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Laboratory Experiments in Principles of Chemistry Experiment 9 Synthesis and Empirical Formula of Zinc Iodide Synthesis and Empirical Formula of Zinc Iodide OBJECTIVES To perform a microscale synthesis of zinc iodide. To determine the empirical formula of the prepared compound. DISCUSSION The simplest formula of a compound containing the lowest possible ratio of elements is called the empirical formula. The actual formula of a compound is called its molecular formula. The molecular formula is an integral multiple of the empirical formula. The empirical formula may or may not be the molecular formula. The molecular formula can only be determined if the exact molecular weight of the compound is known. To experimentally determine the empirical formula, the exact mass of the elements that will combine to form the compound must be known. Use atomic weights to convert each mass to amount in moles. Divide each amount by the smallest number of moles to obtain whole numbers. If fractions are obtained, multiply all ratios by the smallest positive integer to get whole numbers. This whole number ratio is the same as the ratio of individual atoms that are expressed in the empirical formula. In this experiment, zinc reacts with iodine in water to form zinc iodide. The excess reagent selected is zinc. Since the product is soluble in water, it can be easily decanted from the unreacted zinc, the latter of which

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