Deyiations from Raoult's law lead to the formation of azeotropes, constant boiling mixtures that cannot be separated by distillation, making industrial separations difficult. For components \(A\) and \(B\), there is a positive deviation if the \(A\) - \(B\) attraction is less than A-A and B-B attractions (A and B reject each other), and a negative deviation if the \(A-B\) attraction is greater than \(A-A\) and B-B attractions. If the A-B attraction is nearly equal to the A-A and \(\mathrm{B}-\mathrm{B}\) attractions, the solution obeys Raoult's law. Explain whether the behavior of each pair of components will be nearly ideal, show a positive deviation, or show a negative deviation: (a) Benzene \(\left(\mathrm{C}_{6} \mathrm{H}_{6}\right)\) and methanol (b) Water and ethyl acetate (c) Hexane and heptane (d) Methanol and water (e) Water and hydrochloric acid

Step by step solution

01

- Understand Raoult's Law Deviation

Recall that deviations from Raoult's law depend on the relative attractions between the components. Positive deviations occur when the attraction between the different components (A-B) is less than the attraction between similar components (A-A and B-B). Negative deviations occur when the A-B attraction is greater than the A-A and B-B attractions. If the attractions are nearly equal, the solution obeys Raoult's law.

02

- Analyze Benzene and Methanol

Benzene is non-polar while methanol is polar and can form hydrogen bonds. The A-B attraction (benzene-methanol) is significantly weaker compared to the individual A-A (benzene-benzene) and B-B (methanol-methanol) attractions. Therefore, this pair shows a positive deviation.

03

- Analyze Water and Ethyl Acetate

Water is highly polar and capable of hydrogen bonding, while ethyl acetate is less polar and does not hydrogen bond as strongly. The A-B attraction (water-ethyl acetate) is weaker than the individual A-A (water-water) and B-B (ethyl acetate-ethyl acetate) attractions. This pair will show a positive deviation.

04

- Analyze Hexane and Heptane

Both hexane and heptane are non-polar hydrocarbons. The A-B attraction (hexane-heptane) is nearly equal to the individual A-A (hexane-hexane) and B-B (heptane-heptane) attractions. This pair will be nearly ideal and obey Raoult's law.

05

- Analyze Methanol and Water

Both methanol and water are polar and can form hydrogen bonds with each other. The A-B attraction (methanol-water) is strong and comparable to the individual A-A (methanol-methanol) and B-B (water-water) attractions. This pair will be nearly ideal and obey Raoult's law.

06

- Analyze Water and Hydrochloric Acid

Water is polar and capable of hydrogen bonding, and hydrochloric acid, when dissolved in water, ionizes completely creating strong ion-dipole interactions. The A-B attraction (water-HCl) is stronger than the individual A-A (water-water) and B-B (HCl-HCl) attractions. This pair will show a negative deviation.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Positive Deviation

Positive deviations from Raoult's Law occur when the attraction between different components (A-B) in a solution is weaker than the attractions between similar components (A-A and B-B). This happens because the two different molecules do not interact strongly, leading them to prefer their own kind. This can increase vapor pressure above what Raoult's Law predicts. For example, consider Benzene (C₆H₆) and Methanol. Benzene is non-polar, while Methanol is polar and capable of hydrogen bonding. The attraction between Benzene and Methanol molecules (A-B) is significantly weaker compared to the attraction between Benzene-Benzene (A-A) and Methanol-Methanol (B-B) molecules. As a result, this pair shows a positive deviation. Always look for mismatched or weak interactions between different molecules to identify positive deviations.

Negative Deviation

Negative deviations occur when the attraction between different components (A-B) is stronger than the attractions between similar components (A-A and B-B). This means that the different molecules strongly attract each other, which can lead to a lower vapor pressure than predicted by Raoult's Law. A classic example is Water and Hydrochloric Acid (HCl). Water is polar and capable of hydrogen bonding, while when HCl is dissolved in water, it ionizes completely, creating strong ion-dipole interactions. The attraction between Water and Hydrochloric Acid (A-B) is stronger than the attraction between Water-Water (A-A) and HCl-HCl (B-B). Therefore, this pair shows a negative deviation. Look for strong bonding interactions or ion-dipole forces between different molecules to identify negative deviations.

Ideal Solution

An ideal solution is one where the attraction between different components (A-B) is nearly equal to the attractions between similar components (A-A and B-B). In such cases, the solution follows Raoult's Law closely, meaning the vapor pressure behaves predictably according to the law. For example, Hexane and Heptane are both non-polar hydrocarbons. The attraction between Hexane and Heptane molecules (A-B) is nearly equal to the attraction between Hexane-Hexane (A-A) and Heptane-Heptane (B-B) molecules. Thus, the mixture of Hexane and Heptane behaves as an ideal solution and obeys Raoult's Law. Look for molecules that are chemically similar in terms of polarity and bonding capacity to identify nearly ideal solutions.