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Properties of Hydrates Essay

Purpose:

The purpose of the “Properties of Hydrates” lab is to study hydrates, and be able to identify them. This lab also focuses on observing the reversibility of hydration reactions by hydrolysis, and also testing substances for efflorescence of deliquescence.

Procedure:
A.Identification

1. Place 0.5 grams of each compound (Nickel Chloride, Potassium Chloride, Sodium Tetraborate, Sucrose, Calcium Carbonate, and Barium Chloride) in a small dry test tube. 2. Heat gently with a burner flame and observe carefully. If droplets of water appear on the test tube it may be a hydrate. Note the nature and color of the residue. 3. Let the tube cool, and try to dissolve the residue in a few cm3 of water, warming if necessary. A true hydrate will dissolve in water, producing a color similar to that of the original hydrate. A carbohydrate will give off water, but tends to char. The residue will also often be a caramel color.

B.Reversibility

1. Gently heat a few crystals of about 0.3 grams of hydrated Cobalt(II) Chloride, CoCl2 x 6H2O in an evaporating dish until the color change appears to be complete 2. Dissolve the residue in the evaporating dish in a few cm3 of water from the wash bottle 3. Heat the residue to a boiling and carefully boil it to dryness. Note any color changes. 4. Put the evaporating dish on the lab bench and let it cool.

C.Deliquescence and Efflorescence

1. Place a few crystals of Na2CO3 x 10H2O, CaCl2, KAl(SO4)2 x 12 H20, and CuSO4 in an a separate evaporating dish next to the CoCl2 prepared in part B. 2. To see weather the samples gained or lost mass, weigh each of them on a top-loading balance and record to the nearest hundredth. 3. Weight them again after an hour to detect ANY changes in mass. 4. Observe the samples occasionally. Note any structures in color and structure and degree of wetness.

D. Percent of Water in Hydrate

1. Clean crucible and its cover, and also make sure that crucible tongs are clean. Put over fire, and let cool. 2. Weight the crucible to the nearest thousandth. Handel with tongs 3. Obtain a sample of an unknown hydrate, and place about 1 gram in the crucible. 4. Weight the crucible, cover and sample on the balance. 5. Put the crucible on the clay triangle, with the cover off center to allow water vapor to escape. 6. Heat again, gently at first, and then with the bottom red for about 10 minutes. 7. Center the crucible cover, and let it cool to room temperature. 8. Weight the cooled crucible and with its cover and contents. 9. Examine the solid residue.

10. Add water until the crucible it two thirds full. Warm gently if the residue doesn’t readily dissolve. 11. Does the residue appear to be soluble?

Waste Disposal:

Dispose of the Copper mixture, and the Aluminum mixture in the correct bowl under the waste hood. All of the acids and bases can be disposed of down the sink. If the compound isn’t water soluble put in the organic container.

Chemical Principles in the Laboratory: Experiment 6

Conclusion:

The purpose of the Properties of Hydrates lab was to be able to identify if a substance was a hydrate or not. In lab, experiments where conducted to see if a compound was a hydrate or not. In order for the compound to be deemed as a hydrate it had to:

1. Release water upon heating
2. The anhydrous residue had to be water soluble
3. Exhibit reversibility

If, and only if the compound showed that it could exhibit all three of these properties, could it be distinguished a hydrate. In part “A” of the experiment, Nickel Chloride and Sodium Tetraborate were the only two compounds that were true hydrates. Both of these showed water residue when heating, where soluble in water after heating, and converted back to it original color after performing the first two experiments. Some of the other compounds had positive results for one or two test but not all three. For example, Sucrose, when heated, water residue appeared on the test tube, and was soluble in water, but the compound didn’t show reversibility.

In part “B” of the experiment, CoCl2*6H2O was heated, dissolved, and then heated again to show that it was a true hydrate. When the Cobalt Chloride was heated, it turned from the color of fuchsia pink, to a light blue. And then after being dissolved into water, the compound turned back to its original color of fuchsia pink, demonstrating reversibility. The color change in this compound shows that by adding water to the anhydrous residue, that the same bonds that were broken my dehydrating the compound where reformed when adding water.

In part “C”, four compound, plus the Cobalt Chloride mentioned above were tested for deliquescence, and efflorescence. Only one compound turned about to be efflorescent, which means that it lost water, which was Sodium Carbonate. The compounds mass before sitting out was 50.645g, after being exposed to the conditions of the laboratory for an hour, the sample weight 50.603g losing approximately 0.042g over the period of an hour. The Calcium Chloride (gained 0.258g), Copper Sulfate (gained 0.007g) and Cobalt Chloride (gained 0.068g) where all deliquescent, meaning that again mass while sitting in the laboratory. The Potassium Aluminum sulfate, exhibited stability while sitting out for an hour, neither gaining nor losing mass.

For part “D” of the experiment, the percent of water in the unknown hydrate was %12.290. The closet percent of the given facts of the unknown was Barium chloride (BaCl2*2H2O), which has %14.8 water in it. This percent was found by using the formula below: % water in hydrate=(mass of water in hydrate/mass of the entire hydrate)

The wide range of difference between the percent of the given and the unknown could have been due to the fact that there was wood debris in the unknown sample . This could have thrown off the amount of water present in the sample, and messed up the amount of water able to evaporate.


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