Hydrate Lab

This lab will go in your lab book. Follow the directions below to complete the lab.

Purpose (put into lab book)

  • The purpose of this lab is to determine the relationship between moles of copper sulfate and moles of water in a hydrate. Then use that information to write the formula of the hydrate.

Background (put into lab book)

  • Hydrate: A compound that contains the water molecule. This compound is not dissolved in water, the water is part of the formula and is a solid.

  • Anhydrate: The compound after the water molecule has been removed.

  • X is a specific whole number value. Our goal is to determine this value by comparing the moles of copper sulfate (anhydrate) to the moles of water.

Hypothesis (answer in a complete sentence in lab book)

  • How many moles of water (x) do you think are in this hydrate?

Procedure (summarize in lab book)

  1. Crush the copper sulfate hydrate (blue compound) using a mortar and pestle.

  2. Measure the mass of the empty crucible using the balance.

  3. Measure out between 1 and 4 grams of copper sulfate hydrate that you have crushed into the crucible.

    • Remember the hydrate is in the crucible so you need to subtract the mass of the crucible to get the mass of just the hydrate.

  4. Place the crucible on the triangle and ring stand over the bunsen burner and heat until it turns white.

    • When it is all white the water has been removed and the anhydrate is left.

  5. Cool (approximately 10 minutes) and get the mass of the anhydrate (white compound).

    • When you get this mass remember it includes the mass of the crucible so you need to subtract the mass of the crucible from the total mass.

Data (put into lab book)

    • Use the information collected in lab found below to fill in the blanks for the gram amounts above:

            • Empty Crucible on Balance

            • Hydrate with Crucible on Balance

            • Anhydrate with Crucible on Balance

            • Use this picture to get the mass of the empty crucible and fill it in above.

            • This mass was taken before the substance was heated. Use this picture to get the mass of the hydrate (blue powder). Be sure to subtract out the crucible before putting it into the proper space above.

            • This mass was taken after the substance was heated. Use this picture to get the mass of the anhydrate (white powder). Be sure to subtract out the crucible before putting it into the proper space above.

    • To determine the mass of the water, subtract the anhydrate from the hydrate and put it in the proper space above.

Calculations (put into lab book)

Step 1: Find the moles of the Copper Sulfate anhydrate (white powder).

    • For this step, you are just changing your grams of copper sulfate anhydrate (white powder) to moles using factor labeling.

Step 2: Find the moles of the water.

    • For this step, you are just changing your grams of water to moles using factor labeling.

Step 3: Find the ratio.

  • Examine your moles of anhydrate and moles of water that you just calculated, divide each by the smaller mole amount.

  • The copper sulfate moles should be the smaller. So you will get 1 copper sulfate and your amount of water should be larger than 1 when you divide by the smallest.

  • The number you found for the water replaced the x in the formula CuSO4 • xH2O

  • The actual (true) value is 5, so the formula would be CuSO4 • 5H2O. We would call this copper sulfate pentahydrate.

Conclusion (put into lab book)

Academic Chemistry - Three paragraph conclusion

Paragraph #1: Purpose and a brief description of what you did.

Paragraph #2: What did you learn? What did your group get as the formula of the hydrate? How did it compare to the actual (it is given to you in step 3 of the calculations)? What does that x value tell you?

Paragraph #3: An error and how to fix it.

Honors Chemistry - You do not need to write three paragraphs for this conclusion. Instead you are to complete the three problems below in your lab book using what you learned from the lab.

Problem #1: A 15.67 g sample of a hydrate of magnesium carbonate was heated, without decomposing the carbonate, to drive off the water. The mass was reduced to 7.58 g. What is the formula of the hydrate?

Problem #2: A hydrate of Na2CO3 has a mass of 4.31 g before heating. After heating, the mass of the anhydrous compound is found to be 3.22 g. Determine the formula of the hydrate and then write out the name of the hydrate.