Weather: Thermometers

We jumped into the short week with a lab designed to help students understand the relationship between temperature and pressure.  The Lesson 52 Worksheet has two parts, and we conducted the lab for part 2.  We adjusted the lab procedure as follows:

  1. Bring 200 mL of water to 80 degrees Celsius, measuring temperature with a digital thermometer.
  2. Invert a 10 mL graduated cylinder and place in the heated water for 3 minutes.
  3. Quickly and carefully move the graduated cylinder from the heated water into 100 mL of room temperature water (colored blue with 2 drops of food coloring) and quickly add ice to chill the water.
  4. Record observations throughout the experiment.

Several groups had difficulty observing the intended outcome, so I conducted a quick demonstration toward the end of class and we discussed why the results occurred.  The picture below shows cold water entering the graduated cylinder and rising above the water line.IMG_0547

Students successfully reasoned that at the beginning of the experiment, the graduated cylinder contains room temperature air.  When placed in the heated water, the steam (evaporated water molecules) displace the room temperature air in the graduated cylinder, as evidenced by the bubbles observed leaving the graduated cylinder.  When the steam-filled graduated cylinder was transferred to the cold water, the decrease in temperature caused the steam to condense back into liquid form, and the volume of space occupied by the liquid water decreased.  As a result, cold water was drawn into the graduated cylinder.  The concepts of pressure and vacuum were introduced by students looking to explain further, and those concepts will be introduced in upcoming lessons.  For reference, the Lesson 52 PowerPoint is attached.  For homework, students should complete textbook questions 5-9 or take notes on the lesson.


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