Experiment 4: Limiting Reactants, Theoretical Yield, and Percent Yield

Objective: To determine the percent yield of a product from precipitation reaction Background: The word "metathesis" comes from a Greek root that means "to transpose," During a metathesis reaction also known as "double replacement reaction" two reactant compounds exchange, or transpose, their cations (or anions). This reaction appears in various forms including neutralization, precipitation, or gas evolving reaction. In this experiment we will perform a precipitation reaction between barium chloride dihydrate and sodium phosphate dodecahydrate. Materials: Na.PO..12HO BaCl2H2O NaOH(aq),6M "Warning: Please note that Ba is heavy metal element and is toxic. Any solid waste containing Ba should be disposed into the solid waste container. Any solution containing Ba should be disposed into the liquid waste container. Pre-lab: Write the balanced reaction between the two above-mentioned ionic compounds: 2Na3PO412H2O+3BaCl22H2OBa3(PO1)2+6NaCl+3OH2O Your instructor will assign one of the following combinations to you. Calculate the required corresponding masses for each compound in the following Table: Procedure: Lab Pcriod 1 1) Weigh out the required masses of the reactants based on your assigned combination. 2) Transfer the reactants to two separate 250ml beakers. 3) In a graduate cylinder, measure 3ml6M solution of NaOH. 4) Add 50ml of deionized water to each beaker and by stirring the mixtures (with your stirring rods) make sure that all the solids are dissolved in water. (If there is still undissolved solid, you can add some more waterl) 5) Add the measured NaOH solution to your Na3PO4 solution. This step is very important for obtaining a pure product. As you have shown in your pre-lab, the target compound (as product) is a phosphate. The produced PO43 (aq) ions from dissociation of sodium phosphate undergoes un-wanted reactions resulting in HPO42 and H2PO4 according to the following equilibrium reactions. PO2+H3OHPO+OHHPO2+H2OHPO++OH In presence of hydrogenphosphate and dihydrogenphosphate anions, you would obtain mixtures of various insoluble ionic compounds with different molar masses and your actual yield will be fundamentally different from the theoretical yield (which was calculated based on pure phosphate). Next semester you will learn about Le Chatelier's principle. According to the Le Chatelier's principle, addition of sodium hydroxide solution will increase the concentration of hydroxide ions towards the left side of the equilibrium equations, in favor of high concentration of phosphate ions. 6) Add the content of beaker from previous step, to the beaker containing barium chloride. 7) Stir the mixture and allow the formation of precipitate. 8) Take a piece of filter paper and weight it very accurately. 9) Prepare your filtration set up, using a funnel, folded filter paper and an Erlenmeyer flask 10) Collect the formed precipitate on your filter paper 11) Transfer your filter paper (containing your product) to a watch glass and put it in oven for drying process. Lab Period 2 1) Weigh out an empty beaker 2) Transfer the product along with your filter paper to the beaker and weigh it again. Instnuctor's signature: Calculations: Showing your calculation determine the limiting reactant, theoretical yield and the percent yield for your experiment: e Limiting Reactant: Text Text Theoretical yield