QUANTITATIVE REACTIONS 1.0 INTRODUCTION A limiting reagent (sometimes called limiting reactant) is the reagent that is completely consumed during a chemical reaction. Once this reagent is consumed the reaction stops. An excess reagent (sometimes called excess reactant) is the reactant that is left over once the limiting reagent is consumed. The maximum yield of a chemical reaction is dependent upon the limiting reagent thus the one that produces the least amount of product is the limiting reagent. In class, stochiometric calculations are used to identify the limiting and excess reagents. In lab, we can identify the limiting and excess reagents experimentally. In this experiment you will be create a mixture of two ionic solutions, Co( NO 3 ) 2 and Na 3 PO 4 . When the solutions are mixed, they will react to form an insoluble salt, which can be separated from the liquid. Precipitate is the term used for an insoluble solid which is produced by mixing two solutions. The liquid above the precipitate is called the supernatant. When the mixture is poured into a filter, the solid precipitate is trapped by the filter and the liquid supernatant passes through as the filtrate. You will then test the filtrate to find out the limiting reagent. 2.0 SAFETY PRECAUTIONS AND WASTE DISPOSAL 0 !!Wear your safety goggles!! When you are finished with the experiment, place any solid that contains cobalt in the proper container for solid waste. Pour any solution that contains cobalt in the proper container for liquid waste. Solutions without cobalt may be safely disposed of down the drain. 3.0 CHEMICALS AND SolutionS 0 1 2 3 Chemical Concentration Approximate amount Notes Co(NO3)2.6H2O NaN About the size of a pea (0.25 g) NaN Na3PO4.12H2O NaN About the size of a pea (0.25 g) NaN K3PO4 NaN About the size of a pea or less NaN CoCl2.2H2O NaN About the size of a pea or less NaN NaNO3 NaN About the size of a pea or less NaN Co(NO3)2 solution 0.0183g/mL 90 mL Record the exact concentration as printed on the bottle Na3PO4 solution 0.0156g/mL 60 mL Record the exact concentration as printed on the bottle 4.0 GLASSWARE AND APPARATUS 0 1 2 Item Use Notes Several beakers of any size Preparing and mixing solutions Rinse well before reusing a beaker (they do not have to be dry). 4 funnels For gravity filtration NaN 5 sheets(circles) of filter paper For gravity filtration NaN Buret or volumetric pipets of 5.0, 10.0, 15.0, 20.0 mL and bulb For careful quantitative measurements of aqueous solutions Either set of devices work, check stockroom for availability 5.0 PROCEDURE Careful records of your observations are key to answering questions posed by your investigation. A bound laboratory notebook is one way to secure and maintain your records. Investigation: Conduct and analyze the chemical reaction between Co( NO 3 ) 2 and Na 3 PO 4 (Part 1). First, let us explore the reaction without doing any careful measurements. In a beaker, dissolve about a pea-sized amount (about 0.25 g) of solid Co( NO 3 ) 2 . 6H 2 O in approximately 20 mL of laboratory water. Label this beaker “Co( NO 3 ) 2 solution”. Record the appearance of the solution (Clear? Cloudy? Colored?) in Data Table 1 in Section 6. In a second beaker, dissolve about a pea-sized amount (about 0.25 g) of solid Na 3 PO 4 . 12H 2 O in approximately 20 mL of laboratory water. Label this beaker “ Na 3 PO 4 solution”. Record the appearance of the solution (Clear? Cloudy? Colored?) in Data Table 1 in Section 6. Start the chemical reaction by transferring about half of each solution into a third beaker and mixing well. Label this third beaker as “Reaction between Co( NO 3 ) 2 and Na 3 PO 4 ”. Record the appearance of the solution (Clear? Cloudy? Colored?) in Data Table 1 in Section 6. Although you could use solubility rules (a topic discussed in class) to predict the products of today’s reaction, let us instead conduct some additional experiments to determine the identity of the product. In Data Table 1 in Section 6, list the two ions formed when Co( NO 3 ) 2 and Na 3 PO 4 dissolves. Assuming that the reaction involves two ions bonding together, list all possible chemical formulas for the product that might result from the mixing of Co( NO 3 ) 2 and Na 3 PO 4 in Data Table 1 in Section 6. For each chemical formula that you listed, design and conduct a reaction to make the compound with that chemical formula. (Additional chemicals should be available in lab). For example, perhaps Co 3 (PO 4 ) 2 is a product, so try reacting CoCl 2 . 2H 2 O with K 3 PO 4 to make Co 3 (PO 4 ) 2 . List the chemicals used, appearance of each solution and reaction mixture, as well as ions and products of each mixture in Data Table 2 in Section 6. How do these reaction mixtures compare with the contents of the beaker labeled “Reaction between Co(NO 3 ) 2 and Na 3 PO 4 ”. Filter the mixture from the beaker labeled “Reaction between Co(NO 3 ) 2 and Na 3 PO 4 ”. The liquid obtained after filtration is called the supernatant, and it contains the product that is not a solid. However, we did not measure the reagents carefully, so there may be some leftover reagents also dissolved in the supernatant. Let us find out which reagent, if any, is still present in the supernatant. Pour half of the supernatant into an empty beaker, and then pour the remainder of the supernatant into a second empty beaker. Pour some Co( NO 3 ) 2 solution into the first beaker, and pour some Na 3 PO 4 solution into the second beaker. In Data Table 3 in Section 6, record your observations and indicate the chemicals present in your supernatant. Did your supernatant contain Co( NO 3 ) 2 or Na 3 PO 4 or neither? How do you know? Investigation: Conduct and analyze the chemical reaction between Co( NO 3 ) 2 and Na 3 PO 4 (Part 2). Now let us repeat today’s reaction by taking very careful measurements. Obtain 4 clean beakers and label them #1, #2, #3, and #4. Into each beaker, place 20.0 mL of the 0.0183g/mL Co( NO 3 ) 2 solution from the stockroom. Record the actual volume measurements and concentration in Data Table 4 in Section 6. Now transfer different amounts of the Na 3 PO 4 solution into beakers #1, #2, #3, and #4. Suggested amounts are 5.0, 10.0, 15.0, and 20.0 mL. Record the the actual volume measurements and concentration in Data Table 4 in Section 6. Mix each solution completely and let sit for at least 5 minutes. Let us find out which reagent, if any, is still present in the supernatant. Filter each reaction mixture and collect the supernatants into another set of 4 labeled beakers. You do not have to collect all of the supernatant from each reaction but collect at least 10 mL that is devoid of any solids. Divide each supernatant into 2 portions: into one portion, add at least 5 drops of Co( NO 3 ) 2 solution; into the other portion, add at least 5 drops of Na 3 PO 4 solution. Examine each of these new reactions for a precipitate (a solid). The appearance of a solid will help us identify if a reagent was still present in the supernatant. Complete Data Table 5 in Section 6 testing each filtrate. Now that we know which reagent was present in the supernatant, then the other reagent must have been the limiting reagent! For example, if the supernatant from Beaker #1 produced a solid when Na 3 PO 4 was added, then Na 3 PO 4 must have been the limiting reagent because it was used up first, leaving behind some unreacted Co( NO 3 ) 2 . 6.0 DATA RECORDING SHEET 0 1 2 3 4 Last Name First Name First Name Partner Name(s) Date NaN NaN NaN NaN NaN Data Table 1. Qualitative Data Co(NO3)2 + Na3PO4 Data Table 1. Qualitative Data Co(NO3)2 + Na3PO4 NaN NaN NaN NaN Appearance Ions When Dissolved NaN NaN Co(NO3)2.6H2O NaN NaN NaN NaN Na3PO4.12H2O NaN NaN NaN NaN NaN Appearance Product Chemical Formulas NaN NaN Mixture NaN NaN NaN NaN 0 1 2 Data Table 2. Qualitative Data Reactions to Form Products Data Table 2. Qualitative Data Reactions to Form Products Data Table 2. Qualitative Data Reactions to Form Products Product Being Formed: ________________ Product Being Formed: ________________ Product Being Formed: ________________ Chemical Used Appearance Ions When Dissolved NaN NaN NaN NaN NaN NaN NaN Appearance Product Chemical Formulas Mixture NaN NaN Product Being Formed: ________________ Product Being Formed: ________________ Product Being Formed: ________________ Chemical Used Appearance Ions When Dissolved NaN NaN NaN NaN NaN NaN NaN Appearance Product Chemical Formulas Mixture NaN NaN 0 1 2 Data Table 3. Qualitative Data Supernatant Test Data Table 3. Qualitative Data Supernatant Test Data Table 3. Qualitative Data Supernatant Test NaN Appearance Appearance Addition of Co(NO3)2 NaN NaN Addition of Na3PO4 NaN NaN NaN NaN NaN Chemicals Present in Supernatant: Chemicals Present in Supernatant: Reasoning: 0 1 2 3 4 Data Table 4. Quantitative Data Co(NO3)2 + Na3PO4 Data Table 4. Quantitative Data Co(NO3)2 + Na3PO4 Data Table 4. Quantitative Data Co(NO3)2 + Na3PO4 Data Table 4. Quantitative Data Co(NO3)2 + Na3PO4 Data Table 4. Quantitative Data Co(NO3)2 + Na3PO4 Concentration of Stock Co(NO3)2 _________________ g/mL Concentration of Stock Co(NO3)2 _________________ g/mL Concentration of Stock Co(NO3)2 _________________ g/mL Concentration of Stock Co(NO3)2 _________________ g/mL Concentration of Stock Co(NO3)2 _________________ g/mL Concentration of Stock Na3PO4 _________________ g/mL Concentration of Stock Na3PO4 _________________ g/mL Concentration of Stock Na3PO4 _________________ g/mL Concentration of Stock Na3PO4 _________________ g/mL Concentration of Stock Na3PO4 _________________ g/mL Beaker Volume (mL) of Co(NO3)2 Volume (mL) of Na3PO4 Grams of Co(NO3)2 Grams of Na3PO4 #1 NaN NaN NaN NaN #2 NaN NaN NaN NaN #3 NaN NaN NaN NaN #4 NaN NaN NaN NaN 0 1 2 3 4 5 6 7 Data Table 5. The Testing of the Supernatants Data Table 5. The Testing of the Supernatants Data Table 5. The Testing of the Supernatants Data Table 5. The Testing of the Supernatants Data Table 5. The Testing of the Supernatants Data Table 5. The Testing of the Supernatants Data Table 5. The Testing of the Supernatants Data Table 5. The Testing of the Supernatants Supernatant from Beaker # 1 Supernatant from Beaker # 1 Supernatant from Beaker # 2 Supernatant from Beaker # 2 Supernatant from Beaker # 3 Supernatant from Beaker # 3 Supernatant from Beaker # 4 Supernatant from Beaker # 4 To half of the supernatant, add… To half of the supernatant, add… To half of the supernatant, add… To half of the supernatant, add… To half of the supernatant, add… To half of the supernatant, add… To half of the supernatant, add… To half of the supernatant, add… 5 drops of Co(NO3)2 5 drops of Na3PO4 5 drops of Co(NO3)2 5 drops of Na3PO4 5 drops of Co(NO3)2 5 drops of Na3PO4 5 drops of Co(NO3)2 5 drops of Na3PO4 Did a solid form? Did a solid form? Did a solid form? Did a solid form? Did a solid form? Did a solid form? Did a solid form? Did a solid form? NaN NaN NaN NaN NaN NaN NaN NaN If yes, which reagent was still present in Beaker #1? If yes, which reagent was still present in Beaker #1? If yes, which reagent was still present in Beaker #2? If yes, which reagent was still present in Beaker #2? If yes, which reagent was still present in Beaker #3? If yes, which reagent was still present in Beaker #3? If yes, which reagent was still present in Beaker #4? If yes, which reagent was still present in Beaker #4? NaN NaN NaN NaN NaN NaN NaN NaN CALCULATIONS AND DATA ANALYSIS 7.1 Investigation: Conduct and analyze the chemical reaction between Co( NO 3 ) 2 and Na 3 PO 4 (Part 1). How did the reaction mixtures in Data Table 2 compare with the contents of the beaker labeled “Reaction between Co(NO 3 ) 2 and Na 3 PO 4 ” from Data Table 1? Use and discuss these experimental results to identify the solid formed in the beaker labeled “Reaction between Co(NO 3 ) 2 and Na 3 PO 4 ”. Now that you have identified the solid formed in the reaction between Co(NO 3 ) 2 and Na 3 PO 4 , write the BALANCED chemical equation for this reaction. Include physical states in your balanced equation. Your balanced equation should contain two reagents and two products (one product is a solid and one product is aqueous). Investigation: Conduct and analyze the chemical reaction between Co( NO 3 ) 2 and Na 3 PO 4 (Part 2). Review your results for the “The Testing of the Supernatants” in Data Table 4. Did all four supernatants give the same result? Discuss why or why not. Now confirm your experimental results by calculating the limiting reagent for each reaction #1, #2, #3, #4. The following data tables will help you with this. 0 1 2 Beaker 1 Beaker 1 Beaker 1 Line 1 Number of grams of Co(NO3)2 present (refer to Quantitative Data Table 4) NaN Line 2 Molar mass of Co(NO3)2 NaN Line 3 Number of moles of Co(NO3)2 present NaN Line 4 Using the balanced equation, how many moles of Na3PO4 are required to react with the Number of moles of Co(NO3)2 on Line 3? NaN 0 1 2 Line 5 Number of grams of Na3PO4 present (refer to Quantitative Data Table 4) NaN Line 6 Molar mass of Na3PO4 NaN Line 7 Number of moles of Na3PO4 present NaN Line 8 Using the balanced equation, how many moles of Co(NO3)2 are required to react with the Number of moles of Na3PO4 on Line 7? NaN If Line 8 is larger than Line 3 AND if Line 7 is larger than Line 4, then Co(NO 3 ) 2 is the limiting reagent. However, if Line 4 is larger than Line 7 AND if Line 3 is larger than Line 8, then Na 3 PO 4 is the limiting reagent. Identify the limiting reagent for Beaker #1 _______________ 0 1 2 Beaker 2 Beaker 2 Beaker 2 Line 9 Number of grams of Co(NO3)2 present (refer to Quantitative Data Table 4) NaN Line 10 Molar mass of Co(NO3)2 NaN Line 11 Number of moles of Co(NO3)2 present NaN Line 12 Using the balanced equation, how many moles of Na3PO4 are required to react with the Number of moles of Co(NO3)2 on Line 11? NaN 0 1 2 Line 13 Number of grams of Na3PO4 present (refer to Quantitative Data Table 4) NaN Line 14 Molar mass of Na3PO4 NaN Line 15 Number of moles of Na3PO4 present NaN Line 16 Using the balanced equation, how many moles of Co(NO3)2 are required to react with the Number of moles of Na3PO4 on Line 15? NaN If Line 16 is larger than Line 11 AND if Line 15 is larger than Line 12, then Co(NO 3 ) 2 is the limiting reagent. However, if Line 12 is larger than Line 15 AND if Line 11 is larger than Line 16, then Na 3 PO 4 is the limiting reagent. Identify the limiting reagent for Beaker #2 _______________ 0 1 2 Beaker 3 Beaker 3 Beaker 3 Line 17 Number of grams of Co(NO3)2 present (refer to Quantitative Data Table 4) NaN Line 18 Molar mass of Co(NO3)2 NaN Line 19 Number of moles of Co(NO3)2 present NaN Line 20 Using the balanced equation, how many moles of Na3PO4 are required to react with the Number of moles of Co(NO3)2 on Line 19? NaN 0 1 2 Line 21 Number of grams of Na3PO4 present (refer to Quantitative Data Table) NaN Line 22 Molar mass of Na3PO4 NaN Line 23 Number of moles of Na3PO4 present NaN Line 24 Using the balanced equation, how many moles of Co(NO3)2 are required to react with the Number of moles of Na3PO4 on Line 23? NaN If Line 24 is larger than Line 19 AND if Line 23 is larger than Line 20, then Co(NO 3 ) 2 is the limiting reagent. However, if Line 20 is larger than Line 23 AND if Line 19 is larger than Line 24, then Na 3 PO 4 is the limiting reagent. Identify the limiting reagent for Beaker #3 _______________ 0 1 2 Beaker 4 Beaker 4 Beaker 4 Line 25 Number of grams of Co(NO3)2 present (refer to Quantitative Data Table) NaN Line 26 Molar mass of Co(NO3)2 NaN Line 27 Number of moles of Co(NO3)2 present NaN Line 28 Using the balanced equation, how many moles of Na3PO4 are required to react with the Number of moles of Co(NO3)2 on Line 27? NaN 0 1 2 Line 29 Number of grams of Na3PO4 present (refer to Quantitative Data Table) NaN Line 30 Molar mass of Na3PO4 NaN Line 31 Number of moles of Na3PO4 present NaN Line 32 Using the balanced equation, how many moles of Co(NO3)2 are required to react with the Number of moles of Na3PO4 on Line 31? NaN If Line 32 is larger than Line 27 AND if Line 31 is larger than Line 28, then Co(NO 3 ) 2 is the limiting reagent. However, if Line 28 is larger than Line 31 AND if Line 27 is larger than Line 32, then Na 3 PO 4 is the limiting reagent. Identify the limiting reagent for Beaker #4 _______________ Record the identities of the limiting reagents in the table below. 0 1 2 Beaker Limiting Reagent By Testing the Supernatants Limiting Reagent By Calculations #1 NaN NaN #2 NaN NaN #3 NaN NaN #4 NaN NaN Do your results make sense? Suggest reasons for any unusual result(s).