**(a)** Based on Diagram 7.1,
(i) Give a homologous series for element M.
(ii) Which element has the same homologous series as methane gas?
**(b)** Explain how to produce methane gas.
**(c)** State one difference between hydrocarbon compounds L and M.
**(d)** Based on Diagram 7.2, which energy source is the most environmentally friendly? Explain your answer.
Diagram 7.1 shows two examples of hydrocarbon compounds:
H H H H
| | | |
H-C-C-C-C-H
| | | |
H H H H
L
H H
| |
C=C
| |
H H
M
Diagram 7.2 shows a graph of carbon dioxide gas emissions from the use of different energy sources:
Mass of carbon dioxide (g)
900 820 600 490 300 230 41 38 24 12 0
Energy sources:
Coal, Natural gas, Biomass, Solar, Geothermal, Hydro, Nuclear
Answer (1)
(a) (i) A homologous series is a group of organic compounds that have the same functional group and similar chemical properties, with each successive compound differing by a CH₂ unit. The element M in Diagram 7.1 is given by the structural formula H-C=C-H. This represents an alkene because it contains a carbon-carbon double bond (C=C). Therefore, the homologous series for element M is alkenes.
(ii) Methane gas (CH₄) is a part of the alkane homologous series, which consists of hydrocarbons with single carbon-carbon bonds only. The element that would have the same homologous series as methane gas is L, shown with four single-bonded carbon atoms (H-C-C-C-C-H), which belongs to alkanes because it also contains only single C-C bonds.
(b) Methane gas (CH₄) can be produced through several methods, including:
Biogas Production: Methane is a major component of biogas, which is produced by the anaerobic digestion of organic matter by microorganisms. Common sources include waste materials such as manure, sewage, plant residues, and food waste.
Synthetic Production: Methane can be synthesized through the reaction of carbon monoxide and hydrogen in the presence of a catalyst, known as the Fischer-Tropsch process.
Natural Extraction: Methane is extracted from natural gas reserves, where it occurs naturally as a gas under high pressures.
(c) One primary difference between hydrocarbon compounds L and M is the type of bonding between the carbon atoms:
Compound L is an alkane, which consists of only single bonds between carbon atoms (C-C), leading to saturated hydrocarbons.
Compound M is an alkene, characterized by at least one carbon-carbon double bond (C=C), making it an unsaturated hydrocarbon.
(d) Based on Diagram 7.2, the energy source that is most environmentally friendly in terms of carbon dioxide emissions is shown to be nuclear energy, followed by hydro, solar, and geothermal, with nuclear energy having the lowest emissions at 0 grams of carbon dioxide.
Nuclear energy is considered environmentally friendly in terms of emissions because it does not release carbon dioxide during operation, making it a low-carbon energy source, despite some concerns about nuclear waste management and safety.
