MHS Chemistry
Thermometer Calibration

Introduction

In this activity we will be determining the correction factor for a spirit thermometer.  We will base this correction on the original basis for the centigrade temperature scale.

Temperature scales should be based on two temperatures that are easily reproducible in any lab.  The fahrenheit scale is based on the lowest temperature that can be reached with a mixture of snow, ammonium chloride, and alcohol (called 0 degrees), and average human body temperature (called 100 degrees).  According to legend, Mr. Fahrenheit did not sample the temperature of many people (he used his wife!), so his 100 degree mark is a little high.  More likely, the 100 degree mark was adjusted to make the melting point of ice an even 32 degrees F, and the boiling point of water was 212 degrees F.

The centigrade scale was designed to be more easily repeatable by people in other labs (eventually, Mrs. Fahrenheit died, and became unavailable for checking the accuracy of thermometers).  The freezing point of pure water was set at 0 degrees C, and the boiling point of pure water (at standard atmospheric pressure) was set at 100 degrees C.  These two conditions are relatively easy to reproduce in our chemistry lab.  It is recognized the "C" as a label means "degrees Centigrade."

Thermometer Notes:  Never rest a thermometer on it's bulb.  Never lay a thermometer flat.  Never let a thermometer roll.  Never leave a thermometer leaning in a beaker.  Always use rubber stoppers and glycerin.

Procedure

1. Obtain a thermometer from the rack in front of the class.  Make sure that the column of fluid has not separated.
2. Place the thermometer in a split rubber stopper as demonstrated, then immerse the bottom inch or so in slushy ice water.  When the temperature has steadied, record it in the data table below.
3. Immerse the thermometer in a beaker of boiling water. When the temperature has steadied, record it in the table below.  Don't put your thermometer away until after analysis part 1.
Data
 Reading Actual Temperature Freezing Point _______________ _______________ C Boiling Point _______________ _______________ C

Analysis - part 1

1. Plot a graph of "Actual Temperature" vs. "Readings."  Make the scales big enough to cover the entire range of the thermometer.  This should be a proper graph.
2. Draw a straight line going through both points.
3. Determine the equation for the line, with the form A = mR + b.   "A" is the actual temperature, "R" is the reading, "m" is the slope of the line, and "b" is the A-intercept.
4. Attach a label to your thermometer that has the two points you graphed (R, A), or the equation from #3.  Use a sharpie pen so this label lasts all year (ask your teacher to borrow a sharpie pen).
5. What is the actual temperature when your thermometer reads 55.1 C?
6. What is the actual temperature when your thermometer reads 119.3 C?
7. What is the actual temperature when your thermometer reads -26.4 C?
Analysis - part 2
1. Plot a graph of "Degrees F" vs. "Degrees C."  Use the freezing point and boiling point of water in each scale for your points.  This should be a proper graph, with "F" on the y-axis and "C" on the x-axis.
2. Draw a straight line going through both points.
3. Determine the equation for the line, with the form F = mC + b.   "F" is the Farenheit temperature, "C" is the centigrade temperature, "m" is the slope of the line, and "b" is the F-intercept.
4. What is the Farenheit temperature when the actual temperature is 55.1 C?
5. What is the Farenheit temperature when the actual temperature is 119.3 C?
6. What is the Farenheit temperature when the actual temperature is -40.0 C?
What to Pass In
1. This sheet.
2. The graph, completed as described in "Analysis - part 1."
3. A sheet of paper with your work and answers to 3, 5, 6, & 7 in "Analysis - part 1."  For the equation of the line, you may chose to show the work on the graph.
4. The graph, completed as described in "Analysis - part 2."
5. A sheet of paper with your work and answers to 3 - 6 in "Analysis - part 2."  For the equation of the line, you may chose to show the work on the graph.
6. Of course, remember the usual title stuff and neatness requirements.