University of Virginia
Physics Department

## Mixing Warm and Cold Water

A Physical Science Activity

### Student Activity

Materials

• CBL system
• TI-83 graphing calculator
• 2 Vernier temperature probes
• Styrofoam cup
• 250-mL beaker
• Cold water
• Warm water
• Stirrer

Procedure

1. Put your safety goggles on. NOTE: Goggles should be worn throughout the activity.
2. Plug in the first temperature probe into the first CBL input, and the second temperature probe into the second CBL input.
3. Run the Vernier program PHYSICS on the calculator.
4. Set up the calculator and CBL unit for two temperature probes, one in channel one and the other in channel two.
5. To setup the calculator for data collection:
1. Change the data collection speed by selecting COLLECT DATA from the main menu, then select TIME GRAPH from the data collection menu.
2. Enter 2 as the time between samples, in seconds
3. Enter 45 as the number of samples
4. Press enter, then select USE TIME SETUP to continue.
5. Select LIVE DISPLAY
6. Enter 0 as the minimum temperature (Ymin)
7. Enter 50 as the maximum temperature (Ymax)
8. Enter 5 as the temperature increment (Yscl)
6. Construct a calorimeter by placing a Styrofoam cup into a 250-mL beaker.
7. Measure 50 mL of cold water with a graduated cylinder and pour this into the calorimeter. Put probe 1 in the cold water.
8. Measure 50 mL of warm water using the graduated cylinder and leave this water in the cylinder. Put probe 2 into the graduated cylinder.
9. The probes must be in for at least 45 s to measure the correct temperature. When the probes have been in for that time, start data collection.
10. After the first few readings are made, pour the warm water into the Styrofoam cup also transferring the probe. Stir with stirrer until the data collection is complete.
11. Proceed to the graph displaying the curves by pressing ENTER. At SELECT GRAPH, choose option 3, BOTH to display probes 1 and 2 on the same graph. Press ENTER. Observe that they both converge on the same temperature, because the temperature in the Styrofoam cup at the end is at only one temperature. Find the maximum and minimum values that were found for Probe 1 and Probe 2 and record. Use the up and down arrows to move from the probe 1 graph to the probe 2 graph.

Data Sheet

 Cold Water (Probe 1) Hot Water (Probe 2) Minimum Temperature (°C) Maximum Temperature (°C) Change in Temperature DT (°C)

Questions:

1. Calculate the heat gained by the cold water and the heat lost by the hot water by the equation: Q = DT * m * c where m = 50 g of water and c = 4.184 J/g°C for water.

2. Calculate the percent difference of the heat gain and the heat loss: % Difference = [((heat lost - heat gained)/ heat lost] * 100