Lab #4 Report

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Dec 6, 2023

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General Chemistry Lab I CHEM 1111.001 Experiment #8: Percent Composition from Gravimetric Analysis Student’s name: Retha (Kaleigh) LaForge Lab partner(s) name: Richard Ramirez Date: 13 October 2023

Objectives/Goals : Use your understanding of solubility rules and precipitation reactions to isolate calcium (and ions, in general) from a real-world sample. Use the mass relationships to determine the percent composition of calcium carbonate in limestone. Safety Concerns: Gloves and safety goggles should be worn at all times. Hydrochloric acid is toxic by ingestion and inhalation and corrosive to skin and eyes; avoid contact with body tissues. Aqueous ammonia (NH3) solution is corrosive and contact with the skin or eyes should be avoided. Work in a well-ventilated area. Procedure/Methodology: Grinded a piece of limestone until it was in a powered form. Measured the mass of 2 separate amounts of limestone using a digital balance. Measured a total mass between 1.5 and 2 grams for each amount of limestone. Measured 25 mL of 3.00 M HCL using a graduated cylinder and added it to a clean and dry 125 mL Erlenmeyer flask. Measured and recorded the mass of each flask. Added the first amount of limestone into one flask, and the second amount into another. Observed the limestone dissolve until the reaction was complete. Once complete, measured the final mass of the flask. Calculated the moles and mass of CO2 released, the moles and mass of CaCO3 in limestone, and the percent of CaCO3 in limestone. Using filter paper, filtered all the solid parts that did not dissolve in each flask. Place the filtered sample into a new flask. Measure the mass of a new piece of filter paper for each flask, added 10 drops of methyl red indicator to each reaction, and observed changes in pH occur when mixture turned pink. Pink, meaning the pH is less than 4.4. Added 3.00g of (NH4)2SO4 to each flask while stirring. Continued constant stirring, slowly added 2.00 M NH3 until the color shifted from pink to a pale yellow, indicating a change in pH to approximately 6.2. Filtered precipitate using measured filtered paper into a 250 mL flask for each solution. Washed remaining solid from the flask with water. Once the filtrate completely passed through the filter, it was washed with water and then transferred to dry. Once dry recorded the mass of the filter paper plus the precipitate, and calculated the mass of CaSO4 precipitate, moles of CaSO4, moles and mass of CaCO3 in limestone, and the percent od CaCO3 in limestone.

Observations/Data: Balanced equation: CaCO3(s) + 2HCL(aq) CaCl2 (aq) + H2CO3(aq) Part I: Carbonate in Limestone Measurement Trial 1 Trial 2 Mass of Limestone (g) 1.742 1.626 Mass of Container + HCL (g) 169.436 118.451 Final Mass of Container + Contents (g) 170.441 119.446 Mass of CO2 Released (g) 0.737 0.631 Moles of CO2 Releases (mol CO2) 0.0167 0.0143 Moles of CaCO3 in Limestone (mol CaCO3) 0.0167 0.0143 Mass of CaCO3 in Limestone (g) 1.670 1.430 Percent of CaCO3 in Limestone (%) 98.00 83.90 Average Percent of CaCO3 in Limestone (%) 90.95 To find the amount of moles of CO2 released: mass of limestone + Mass of container and HCL – Final mass/ molar mass Molar mass of CO2 = 44.01g/mol Trial I: 1.742g+169.432g-170.441g/44.01g/mol=0.737 mol CO2 Trial II: 1.626g+118.451g-119.446g/44.01g/mol=0.631 mol CO2 Moles of CaCO3 = Moles of CO2 since the mole-to-mole ratio is 1:1 Mass of CaCO3 = Moles of CaCO3 x molar mass Molar mass of CaCO3 = 100.1g/mol Trial I: 0.0167mol CaCO3x100.1g/mol=1.670g Trial II: 0.0143mol CaCO3x100.1g/mol=1.430g Percent of CaCO3 in limestone = mass of CaCO3/ mass of limestone x100 Trial I: 1.670g/1.742g x 100 = 98.00% Trial II: 1.430/1.626 x 100 = 83.90%

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Part II: Calcium in Limestone Measurement Trial 1 Trial 2 Mass of Filter Paper (g) 0.225 0.230 Mass of Filter Paper + Precipitate (g) 3.320 2.220 Mass of CaSO4 Precipitate (g) 2.095 1.990 Moles of CaSO4 (mol CaSO4) 0.0154 0.0146 Moles of CaCO3 in Limestone (mol CaCO3) 0.0154 0.0146 Mass of CaCO3 in Limestone (g) 1.541 1.461 Percent of CaCO3 in Limestone (%) 88.46 83.89 Average Percent of CaCO3 in Limestone (%) 86.18 Mass of CaSO4 Precipitate = Mass of Filter Paper and Precipitate – Mass of Filter Paper Trial I: 3.320g-0.225g = 2.095g Trial II: 2.220g-0.230g = 1.990g Moles of CaSO4 = mass of CaSO4 / molar mass CaSO4 molar mass = 136.14g/mol Trial I: 2.095g/136.14g/mol = 0.0154 mol CaSO4 Trial II: 1.990/136.14g/mol = 0.0146 mol CaSO4 Mols of CaSO4 = Mols of CaCO3 since the mole-to-mole ratio in the balanced equation is 1:1 Mass of CaCO3 = Mol of CaCO3 x molar mass Molar mass = 100.1g/mol Trial I: 0.0154 mol CaCO3 x 100.1g/mol = 1.541 g Trial II: 0.0146 mol CaCO3 x 100.1 g/mol = 1.461 g Percent of CaCO3 in limestone = mass of CaCO3/ mass of limestone x100 Trial I: 1.541g/1.742g x 100 = 98.00% Trial II: 1.461g/1.626 x 100 = 83.90%

Conclusion: The experiment yielded several different results. The experiment yielded several different results. The percent of CaCO3 was calculated by the given equation mass of interest/total mass x 100 = percent of composition. Both the interest of mass was measured, and the total mass of each solution was measured to calculate a percent of 90.95 in Part I and 86.18 in part II. These results were found by obtaining the mass of CaCO3, and CO2, and converting them into moles using their molar mass and the mole-to-mole ratio given in the balanced equation. If I were to complete this experiment again, I would be more precautious to the specific amounts of each liquid used. For instance, the amount of 2 M NH3 added to the solution. This would give more precise and accurate data. I would also like the same tools to be used in each trial, as this would eliminate possible reasons of error.