Name _____________________________________ Chem 177L Summer 2002 Section/TA ________________________

This pre-lab exercise is designed to accompany the calorimeter experiment. Work in groups of two or three. If you need help in order to do a problem or activity, your TA will assist you. Please turn in the pre-lab exercise when you are done.

Activity 1. Comparison of the heat exchanged by metals. The computer simulation is located at:http://www.chem.iastate.edu/ChemEdGroup/GREENBOWE/sections/projectfolder/flashfiles/thermochem/heat_metal.html

Choose two metals to work with from the menu. You will place a piece of warm metal in cool water in a calorimeter. Make a prediction of which metal will raise the temperature of water the highest. You need to make a fair comparison. For example if you use 10 g of metal A at 80°C and 50 mL of water at 25°C, you should use 10 g of metal B at 80°C and 50 mL of water at 25°C.The initial temperature of the metal (T_i) should be greater than the initial temperature of the water (T_i ^' ). Note: T_i > T_i^' . The temperature of the metal must be hotter than then temperature of the water.

Metal A ___________________ Metal B ___________________ Prediction ____________________________________

Explain. Note: We already know that each metal has a different specific heat. Just telling us this fact is not an explanation.

Use the computer simulation to do your experiment. Record your data here. The specific heat of water is 4.18 J/g°C. The density of water is 1.00 g/mL.

mass T_i specific heat T_f êT

Metal A

Water

Metal B

Water

Did your prediction match your experimental results? Explain.

In your experiment, heat was transferred from ___________________________ to _______________________________

Calculate the heat that was exchanged by the water. You may use the formula q = mcêT. Show all steps and be sure to include units in all steps and in your answer. Be sure to indicate the "sign" (i.e. positive or negative).

Calculate the heat that was exchanged by the metal. Show all steps and be sure to include units in all steps and in your answer. Be sure to indicate the "sign" (i.e. positive or negative).

Compare the values of the heat exchanged by the water and the metal. Within experimental error, was the Law of Conservation of Energy obeyed?

Activity 2.

If you double the mass of metal A, keeping everything else the same, what will happen to the êT of the water ___________

If you double the mass of water, keeping everything else the same, what will happen to the êT of the water ___________

Do these two experiments using the computer simulation. Did your predictions match the results of the computer simulation? Explain.

Activity 3. Determination of the specific heat of an unknown metal.

Choose either Metal X or Metal Y (circle your choice). Design and carry out an experiment that will help you determine the specific heat of this metal.

Procedure:

Observations:

Evidence:

Claim: The specific heat of metal _________ is __________________________.

Activity 4. Investigating the heat exchanged when an acid and base react. URL:

http://www.chem.iastate.edu/ChemEdGroup/GREENBOWE/sections/projectfolder/flashfiles/thermochem/calorimetry.html

Use the computer simulation and select an acid and a base to work with. Set the volume and the concentration of the acid and the base. Record the initial temperature of each solution. Mix the solutions. Record the final temperature of the resultant solution.

Write a balanced chemical equation for this reaction.

What gained heat? _____________________________ What gave up heat ? _______________________________

Calculate the heat exchanged by the chemical reaction. Check your answer with your TA.

If you keep the concentration of your acid and base the same, but double the volume of acid and base, and if you mix these two solutions, what will happen to the êT of the solution compared to what you just did?

Prediction _______________________________. Explain

What will happen to the heat exchanged by the chemical reaction compared to what you just did?

Prediction _______________________________. Explain

Use the computer simulation to do your experiment and compare the results of the simulation to your prediction.

êT ________________________

Calculate the heat exchanged by this chemical reaction. Check your answer with your TA.

Activity 5A. Consider the following thought experiment. 50 micro-heaters having negligible mass are evenly distributed throughout 200.0 g of water in a calorimeter. When these micro-heaters are turned on and off very quickly the temperature of the water increases from 24.0°C to 30.0°C.

What gained heat? _____________________________ What gave up heat ? _______________________________

Calculate the heat exchanged by the micro-heaters. Check your answer with your TA.

Activity 5B. If you keep the mass of water the same, but double the number of micro-heaters, what will happen to the êT compared to what you did in 3A?

Prediction _______________________________. Explain

What will happen to the heat exchanged by the micro-heaters compared to what you just did?

Prediction _______________________________. Explain

Activity 5C. If you double the mass of water and double the number of micro-heaters, what will happen to the êT of the water compared to what you did in 3A?

Prediction _______________________________. Explain

What will happen to the heat exchanged by the micro-heaters compared to what you just did?

Prediction _______________________________. Explain