Grade 12U Chemistry Lab: Structure and Properties of Matter

Introduction: This activity illustrates the effect of intermolecular forces on surface tension of a liquid. Students attempt to place drops of various types of liquids on the face of a penny (or any available coin). The substances with stronger intermolecular forces have greater surface tensions and hence it is possible to place more drops on the face of the penny.

Purpose: To determine the polarity of water, ethanol, and vegetable oil, and to determine relative strengths of their intermolecular forces.

Hypothesis: develop your own hypothesis (make an educated guess as to what you predict is going to occur)

Materials Safety goggles 3 clean pennies (or nickels) 3 small beakers (50 mL or 100 mL) 3 clean eye droppers Distilled water Ethanol Vegetable oil Paper towel

Procedure1. Put on safety goggles2. Gather all necessary materials and equipment. 3. Ensure that the pennies are clean and similar to each other and the eyedroppers are similar and clean.

Note that you should not use soap to clean the pennies or eyedroppers – this will affect the results.4. Predict which substance (water, ethanol or vegetable oil) could have the most drops placed on the

face of a penny. 5. Place a penny on a dry piece of paper towel. Note that it may matter if the penny is placed heads up or

tails up, so it is best to be consistent between materials. Think about why this may matter.6. Choose one of the liquids to start with. Using the eyedropper, place drops of the liquid on the surface

of the penny. Count and record the number of drops that can be placed on the penny before the liquid spills over the side of the penny onto the paper towel.

7. Repeat steps 5 and 6 for the two remaining liquids. Be sure that clean pennies and eyedroppers are used for each trial.

8. Revisit your earlier prediction, and explain any differences.

Conclusion: Write a conclusion for this lab (think about predictions vs. results, non-human sources of error, etc). (3 marks)

Analysis Questions:1. What are intermolecular forces? How does their strength change from one compound to another

(what are factors that influence their strength)? (2 marks)2. Based on what you know about soap structure/function, why could it have altered the results of the

lab if you had washed the pennies with soap? (2 marks)3. You made predictions about which substances would have the most drops of each liquid placed on the

penny. Justify your predictions with an explanation that relates to intermolecular forces. (3 marks)4. Do you think your results would have been different if you used tap water instead of distilled water?

Explain your answer. (2 marks)

Safety ConsiderationsEye protection must be worn when handling chemicals and glassware. Ethanol is flammable. It should be used only in a well-ventilated area well from any open flames or other sources of ignition.

Mrs. Giovannone