Screen K

3.K Surface Tension for Paraffins Back to Main

This page is used to determine the surface tension of four different hydrocarbon compounds; Paraffins, Aromatics, Alcohols, and Ketones. Surface tension is the intermolecular, cohesive attraction that causes a liquid to minimize its surface area. A molecule on the surface of a liquid is subject to an inward force as a result of the attraction between molecules. The surface molecule tends to adjust itself to a minimum surface area causing the droplets to assume a spherical shape. Work is necessary to extend this surface or to bring molecules from the bulk of the liquid into the surface. One simple approach for calculating surface tension is found using

Equation (3.26)

Where: s = Surface tension, dynes/cm

M = molecular weight

C = use table

n = use table

Compound | C | n
Paraffin hydr. | 2.26 | 0.47
Aromatic hydr. | 23.0 | 0.05
Alcohols | 14.5 | 0.12
Ketones | 12.0 | 0.17

To calculate the surface tension, a compound type must be decided. Choose Paraffin, Aromatic, Alcohol, or Ketone by clicking on and shading the circle provided for that selection.

A. Paraffin

Paraffins are hydrocarbons that end in –ane, and in each case the number of hydrogen atoms are two times the number of carbon atoms plus two more for the ends of the chain.

Example: Methane (CH4)

|  | H |  |
H | - | C | - | H
|  | H |  |

B. Aromatic

Aromatic is the word used to describe an unsaturated hydrocarbon molecule where the carbon atoms for a ring, a cyclic compound. Benzene, the parent compound of the series, has the structural formula of .

C. Alcohol

The common alcohols are formed from the addition of a single hydroxyl radical to an alkyl radical. The name of the alcohol ends in "ol,"or the word "alcohol" follows the name of the alkyl radical.

Example: Methanol or methyl alcohol

Ethanol or ethyl alcohol

D. Ketone

Ketone is a compound in which the carbonyl group occurs at the interior of a carbon chain and is therefore flanked by carbon atoms.

Example: Acetone

|  | O |  |
| - | C | - |

Example: Ethyl methyl ketone

|  | O |  |  |
| - | C | - |  |

To calculate surface tension at 20° C [68° f] use the mouse to click the curser in the entry space provided for the molecular weight and input the data. Once this has been done, select Run to execute the solution.

The values for surface tension from the equation (3.26) apply at 20° C and atmospheric pressure.

The surface tension can be calculated at other conditions. Correction for temperature is done by the equation

Equation (3.27)

Where: and = conditions other than 20° C

To calculate the surface tension for temperatures other than 20° C [68° F] use the mouse to click on the "Do you wish surface at temperature other than 20° C [68° F]" box, so that a check mark is placed inside of it. Once that has been done the Temperature and Critical Temperature of the hydrocarbon must be entered into their entry spaces. To do so use the mouse to click the courser in the entry spaces and input the data. Once this has been done, select Run to execute the solution.

For information about critical temperature and pressure, please refer to example 3.1, page 57 in Volume 1 or screen 3.A of GCAP.

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