Purpose
In this lab you will calculate the energy required to change one gram
of ice to water at its melting point (0 °C). This is also the
energy that must be removed from one gram of water at its freezing to point
to change it ice. This quantity is known as "the Specific Heat of
Fusion of Ice," and has the symbol DHf.
Materials
lots of ice
calorimeter
2 thermometers
graduated cylinder
Procedure
Let the tap water run hot for a few minutes to get the hottest possible
water coming out. Record the mass of the empty calorimeter cup, and
the mass of the same cup with about 200 mL of hot water in it. Place
a thermometer in the cup and wait until the temperature steadies.
Obtain about 50 g of ice. That's about 1/2 a handful. Make sure it has a minimal coating of water from melting.
Record the temperature of the hot water immediately before adding the ice. Record the temperature every five seconds until it has been constant for 25 sec. What is the final temperature?
Measure the final mass of the mixture and cup.
Data
| T of ice water (°C) |
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| V of hot water (mL) |
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| T of hot water (°C) |
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| Final V of water mix (mL) |
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| Final T of water mix (°C) |
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Calculations & Results
| m of water mix (g) |
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| m of hot water (g) |
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| mass of ice (g) |
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| DT hot water (C°) |
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| DT melted ice (C°) |
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| Cp water (cal/gC°) |
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| DHf ice (cal/g) |
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| Avg DHf ice (cal/g) | __________ | ||||
| % error (%) |
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Hints
Remember that the heat gained or lost by a substance that changes temperature
(but not phase) can be found by the formula
When a substance changes state, there is an energy change, but instead of a change in temperature, the molecules change their positions relative to each other (this is a potential energy change). The energy change for this is calculated by
Use the formula qmelt + qwarm up + qcool down = 0 to calculate the heat of fusion of water in cal/g. Compare to the book's value (seee p. 385; it’s in kJ/mole so you may have to convert). This TOTAL energy change is zero because all the energy in water to start with is still there at the end.
Be careful to show all labels and calculations!