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Title: Hydrates

Purpose: To determine the chemical formula of a hydrate.

Procedure:

1. Measure the mass of a clean, empty evaporating dish. Measure the mass of 2 scoops of hydrated copper sulfate directly into the evaporating dish.

2. Set up a steam bath as demonstrated by your instructor.

3. Heat the hydrated copper sulfate until it is dehydrated—its color will be white.

4. Allow the copper sulfate to cool until it is safe to touch. Make sure the evaporating dish is dry.

5. Measure mass of the dish and copper sulfate again.

6. Heat the dish and copper sulfate on the steam bath again for five additional minutes.

7. Repeat the cooling/weighing procedure.

8. Continue to heat and weigh until you achieve a constant mass to the nearest 0.1 g.

Analysis:

1. Calculate the mass of water lost.

2. Calculate the moles of water lost.

3. Using the mass of dehydrated copper sulfate, calculate the moles of dehydrated copper sulfate.

4. Using the moles of water and moles of copper sulfate, find the empirical formula of hydrated copper sulfate—this is the chemical formula.

Questions:

1. What is happening to the copper sulfate as it changes color from blue to white?

2. Why is it necessary to repeat the heating/cooling/weighing process more than one time?

3. Would the calculated mass of water lost have been higher or lower if the evaporating dish had not been dried off? Explain.