Constant Temperature During a Phase Change Lab

10 points

 

Purpose:  To illustrate that while ice is melting, its temperature is constant until all of the ice has melted. 

 

The Set-Up:

     Set up your lab to look like the drawing on the board.  Do not let your thermometer bulb touch the bottom of the test tube.  Putting the thermometer bulb in the middle of the water in the test tube is the best.

 

 

     Make a data table to collect Time and Temperature data.  Just a simple two-columned sheet will work fine.  Title one column “Time” and the other “Temperature”.  You are going to collect about 20 points of data.

 

 

The Experiment:

     1.  Mix about 3 spoonfuls of salt into the ice in the 400 mL beaker – STIR.  You can add a small amount of tap water to the salty ice just to get it to mix through well.

     2.  Pour 10 mL of DISTILLED water into the test tube.  Distilled water is in the “squirt bottles”.  DON’T use tap water!

     3.  Place cork with thermometer into test tube and lower the test tube into ice bath.

     4.  As the distilled water cools, it may or may not freeze.  In fact, you might notice that the temperature dips below freezing and yet you still have liquid water in the tube.  If this happens (you are so LUCKY), at around –5oC, you can take the test tube/cork/thermometer out of the salty ice water bath and carefully lift the cork out of the test tube – but try to keep the bulb of the thermometer inside of the water (in other words, don’t lift it too far out of the water).  If you then dip the thermometer up and down and up and down in the super cold water, you should notice a very quick freeze.  THIS IS VERY COOL!

 

     5. record the initial temperature of your frozen ice (it should be BELOW zero).  Take the test tube out of the ice bath and then Record the temperature every 30 seconds.  Record on your data table of TIME vs. TEMPERATURE.

 

 

     6.  After about 4 minutes, place the test tube/cork/thermometer apparatus into the palm of your warm (37oC) hand.  You should still record the temperature every 30 seconds, but you will notice that it starts melting very quickly!  This should speed up the melting process, but will it affect the temperature of the ice before it melts away?  You’ll find out, won’t you…..  (hint:  So long as the bulb of the thermometer is surrounded by ice, the temperature should remain constant.  Once the tiniest bit of water hits the bulb, LOOK OUT FOR RISING TEMPERATURES!)

 

Questions:

     1.  Why do you think you used distilled water and not tap water?

 

     2.  Why does adding salt to ice reduce the freezing point of the ice? (hint:  Look on notes from chapter 14 or look in chapter 14 of your textbook.  Don’t just say “colligative properties”.  Explain it too!)

 

     3.  True or False:  Putting the ice in the warm water bath made the temperature of the ice increase.

 

     4.  True or False:  Putting the ice into your warm hand made the ice melt faster.

 

     5.  What is all of the heat from the room (or your hand) being used to do to the ice?

 

     6.  Graph the results of temperature (y-axis) vs. time (x-axis).

 

     7.  What was the slope of the graph during the time the ice was melting? 

           Remember the formula for finding slope:  y2-y1/x2-x1

 

     8.  Calculate the q for the 10 mL of ice going from below freezing (-5oC) to its freezing point.  (Specific heat for ice is 2.03 J/goC).  (Density of water is 1 g/mL)

 

     9.  Calculate the q for the ice as it was melting.  (heat of fusion of water is 334 J/g.)

 

     10.   Calculate the q for the liquid water as it warmed its way up to 6oC (specific heat of liquid water is 4.18 J/goC).

 

What is due for this lab:

1.  Data table (Temperature vs. Time)

2.  Graph (Temperature vs. Time)

3.  Answer the questions and show work when there is a formula necessary.