CHMI30 determinations, record all digits shown on the balance directly onto the

Question

CHMI30 determinations, record all digits shown on the balance directly onto the data sheet. Place about 2.5 g of unkn and cover plus the hydrate Pl own hydrate in the crucible and precisely determine the mass of the crucible ace the crucible with the cover slightly ajar on the clay triangle and heat vigorously for 15 minutes Cool on the ring stand for 10 minutes. Do not place the hot crucible on the benchtop. Precisely determine the mass of the crucible and cover plus the solid residue inside. To assure that all the water has been driven off. heat for an additional 5 minutes. Cool for 10 minutes and again determine the mass. These successive readings should not differ by more than 0.02 grams. If they do differ by more than 0.02 grams, a third heating and cooling followed by a new determination of mass must be performed Dispose of residue in the waste container provided. Qualitative Determination: Place about 5 grams of copper(II) sulfate pentahydrate in a test tube as shown in the figure on the right Heat the test tube gently with a Bunsen burner and collect some of the liquid driven off. Describe your observations on the second page of the data sheet. Test the liquid with cobalt chloride test paper by dipping a glass stir rod into the liquid and touching it lightly to the test paper. Repeat this test using deionized water. Describe your observations on the second page of the data sheet. Place the solid residue remaining in the test tube on a clean watch glass, and use a spatula to divide the sample into two portions. Transfer one portion to a second watch glass. Add several drops of water to one portion. Add several drops of the liquid collected in the first part of the experiment to the other portion. Describe your observations on the second page of the data sheet

Explanation / Answer

CuSO4.5H2O

mass of hydrate salt = 5.0 g

mass of anhydrous salt = 2.678 g

moles anhydrous CuSO4 = 2.678 g/159.609 g/mol = 0.017 mol

mass of water lost = 5 - 2.678 = 2.322 g

moles of water = 0.129 mol

moles of water/moles of CuSO4 = 0.129/0.017 = 6

which is higher than expected value of 5. therefore all the water has been driven off from the hydrate salt.

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