Name: ____ KEY_____________________________________ Date: ____________ Per: _________ Introduction to Science: LAB ACTIVITY Surface Tension of Water Surface tension refers to water’s ability to “stick to itself”. Surface tension can be measured and observed by dropping water onto a penny. The more drops that fit onto the penny means a greater surface tension, the fewer drops means a lower surface tension. Purpose: To design and test a hypothesis. Problem: How does soap affect the surface tension of water? Materials: - One penny Beaker with plain water Beaker with soapy water 2 droppers paper towels Initial practice trial: Use the plain water dropper to see how many drops of water you can fit on the penny. Make sure that the dropper does not come in contact with the water on the penny. Record the number of drops below. Initial trial number of drops __________ Before beginning lab, develop a hypothesis that answers the problem statement above. Remember to form your hypothesis using an “if ________, then________” statement. Record your hypothesis below. These are examples of how your hypothesis might look: “If we add soap to water, then the surface tension will_______________.” ‘If we add soap to water, then the number of drops will _______________.” “If we add soap to water then the stickiness of the water will _____________.” Procedure: Test your hypothesis by comparing the number of drops of plain water that can fit onto a penny to the number of drops of soapy water that can fit onto a penny. Complete five trials for each. Try to hold the dropper in the same way each time. Record your data in the table below. SAMPLE DATA Number of Drops of Plain Water and Soapy Water on a Penny Trial 1 Trial 2 Trial 3 Plain Water Soapy Water Average Examining your Hypothesis – Read your hypothesis written in Part A, Number 3. Consider your hypothesis and the results of the experiment to answer the questions below. Identify the parts of the above experiemnt: Control Group: Plain Water Independent Variable: Constants: Experimental Group: Amount of Soap Water with Soap Dependent Variable: Number of Drops Penny, Side of Penny, How the drops were dropped, number of trials Analysis: 1. Based on the analysis of your data, explain how adding soap to water affects the surface tension of water. The data shows that as soap is added to water, the number of drops the penny is able to hold decreases. A lower number of drops means the surface tension of the water decreased. 2. Does your data appear to support your original hypothesis? Depends on hypothesis Explain why/ why not. The data supports that adding soap lowers the surface tension of water. The data would not support that adding soap would increase the surface tension. Conclusion: 1. Based on your data, would you accept or reject your hypothesis? Depends on hypothesis Explain how your data supports/ does not support your hypothesis. If the data supported your hypothesis, then you would accept it. If the data does not support you hypothesis, then you would reject it. 2. Suggest a reason why it was best to complete many trials and calculate the average rather than completing only one trial when drawing conclusions about your hypothesis. If you only do one trial your results would be affected if it was not correctly done. If you complete many trials and only one was not correctly done, the results would still be meaningful. The more data you collect the more valid your results will be. 3. In any experiment, why is it important to test only one variable at a time? If you test more than one variable, then you may not know for sure which variable caused the change to occur. By only having one variable, you can link the independent variable directly to the dependent variable.
