Organic chemistry - Fuels (3)
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1.
Name the three main fossil fuels and briefly describe their formation.
The three main fossil fuels are: coal, natural gas, and petroleum.
Coal is formed from the remains of ancient plants that accumulated in swampy environments. Over millions of years, these plants were buried, subjected to heat and pressure, and transformed into peat, then lignite, then bituminous coal, and finally anthracite.
Natural gas is primarily composed of methane (CH4). It forms in a similar way to coal, from the decomposition of organic matter in anaerobic conditions. The organic matter is buried and subjected to heat and pressure, leading to the formation of hydrocarbons, including methane.
Petroleum (also known as crude oil) is formed from the remains of microscopic marine organisms, such as algae and plankton. These organisms accumulate on the seabed and are buried under layers of sediment. Over millions of years, heat and pressure transform the organic matter into hydrocarbons, including petroleum.
2.
Describe a test that could be used to identify the presence of hydrocarbons in a sample. Include the reagents required and the expected observation.
A test for hydrocarbons involves burning a small amount of the sample in a test tube. The reagents required are a Bunsen burner and the sample itself. The expected observation is the production of a flame. Hydrocarbons are highly flammable and will readily ignite in the presence of oxygen. The flame will typically be pale blue, indicating complete combustion, although the colour can vary depending on the specific hydrocarbon.
3.
Describe the process of fractional distillation used to separate the components of natural gas. Include in your description the relative boiling points of methane and other components.
Fractional distillation is used to separate the components of natural gas because the components have different boiling points. The process involves cooling the natural gas to a very low temperature, turning it into a liquid. This liquid mixture is then pumped into a fractionating column.
The column is hotter at the bottom and cooler at the top. The components with higher boiling points (e.g., ethane, propane, butane) vaporize at the bottom of the column and travel upwards. As they rise, they cool and condense at different levels within the column, allowing them to be collected separately.
Methane has a very low boiling point (-161.5 °C) and therefore remains in the gaseous phase at the top of the column. Components like propane (boiling point -42 °C), butane (boiling point 0 °C), and ethane (boiling point -88 °C) condense at different heights within the column, enabling their separation. The relative boiling points are crucial for the effective separation process.