Procedure and Results
Preparation of detergent solutions
Prepare four solutions having different concentrations of detergent. The compositions of each of these are:
Measure the surface tension and bubble size of each solution as described in the sections, "Measuring Surface Tension" and "Measurement of Bubble Size" below.
To study the effect of added glycerin, prepare 500 mL of a detergent-water solution of the same concentration as one of your previous solutions. For example, prepare 500 mL of a solution containing 1.0 g of detergent in 100 mL of water, by adding 5.0 g of detergent to 500 mL of water, and stir well. Pour out exactly 100 mL of this solution into each of four beakers. To the first beaker add 2 drops of glycerin and mix thoroughly. Add 4, 6, and 8 drops, respectively, to each of the remaining beakers. Be sure that you mix these thoroughly also. Measure the surface tension and bubble size for each of these solutions.
Measuring surface tension
Make two marks on a disposable pipet as shown below:
With a rubber bulb, fill the pipet with water to a level above the upper mark. Using your finger let the level drop to the upper mark. Let the pipet drain slowly to the lower mark counting the drops. Record the number of drops and repeat one more time. Tabulate your results and calculate and record the average of the two trials.
The greater the number of drops the lower the surface tension. When repeating this with detergent solutions use air from the pipet to prevent foam from entering the pipet. Let this drain back into the beaker to conserve the detergent solution.
Measurement of bubble size
Measure and record the diameter of 5 bubbles for each of your detergent solutions and each of the detergent-glycerin solution. Calculate the average bubble size for each of the solutions from the five trials.
Your results section should contain a table with each of the two values of surface tension (number of drops) for each of the detergent solutions and each of the detergent-glycerin solutions. The average values should also be entered in your table. There should also be a corresponding table containing the individual bubble sizes with their average values (in cm).
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