Question

Which of the following can be separated into its pure components by fractional distillation? (a) \(\mathrm{C}_{6} \mathrm{H}_{6}+\mathrm{C}_{7} \mathrm{H}_{\mathrm{s}}\) (b) \(\mathrm{H}, \mathrm{O}+\mathrm{HCl}\) (c) \(\mathrm{H}_{2} \mathrm{O}+\mathrm{HNO}_{3}\) (d) \(\mathrm{H}_{2} \mathrm{O}+\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\)

Short answer

(a), (c), and (d) are mixtures that can be separated into pure components by fractional distillation, since their components have sufficiently different boiling points.

Step-by-step solution

Understand Fractional Distillation

Fractional distillation is a method used to separate mixtures of liquids with different boiling points. During this process, the mixture is heated, vaporizing the component with the lower boiling point, which is then condensed back into liquid and collected separately.

Identify the Components of Each Mixture

Analyze the mixtures given in the options to identify the components in each. Idenfity whether each mixture consist of substances with significantly different boiling points, which is crucial for the fractional distillation process to work.

Determine Applicability of Fractional Distillation

Evaluate each mixture to determine if fractional distillation can be used to separate its components based on the boiling point criteria. A mixture will be a good candidate for fractional distillation if its components have sufficiently different boiling points.

Analyze Each Option

(a) Benzene (\(C_6H_6\) - Boiling point: about 80.1 degrees Celsius) and heptane (\(C_7H_{16}\) - Boiling point: about 98.42 degrees Celsius) can be separated due to the difference in their boiling points. (b) Water (Boiling point: 100 degrees Celsius) and hydrochloric acid (\(HCl\) - Boiling point: -85 degrees Celsius for the gas phase, but it is typically used in solution and the boiling point of the azeotrope with water is about 108.6 degrees Celsius) is not applicable for fractional distillation when the HCl is in gaseous form, but if hydrochloric acid is in solution as part of a hydrochloric acid/water mixture, it is also possible to separate HCl due to the boiling point difference. (c) Water (\(H_2O\) - Boiling point: 100 degrees Celsius) and nitric acid (\(HNO_3\) - Boiling point: 83 degrees Celsius) have sufficient difference in boiling points and can be separated. (d) Water (\(H_2O\) - Boiling point: 100 degrees Celsius) and ethanol (\(C_2H_5OH\) - Boiling point: about 78.37 degrees Celsius) can also be separated as they also have different enough boiling points.

Key concepts

Separation of Mixtures

Separation of mixtures is a fundamental concept in science, where the components of a mixture are divided to obtain pure substances. Mixtures can be homogeneous or heterogeneous, and the methods used for their separation are based on the physical properties of the components, such as size, state of matter, solubility, and boiling point.

Fractional distillation is an advanced separation technique specifically tailored to separate homogeneous mixtures - usually liquids - based on the variance in boiling points of the individual substances. When a mixture is heated, the substance with the lower boiling point vaporizes first, and by controlling the temperature, one can selectively condense and collect the vaporized substance, thus achieving separation.

This process is commonly used in industries such as petrochemical refining and the manufacturing of spirits. Understanding how to effectively use this method is essential for students and professionals in chemistry and related fields.

Boiling Point Difference

The boiling point difference is the cornerstone of the fractional distillation process. It refers to the varying temperatures at which different substances transition from liquid to gas. A significant difference in the boiling points of the components in a mixture is critical for successful separation by fractional distillation.

This temperature gap allows the distillation apparatus to create a phase change only in the intended component, leaving the rest in the liquid state while the desired component is vaporized and then condensed. For instance, the separation of a volatile organic compound from water would require a scenario where their boiling points do not overlap or are sufficiently apart to facilitate distinct phases of vaporization.

Precise control over temperature and an understanding of the substances' thermodynamic properties are essential. When students grasp this concept, they can predict whether a mixture can be separated using fractional distillation, an invaluable skill in practical chemistry.

Physical Chemistry

Physical chemistry is the study of how matter behaves on a molecular and atomic level and how chemical reactions occur. From our text, fractional distillation is a physical process and exemplifies the principles of physical chemistry, demonstrating the interplay between the physical properties of substances and their changes under varying conditions.

In physical chemistry, students learn about phase diagrams, vapor pressure, and intermolecular forces, all of which are relevant to understanding fractional distillation. For example, analyzing the boiling point relates to the substance's intermolecular forces; the weaker these forces, the lower the boiling point. Understanding the molecular foundations that govern boiling points can enhance a student's ability to predict and manipulate the outcomes of distillation procedures.

Topics such as thermodynamics, kinetics, and spectroscopy are also important in physical chemistry and are the theoretical backbone that supports techniques like distillation. Incorporating such theoretical knowledge with practical applications is key for academic and career development in scientific fields.

Competitive Examinations Preparation

Preparation for competitive examinations often requires a firm grasp of core concepts in chemistry, including the separation of mixtures through processes such as fractional distillation. These concepts are frequently tested in various forms, from multiple-choice questions to lab-based practicals.

As we've seen in the exercise, understanding not only the methodology but also the theory behind processes like fractional distillation is essential. For students preparing for competitive exams, it is advisable to practice various distillation problems, focus on the conceptual understanding of physical property-based separation techniques, and familiarize themselves with related thermodynamic principles.

Regular revision of these concepts, accompanied by solving past exam questions and taking mock tests, can greatly enhance a student's ability to perform well. Moreover, being proficient in these key concepts in physical chemistry ensures students are well-prepared for higher education and professional careers in science and engineering disciplines.