Experiment 12

Calorimetry

Objectives

To use calorimetry techniques to find the specific of aluminum and the heat of fusion of ice.

Introduction

When the temperature of a body is changed an amount AT, the amount of heat gained or lost is

where m is the mass of the body in grams and c is the specific heat in cal /g-C. One calorie is the amount

of heat required to raise the temperature of one gram of water one degree Celsius. ΔQ is in calories.

Measurements of such heat changes are made in a calorimeter which is basically an insulated cup. The

insulation helps limit the normal exchange of heat with outside, but it is not perfect. Therefore, to further

reduce the influence of the outside, one tries to begin measurements with the contents of the cup below

room temperature and to end measurements when the cup contents are as far above room temperature as

they were below room temperature at the beginning. Heat gained by the surroundings is then

approximately equal to heat lost to the surroundings.

Procedure 1

You will determine the specific heat of aluminum metal by placing heated aluminum pellets into distilled

water in your calorimeter. Put about 80g of Al pellets in the top of your double boiler along with a

thermometer. Fill the double boiler about ¼ full of water and start heating it. Place about 80g of cold

water in the calorimeter cup. Check the temperature of the water and let it warm until it is about 5^o C

below room temperature. Monitor the temperature, stirring the water occasionally, until equilibrium

temperature is reached. Record that temperature. Be sure you know: the exact weight of water in the

cup, the exact dry weight of the pellets, the starting temperatures of the pellets and water, and final

temperature of both. Calculate the specific heat of aluminum from this data and compare with the

accepted value of 0.22 cal/g-C^o.

Procedure 2

You will find the heat of fusion of ice (the heat 1 g of ice at O^o C requires to melt to water at 0^o C) by adding

about 25 g of ice to about 100 g of water. By weighing the cup before and after the measurements you

will be able to measure both the mass of water and the mass of the ice. Be sure the water is about 5^o C

above room temperature at the beginning. Assume the ice is initially at O^o C. Be sure the ice is dry before

you put it in the water. Calculate the heat of fusion for ice and compare your value with the known value

of 80 cal/g.