(a) Would you expect the viscosity of isopropanol, \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CHOH},\) to be larger or smaller than the viscosity of ethanol, \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) ? (b) Would you expect the viscosity of isopropanol to be smaller or larger than the viscosity of 1-propanol, $\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{2} \mathrm{OH}$ ?

Let's first examine the molecular structures of the three compounds. 1. Isopropanol: \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CHOH}\) 2. Ethanol: \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) 3. 1-Propanol: \(\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{2} \mathrm{OH}\) As mentioned earlier, all three compounds have similar structures. They all have an alcohol group (-OH) and carbon atoms bonded to hydrogen atoms. However, the arrangement of these carbon and hydrogen atoms affects the overall shape and size of the molecules, which in turn impacts their viscosities.

Now let's compare the molecular structures of isopropanol and ethanol to determine which one might have a larger viscosity. Isopropanol has two methyl groups \(\mathrm{(CH}_3)\) directly attached to the carbon with the alcohol group, whereas ethanol has only one methyl group and one hydrogen attached. This makes the isopropanol molecule larger and more branched than the ethanol molecule. Larger and more branched molecules generally have greater viscosities, because they have more complex shapes that can hinder the movement of the molecules relative to one another. Additionally, the increased molecular size might lead to stronger intermolecular forces (e.g., London dispersion forces) between the isopropanol molecules, adding to the resistance against flow. Thus, we would expect isopropanol to have a greater viscosity than ethanol. So the answer to part (a) is that isopropanol would have a larger viscosity than ethanol.

Next, let's compare the molecular structures of isopropanol and 1-propanol to determine which one might have a larger viscosity. Isopropanol has its alcohol group attached to a central carbon, which is connected to two methyl groups. On the other hand, 1-propanol has its alcohol group attached to a terminal carbon, which is connected to two other carbon atoms along a straight chain. Although the overall number of carbon atoms is the same in both molecules, their arrangements differ. Isopropanol is more branched, while 1-propanol has a more linear arrangement. While larger and more branched molecules, like isopropanol, generally have greater viscosities, 1-propanol also has a longer carbon chain. Longer carbon chains have more extensive electron clouds that lead to stronger London dispersion forces between the molecules, which can increase viscosity. In this specific comparison, these forces tend to have a stronger impact on viscosity than the branching effect observed in isopropanol. So the answer to part (b) is that isopropanol would have a smaller viscosity than 1-propanol.