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Chapter 11: Problem 80

Ethylene glycol \(\left(\mathrm{HOCH}_{2} \mathrm{CH}_{2} \mathrm{OH}\right)\) and pentane \(\left(\mathrm{C}_{5} \mathrm{H}_{12}\right)\) are both liquids at room temperature and room pressure, and have about the same molecular weight. (a) One of these liquids is much more viscous than the other. Which one do you predict is more viscous? (b) One of these liquids has a much lower normal boiling point \(\left(36.1^{\circ} \mathrm{C}\right)\) compared to the other one \(\left(198^{\circ} \mathrm{C}\right)\). Which liquid has the lower normal boiling point? (c) One of these liquids is the major component in antifreeze in automobile engines. Which liquid would you expect to be used as antifreeze? (d) One of these liquids is used as a "blowing agent" in the manufacture of polystyrene foam because it is so volatile. Which liquid would you expect to be used as a blowing agent?

Short Answer

Expert verified
(a) Ethylene glycol is more viscous than pentane due to its larger amount of intermolecular bonding brought about by its two hydrogen-bonding hydroxyl groups. (b) Pentane has a lower normal boiling point (36.1 degrees Celsius) because its intermolecular forces, specifically van der Waals interactions, are weaker compared to ethylene glycol. (c) Ethylene glycol is the major component in antifreeze because it has a high boiling point thanks to its hydrogen bonding capacity, a low freezing point, and efficient heat transfer characteristics. (d) Pentane, with its lower boiling point and higher volatility, would be used as a blowing agent during the production of polystyrene foam, to generate bubbles or pores within the material.

Step by step solution

01

(a) Predicting viscosity based on molecular structure

Viscous liquids are thicker and resist flow more than less viscous liquids. Ethylene glycol has two hydrogen-bonding hydroxyl groups, which means that it will have a higher degree of intermolecular bonding. This bonding makes the liquid thicker. Pentane, on the other hand, only has weak van der Waals interactions. Based on this information, it is predicted that ethylene glycol is more viscous than pentane.
02

(b) Comparing normal boiling points based on molecular interactions

The boiling point is related to the strength of the intermolecular interactions between molecules, as stronger interactions require more energy to break and allow the molecules to move apart from one another. Ethylene glycol has stronger intermolecular forces due to its hydrogen bonding ability. Pentane, on the other hand, only has weak van der Waals interactions. Therefore, ethylene glycol will have a higher boiling point than pentane. This means that pentane has the lower normal boiling point, at 36.1 degrees Celsius.
03

(c) Identifying the major component of antifreeze

Antifreeze is used in automobile engines to prevent freezing and reduce corrosion. It should have a high boiling point, a low freezing point, and good heat transfer properties. Ethylene glycol meets these requirements, as it has a high boiling point due to its hydrogen bonding capacity and can effectively transfer heat. Therefore, ethylene glycol is the major component in antifreeze.
04

(d) Predicting the use of a blowing agent in polystyrene foam production

A blowing agent is used in the manufacture of polystyrene foam to create bubbles, or pores, within the material. The ideal blowing agent will have a low boiling point and be volatile, as this means that it will easily transition from a liquid to a vapor and create the desired porous structure. Pentane has a low boiling point and is quite volatile, so it would be the ideal choice for use as a blowing agent in the manufacture of polystyrene foam.

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Most popular questions from this chapter

Propane \(\left(\mathrm{C}_{3} \mathrm{H}_{8}\right)\) is pressurized into liquid and stored in cylinders to be used as a fuel. The normal boiling point of propane is listed as \(-42^{\circ} \mathrm{C}\). (a) When converting propane into liquid at room temperature of \(25^{\circ} \mathrm{C},\) would you expect the pressure in the tank to be greater or less than atmospheric pressure? How does the pressure within the tank depend on how much liquid propane is in it? (b) Suppose the fuel tank leaks and a few liters of propane escape rapidly. What do you expect would happen to the temperature of the remaining liquid propane in the tank? Explain. (c) How much heat must be added to vaporize $20 \mathrm{~g}\( of propane if its heat of vaporization is \)18.8 \mathrm{~kJ} / \mathrm{mol} ?\( What volume does this amount of propane occupy at \)100 \mathrm{kPa}\( and \)25^{\circ} \mathrm{C} ?$

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For a given substance, the liquid crystalline phase tends to be more viscous than the liquid phase. Why?
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