Worksheet: Viscosity

In this worksheet, we will practice explaining differences in the viscosities of liquids based on the relative energies of their intermolecular forces.

Q1:

Under standard conditions, š¯‘› -butanol has a surface tension of 24.3 mJ/m2 and a viscosity of 2.593 MPaā‹…s, while tert-butanol has a surface tension of 19.2 mJ/m2 and a viscosity of 3.35 MPaā‹…s. The structures of the compounds are shown below.

tert -butanol C H 3 C C H 3 O H C H 3 n -butanol C H 3 C H 2 C H 2 C H 2 O H

Explain the difference between the surface tensions of the two liquids.

  • AMolecules of š¯‘› -butanol are more linear so a larger transient dipole can develop, producing stronger dispersion forces.
  • BThe greater branching in tert-butanol reduces the strength of each hydrogen bond.
  • CMolecules of tert-butanol have a smaller dipole moment so form weaker dipole-dipole attractions.
  • DMolecules of š¯‘› -butanol are more linear so can pack more closely together.
  • EMolecules of tert-butanol are more symmetrical so form more ordered arrangements at the liquid surface.

Explain the difference between the viscosities of the two liquids.

  • AMolecules of š¯‘› -butanol are more linear so flow past each other more easily.
  • BMolecules of tert-butanol form crystalline species which flow less easily.
  • CMolecules of š¯‘› -butanol have a smaller dipole moment so form weaker dipole-dipole attractions.
  • DThe greater branching in tert-butanol increases the strength of each hydrogen bond.
  • EThe more symmetrical vibrations of tert-butanol produce a stronger resistance to the liquid flow.

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