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Chapter 11: Problem 3

(a) Do you expect the viscosity of glycerol, \(\mathrm{C}_{3} \mathrm{H}_{5}(\mathrm{OH})_{3}\) , to be larger or smaller than that of 1 -propanol, \(\mathrm{C}_{3} \mathrm{H}_{7} \mathrm{OH}\) ? (b) Explain. [ Section 11.3\(]\)

Short Answer

Expert verified
(a) The viscosity of glycerol, \(\mathrm{C}_{3}\mathrm{H}_{5}(\mathrm{OH})_{3}\), is expected to be larger than that of 1-propanol, \(\mathrm{C}_{3}\mathrm{H}_{7}\mathrm{OH}\). (b) This is because glycerol has more hydroxyl groups, allowing for more hydrogen bonding between its molecules, which creates greater resistance to flow and thus higher viscosity compared to 1-propanol that has fewer hydrogen bonds between its molecules.

Step by step solution

01

Understand the molecular structure of glycerol and 1-propanol

First, let's examine the molecular structures of glycerol and 1-propanol. Glycerol has the formula \(\mathrm{C}_{3}\mathrm{H}_{5}(\mathrm{OH})_{3}\), which means it contains 3 carbon atoms, 5 hydrogen atoms, and 3 hydroxyl (OH) groups. 1-Propanol has the formula \(\mathrm{C}_{3}\mathrm{H}_{7}\mathrm{OH}\), which indicates that it has 3 carbon atoms, 7 hydrogen atoms, and 1 hydroxyl group.
02

Analyze the intermolecular forces

Now, we need to analyze the intermolecular forces between the molecules of the two substances. Intermolecular forces play a critical role in determining the viscosity of a substance. There are three main types of intermolecular forces to consider: London dispersion forces, dipole-dipole forces, and hydrogen bonding.
03

Compare the hydrogen bonding in glycerol and 1-propanol

Both glycerol and 1-propanol have polar functional groups (hydroxyl groups), which allow for hydrogen bonding between the molecules. However, glycerol has 3 hydroxyl groups while 1-propanol has only 1. This means that each glycerol molecule can participate in more hydrogen bonding compared to 1-propanol. As hydrogen bonding is the strongest type of intermolecular force, this factor will significantly impact the relative viscosity of the two substances.
04

Compare the London dispersion forces and dipole-dipole forces

The London dispersion forces and dipole-dipole forces should also be considered. However, due to similar molecular size and polarities of glycerol and 1-propanol, these forces will not have a significant difference between the two substances. Therefore, the hydrogen bonding will be the dominant factor in comparing the viscosities.
05

Predict and explain the relative viscosities of glycerol and 1-propanol

(a) Given that glycerol can participate in more hydrogen bonding than 1-propanol due to its greater number of hydroxyl groups, we can predict that the viscosity of glycerol will be larger than that of 1-propanol. (b) The explanation for this is that the increased hydrogen bonding in glycerol creates more resistance to flow, leading to a higher viscosity compared to 1-propanol which has fewer hydrogen bonds between its molecules.

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Most popular questions from this chapter

Propyl alcohol \(\left(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}\right)\) and isopropyl alcohol \(\left[\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CHOH}\right],\) whose space- filling models are shown, have boiling points of 97.2 and \(82.5^{\circ} \mathrm{C}\) , respectively. Explain why the boiling point of propyl alcohol is higher, even though both have the molecular formula, \(\mathrm{C}_{3} \mathrm{H}_{8} \mathrm{O}\) .

In terms of the arrangement and freedom of motion of the molecules, how are the nematic liquid crystalline phase and an ordinary liquid phase similar? How are they different?

Acetone \(\left[\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CO}\right]\) is widely used as an industrial solvent. (a) Draw the Lewis structure for the acetone molecule and predict the geometry around each carbon atom. (b) Is the acetone molecule polar or nonpolar? (c) What kinds of intermolecular attractive forces exist between acetone mol-ecules? (\boldsymbol{d} 1 Propanol ~ ( C H ~ \(_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}\) ) has a molecular weight that is very similar to that of acetone, yet acetone boils at \(56.5^{\circ} \mathrm{C}\) and 1 -propanol boils at \(97.2^{\circ} \mathrm{C}\) . Explain the difference.

(a) Which type of intermolecular attractive force operates between all molecules? (b) Which type of intermolecular attractive force operates only between polar molecules? (c) Which type of intermolecular attractive force operates only between the hydrogen atom of a polar bond and a nearby small electronegative atom?

At room temperature, Si is a solid, \(\mathrm{CCl}_{4}\) is a liquid, and Ar is gas. List these substances in order of (a) increasing intermolecular energy of attraction and (b) increasing boiling point.
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