Determination of the amount of water in a crystalline solid hydrate

Pre-lab activity problems (answer these questions before you start the computer simulation).

1. Ba(OH)₂^.8H₂O is called barium hydroxide octahydrate. It is a solid compound.

a. How are the water molecules bonded to the Ba(OH)₂ structure? Draw a diagram if it helps.

b. Define the terms "hydrate" and "anhydrous" in a chemistry context?

c. What is the % by mass of H₂O in Ba(OH)₂.8H₂O?

Activity: When copper(II) sulfate hydrate, a blue crystalline solid containing embedded water molecules (called a hydrate), is heated in air, it loses the water molecules and the blue solid is transforrmed to a white anhydrous (no water) crystal known as coppr(II) sulfate. Use the computer simulation to determine the number of water molecules per unit of copper(II) sulfate hydrate: CuSO₄^.xH₂O. Determine "x", where x is a whole number. The computer simulation can be found at the following URL:

http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/flashfiles/stoichiometry/empirical.html

Note the initial and final masses of the compound from the simulation. Calculate mass and hence moles of H2O that was driven off. Calculate the number of moles of CuSO4 present. Determine the ratio of moles of water to moles of CuSO4. Show calculations. Write the complete formula for copper (II) sulfate hydrate, CuSO4.xH2O.

Post-lab Questions and Problems

2. What would happen if a small amount (0.2ml) of water is added to 10.0g of solid anhydrous CuSO₄? What happens to the color? Write an equation that describes this process. How is this different from the experment that you did in the simulation?

3. What type of compound is CuSO4 (ionic,covalent...)? Write an equation for the process of solid CuSO₄ dissolving in water. How is this different from the process in Question 2?

4. Aluminium sulfate hydrate Al₂(SO₄)₃.xH₂O contains 13.63% Al by mass. Calculate x, that is, the number of water molecules associated with each Al₂(SO₄)₃unit.