Crude Oil Fractional Distillation

Question 1

• The table shows the percentage of each fraction obtained by the fractional distillation of crude oil. This process involves the separation of a complex mixture into its individual components or "fractions" based on differences in their boiling points. Each fraction collected has distinct properties and uses in industry.
• Name of fraction and Percentage are given; this often includes fractions such as gases, naphtha, kerosene, and fuels, each with specific applications. An understanding of the relationship between the composition and characteristics aids in refining processes.
• Example: Fuel oil and bitumen = 48%. Such examples help illustrate the diversity of products derived from crude oil and their varying proportions. For instance, the heavier fractions like fuel oil are used for heating and power generation, while naphtha serves as a feedstock for petrochemical production.
• Describe the relationship between the number of carbon atoms and the percentage composition. Generally, as the number of carbon atoms in a hydrocarbon chain increases, the boiling point and thus the condensation temperature of the substance also increases. Subsequently, larger molecules are obtained in lower proportions due to their higher boiling points making them less volatile. This pattern allows understanding of why lighter fractions are collected at higher sections of the distillation column.
• Describe a process used to obtain the fractions we need the most. The process of fractional distillation involves heating crude oil in a distillation column. The oil is heated to elevated temperatures, causing it to vaporize. The vapor rises through the column where cooler temperatures at various levels cause the vapors to condense at specific locations, allowing the fractions to be collected separately based on their boiling ranges.
• State the name of the homologous series which are produced as a by-product of this process. The homologous series of alkanes, alkenes, and cycloalkanes among others can be produced, with alkenes often considered significant as they serve as essential reagents in many chemical reactions and industrial applications.
• Complete the following balanced symbol equation, example: C12H26→ C6H14. For example, the equation for the cracking of dodecane could be represented as C12H26 → C6H14 + C6H12, where larger hydrocarbons are broken down into smaller, more valuable fractions through processes such as cracking.

Question 2

• A fractional distillation column, shown in the diagram, is used to separate crude oil into its fractions. The distinct sections within the column reflect a temperature gradient where different hydrocarbons condense at respective boiling points, allowing for efficient separation.
• Diagram shows a column with temperature gradient from 350°C to 25°C with fractions A to H marked. The highest temperatures are typically at the bottom, where heavier fractions tend to condense, and lower temperatures are found at the top, hosting lighter, more volatile components.
• Describe how fractional distillation works. The process operates on the principle that components of crude oil have a range of boiling points. By heating crude oil, it vaporizes into gas which moves through the column. As the gas rises, it cools; lower boiling point components condense and are collected at different heights in the column. This hierarchy allows for separate collection of various hydrocarbons.
• Identify which fraction, from C, D or E has the highest volatility. Typically, fraction C would be expected to exhibit the highest volatility, as it would be collected higher up the column where the temperatures are lower, indicating potential lighter hydrocarbons.
• Identify which fraction, from A, C or F has the highest viscosity. Fraction A, containing the heaviest components, would typically have the highest viscosity due to its larger molecular size and weight, resulting in slower flow rates.
• Identify which fraction, from A to H, is most likely to be used as jet fuel. Fraction D, which is generally comprised of kerosene-like components, is most likely to be used as jet fuel because it meets the necessary specifications for combustion performance and energy density required for aviation.

Question 3

• Ethanol is an important fuel. It is widely recognized for its role as a renewable alternative to fossil fuels, significantly contributing to reductions in greenhouse gas emissions when blended with conventional gasoline.
• State one other use of ethanol. Beyond its application as a fuel additive, ethanol is also used as a solvent in the manufacturing of personal care products, inks, and food flavorings, showcasing its versatility.
• Ethanol can be produced by fermentation or by the addition of steam to ethene under certain conditions. During fermentation, sugars are converted to ethanol and carbon dioxide by yeast, while the addition of steam to ethene takes place through a catalytic process called hydration.
• Compare and contrast the advantages and disadvantages of both methods. Fermentation is a natural process, using renewable resources without the need for external heat sources; however, it has a lower yield and requires longer durations. On the other hand, steam hydration is efficient and produces high purity ethanol in less time, yet it relies on fossil fuels for ethene production and may have higher associated costs.
• Butanol is another alcohol. Butanol can serve as another fuel source and as an industrial solvent or intermediate in chemical synthesis, expanding its functional utility beyond that of ethanol.
• Chemical structures of Molecule A, Molecule B, and Molecule C are given. Understanding these structures is critical in identifying isomers and conformations that can impact the properties of these alcohols.
• Which diagram shows a structural isomer of butanol? A structural isomer is a compound that has the same molecular formula but different connectivity. Identifying such diagrams requires a detailed examination of carbon arrangements.
• Which diagram shows a molecule in the same homologous series as butanol? To determine if the molecules belong to the same homologous series, we must examine their functional groups and count the number of carbon atoms, verifying their classification as linear or branched alcohols.

Question 4

• A number of chemical compounds are listed. These compounds are essential for understanding organic chemistry and the basis of many biochemical processes.
• Label the compounds as either: alkane, alkene, alcohol, or carboxylic acid. Proper classification allows students to understand the different functional groups and their reactivity in organic chemistry.
• Chemical structures (i), (ii), (iii), and (iv) are given. Analyzing these structures helps develop skills in recognizing features like double bonds in alkenes and functional groups in alcohols and acids.
• State the name of the compound from part (a) that can be polymerised to form poly(ethene). The compound usually identified is ethene itself, which is the starting material for the polymerization that results in poly(ethene), a crucial plastic used in various applications.
• Complete the following structural equation of the reaction between the alkane, ethane, and oxygen. The combustion reaction is generally represented as C2H6 + O2 → CO2 + H2O, showing how hydrocarbons release energy when combusted in the presence of oxygen.

Question 5

• Polymerisation is a type of reaction in which subunits called monomers join together in long chains. This process is fundamental in materials science and helps create various synthetic products such as plastics, nylon, and other important materials.
• There are two types of polymerisation reactions. The first type, addition polymerization, involves the adding of monomers with unsaturated bonds, while the second, condensation polymerization, results in polymer chains formed via the elimination of small molecules like water or methanol.
• State the main two types of polymerisation reactions. Addition polymerization generally focuses on alkenes, while condensation polymerization often involves monomers bearing two different functional groups that react together to form complex materials.
• Draw the general formula of the compound produced when ethene goes through a polymerisation reaction. The general formula CnH2n corresponds to the series produced from ethene polymerization, resulting in long chains of polyethylene.
• Explain the role of catalysts during polymerisation reactions. Catalysts are substances that speed up the reactions by lowering the activation energy required, thereby allowing the process to proceed at a more efficient rate, which is particularly important in industrial applications.

Question 6

• Ethanoic acid is a carboxylic acid commonly found in vinegar. It contributes to vinegar’s characteristic flavor and smell while also having applications in food preservation and the manufacturing of various chemicals.
• State which of the following diagrams shows the structure of ethanoic acid. Recognizing the specific arrangement of carbon, oxygen and hydrogen will lead to identifying the correct molecular depiction.
• Chemical structures (i), (ii), and (iii) are given. Familiarity with these structures enhances the understanding of functional groups, especially carboxylic acids that feature the -COOH group.
• State the functional group in all carboxylic acids. The carboxyl group (-COOH) is characteristic of carboxylic acids and is pivotal for their acidic properties, influencing reactivity and solubility.
• State what pH range carboxylic acids such as ethanoic acid would have, choose from options (i) 0-3, (ii) 4-6, (iii) 6-9, (iv) 9-14. Generally, carboxylic acids have a pH range of 4-6, marking them as weak acids that still exhibit acidic properties but are less potent than strong acids.
• The diagram below shows the reaction between ethanoic acid and ethanol: This depicts the condensation reaction or esterification process, critical in the chemistry of organic compounds.
• State what type of compound ethyl ethanoate is. Ethyl ethanoate, also known as ethyl acetate, is an ester, which is formed via the reaction of an alcohol with a carboxylic acid.
• State the catalyst that needs to be present for this reaction to occur. A common catalyst used for this reaction is sulfuric acid, which serves to enhance the reaction rates by providing an acidic medium that facilitates the esterification.

Question 7

• Define the term homologous series. A homologous series is a sequence of compounds that share a common functional group and similar chemical properties, each differing by a fixed unit, typically a -CH2 group, in their molecular structures.
• State one chemical property of alkanes. Alkanes are generally characterized by their lack of reactivity under most conditions due to the presence of single covalent bonds, making them relatively inert compared to other classes of hydrocarbons like alkenes and alkynes.
• Give the general formula for alkenes. The general formula for alkenes is CnH2n, indicating that alkenes have at least one double bond in their structure which is responsible for their unique reactivity that distinguishes them from alkanes.
• State the name used to describe compounds with the same molecular formula but different structural formulae. These are known as isomers, which include structural isomers, where compounds may have different arrangements of atoms, leading to variations in physical and chemical properties.
• State which of the following compounds does not have the same molecular formula as butane. This requires comparing the provided structures in context with butane (C4H10) to identify any discrepancies in molecular composition.
• Chemical structures (i), (ii), and (iii) are given. Through this analysis, one can focus on counts of carbon and hydrogen atoms to ascertain molecular congruity with butane.

Question 8

• An experiment was conducted as shown in the diagram. This involves a practical demonstration of distillation to separate liquid mixtures based on boiling points.
• Diagram shows a distillation setup, including: Thermometer, Fractionating column, Condenser, Water out, Water in, Round-bottom flask, Bunsen burner. This setup is crucial for teaching fundamental concepts in thermodynamics and separation techniques in laboratory practices.
• State the name of the process being carried out in this experiment. The process involved is known as simple distillation, which allows for the separation of components in a mixture based on differing boiling points, facilitating the isolation of pure substances from a mixture.
• Explain why water is passed through the condenser. Water is utilized in the condenser to provide a cooling mechanism, allowing vapor to condense back to liquid form effectively. This is vital to increase the efficiency of the separation process.
• Explain why water is connected to the bottom of the condenser and not the top. Connecting water to the bottom ensures that the cool water flows up through the condenser, maximizing the contact surface area with hot vapor to promote efficient condensation as the vapor rises through the column.
• State a safety procedure that should be followed when conducting this experiment. Standard safety procedures include wearing lab coats and goggles to protect against splashes, securing all apparatus to prevent spills, and ensuring there is proper ventilation to deal with any fumes generated during the distillation process.