Author

Mara Desso, Valencia High School

Sensor / Probe: iCelsius

The iCelsius is a probe that attaches to iPods, iPads, and iPhones and reads the temperature of a substance while generating a temperature versus time graph on the Apple device. Features include:

·Live Display - shows useful temperature data in one shot

·Graphs - with pan and zoom touch support

·Alarms - Generate alarms when temperature goes outside configurable (lower and/or upper) limit

·Snapshot Record - Ability to record a single reading, along with title, picture and note

·Continuous Record - Ability to continuously record as well as to add notes, take a picture and drop a pin on the graph

·History - Access all your previous records

·Recipes - For cooking and barbecue, choose preset recipe or create your own

Sample Investigation: Heating Curve of Lauric Acid Lab

Independent variable- time (seconds)

Dependent variables- temperature (celsius)

Constants- substance is lauric acid, tested in the same room, temperature of the room is constant, air pressure is constant

Controls- Unheated lauric acid

Materials

chemical splash goggles

beaker tongs

2 beaker, 400-mL

hot plate

2 thermometers

large test tube

lauric acid (C₁₂H₂₄O₂)

test-tube holder

stop watch

2 pens or pencils of different colors

Safety

Wear safety goggles at all times in the laboratory. Hot plates and heated glassware can cause burns. Avoid touching the hot plate or the heated beaker of water. Handle the heated test tube with a test-tube holder. Note the caution alert symbols here and with certain steps of the Procedure.

Procedure

Part A

1. Put on safety goggles

2. Fill one 400-mL beaker with 250ml of tap water and heat it on the hot plate. Use the iCelsius probe to monitor the water’s temperature, and adjust the hot plate as needed to keep the temperature constant at about 60°C. CAUTION: Do not touch the hot pate or beaker.

3. Use hot and cold tap water to fill the second 400-mL beaker to 250 ml of water that is adjusted to a temperature of about 30°C. ( add ice if needed)

4. Obtain a large test tube containing about 15g of lauric acid from the teacher and place the test tube in the 60°C water bath, as shown in Figure 41-1. (adjust hot plate to #3 setting, use beaker tongs to move the beaker on and off the hot plate as needed to maintain 60°C )

5. Insert the iCelsius probe into the lauric acid test tube and as the solid begins to melt record the approximate temperature at which melting occurs, and continue heating the lauric acid until the temperature is about 10°C higher.

6. Using the test-tube holder, remove the test tube from the 60°C water bath and place it in the 30°C water bath. Make sure that the level of the water in the beaker is above the level of the liquid in the test tube.

7. Slowly swirl the liquid. When the temperature of the liquid decreases to 55°C, begin taking temperature readings every 30 seconds. (One lab partner should stir and read the thermometer, while the other partner watches the clock and records the temperature readings.) Record the temperature to the nearest 0.2°C.

8. When the sample is mostly solid, stop swirling. Continue to take temperature readings until the data table is filled.

Part B

9. Check the temperature of the hot-water bath and adjust it to 60°C if necessary.

10. Remove the test tube from the 30°C water bath and place it in the beaker of water at 60°C. Immediately begin to take temperature readings every 30 seconds. Begin stirring gently as soon as one is able to move the thermometer easily. Continue to measure and record the temperature until the lauric acid is completely melted.

11. Turn off the hot plate. Carefully remove the thermometer from the sample of lauric acid and return the test tube to the teacher. Pour the water in the beakers down the drain, wipe and dry the thermometers with a papertowel.

12. Clean up the work area and wash hands before leaving the laboratory.

Sample Data & Analysis and Interpretation

Sample Data Set

As the lauric acid is cooled, the temperature decreases logarithmically. As the lauric acid goes through the phase change from liquid to solid (freezing) all of the energy being lost is causing the particles to form stronger intermolecular forces rather than slowing down. Alternatively, when the lauric acid is heated and melts, the energy during the phase change is being used to break the intermolecular forces rather than causing molecules to speed up.

Photos

Movies

Full Length Video- part 1 and 2