Adapted from a lab described by Bob Becker, Kirkwood High School, Kirkwood, MO
rbecker@stlnet.com

Introduction:

You will determine the heats of solution of both a hydrated and an anhydrous sample of copper(II) sulfate. You will prepare the anhydrous sample yourself, and in doing so, you will also have the necessary data to calculate the number of waters of hydration present in the hydrated sample.

Your introduction should therefore include:

1. the definitions of heat of solution, hydrated, anhydrous, water of hydration
   
2. how "q" is used to determine Delta H_solution
   
3. interpretation of the equation, q = m . SH . Delta t

Procedure:

Measure out approximately 3 g of hydrated copper(II) sulfate on one of the three-place balances, then use a mortar and pestle to pulverize it as fine as you can get it. Dissolve in approximately 25 mL of distilled water which you have previously massed out on the same balance. Carefully measure the temperature change with the thermister connected to the ULI.

Click here for instructions on how to set up the Vernier ULI with the computer.

Pour your solution into a pre-weighed Petri dish labeled with your initials and set aside to allow the water to evaporate.

Obtain another 3 gram sample and place the sample in a previously massed, clean crucible. Do not pulverize this sample. Heat over a small COOL flame (don’t torch it in this lab!!) for about ten minutes. Cool and mass. Reheat for another minute, cool again and remass. If the mass is within 0.03 grams you can consider all of the water of hydration to be removed. If not, continue until you have reached this amount.

Repeat the first part of this lab with your heated sample. DON'T forget to get the mass of the water you put in the coffee cup calorimeter.

Calculations:

Calculate the value of "q" for the water in the calorimeter and then Delta H of solution in kJ / mol for both the hydrated and anhydrous samples.

Calculate the coefficient of the waters of hydration for the hydrated copper(II) sulfate.

Write the balanced equation for the dissolving of the two different samples, the hydrated and anhydrous samples and calculate the theoretical values of Delta H of solution for each. Then calculate your percent error.

Use the values of Delta H_f from your reference tables to do the calculations of theoretical values.