Limiting Reagents June 2010

Limiting Reagents June 2010 - EXPERIMENT 4 LIMITING...

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EXPERIMENT 4 LIMITING REAGENTS EXPERIMENT 4 LIMITING REAGENTS I. INTRODUCTION Summary In this experiment equal amounts of copper (II) chloride and aluminum will be reacted together. The limiting reagent will be determined and the percent yield calculated. The amount of the unreacted excess reagent will also be determined. Discussion In a laboratory or industrial chemical reaction, the reactants are not added in their precise stoichiometric ratios. Usually one reactant is consumed before the other. This reactant is known as the limiting reagent . The other reactant(s) present are in excess, and some quantity of them are left over after the reaction is complete. These are called excess reagents . The amounts of the reactants are determined so that the yield of the desired product is maximized, while the cost is kept to a minimum. The most expensive reactant is usually set as the limiting reagent. This experiment contains other terms that are used both in the laboratory and industry in addition to the terms limiting reagent and excess reagent. A reactant is a compound on the left side of the balanced chemical equation and is a starting material of the process. A product is a compound on the right side of the balanced chemical equation, and is a compound produced in a chemical reaction. An insoluble reaction product is called a precipitate . When separating a precipitate from a solution in a laboratory, the solution is called the supernatant , and it is decanted , or poured off. The % yield of a reaction is defined as follows: % yield  =   100 x yield l theoretica yield actual where the actual yield is the amount of the product experimentally collected and the theoretical yield is the amount of the product that would be obtained if every molecule of the limiting reagent was reacted and collected. The yield of a reaction can range from 0 to 100%. The % purity of a compound is the percentage of the pure compound present in an impure sample.
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EXPERIMENT 4 LIMITING REAGENTS Example 0.8653 g of magnesium nitrate hexahydrate and 0.7215 g of potassium hydroxide react in aqueous solution. (a) Predict the products, and write the balanced molecular equation (including states) for this reaction. (b)Determine the limiting reactant and the amount of precipitate that should be formed. (c) Determine the amount of excess reactant present at the end of the reaction. (d)Determine the % yield of the reaction if 0.1841 g of the precipitate are isolated. (a) Predict the products, and write the balanced molecular equation (including states) for this reaction. To predict the products in aqueous solution, it is helpful to first break up the reactants into their ionic components. In a double displacement reaction like this, switch the positive and negative ions or polyatomic ions and then balance the molecule using the oxidation states. In this example, Mg(NO 3 ) 2 and KOH will dissociate in water to give Mg 2+ + NO 3 and K + + OH Switching the ions from one compound to the other gives
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This note was uploaded on 05/07/2011 for the course CHEMSTRY 101 taught by Professor Intesar during the Spring '11 term at Aquinas.

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Limiting Reagents June 2010 - EXPERIMENT 4 LIMITING...

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