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INTRODUCTION: As you have learned, given a balanced chemical equation and the mass of one of the substances in the reaction, the mass of any other substance in the reaction can be calculated. Calculations in which a known mass is used to find an unknown mass in a chemical reaction are called mass-mass calculations (stoichiometry). In this experiment, a double replacement reaction will occur when an aqueous solution of lead (II) nitrate is mixed with an aqueous solution of potassium iodide. There are two products of this reaction. One is an insoluble solid, lead (II) iodide, which will precipitate out of solution. The other is a soluble salt, potassium nitrate, which will remain in solution. The insoluble solid will be separated from the liquid, dried, and its mass determined. The value of the experimentally measured mass of the compound will be compared to the theoretical mass of the compound predicted by a mass-mass calculation. PURPOSE: EQUIPMENT: MATERIALS: -balance -ring stand -lead (II) nitrate, Pb(NO3)2 -graduated cylinder, 100ml -iron ring -potassium iodide, KI -beakers, 250ml (2) -funnel -beaker, 100ml -safety glasses -stirring rod -filter paper PROCEDURE: 1. Using the balance, measure out exactly 3.31 g of lead (II) nitrate, Pb(NO3)2. Record this mass in your data table. 2. Place the Pb(NO3)2 in a clean 250ml beaker and add 50ml of water. Stir thoroughly to ensure that all of the crystals are dissolved. Rinse off the stirring rod. 3. Measure out approximately 3.50 g of potassium iodide, KI. Record this mass in the data table. Place it in a clean 100ml beaker and add 50ml of water. Stir until all of the crystals are dissolved. 4. Pour the KI solution into the 250ml beaker containing the Pb(NO3)2 solution. Stir. Record your observations in the data table. 5. Find the mass of a piece of filter paper. Record this mass in your data table. Fold the filter paper and place it in the funnel as shown. 6. Pour the mixture from the 250ml beaker into the funnel as shown. POUR SLOWLY. Do not allow the liquid to rise above the edge of the filter paper in the funnel. 7. Rinse the beaker with about 20ml of water. Pour the rinse water through the filter. Repeat the rinsing and filtering until all of the precipitate is out of the beaker. 8. Wash the precipitate by pouring about 10ml of clean water through the filter. 9. Remove the filter paper and precipitate from the funnel and place in your lab drawer to dry. 10. Find the mass of the dry precipitate + filter paper and record in your data table. OBSERVATIONS AND DATA mass of Pb(NO3)2 mass of KI mass of filter paper mass of filter paper + precipitate observations: CALCULATIONS: 1. Write a balanced equation for the double replacement reaction. 2. Using stoichiometry, find the theoretical mass of the PbI2 precipitate that should be produced when the 3.31 g of Pb(NO3)2 completely reacts. 3. Calculate the experimental mass of PbI2 formed. 4. Calculate your experimental error. 5. List possible causes of your percent error. 6. Calculate the percent yield of PbI2 formed. 7. Which of the reactants is the limiting reactant in this experiment?
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