Question

Comparing molecules of similar size with different functional. groups, what can yoe conclude aboet the variation of boiling point with molecular polarity and types of intermolecular forces? 5. You are heating a misture of (flamerable) sycloherane and toluene in a round botiomed flak. What is the bed beating sousce? Circle the richt answer. a. Buasen burner (open flame) b. Heating Mantle (rincludes circular beating well and voltage control) d. Hot plate with voltage regulation (flat hot surface) a. Using the graph in Figure 1, identify the boiling point for water in degrees C at the locations indicated below: Use the given atmospheric pressure at each location. ( I atm =101.3kPa ) a) Houston, Texas (740 torr) b) Denver, Colorado (615 torr) c) Near the top of Mount Evercht (250 tort). 2. Vacuum distillation is applied in the production of fresh water by desalination of ocean water. Using the graph in Figure 1 , indicate what the pressure would have to be in order for water to boil at 601C ? 8. What method would you ase to scoparate a mixture of propanoic acid and I-butanol? (Lock up the physieal properties of the two compounds.) Fyplain why yoa would choose that particular method. - A liquid A (vapor pressure 500 torr at 60∘C) is combined with a liquid B (vapor pressure 300 toer at 60 (C) to form a homogenous mixture. If 3 moles of A is mirued with 2 moles of B in a distilling flask heated to 60CC. a) What is the mole fractica of A in the liquid initially? b) What is the fraction of A in the vapor phase initially? c) If the above mixture of A and B is distilled, what will happen to the mole fraction of A in the distilling flask as the distillation proceeds? Why? 4. Comparing molecules of similar size with different functional groups, what can you conclude about the variation of boiling point with molecular polarity and types of intermolecular forces? cthane −89∘C ethanol ethanoic acid (Acetic acid) acetaldehyde acetonitrile ​78.4∘C118∘C20.2∘C82∘C​ 5. You are heating a mixture of (flammable) cyclohexane and toluene in a round bottomed flask. What is the best heating source? Circle the right answer. a. Bunsen burner (open flame) b. Heating Mantle (includes circular heating well and voltage control) d. Hot plate with voltage regulation (flat hot surface) 6. Using the graph in Figure 1, identify the boiling point for water in degrees C at the locations indicated below. Use the given atmospheric pressure at each location. (1 atm=101.3kPa) a) Houston, Texas ( 740 torr) b) Denver, Colorado (615 torr) c) Near the top of Mount Everest (250 torr). 7. Vacuum distillation is applied in the production of fresh water by desalination of ocean water. Using the graph in Figure 1, indicate what the pressure would have to be in order for water to boil at 60∘C ? 8. What method would you use to separate a mixture of propanoic acid and 1-butanol? (Look up the physical properties of the two compounds.) Explain why you would choose that particular method. 9. A liquid A (vapor pressure 500 torr at 60∘C ) is combined with a liquid B (vapor pressure 300 torr at 60∘C ) to form a homogenous mixture. If 3 moles of A is mixed with 2 moles of B in a distilling flask heated to 60∘C, a) What is the mole fraction of A in the liquid initially? b) What is the fraction of A in the vapor phase initially? c) If the above mixture of A and B is distilled, what will happen to the mole fraction of A in the distilling flask as the distillation proceeds? Why?

Answer 1

4. When comparing molecules of similar size with different functional groups, we can conclude the following about the variation of boiling point with molecular polarity and types of intermolecular forces:

- Molecular Polarity: Molecules with higher polarity tend to have higher boiling points. This is because polar molecules have stronger intermolecular attractions, such as dipole-dipole interactions or hydrogen bonding, which require more energy to break and transition from the liquid to the gaseous state.

- Intermolecular Forces: The type of intermolecular forces present in a molecule affects its boiling point. Molecules with stronger intermolecular forces, such as hydrogen bonding or ion-dipole interactions, have higher boiling points compared to molecules with weaker forces, such as London dispersion forces.

In the given examples:

- Methane (boiling point -89°C): It is nonpolar and experiences only London dispersion forces.

- Ethanol (boiling point 78.4°C): It is polar and experiences both hydrogen bonding and dipole-dipole interactions.

- Ethanoic acid (Acetic acid) (boiling point 118°C): It is polar and forms hydrogen bonds.

- Acetaldehyde (boiling point 20.2°C): It is polar and experiences dipole-dipole interactions.

- Acetonitrile (boiling point 82°C): It is polar and experiences dipole-dipole interactions.

From these examples, we can see that as the molecular polarity and strength of intermolecular forces increase, the boiling point also increases.

5. The best heating source for a mixture of flammable cyclohexane and toluene would be the Heating Mantle. It provides controlled and uniform heating through the circular heating well, reducing the risk of an open flame from the Bunsen burner igniting the flammable mixture. The voltage control also allows for precise regulation of the heating temperature.

6. Using the graph in Figure 1, we need to identify the boiling point for water (H2O) in degrees Celsius at the given locations and atmospheric pressures:

a) Houston, Texas (740 torr): The boiling point for water at 740 torr is approximately 97.7°C.

b) Denver, Colorado (615 torr): The boiling point for water at 615 torr is approximately 94.4°C.

c) Near the top of Mount Everest (250 torr): The boiling point for water at 250 torr is approximately 68.2°C.

7. Vacuum distillation is applied in the production of fresh water by desalination of ocean water. To boil water at 60°C, the pressure would need to be lowered to the corresponding value on the graph in Figure 1. Unfortunately, the provided graph is missing, so the specific pressure cannot be determined.

8. The method that can be used to separate a mixture of propanoic acid and 1-butanol depends on their physical properties. One possible method is fractional distillation. Propanoic acid and 1-butanol have different boiling points (propanoic acid: boiling point around 141°C, 1-butanol: boiling point around 117°C), allowing them to be separated based on the difference in boiling points. Fractional distillation involves heating the mixture and collecting the fractions with different boiling points as they evaporate and condense.

9. Given:

- Liquid A: Vapor pressure = 500 torr at 60°C

- Liquid B: Vapor pressure = 300 torr at 60°C

- Moles of A: 3

- Moles of B: 2

a) The mole fraction of A in the liquid initially can be calculated using the formula:

Mole fraction of A = (moles

of A) / (moles of A + moles of B)

Mole fraction of A = 3 / (3 + 2) = 0.6

b) The fraction of A in the vapor phase initially can be approximated using Raoult's Law, which states that the vapor pressure of a component is proportional to its mole fraction:

Fraction of A in vapor phase = mole fraction of A = 0.6

c) During distillation, the more volatile component (with a higher vapor pressure) will preferentially evaporate and condense in the distillate. As distillation proceeds, the mole fraction of A in the distilling flask will decrease because more of the volatile component A is being collected in the distillate. Therefore, the mole fraction of A in the distilling flask will decrease with time as the distillation proceeds.