37 - A P CHEMISTRY Lab 2-1 Determination of the Formula of...

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A P CHEMISTRY Lab 2-1 Determination of the Formula of a Hydrate Pre-Lab Questions - (Must be completed before lab work begins.) 1. Suppose 2.3754 g of copper (II) sulfate pentahydrate is heated to drive off the water of crystallization. Calculate what weight of anhydrous salt will remain. 2. In CuSO 4 . 5H 2 O, it was mentioned that four of the five water molecules held per formula unit of the salt were attached by coordinate covalent bonds to the copper ion. The fifth water molecule is attached to the sulfate ion, but by a different mechanism. Use your textbook or a chemical encyclopedia to determine how a water molecule might be bonded to a sulfate ion. INTRODUCTION - Many hydrated substances lose their water of crystallization readily if the hydrate is heated to a few hundred degrees. Usually the water of crystallization can be observed as steam escaping from the crystals as they are heated or as a condensate on a cooler portion of the vessel used for the heating. A common experiment in the characterization of new or unknown compounds is to measure the mass of water driven off from a sample of the compound when it is heated. This is true whether the compound is a hydrate or has merely adsorbed water on the surface of its crystals. For a true hydrate, it is often possible to determine the molar ratio in which water is combined in the hydrated compound. Many hydrates, especially those of transition metals, are stable and stoichiometric. That is, they contain a specific, definite amount of water per mole of metal ion present. In this experiment, you will be given a sample of an unknown hydrated metal salt. You will be told what ions are present in the sample, but will not be told how many water molecules are bound in the compound per mole of metal ion. By determining carefully the weight lost on heating a weighed sample of the unknown, you will be able to calculate the percentage of water in the hydrated metal salt. From the percentage, you will be
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