Experiment 5

Surface Tension and Soap Bubbles

Purpose, Conclusions and Extensions

Purpose

There are several purposes for this experiment :

1) Is there an effect of the composition of a soap solution on its surface tension?

This will be explored by preparing several solutions of different concentrations of the liquid detergent "Joy" and measuring the surface tension of these solutions. Here the concentration of the "Joy" is the independent variable and the surface tension is the dependent variable.

It is widely accepted that addition of glycerin (glycerol) to soap solutions results in stronger, longer lasting bubbles. But are the properties of the solution changed? This can be tested by adding glycerin to a soap solution and measuring the effect of several concentrations of glycerin on the surface tension. Here the concentration of the glycerin is the independent variable and the surface tension is the dependent variable. The concentration of the "Joy" is kept constant.

2) Is there an effect of the composition of a soap solution on the size of the soap bubble it forms?

Using the Stanislaus Bubblometer the average size of bubbles obtained with your solutions can be measured. In this part of the experiment, the concentration of the "Joy" and the concentration of the glycerin are the independent variables and the bubble size is the dependent variable.

3) Finally, is there is a correlation between the surface tension of a soap solution and the bubble size?

This question can be answered from the data collected in the first two parts. No additional experiments are needed. By plotting the values of surface tension (independent variable) versus the bubble size values (dependent variable), the existence of a correlation can detected.

Conclusions

Use the data tabulated and plotted in your Results section to draw conclusions to the purposes stated above.

1. Is there an effect of the concentrations of "Joy" and of glycerin in a soap solution on its surface tension? If so, describe the effects.
2. Is there an effect of these concentrations on the size of the soap bubble formed? If there is, describe these effects.
3. Finally, is there is a correlation between the surface tension of a soap solution and the size of the bubble it forms?

Extensions

It is reported that these bubble solutions work better after being stored for at least 24 hrs in the dark. Other recipes have been suggested. There is evidence that Castile soap, because its formed from olive oil, makes excellent bubbles. Different soaps, detergents, and aging could be evaluated in order to determine the optimum system for maximum bubble size.

An interesting challenge is to develop a method of providing a constant gas flow rate to allow study of bubbles in other places.

Other possible extensions include a study the effect of the rate of air flow on bubble size or the effect of the bubble size on its lifetime.