Purpose: To calculate the molar enthalpy of dissolving for three ionic solids, and to use this information to design a cold pack.
In this experiment you will measure the heat changes which occur from various salts dissolving in water, and then you will use this information to design a hot pack and a cold pack to generate a certain temperature change.
Before the Activity
Setup temperature probe and graphing calculator with EasyData. Set up equipment- cup, and three ionic salts.
During the Activity
Measure out 100 ml of distilled water in a graduated cylinder.
Add the water to the coffee cup. Lower the temperature probe into the water in the Styrofoam cup.
Measure out 5.0 g of NH4NO3. Record the exact mass of the salt used. Do no add it to the cup.
Begin recording the temperature of the water in the cup, Ti. Select to begin to monitor temperature. The temperature reading, in C, is displayed on the upper-right corner of the graph. Record the temperature for 5 seconds.
Add the 5.0 g of NH4NO3 to the water in the coffee cup and place the lid on top. Stir the solid until it dissolves.
Record the highest temperature reached,Tf.
Empty out the coffee cup, rinse. Now repeat steps #1- #10 using 5 grams CaCl2.
1. Calculate the molar heat ( H) for the dissolving of the three solids. The formula is given below
nH substance=m * c * t
2. m = mass of the substance in grams
c= specific heat capacity of water (4.18 J/g*oC)
t = temperature change in water in calorimeter
After the Activity
Problem: Based on your calculations in your experiment chose one of the salts and design a cold pack. The total mass of the pack (salt and water ) is 400 g. The temperature change desired is 10 ?C. Assume that the specific heat of the pack (salt and water) is 4.18 J/g?C and that the cold pack is initially at 23 ?C.
Repeat the same procedure to design a hot pack.