The Removal of Water from a Barium Chloride Hydrate

Water of Hydration;

The Removal of Water from a Barium Chloride Hydrate

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Introduction:

1) Salts are compounds that are metal elements bound to non–metal elements through ionic bonding.

a. Examples: NaCl, CaSO4

2) Hydrates (or hydrated salts) are compounds which contain a specific amount of water chemically bound.

a. Iron (II) Sulfate Monohydrate (or Ferrous Sulfate Monohydrate): FeSO4H2O

b. The polar water molecules are held by the attractive forces to the positively charged iron atom.

3) Following heating, the attractive forces can be overcome and the water is liberated as a gas.

a. This leaves behind an anhydrous salt.

b. FeSO4H2O(s)

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FeSO4(s) + H2O(g) 

c. The formula mass for FeSO4H2O (before heating) is 169.926 g/mol.

i. Of this, 18.016 g/mol is comprised of H2O.

ii. Thus, 10.6% of the hydrate’s mass is due to the water.

d. After heating, the formula mass of anhydrous iron (II) sulfate is 151.91 g/mol.

i. The mass should have decreased by 10.6%.

Substances to include in the Table of Chemical and Physical Properties:

The molar mass and safety precautions for the following substances: barium chloride, barium chloride dihydrate, water.

Procedure for Barium Chloride Hydrate (BaCl2∙nH2O):

1) Obtain one crucible. Clean and dry if necessary.

a. Record an initial mass of the crucible.

2) Heat the empty crucible (without a lid) for 5 minutes on a hot plate in high setting to drive away adsorbed water.

a. Be careful to handle only with crucible tongs when hot!

3) Allow to cool to room temperature.

4) Record the mass of the cooled crucible.

5) Place crucible back onto the hot plate and reheat the crucible for 2 minutes.

a. Allow to cool to room temperature and determine mass.

b. If there has not been a significant change in mass, record the mass and continue on with the experiment.

i. A significant change in mass can include a mass difference of ≥ 0.01g.

c. If there has been significant change in mass, reheat (for 2 minutes) until a constant mass is obtained. Record the constant mass.

6) Weigh out 1.0 g of the barium chloride hydrate on an analytical balance.

a. It would be advisable to place the crucible of constant mass on the balance and tare it (set it equal to zero) and then weigh the sample into the crucible.

b. Record the actual amount used.

7) Heat the crucible with the sample for 10–15 minutes.

a. Note the initial and final appearance of your crystals.

8) Allow to cool to room temperature.

9) Record the mass of the cooled crucible with the sample inside.

a. Subtract the mass of the empty crucible from this recorded mass to obtain the mass of the anhydrous salt.

b. Create a data table similar to the example attached.

10) If instructed, repeat the above process for a second trial using a separate quantity (between 1–2 g) to ensure results are reproducible.

Clean – Up:

11) Place all anhydrous powder products in the appropriately labeled container.

12) Make sure that all gas valves are turned off!

Sample Data Table:

a) Initial Mass of Crucible: ________

b) Mass of Crucible After First Heating: ________

c) Mass of Crucible After Second Heating: ________

d) Stable Mass of Crucible: ________

e) Initial Mass of Barium Chloride Hydrate: ________

f) Mass of Sample + Crucible After Heating: ________

g) Mass of Barium Chloride After Heating (f – d): ________

h) Moles of Barium Chloride After Heating: (g/Mm): ________

i) Mass of Water Lost After Heating (e – g): ________

j) Moles of Water Lost After Heating (i/Mm): ________

k) Experimental Mole to Mole Ratio of BaCl2 to H2O*: ____:_____

l) Experimental Formula for Barium Chloride Hydrate: ________

m) True Mole to Mole Ratio of BaCl2 to H2O: ____:_____

n) True Formula for Barium Chloride Hydrate: ________

o) Experimental/Observed Percent Water in Hydrate ((i/e) x 100%): ____

p) True/Theoretical Percent Water in Hydrate: _________

q) Percent Error for Percent Water in Hydrate: _________

*To determine the mole to mole ratio in whole numbers, divide the number of moles for both BaCl2 and H2O by the smallest number of moles from the two. Round to the nearest whole number.

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