Chemistry 111 Laboratory Alum Preparation Pre Lab Assignment Page C 1 PRE LABORATORY ASSIGNMENT SYNTHESIS OF POTASSIUM ALUMINUM SULFATE ALUM Name Section Chemical reactions are rarely as efficient as chemists would like The amount of pure isolated product is usually less than the theoretically possible yield Reactions differ in their efficiency so it is customary to record the yield actually obtained from a reaction sequence and compare it with the theoretical yield reporting the comparison as the percentage yield for the sequence Percent yield actual yield g x 100 theoretical yield g The actual yield is obtained by weighing the final product The theoretical yield can be calculated from the balanced equation for the overall process and the amounts of starting materials used The calculation is often complicated slightly by the fact that some of the reactants are in excess so the starting material which limits the amount of product obtainable the limiting reagent must be determined first Pre Laboratory Exercise If you heat magnesium in air it reacts with oxygen to give magnesium oxide according to the following unbalanced equation Mg s O2 g MgO s a Balance the equation b If you begin with 10 0 g of Mg what mass of MgO can be theoretically obtained c If you actually obtain 14 5 g of MgO what is the percentage yield of this metal oxide Chemistry 111 Laboratory Preparation of Alum Page C 2
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