Polarity Lab
adapted from Patti Mason, Delphi High School, Indiana

Observations about water in space:

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Question:

Pre-Lab Questions (textbook pages 34-35):

  1. What causes some bonds to be polar?
  1. Describe hydrogen bonds. Draw a diagram showing hydrogen bonds.
  1. Define cohesion: Draw a diagram representing an example of cohesion
  1. Define adhesion: Draw a diagram representing and example of adhesion.
  1. If a molecule was not polar, would it have stronger or weaker cohesion? Explain.

Part 2Measuring Adhesion by Capillary Action

Capillary action depends on the polarity of the molecules of the liquid and the polarity of the material they are touching. An attraction between a liquid and some material it contacts will cause a liquid to “climb”upwards. As one molecule moves upwards due to, it attracts neighboring molecules in the liquid, which in turn attract their neighbors. An example of this can be found in plants, which must move water from their roots upward.

Procedure:

  1. Obtain6 strips of coffee filter and a beaker of each liquid.
  2. Mark each strip with a line 5 mm from the bottom.
  3. Holding the papers upright,dip them into the separate liquids,just up to the line you drew (5 mm of paper should be in liquid).
  4. Continue holding them upright in the liquid for 30 seconds, then remove them. Measure how high each liquid climbed in millimeters.Record the data.
  5. Repeat.

Liquid / Height (trial 1) / Height (trial 2) / Average
Water
Ethanol
Oil
3% Salt water
  1. Sketch the filter paper with beaker in the space to the right.
  2. What force is pulling the liquid up?Draw and label an arrow to show this.
  3. What force is pulling the liquid down? Draw and label an arrow to show this.
  4. Based on your results from the capillary activity, what do you conclude about the relative polarity of different molecules tested? Explain in complete sentences.

Part 2 Measuring Cohesion with Drops on a Penny

Hydrogen bonding is often an inter-molecular bond. That means it occurs betweenseparate molecules. Water hashighcohesion and surface tensiondue to hydrogen bonding. In this activity, you will investigate how strongly different types of solutions are held together by cohesive hydrogen bonding forces. You will do this by measuring how many drops of a liquid you can place on a penny before it runs over.

Note: Dry the penny between each trial! Use different droppers for the different liquids!

Do oil LASTand then place pennies in soapy water.

Trial #1 / Trial #2 / Trial #3 / Average
Water
Ethanol
Salt Water
Oil

Sketch the penny (side view) just before it over flowed. What force is pulling the water apart? What force is holding the water together? Draw and label arrows to show these.

Based on your results from the penny activity, what do you conclude about the relative strength of hydrogen bonds in each liquid tested?

Write up (due next class)

Graphs

Make 2 bar graphs to show your data. Remember to label axes and give your graphs titles! Make the graphs on a computer.

Written summary and discussion:

Paragraph 1: Explain the question you were trying to answer, and how the experiments relate to this question.

Paragraph 2: Describe your observations and data, and sources of error.

Paragraph 3: Discuss what your data suggests about the different polarity/hydrogen bonding abilities of the substances tested. Predict how these liquids would compare if used in space like we saw in the videos with astronauts

Write up (due next class)

Graphs

Make 2 bar graphs to show your data. Remember to label axes and give your graphs titles! Make the graphs on a computer.

Written summary and discussion:

Paragraph 1: Explain the question you were trying to answer, and how the experiments relate to this question.

Paragraph 2: Describe your observations and data, and sources of error.

Paragraph 3: Discuss what your data suggests about the different polarity/hydrogen bonding abilities of the substances tested. Predict how these liquids would compare if used in space like we saw in the videos with astronauts

Write up (due next class)

Graphs

Make 2 bar graphs to show your data. Remember to label axes and give your graphs titles! Make the graphs on a computer.

Written summary and discussion:

Paragraph 1: Explain the question you were trying to answer, and how the experiments relate to this question.

Paragraph 2: Describe your observations and data, and sources of error.

Paragraph 3: Discuss what your data suggests about the different polarity/hydrogen bonding abilities of the substances tested. Predict how these liquids would compare if used in space like we saw in the videos with astronauts