Heat of Solution

Both the Heat of Solution and Heat of Reaction experiments will be carried out by measuring the change in temperature using a temperature probe interfaced with a computer.
To do this you will use the LoggerPro® calorimetry program.
There is a ......................TUTORIAL on using LoggerPro.

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HEAT of SOLUTION

You will weigh your Sample tube containing the UNKNOWN as well as the water you put into the calorimeter.
Insert the temperature probe in the water in the styrofoam cup calorimeter. Start the stirring.
Start the experiment. The first 20 seconds will give you the initial temperature of the water.
The soluble salt is then added from the sample tube. Make sure the stirring does not stop. The temperature should change rapidly, rising or falling and then leveling off. Continue until the experiment shuts itself off, a total of 120 seconds.
Record the average temperature before the addition.
If on solution, the temperature fell, record the lowest temperature. If it rose, record the maximum temperature.
Reweigh the sample tube to determine how much UNKNOWN you used.

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POSSIBLE PROBLEMS

• Make sure the magnetic stirring bar keeps stirring after the UNKNOWN is added.
• Swirl the calorimeter cup if necessary to maintain thorough mixing.
• Make sure all the UNKNOWN has dissolved at the end of the 120 sec. If not you should repeat the experiment.

CALCULATIONS

HEAT of SOLUTION is defined as...... joules of energy required to dissolve one gram of solute.
If energy is given off by the solution, the HEAT OF SOLUTION is negative.

Temperature_final-Temperature_initial = Temperature Change_water

(weight_water)(-Temperature change_water)(4.18 j/gºC) = Energy Change

Energy Change/(weight of UNKNOWN used) = DH solution

Always make the following checks of your calculations.....

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Why is the dissolving of some solids exothermic, while others are endothermic?