In Table $11.3,$ we saw that the viscosity of a series of hydrocarbons increased with molecular weight, doubling from the six-carbon molecule to the ten-carbon molecule. (a) The eight-carbon hydrocarbon, octane, has an isomer,isooctane. Would you predict that isooctane would have a larger or smaller viscosity than octane? Why? (b) Predict the relative order of boiling points of the hydrocarbons in Table $11.4,$ from lowest to highest. (c) The surface tension of the hydrocarbon liquids in Table 11.4 does increase from hexane to decane, but only by a rather small amount $(20 \%$ overall, compared to the doubling of viscosity). Which of the statements below is the most likely explanation for this phenomenon? (i) The flexibility of the molecules has a much larger effect on viscosity than on surface tension.(ii) Viscosity only depends on molecular weight, but surface tension depends on molecular weight and on intermolecular forces. (iii) Larger molecules can make larger liquid droplets and therefore have lower surface tension. (d) Nonane has a viscosity of $7.11 \times 10^{-4} \mathrm{kg} / \mathrm{m}-\mathrm{s}$ at $20^{\circ} \mathrm{C}$ .
n-octyl alcohol, $\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{7} \mathrm{OH},$ has almost thesame molecular weight as no name, but its viscosity is $1.01 \times 10^{-2} \mathrm{kg} / \mathrm{m}-\mathrm{s}$at $20^{\circ} \mathrm{C} .$ Which of the following statements is the most
likely explanation for this phenomenon? (i) The stronger the intermolecular forces in a liquid, the smaller its viscosity. (ii) The stronger the intermolecular forces in a liquid, the larger its viscosity
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