Hydrates By Steven Piacente, Class of 2000

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Hydrates
By Steven Piacente, Class of 2000

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By: Steven Piacente

Hydrates:

A Hydrate is a crystalline compound in which the ions are attached to one or more water molecules. We can dry these compounds by heating them over a Bunsen burner to get rid of the water. You can than measure how much smaller the mass is without the water.

Here is an example of a Hydrate Calculation problem:

We have a 10.407-g sample of hydrated barium iodide. The sample is heated to drive off the water. The dry sample has a mass of 9.520 g. What is the mole ratio between barium iodide, BaI2, and water, H2O? What is the formula of the hydrate?

The solving process is very easy:

1. First find the mass of water driven off by subtracting the mass of the dry sample from the initial mass of the hydrate.

2. Now the mass of the water and the mass of the dry sample are converted to moles. You do this by taking the mass of the compounds and divide them by their molar mass.

3. Next you would divide both results by the smaller of the two results to obtain a ratio. You would than write out the formula according to the ratio.

Here is how to do the problem above:

1. Mass of hydrate               10.407 g
     Mass of dry sample       - 9.520 g
     Mass of water                   0.887 g

2. 9.520 g BaI2
   391 g BaI2
        = 0.0243 x (1 mol BaI2)
      = 0.0243 mol BaI2

    0.887 g H2O
   18.0 g H2O
       = 0.0493 x (1 mol H2O)
       = 0.0493 mol H2O

3. 0.0243
0.0243 = 1

0.0493
0.0243 = 2.03

Ratio = 1 to 2
Formula = BaI2•2H20

Now using my tips, try to do these on your own:
(Answers are at the bottom of the page)

Find the formulas for the following hydrates.

1. 0.737 g MgSO3, 0.763 g H20

2. 0.391 g Li2SiF6, 0.0903 g H20

3. 76.9% CaSO3, 23.1% H20

_____________________________________________________________

Answers:

1. MgSO3•6H20

2. Li2SiF6•2H20

3. CaSO3•2H20

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