Chem 163L 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. Calculate the percentage of silver in silver sulfide, Ag2S.

 

2.Calculate the mass (in grams) of silver in 10.0 grams of silver sulfide, Ag2S.

3.     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 10.0 g of Ba(OH)2.8H2O?


Activity: Treat this activity as you would a normal laboratory activity. Use the Science Writing Heuristic format to write a short lab report. Turn-in your lab report to your TA. 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 copper (II) sulfate.

Use the computer simulation  to determine a) the percentage of water in copper (II) sulfate hydrate and

b) optional at this time, but good to learn how to do because you will need to know how to do this for Exam 2: 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

1. What would happen if a small amount (0.2ml) of water is added to 10.0 g 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?

2. What type of bonding is used between the Cu2+ cation and the SO42- anion, in CuSO4 (ionic, covalent...)? Write an equation for the process of solid CuSO4.xH2O dissolving in water. How is this different from the process in Question 1? Write an equation for the process of solid CuSO4 dissolving in water.

3.  Optional: 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.