CHEM 117 Lab 2 - Lab report on Determining the Composition of a Mixture PDF

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Lab report on Determining the Composition of a Mixture...

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Sadaf Tauhid Chem 117: Section 2 Work Station 5, TA Daniela Graf Stillfried 4 March 2019 Lab 2: Determination of the Composition of a Mixture Introduction: Green Chemistry is a sub-division of Chemistry that tends to focus in on how chemistry that’s used in day-to-day lives—for example research, and medication—can be made safer, while being structured and saving. However, some resources may be limited so chemists try and find alternatives, to not cause environmental damage. The main principles of Green Chemistry seek to address twelve principles that stress the depletion of danger to humans and the environment, alongside the conservation of natural resources. The twelve overall principles of Green Chemistry include: prevention, atom economy, smaller hazardous chemical syntheses, safer chemicals, safer solvents, a design for energy efficiency, renewable feedstocks, reduce derivatives, catalysis, a design for degradation, analysis for prevention of pollution, and safer chemistry in general for accident prevention. In this experiment, the three most common used principles were prevention, atom economy, and smaller hazardous chemical syntheses. Prevention is an essential part of Green Chemistry because it focuses on how the reuse of waste after it’s been made. Often times, the waste that’s normally produced is either placed in containers or diluted with substances so it can be released into the environment. With prevention, Green Chemistry tries to ensure that the wastes that are produced, are recycled over and over again to reduce the amount of waste that’s produced in general. Atom economy is used to help determine how “green” a chemical process is. It helps to determine how accurately the process uses the initial substance—the higher the atom economy turns out to be, the less waste there was produced, making the process “greener.” Smaller hazardous chemical syntheses is used to help produce alternatives by studying the damage it would cause to natural resources, in order to not cause any more environmental damage. The relationship between mass and moles, alongside the relationship between reactants and products was observed in this experiment. The balanced equation used for the reaction in this experiment: 2 NaHCO₃(s)  Na2CO3(s) + H2O(g) + CO2(g) The equation shows that sodium bicarbonate, the reactant, was burned which caused the final products to be sodium carbonate, water and carbon dioxide. Carbon dioxide and water are gaseous, and hence released into the environment. Data: Table 1 shows the mass of the crucible without the lid, the mass of the crucible lid, and the initial exact mass of the unknown mixture of NaHCO₃ and Na₂CO₃. The mass of each is given in grams and was determined using an analytic balance. Table 1. Mass of Crucible and Initial Mass of Mixture

Mass of crucible (without the lid) Mass of crucible lid Exact mass of mixture

19.5631 g 10.7303 g 4.338 g

Table 2 shows the mass of the crucible, with the lid, and the mixture contained within it, after two trials—each of four minutes—was conducted. The mass of each trial is given in grams and was determined using an analytic balance. Table 2. Mass of Trials 1 and 2 Mass of Trial 1 Mass of Trial 2

32.3350 g 32.3270 g

Table 3 shows the atomic mass of all of the reactants and products that were used to calculate the mass lost, moles of loss, percent mass of H₂O loss, mass of NaHCO₃, and the theoretical atom economy of NaHCO₃ . The atomic mass was found on the periodic table and is given in grams. Table 3. Atomic Mass of Reactants and Products Na₂CO₃ 2NaHCO₃ H₂O CO₂

105.988 g 167.997 g 17.9994 g 44.0095 g

Calculations: 1. mass lost (CO₂ + H₂ O) = initial mass - final mass initial mass = mass of crucible + mass of crucible lid + exact mass of mixture initial mass = 19.5631 g + 10.7303 g + 4.338 g initial mass = 34.6314 g mass lost (CO₂ + H₂O) = 34.6314 g – 32.3270 g mass lost (CO₂ + H₂O) = 2.3044 g mass loss 2. moles of loss = × 100% MW ( CO ₂+ H ₂ O ) 2.3044 g moles of loss = 44 + 18 moles of loss = 0.03716 g MW ( H ₂O ) 3. % mass of H₂O loss = MW ( CO ₂+ H ₂ O ) 17.9994 g % mass of H₂O loss = 62.0089 g % mass of H₂O loss = 0.29027 g × 100

% mass of H₂O loss = 29.027 g 4. mass loss of H ₂O = (mass loss) × (% mass of H₂O) mass loss of H₂O = (2.3044 g) × (.29027 g) mass loss of H₂O = 0.6689 g 2 mol NaHCO₃ 1mol H 2 O × × 5. mass of NaHCO₃ = mass of H₂O × 2 1 mol H ₂ O 18.01 g H O 84.01 g NaHCO ₃ 1mol NaHCO ₃ 2 1mol H O 167.997 mol NaHCO ₃ × × mass of NaHCO₃ = 0.6689 g × 2 1 mol H ₂ O 18.01 g H O 84.01 g NaHCO ₃ 1mol NaHCO ₃ mass of NaHCO₃ = 6.24 g NaHCO₃ mass NaHCO ₃ 6. % NaHCO₃ = × 100 total mass(initial mass) 6.24 g % NaHCO₃ = × 100 4.33 g % NaHCO₃ = 144% Discussion Questions: 1. In order to determine the percent composition of NaHCO₃ in the mixture, the following calculation was done: 2 2 mol NaHCO₃ 1mol H O × × mass of NaHCO₃ = mass of H₂O × 1 mol H ₂ O 18.01 g H 2 O 84.01 g NaHCO ₃ 1mol NaHCO ₃ 2 167.997 mol NaHCO ₃ 1mol H O × × mass of NaHCO₃ = 0.6689 g × 2 1 mol H ₂ O 18.01 g H O 84.01 g NaHCO ₃ 1mol NaHCO ₃ mass of NaHCO₃ = 6.24 g NaHCO₃ 2. The use of NaHCO₃ in this experiment was an example of Green Chemistry because of two of the three main principles that were focused in on this lab: prevention and atom economy. NaHCO₃ , also known as sodium bicarbonate, can be used over and over again in future experiments because the water and carbon dioxide that’s present in it is eventually released into the environment hence working hand-in-hand with the prevention principle. If the atom economy turns out to be a higher number, that means that there was minimal waste producing, which makes it a “green” chemical. For NaHCO₃ , the atom economy is typically around 84% which means that it produced very little waste and adhered to the atom economy principle. 3. During this experiment, there was an error that happened somewhere. The actual percent composition of NaHCO₃ that was given was 84%, meaning the percent that was calculated was supposed to be around that. However, the percent that was calculated was

144%. The calculations were all correct, but there was probably a discrepancy in some of the numbers. The lid most likely wasn’t placed on top of the crucible before it was removed, or the timing of the crucible must’ve been off. Heating the mixture inside of the crucible for around 4 minutes but not allowing it to cool could’ve also been a cause for error. By not placing the lid on time, it gives way for air and moisture to enter the crucible which would mean that carbon dioxide and water wouldn’t be properly released into the environment because excess water was added. 4. This experiment is an example of Green Chemistry because of how minimal waste is produced, while simultaneously using a chemical that’s considered “green.” Through the process of heating the sodium bicarbonate, it’s burned which causes water and carbon dioxide to be released into the environment. Sodium carbonate is also produced. All in all, the use of sodium bicarbonate produces very little waste while also being beneficial to the environment, whereas it can be recycled and reused in future experiments. 5. In order to calculate the theoretical atom economy of the chemical reaction that occurs in the experiment the follow calculation was done: mass NaHCO ₃ % NaHCO₃ = × 100 total mass(initial mass) 6.24 g % NaHCO₃ = × 100 4.33 g % NaHCO₃ = 144%...