6a-empirical-formula-copper-chloride - CHM151LL: EMPIRICAL...

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CHM151LL: EMPIRICAL FORMULA OF A COPPER CHLORIDE | 1 Empirical Formula of a Copper Chloride OBJECTIVES: Become familiar with single-replacement redox reactions Learn mass and volume measurement techniques Calculate the empirical formula of a copper/chlorine compound DISCUSSION: If you can measure the amounts of each element that constitute a compound, you can determine the ratios of one element to another. In other words, you can determine the empirical formula of the compound. Consider the reaction of Mg with O 2 from the air, an example of a combustion redox reaction. Magnesium, a silvery metal, ignites and burns with a brilliant white incandescence if strongly heated in the presence of air. After the combustion ceases, crumbly white magnesium oxide powder remains. You can calculate the empirical formula of this compound from typical laboratory data. In this example 0.353 g of Mg reacted with O 2 to produce 0.589 g of the oxide. Given: 0.589 g of oxide formed 0.353 g of magnesium reacted molar masses of Mg & O Find: the ratio of oxide ions to magnesium ions in the oxide compound. 0.589 g oxide compound - 0.353 g magnesium = 0.236 g oxygen 0.236 g O 0.353 g Mg ! " # $ % ' 1 mol O 16.00 g O ! " # $ % ' 24.31 g Mg 1 mol Mg ! " # $ % = 1.02 mol O 1 mol Mg The simplest whole-number ratio, one-to-one here, gives an empirical formula of MgO. GENERAL PROCEDURE: In this experiment you will add Al metal to a blue solution that contains a known amount of a copper chloride compound, but you won’t know the charge on the copper ion. You will observe the following single-replacement reaction (shown here as an unbalanced equation): Al (s, silvery) + Cu x Cl y (aq, blue) ! AlCl 3 (aq, colorless) + Cu (s, reddish) As the reaction proceeds the blue color will fade, and finally disappear. During this time, small pieces of reddish Cu metal should form. Once you have recovered all of the copper, you will dissolve any remaining Al with HCl (aq), also by a single-replacement reaction: 2 Al ( s ) + 6 HCl ( aq ) 2 AlCl 3 ( aq ) + 3 H 2 ( g ) Finally, separate the Cu from the solution, then dry and weigh the Cu. With the mass of the Cu recovered and the original mass of the copper chloride in your solution, you have enough information to calculate the empirical formula. CAUTION: Wear approved eye protection. Aqueous copper chloride solutions are toxic and irritating. Hydrochloric acid is toxic, has irritating fumes, and is very corrosive. Avoid contact with skin, eyes and clothing. Immediately wash thoroughly if you are
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This note was uploaded on 02/28/2012 for the course CHEM 151 taught by Professor Wiley during the Spring '12 term at Mesa CC.

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6a-empirical-formula-copper-chloride - CHM151LL: EMPIRICAL...

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