# Pre Lab Chemistry

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WMChemistry Pre lab for Experiment 2.9 In this lab you will calculate the percent yield. The percent yield is an indicator of the efficiency of a particular reaction. There are two factors that determine percent yield; actual yield and theoretical yield. The theoretical yield is the amount of product predicted from the amount of reactants used. This is similar to theoretical percent that you used to calculate the percent error in an experiment. The actual yield is the amount of product that is actually obtained in an experiment. This is similar to the actual or experimental percent you used to determine the percent error in an experiment. The formula for percent yield is Actual yield x 100 Theoretical yield For example: if a reaction actually gave you 6.63 g of nitrogen instead of the predicted 10.6 g, the percent yield of nitrogen would be: 6.63 g N2 x 100 = 62.5 % 10.6 g N2 1. According to her pre-lab stoichiometric calculations, a student’s lab experiment should have produced 5.51 g of NaCl. While actually doing the experiment, this student obtained only 4.32 g of NaCl. What was her percent yield? 2. A student calculated the theoretical yield of barium sulfate in a double replacement reaction experiment to be 1.35 g. When she filtered, dried and weighted her solid (precipitate), however, her yield was only 1.29 g. Calculate the student’s percent yield. 3. Before going to lab, a student reads in his lab manual that the percent yield for a difficult reaction to be studied was likely to be only 40% of the theoretical yield. The student’s pre-lab stoichiometric calculations predict that the theoretical yield should be 12.5 grams. What is the student’s actual yield likely to be? 4. Recall in a balanced chemical equation the coefficients represent the