Lab Report - Aberdeen School District



Lab Report

Title:____

Question:

What is the effect of different amounts of soap on the surface tension of water? (identify m.v. & r.v.)

Background Information:

Properties of water:

One of the properties of water is surface tension, or cohesion. This refers to the ability of water molecules to stick to one another. This is also the reason that “water striders” can walk on the top of the water without falling through.

Soap is a surfactant, which is a “chemical agent that is capable of reducing the surface tension of the liquid in which it is dissolved”.

Hypothesis:

If ______

then _____

because _____

Materials:

• 400-mL plain water in a 600 mL beaker

• 15-mL AJAX orange dish soap

• (2) 100-mL beakers

• one penny (use only one side)

• stir stick

• two pipettes

• paper towels

Procedure:

1. Pour 15-mL dish soap into 100-mL beaker at supply station. Gather remaining materials and take to lab station.

2. Place penny onto a paper towel on a vertical, solid surface.

3. Fill empty 100-mL beaker with 30-mL water.

4. Fill the second pipette with plain water from the small beaker, hold pipette vertically and drop liquid in the pipette slowly onto the penny while counting the number of drops. Continue dropping water until water flows off of penny. Record____________________. Repeat trial 3 more times and record ______________________ for each trial. Compute average drops per trial and record average onto data chart.

5. Rinse and empty beaker and pipette used for dropping liquid onto penny.

6. Refill 100-mL beaker with 30-mL water. Add 3 drops of soap using “soap” pipette”. Stir soap solution gently.

7. Repeat steps 4-5 for soapy water.

8. Refill 100-mL beaker with 30-mL water. Add 9 drops of soap using “soap” pipette”. Stir soap solution gently.

9. Repeat steps 4-5for soapy water.

10. Refill 100-mL beaker with 30-mL water. Add 18 drops of soap using “soap” pipette”. Stir soap solution gently.

11. Repeat steps 4-5 for soapy water.

12. Clean up excess water with paper towels, then clean and return everything to its proper place.

Data:

(title)

Manipulated Variable vs. Responding Variable

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| |Responding Variable |

|Manipulated Variable |(units) |

|(units) | |

| |Trial 1 |Trial 2 |Trial 3 |Trial 4 |Average |

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|Lowest condition | | | | | |

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|Condition 2 | | | | | |

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|Condition 3 | | | | | |

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|Highest condition | | | | | |

Analysis:

Create a hand-drawn line graph following the data table in your lab report. It should have a title, the trials (of dropping liquids—manipulated variable) along the bottom and the number of drops (responding variable) up the right side. The different CONDITIONS should be represented by different lines (of different colors). Provide a “key” or “legend” that shows what condition each trial represents.

Conclusion:

0 Write a conclusion for this experiment.

In your conclusion, be sure to:

• Answer the experimental question.

• Include supporting data from the Soap vs Surface Tension Data table.

(low AND high data averages)

• Explain how these data support your conclusion.

• Provide a scientific explanation for the trend in the data.

|Question: What is the effect of different amounts of added soap on |

|the surface tension of water? |

|Conclusion: (use FIVE bullet points) |

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