Temperature Probes & Heating/Cooling Curves

Author(s): Jim Schwagle, Jim Mauch
Probeware / Instrumentation
SED 695B; Fall 2005

Research Question: What does the temperature vs. time plot look like for a substance undergoing a phase change?

Standards addressed:

H.S. Chemistry

  • 6f.* Students know how molecules in a solution are separated or purified by the methods of chromatography and distillation.
  • 7c. Students know energy is released when a material condenses or freezes and is absorbed when a material evaporates or melts.
  • 7d. Students know how to solve problems involving heat flow and temperature changes, using known values of specific heat and latent heat of phase change.
Independent variable
Dependent variables
Controls
Series
Time
Temperature
None
Lauric Acid, Isopropyl Alcohol, Water
Materials
Procedures
  • Vernier Lab Pro Interface
  • Computer
  • Logger Pro Software
  • Temperature Probe
  • Lauric Acid
  • Isopropyl Alcohol (70% or 90%)
  • Distilled Water
  • Hot Plate

Isopropyl Alcohol & Water

  1. Make a mixture containing approximately 50% Isopropyl Alcohol and 50% Distilled water.
  2. Place in a flask or test tube.
  3. Place three or four porcelain chips in the container to moderate bubbling during boiling.
  4. Stopper the container with a hole for gas to escape and a hole for the temperature probe.
  5. Ensure that the probe or the thermometer extends into the container but above the mixture.
  6. Heat slowly until the mixture boils recording the temperature at regular intervals.

Lauric Acid

  1. Fill a 250 mL beaker or other container approximately 3/4 full with Lauric Acid.
  2. Place the temperature probe in the middle of the acid flakes without touching the sides or bottom.
  3. Heat the acid until it melts completely.
  4. Adjust the data range so that data is taken during the entire time the acid cools and solidifies.
  5. Remove the heat and begin taking data.
  6. Clean container with methanol or benzene.

Caution:

The mixture is flammable and any that boils out of the container can burst into flame. The mixture can and will vigorously boil. Our suggestion is to not use a bunsen burner.

Smaller containers such as a 25mm x 150mm test tube require only a very small heat source such as an alcohol burner. Bunsen burners, even adjusted to a low setting, easily boil out of the test tube. Even with an alcohol burner, care must be taken through adjustment of the position of the burner to slowly boil the mixture.

Larger containers such as a 250 mL flask can be heated with a hot plate more easily and safely than with a bunsen burner.

Lauric Acid is a skin irritant. See the material safety data sheet below.

 
Blank Data Table
Time (s)
Temperature(Celsius)
   
   
   
   
   
   
The data taken is simple. At defined intervals note the time and temperature.
Sample Data Table
Time (s)
Temperature(Celsius)
10
25
20
30
30
35
40
35
50
35
60
35
An example of data that might be taken.
Time vs. Temperature for a Heating Mixture of Water & Isopropyl Alcohol
               
Time (s) Temp(°C) Time (s) Temp(°C) Time (s) Temp(°C) Time (s) Temp(°C)
               
0.0 46.9 812.5 81.9 1625.0 83.6 2763.0 99.6
12.5 47.3 825.0 81.9 1637.5 83.7 2775.5 99.7
25.0 47.8 837.5 81.9 1650.0 83.8 2788.0 99.6
37.5 48.4 850.0 81.9 1662.5 83.9 2800.5 99.7
50.0 48.9 862.5 81.9 1675.0 84.0 2813.0 99.6
62.5 49.7 875.0 81.9 1687.5 84.1 2825.5 99.6
75.0 50.6 887.5 81.8 1700.0 84.1 2838.0 99.7
87.5 51.6 900.0 81.9 1712.5 84.3 2850.5 99.6
100.0 52.7 912.5 81.9 1725.0 84.4 2863.0 99.6
112.5 53.9 925.0 82.0 1737.5 84.5 2875.5 99.6
125.0 55.4 937.5 82.0 1750.0 84.7 2888.0 99.7
137.5 57.2 950.0 82.0 1762.5 84.7 2900.5 99.6
150.0 60.2 962.5 82.1 1775.0 84.9 2913.0 99.6
162.5 65.5 975.0 82.1 1787.5 85.1 2925.5 99.6
175.0 71.2 987.5 82.1 1800.0 85.2 2938.0 99.7
187.5 75.3 1000.0 82.1 2138.0 90.7 2950.5 99.6
200.0 78.8 1012.5 82.1 2150.5 91.1 2963.0 99.7
212.5 80.8 1025.0 82.1 2163.0 91.6 2975.5 99.6
225.0 81.3 1037.5 82.1 2175.5 92.1 2988.0 99.7
237.5 81.6 1050.0 82.2 2188.0 92.6 3000.5 99.7
250.0 81.8 1062.5 82.1 2200.5 93.0 3013.0 99.7
262.5 81.8 1075.0 82.1 2213.0 93.6 3025.5 99.7
275.0 81.8 1087.5 82.1 2225.5 94.1 3038.0 99.6
287.5 81.8 1100.0 82.1 2238.0 94.5 3050.5 99.6
300.0 81.9 1112.5 82.1 2250.5 95.2 3063.0 99.7
312.5 81.9 1125.0 82.2 2263.0 95.7 3075.5 99.6
325.0 81.9 1137.5 82.3 2275.5 96.1 3088.0 99.7
337.5 81.9 1150.0 82.3 2288.0 96.6 3100.5 99.6
350.0 81.9 1162.5 82.3 2300.5 96.9 3113.0 99.7
362.5 81.8 1175.0 82.3 2313.0 97.3 3125.5 99.7
375.0 81.9 1187.5 82.3 2325.5 97.7 3138.0 99.7
387.5 81.9 1200.0 82.3 2338.0 98.0 3150.5 99.6
400.0 81.9 1212.5 82.3 2350.5 98.2 3163.0 99.7
412.5 81.9 1225.0 82.3 2363.0 98.3 3175.5 99.7
425.0 81.9 1237.5 82.4 2375.5 98.5 3188.0 99.7
437.5 81.9 1250.0 82.4 2388.0 98.7 3200.5 99.7
450.0 81.9 1262.5 82.4 2400.5 98.8 3213.0 99.6
462.5 81.9 1275.0 82.4 2413.0 98.9 3225.5 99.6
475.0 81.9 1287.5 82.4 2425.5 99.0 3238.0 99.7
487.5 81.8 1300.0 82.5 2438.0 99.1 3250.5 99.7
500.0 81.9 1312.5 82.5 2450.5 99.2 3263.0 99.6
512.5 81.9 1325.0 82.5 2463.0 99.2 3275.5 99.7
525.0 81.9 1337.5 82.5 2475.5 99.2 3288.0 99.7
537.5 81.9 1350.0 82.5 2488.0 99.3 3300.5 99.7
550.0 81.9 1362.5 82.5 2500.5 99.3 3313.0 99.7
562.5 81.9 1375.0 82.6 2513.0 99.3 3325.5 99.7
575.0 81.9 1387.5 82.6 2525.5 99.5 3338.0 99.7
587.5 81.9 1400.0 82.7 2538.0 99.5 3350.5 99.7
600.0 81.9 1412.5 82.7 2550.5 99.5 3363.0 99.7
612.5 81.9 1425.0 82.7 2563.0 99.5 3375.5 99.7
625.0 81.9 1437.5 82.7 2575.5 99.5 3388.0 99.7
637.5 81.9 1450.0 82.8 2588.0 99.6 3400.5 99.7
650.0 81.9 1462.5 82.8 2600.5 99.5 3413.0 99.7
662.5 81.9 1475.0 82.8 2613.0 99.6 3425.5 99.7
675.0 81.9 1487.5 82.9 2625.5 99.6 3438.0 99.7
687.5 81.9 1500.0 82.9 2638.0 99.6 3450.5 99.7
700.0 81.9 1512.5 83.0 2650.5 99.6 3463.0 99.7
712.5 81.9 1525.0 83.1 2663.0 99.6 3475.5 99.7
725.0 81.9 1537.5 83.2 2675.5 99.6    
737.5 81.9 1550.0 83.2 2688.0 99.6    
750.0 81.9 1562.5 83.3 2700.5 99.6    
762.5 81.9 1575.0 83.4 2713.0 99.6    
775.0 81.9 1587.5 83.4 2725.5 99.6    
787.5 81.9 1600.0 83.4 2738.0 99.6    
800.0 81.9 1612.5 83.6 2750.5 99.6    
Approximately 200mL of a 50/50 mixture of Isopropyl Alcohol and Distilled Water was placed in a flask and heated on a hot plate until boiling. The temperature was recorded at 12.5s intervals for approximately 30 minutes. Data was taken at this short interval to ensure a smooth curve. The Lap Pro software can take data over a wide range of intervals so that the data is appropriate for the experiment. More data was taken here than really necessary.
A 50/50 mixture of Isopropyl Alcohol and Distilled Water was heated until boiling. In section A the mixture heats until approximately 80 C, at which time the Isopropyl begins boiling. This is shown by the flat portion during section B. After all of the Isopropyl has boiled away the remaining water heats, shown in section C until it reaches 100 C in section D where it boils away. Phase changes occur during the flat part of the curve when the temperature remains constant. Heat absorbed during this time is used to change phases and is called the "Latent Heat".
Lauric acid was heated until it melted. After removing the heat, the temperature was recorded at 10s intervals until the Lauric Acid completely solidified, approximately 4 hours. The flat part of the curve denotes the time interval when the Lauric Acid was "freezing", or changing from liquid to solid. It shows that the heat removed during this time was the heat required to change phases, so no temperature change was seen. Heat lost during this time is called the Latent Heat of Fusion.
The temprature probe from Vernier is made of stainless steel and is impervious to a wide range of substances including acids and bases.
The LabPro interface can take data independently or while connected to a computer. It also can be connected to Palm Pilots and TI 80 and 90 series calculators.

References & Links: