CHANGES OF STATE
EXPERIMENT 5
OBJECTIVE
The objective of this experiment is to determine the freezing point using a graph of temperature
versus time and to determine melting points.
EQUIPMENT AND CHEMICALS
Paradichlorobenzene
Biphenyl
400 ml beaker
100 oC thermometer
Ring stand with wire screen
Split cork
Melting point tubes
Bunsen burner
DISCUSSION
Matter exists in three states: solid, liquid, or gas. The particular state that matter exists in depends
upon the temperature and atmospheric pressure. When sufficient heat is applied so that the
individual molecules can overcome their attraction for each other, a transition from one physical
state to another occurs.
The freezing point is the temperature at which a liquid begins to change to a solid and at which point
both states of matter (solid and liquid) exists at the same time. Therefore, the melting and freezing
points are the same temperature.
When a substance goes from one state of matter to another, it is referred to as a change of state.
PROCEDURE
PART A DETERMINATION OF FREEZING POINT
The paradichlorobenzene will be heated past its melting point and allowed to cool. While cooling,
the temperature and time will be recorded. A graph will be plotted to determine the freezing point of
he paradichlorobenzene.
1.
Set up the apparatus as demonstrated by the instructor.
2.
There will be a beaker containing boiling water set up on a hot plate. Insert a thermometer
into a large test tube containing paradichlorobenzene, place the test tube into the boiling
water and allow the paradichlorobenzene to melt. Continue to heat until the temperature of
the dichlorobenzene is above 65 oC.
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3.
While the paradichlorobenzene is heating, add 300 ml of water to your apparatus and heat
the water to 40 oC.
4.
Quickly transfer the melted paradichlorobenzene test tube to your beaker with the 40 oC
water and support as shown in the demonstration apparatus.
5.
Gently stir the paradichlorobenzene with the thermometer while it cools. When the
temperature in the test tube reaches 65 oC, record the temperature every 30 seconds until the
paradichlorobenzene completely solidifies.
6.
Plot a cooling curve using the temperature versus time data. Plot time on the horizontal axis
and temperature on the vertical axis.
6.
Extrapolate the temperature plateau on your graph across to the horizontal axis to find the
freezing point of the paradichlorobenzene.
PART B:
MELTING POINTS
1.
Dab the open end of a melting point tube into a small sample of biphenyl.
2.
Turn the tube open end up and gently tap bottom of the tube to pack the biphenyl to the
bottom of the tube. Repeat this process until there is about 5mm of sample packed into the
bottom of the tube.
3.
Prepare two samples as above.
4.
Attach the melting point tube (the open end up) to the end of the thermometer using a rubber
band.
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5.
Setup the melting point apparatus as
demonstrated by the instructor.
6.
Heat the water rapidly until the biphenyl in
the melting point melts and note this
temperature.
7.
Cool the water bath well below the
temperature at which the biphenyl melted.
8.
Attach the second melting point tube with the
biphenyl in it to the thermometer.
9.
Rapidly heat the water to about 10 oC below
the melting point noted earlier.
10.
Slowly heat the water and note the
temperature range at which the biphenyl
begins to melt until it completely melts.
11.
Obtain an unknown compound and determine
its melting point range.
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NAME ____________________
DATE ____________________
SECTION _________________
CHANGES OF STATE
REPORT SHEET
EXPERIMENT 5
COOLING CURVE DATA
Time
Temperature
Time
0:00
0
7:00
14:00
0:30
7:30
14:30
1:00
8:00
15:00
1:30
8:30
15:30
2:00
9:00
16:00
2:30
9:30
16:30
3:00
10:00
17:00
3:30
10:30
17:30
4:00
11:00
18:00
4:30
11:30
18:30
5:00
12:00
19:00
5:30
12:30
19:30
6:00
13:00
20:00
6:30
13:30
20:30
65 C
Temperature
Time
Temperature
MELTING POINTS
Rapid MP
Gradual MP
Melting point of biphenyl (69 – 71 oC)
___________ oC
___________ oC
Melting point of unknown
___________ oC
___________ oC
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Freezing Point: ________ oC
Paradichlorobenzene Cooling Curve
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