In the table we see that the viscosity of a series of hydrocarbons increases with molecular weight, doubling from the six-carbon molecule to the ten-carbon molecule.
|Hexane||CH3CH2CH2CH2CH2CH3||3.26 x 10–4|
|Heptane||CH3CH2CH2CH2CH2CH2CH3||4.09 x 10–4|
|Octane||CH3CH2CH2CH2CH2CH2CH2CH3||5.42 x 10–4|
|Nonane||CH3CH2CH2CH2CH2CH2CH2CH2CH3||7.11 x 10–4|
|Decane||CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3||1.42 x 10–3|
The surface tension of the hydrocarbon liquids in the table 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
(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.
Frequently Asked Questions
What scientific concept do you need to know in order to solve this problem?
Our tutors have indicated that to solve this problem you will need to apply the Intermolecular Forces and Physical Properties concept. If you need more Intermolecular Forces and Physical Properties practice, you can also practice Intermolecular Forces and Physical Properties practice problems.