Lab 5 Limiting Reagent Lab Report Completed

Lab 5 – Limiting Reagent Study – Lab Report CHM 2045L – Dr. Yavuz Petrowski "I certify that this is my own work and I understand that if I am found to be in violation of the honor code, I will be subject to the highest penalty" PRELAB Purpose of the Experiment The purpose of this experiment is to investigate the concept of limiting reagents by observing the precipitation reaction between cobalt(II) chloride (CoCl?) and sodium carbonate (Na?CO?). The balanced equation for this reaction is: CoCl?(aq) + Na?CO?(aq) ? CoCO?(s) + 2 NaCl(aq) In this experiment, six test tubes are prepared with varying volumes of 0.10 M CoCl? and 0.10 M Na?CO? solutions, keeping the total volume constant at 15.00 mL per tube. Because the volumes (and therefore the moles) of each reagent differ across tubes, one reagent will be completely consumed before the other in most tubes. The reagent that is fully consumed is called the limiting reagent, because it limits the amount of product (CoCO? precipitate) that can form. The key concept being investigated is stoichiometry: the quantitative relationship between reactants and products. Because CoCl? and Na?CO? react in a 1:1 molar ratio, whichever reactant has fewer moles will be the limiting reagent. The amount of precipitate formed is directly proportional to the moles of the limiting reagent. We determine the limiting reagent first by predicting from mole calculations, and then verifying experimentally in Part II using indicator reagents: Na?PO? (which reacts with excess Co²? ions to form a pink precipitate) and BaCl? (which reacts with excess CO?²? ions to form a white BaCO? precipitate). Key equations used: moles = Molarity (M) × Volume (L) Theoretical yield (mol) = moles of limiting reagent This experiment is useful in illustrating how limiting reagents govern chemical reactions in both laboratory and industrial settings, where maximizing yield while minimizing waste of expensive or hazardous chemicals is critical. Flow Chart Note: Flow chart boxes are represented below in sequence. Arrows indicate progression between steps. START ? Label 6 test tubes #1–6 ? Using a buret, deliver the specified volume of 0.10 M CoCl? into each test tube (2.00, 3.00, 4.00, 6.00, 7.50, 10.00 mL) ? Using a second buret, deliver the specified volume of 0.10 M Na?CO? into each test tube (13.00, 12.00, 11.00, 9.00, 7.50, 5.00 mL) ? Stopper each test tube and gently invert 10× to mix ? Allow precipitate to settle (~15 min); record height of precipitate (cm) and color of supernatant and precipitate ? PART II: Transfer 10 drops of supernatant from each tube to two separate spot plates ? To one spot plate well: add 2 drops of 0.10 M Na?PO? ? observe for pink precipitate (indicates excess Co²?) ? To second spot plate well: add 2 drops of 0.10 M BaCl? ? observe for white precipitate (indicates excess CO?²?) ? Record observations and compare to predicted limiting reagent ? Dispose of all waste in designated waste container ? END Waste Collection Chemical Safety Hazards Disposal Cobalt(II) Chloride (CoCl?, 0.10 M aq.) Toxic; suspected carcinogen (IARC Group 2B); irritant to skin, eyes, Collect in labeled heavy-metal and respiratory tract; harmful if ingested; wear gloves and goggles waste container Sodium Carbonate (Na?CO?, 0.10 M aq.) Mild irritant to skin, eyes, and mucous membranes; mildly alkaline; Collect in labeled waste container not acutely toxic at low concentrations or neutralize and flush with water Sodium Phosphate (Na?PO?, 0.10 M aq.) Irritant to skin and eyes; alkaline; avoid inhalation of dust Barium Chloride (BaCl?, 0.10 M aq.) Toxic; barium compounds are harmful if ingested; harmful to aquatic Collect in labeled heavy-metal organisms; do NOT pour down drain waste container Cobalt Carbonate precipitate (CoCO?) Toxic solid; suspected carcinogen; avoid inhalation; avoid skin contact Collect in labeled waste container Collect in labeled solid heavy-metal waste container DATA PROCESS PART I: Calculations and Observations Table 1: CoCl? Data (Concentration = 0.10 M) Tube #1 Tube #2 Tube #3 Tube #4 Tube #5 Tube #6 Concentration (M) 0.10 0.10 0.10 0.10 0.10 0.10 Volume delivered (mL) 2.00 3.00 4.00 6.00 7.50 10.00 0.0002 0.0003 0.0004 0.0006 0.0008 0.0010 Tube #1 Tube #2 Tube #3 Tube #4 Tube #5 Tube #6 Concentration (M) 0.10 0.10 0.10 0.10 0.10 0.10 Volume delivered (mL) 13.00 12.00 11.00 9.00 7.50 5.00 Moles of Na?CO? (mol) 0.0013 0.0012 0.0011 0.0009 0.0008 0.0005 Moles of CoCl? (mol) Table 2: Na?CO? Data (Concentration = 0.10 M) Table 3: Volume Measurements and Observations Height of precipitate (cm) Color of supernatant Color of precipitate Tube #1 Tube #2 Tube #3 Tube #4 Tube #5 Tube #6 5.5 6.4 7.3 8.3 8.0 7.5 Colorless (stoichiometric) Pink/red (excess Co²?) Pink/purple (CoCO?) Pink/purple (CoCO?) Colorless (excess Colorless (excess Colorless (excess Colorless (excess CO?²?) CO?²?) CO?²?) CO?²?) Pink/purple (CoCO?) Pink/purple (CoCO?) Pink/purple (CoCO?) Calculations – Moles of CoCl? and Na?CO? Pink/purple (CoCO?) Using: moles = Molarity × Volume(L) Formula: mol = 0.10 mol/L × V(mL) ÷ 1000 Test Tube #1: mol CoCl? = 0.10 M × (2.00 mL × 1 L/1000 mL) = 0.0002 mol mol Na?CO? = 0.10 M × (13.00 mL × 1 L/1000 mL) = 0.0013 mol Test Tube #2: mol CoCl? = 0.10 M × (3.00 mL × 1 L/1000 mL) = 0.0003 mol mol Na?CO? = 0.10 M × (12.00 mL × 1 L/1000 mL) = 0.0012 mol Test Tube #3: mol CoCl? = 0.10 M × (4.00 mL × 1 L/1000 mL) = 0.0004 mol mol Na?CO? = 0.10 M × (11.00 mL × 1 L/1000 mL) = 0.0011 mol Test Tube #4: mol CoCl? = 0.10 M × (6.00 mL × 1 L/1000 mL) = 0.0006 mol mol Na?CO? = 0.10 M × (9.00 mL × 1 L/1000 mL) = 0.0009 mol Test Tube #5: mol CoCl? = 0.10 M × (7.50 mL × 1 L/1000 mL) = 0.0008 mol mol Na?CO? = 0.10 M × (7.50 mL × 1 L/1000 mL) = 0.0008 mol Test Tube #6: mol CoCl? = 0.10 M × (10.00 mL × 1 L/1000 mL) = 0.0010 mol mol Na?CO? = 0.10 M × (5.00 mL × 1 L/1000 mL) = 0.0005 mol Predictions of Limiting Reagent Because the balanced equation is CoCl? + Na?CO? ? CoCO? + 2NaCl, the molar ratio is 1:1. The reagent with fewer moles is the limiting reagent. Tube mol CoCl? mol Na?CO? Limiting Reagent Reasoning #1 0.0002 0.0013 CoCl? 0.0002 < 0.0013 mol #2 0.0003 0.0012 CoCl? 0.0003 < 0.0012 mol #3 0.0004 0.0011 CoCl? 0.0004 < 0.0011 mol #4 0.0006 0.0009 CoCl? 0.0006 < 0.0009 mol #5 0.0008 0.0008 Neither (equal) #6 0.0010 0.0005 Na?CO? Equal moles – stoichiometric 0.0005 < 0.0010 mol PART II: Verification of Limiting Reagent Table 4: Observations from Indicator Tests Observation Reaction with Na?PO? Reaction with BaCl? Excess ion present Tube #1 Tube #2 Tube #3 Tube #4 Tube #5 Tube #6 No rxn No rxn No rxn No rxn No rxn Pink ppt White ppt White ppt White ppt White ppt No rxn No rxn CO?²? CO?²? CO?²? CO?²? Neither Co²? Part II – Excess and Theoretical Yield Calculations Reaction: CoCl? + Na?CO? ? CoCO? + 2NaCl (1:1 molar ratio, M(CoCO?) = 118.94 g/mol) Test Tube #1: Limiting reagent: CoCl? Excess Co²? = 0 mol (CoCl? is limiting or stoichiometric) Excess CO?²? = mol Na?CO? ? mol CoCl? = 0.0013 ? 0.0002 = 0.0011 mol Theoretical yield of CoCO? = 0.0002 mol CoCl? (or Na?CO?) × (1 mol CoCO? / 1 mol limiting) = 0.0002 mol Theoretical yield in grams = 0.0002 mol × 118.94 g/mol = 0.0238 g Test Tube #2: Limiting reagent: CoCl? Excess Co²? = 0 mol (CoCl? is limiting or stoichiometric) Excess CO?²? = mol Na?CO? ? mol CoCl? = 0.0012 ? 0.0003 = 0.0009 mol Theoretical yield of CoCO? = 0.0003 mol CoCl? (or Na?CO?) × (1 mol CoCO? / 1 mol limiting) = 0.0003 mol Theoretical yield in grams = 0.0003 mol × 118.94 g/mol = 0.0357 g Test Tube #3: Limiting reagent: CoCl? Excess Co²? = 0 mol (CoCl? is limiting or stoichiometric) Excess CO?²? = mol Na?CO? ? mol CoCl? = 0.0011 ? 0.0004 = 0.0007 mol Theoretical yield of CoCO? = 0.0004 mol CoCl? (or Na?CO?) × (1 mol CoCO? / 1 mol limiting) = 0.0004 mol Theoretical yield in grams = 0.0004 mol × 118.94 g/mol = 0.0476 g Test Tube #4: Limiting reagent: CoCl? Excess Co²? = 0 mol (CoCl? is limiting or stoichiometric) Excess CO?²? = mol Na?CO? ? mol CoCl? = 0.0009 ? 0.0006 = 0.0003 mol Theoretical yield of CoCO? = 0.0006 mol CoCl? (or Na?CO?) × (1 mol CoCO? / 1 mol limiting) = 0.0006 mol Theoretical yield in grams = 0.0006 mol × 118.94 g/mol = 0.0714 g Test Tube #5: Limiting reagent: None (stoichiometric) Excess Co²? = 0 mol (CoCl? is limiting or stoichiometric) Excess CO?²? = 0 mol (Na?CO? is limiting or stoichiometric) Theoretical yield of CoCO? = 0.0008 mol CoCl? (or Na?CO?) × (1 mol CoCO? / 1 mol limiting) = 0.0008 mol Theoretical yield in grams = 0.0008 mol × 118.94 g/mol = 0.0892 g Test Tube #6: Limiting reagent: Na?CO? Excess Co²? = mol CoCl? ? mol Na?CO? = 0.0010 ? 0.0005 = 0.0005 mol Excess CO?²? = 0 mol (Na?CO? is limiting or stoichiometric) Theoretical yield of CoCO? = 0.0005 mol CoCl? (or Na?CO?) × (1 mol CoCO? / 1 mol limiting) = 0.0005 mol Theoretical yield in grams = 0.0005 mol × 118.94 g/mol = 0.0595 g Table 5: Summary – Excess Moles and Theoretical Yield Tube Excess Co²? (mol) Excess CO?²? (mol) Theor. Yield (mol) Theor. Yield (g) Limiting Reagent #1 0.0000 0.0011 0.0002 0.0238 CoCl? #2 0.0000 0.0009 0.0003 0.0357 CoCl? #3 0.0000 0.0007 0.0004 0.0476 CoCl? #4 0.0000 0.0003 0.0006 0.0714 CoCl? #5 0.0000 0.0000 0.0008 0.0892 Neither #6 0.0005 0.0000 0.0005 0.0595 Na?CO? DISCUSSION & CONCLUSION ESSAY The purpose of this experiment was to investigate the concept of a limiting reagent by observing the precipitation reaction between cobalt(II) chloride (CoCl?) and sodium carbonate (Na?CO?). The reaction, CoCl?(aq) + Na?CO?(aq) ? CoCO?(s) + 2NaCl(aq), produces a pink-purple cobalt(II) carbonate precipitate. By varying the volumes of each 0.10 M reagent across six test tubes while keeping the total volume constant at 15.00 mL, the amount of precipitate formed in each tube depended entirely on whichever reagent was present in the lesser molar quantity. The limiting reagent is the reactant that is completely consumed in a chemical reaction and thereby limits the amount of product that can be formed. In this experiment, the molar ratio of CoCl? to Na?CO? is 1:1; therefore, the reagent with fewer moles in any given tube is the limiting reagent. For test tubes #1 through #4, CoCl? was the limiting reagent because its mole quantity was smaller (0.0002 to 0.0006 mol) relative to Na?CO? (0.0009 to 0.0013 mol). In test tube #5, both reagents were present in equal molar amounts (0.00075 mol each), making it the stoichiometric point where neither reagent is in excess. In test tube #6, Na?CO? became the limiting reagent (0.0005 mol) because less of it was added relative to CoCl? (0.0010 mol). The precipitate height data supported these calculations. The height of the CoCO? precipitate increased from 5.5 cm in tube #1 to a maximum of 8.3 cm in tube #4, reached 8.0 cm in tube #5 (near stoichiometric), and then decreased to 7.5 cm in tube #6 as Na?CO? became limiting. This pattern is consistent with the theoretical yields calculated: as the moles of the limiting reagent increased from tube #1 to the stoichiometric point (#5), more product formed. The slight decrease in height from tube #4 to #5 may suggest that the maximum yield was actually reached around tube #4 or #5, with tube #5 reflecting slightly less product due to the stoichiometric distribution. In Part II, the predictions made from molar calculations were verified using indicator reagents. The supernatant (the clear liquid above the precipitate) was tested with Na?PO? and BaCl?. A pink precipitate upon addition of Na?PO? indicated the presence of excess Co²? ions: 3Co²?(aq) + 2PO?³?(aq) ? Co?(PO?)?(s). A white precipitate upon addition of BaCl? indicated the presence of excess CO?²? ions: Ba²?(aq) + CO?²?(aq) ? BaCO?(s). As predicted, test tubes #1 through #4 showed a white precipitate with BaCl? (confirming excess CO?²?, i.e., Na?CO? was in excess), test tube #5 showed no reaction with either indicator (confirming stoichiometric conditions), and test tube #6 showed a pink precipitate with Na?PO? (confirming excess Co²?, i.e., CoCl? was in excess). These results completely verified our initial predictions based on mole calculations. The theoretical yield represents the maximum amount of product that could be formed if the limiting reagent were completely consumed with no losses. In this experiment, the theoretical yield of CoCO? was calculated from the moles of the limiting reagent: since the molar ratio is 1:1, one mole of limiting reagent produces one mole of CoCO? (M = 118.94 g/mol). The theoretical yields ranged from 0.0238 g (tube #1) to 0.0892 g (tube #5). Percent yield could only be calculated if the experimental yield (the actual mass of precipitate collected and dried) were measured. In this experiment, we measured the height of the precipitate rather than its mass, so a direct experimental yield in grams was not available. To calculate percent yield, one would need to filter, dry, and mass the precipitate from each tube, then apply: percent yield = (experimental yield / theoretical yield) × 100%. In conclusion, this experiment successfully demonstrated the concept of limiting reagents through a visible, measurable precipitation reaction. The mole calculations accurately predicted which reagent was limiting in each test tube, and the indicator tests in Part II confirmed those predictions with no discrepancies. The concept of limiting reagents has critical practical importance in chemistry and industry: in pharmaceutical synthesis, excess reagents are carefully controlled to maximize product yield while minimizing waste; in manufacturing, understanding stoichiometry helps reduce production costs and environmental impact. This experiment provided a clear, hands-on illustration of how the molar ratio and the relative quantities of reactants determine both the identity of the limiting reagent and the quantity of product formed.