Although viscosity varies over a factor of more than two in the series from hexane to nonane, the surface tension at 25 degrees C increases by only about 20% in the same series. How would I account for this?

Answer 1

Surface tension is the result of intermolecular forces. Viscosity is also the result of intermolecular forces plus additional factors such as entanglement of long molecules. What intermolecular forces are involved from C6H14 to C9H20? How would the increasing length plus increasing London forces affect the viscosity? For more on this, check:
http://www.newton.dep.anl.gov/askasci/mats05/mats05069.htm