process, high temperatures and sometimes catalysts are used to break the carbon-carbon bonds in the larger hydrocarbon molecules. This results in the formation of smaller fragments, some of which can contain double bonds and are therefore alkenes.
Question
Which structure represents poly(ethene)?
▶️Answer/Explanation
Ans: D
Polyethylene is produced through the polymerization of ethylene monomers. When multiple ethylene molecules undergo a chemical reaction, they combine and form long chains of repeating ethylene units, resulting in the polymer known as polyethylene.
Question
P, Q, R and S are four organic compounds.
P is an unsaturated hydrocarbon.
Q burns but otherwise is unreactive.
R contains a C–C single bond and a C=C double bond.
S undergoes addition polymerisation.
Which compounds are alkenes?
A P and R only
B P, R and S
C P, Q and S
D Q, R and S
▶️Answer/Explanation
Ans: B
Alkenes are reactive and can undergo various chemical reactions. One of the primary characteristics of alkenes is their carbon-carbon double bond, which makes them more reactive compared to alkanes (saturated hydrocarbons). Q is not an alkene.