CHEM 121: Chemical Reactions & Stoichiometry Lab Name: Partner(s): In Part A of this lab you will observe nine different

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Chem 121 Chemical Reactions Stoichiometry Lab Name Partner S In Part A Of This Lab You Will Observe Nine Different 1 (68.75 KiB) Viewed 74 times

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CHEM 121: Chemical Reactions & Stoichiometry Lab Name: Partner(s): In Part A of this lab you will observe nine different chemical reactions. These reactions can be classified into four groups-examples of which are shown below. The phases of the reactants and products are indicated (s = solid, 1 = liquid, g = gas, and aq = aqueous solution). Note that although all the formulas are correct, the example equations are not balanced. 1) Combination Reactions (A + B AB): Two elements (or simple compounds) become one compound. Mg(s) + O2(g) MgO(s) S(s) + O2(g) SO₂(g) 2) Decomposition Reactions (AB A+B or ABC AC + BC): A compound becomes two or more elements (or simpler compounds). H₂O(1) H₂(g) + O2(g) CuCO3(s) CuO(s) + CO₂(g) 3) Single Replacement Reactions (A + BC AC + B): An element (a metal or a halogen) replaces another element (metal or halogen) in solution. Zn(s) + CuSO4(aq) ZnSO4(aq) + Cu(s) Cl₂(aq) + NaBr(aq) NaCl(aq) + Br2(aq) 4) Double Replacement Reactions (AB+ CD AD+CB): Two elements "switch" (metals replace each other or hydrogen and a metal replace each other). Nal(aq) + Pb(NO3)2(aq) NaNO3(aq) Pbl2(s) HCl(aq) + NaOH(aq) H₂O(1) + NaCl(aq) Reactions may be done in any order. You DO NOT have to indicate the phase(s) of the products. Record observation(s) and write the balanced chemical equation in Table 1. Reaction #1 has been done for you. 1. Using a test tube and dropper (pipet), add 5 drops Nal(aq) to~1 mL Pb(NO3)2(aq). This is a double replacement reaction. 2. Put a small scoop of copper (II) carbonate, CuCO3(s) into a medium test tube. Using a test tube holder, gently heat the substance using a lab burner for 3 minutes. This is a decomposition reaction.
3. Using a small, disposable test tube, heat a small scoop of sugar, C12H22011(s) in a lab burner flame for 3. This is a decomposition reaction. 4. Using tongs, hold a strip of magnesium, Mg(s) in a burner flame. Caution: do not look directly at the bright light. This is a combination reaction. 5 and 6. In a small test tube held with a test tube holder, add ~1 mL hydrochloric acid, HCl(aq), to a small scoop of magnesium metal powder, Mg(s). Immediately bring a lighted match to the mouth of the test tube. There are two reactions-a single replacement reaction between the acid and the metal, and a combination reaction between the gas produced and oxygen in the air. 7. Place a large test tube (provided) into the three prong clamp on the ring stand and dispense-5 mL of 3 M NaOH into this test tube. Put a digital thermometer probe into this solution and record the temperature. Carefully dispense- 5 mL of 3 M HCI into another large test tube. Add the HCI to the NaOH and monitor the temperature. This is a double replacement reaction. Table 1. Reactions and Observations Observation(s) Reaction #1 Balanced Chemical Equation 2 Nal+ Pb(NO3)2 2 NaNO3 + Pbl2 CUCO3 Reaction #2 Reaction #3 C12H22011 Reaction #4 Mg +02 Reaction #5 Zn + HCT Reaction #6 H₂ + O2 Reaction #7 NaOH + HCT In Part B of this lab, you will study a double replacement reaction as a means of testing whether the amount of "active ingredient" in a commercial antacid tablet can be verified by experiment. Sodium bicarbonate (sodium hydrogen carbonate), NaHCO3, is a common ingredient in antacid medications. It works by a "double replacement reaction with stomach acid (HCI) to produce carbonic acid that then decomposes into water and carbon dioxide. NaHCO3(s) + HCl(aq) → H₂CO3 (1) + NaCl(aq) H₂CO3(1) CO₂(g) + H₂O(l)
So the overall (balanced) chemical equation is: NaHCO3(s) + HCl(aq) H₂0(1) + CO₂(g) + NaCl(aq) Note that one of the products (CO2) is a gas and will escape from the reaction container. We will use this fact, and the stoichiometry of the reaction to test the amount of active ingredient in a commercial antacid tablet. Part B1. Calibrating the method. (Note: this may already have been done in class) 1) Mass - 2 g of sodium bicarbonate (NaHCO3) onto a piece of weighing paper. Record the exact mass in Table 1. 2) Mass an EMPTY 25 mL graduated cylinder. Record the mass in Table 1. Dispense -25 mL of 1.0 M HCI into the graduated cylinder and record the new mass in Table 1. The exact amount DOES NOT MATTER because you are recording the mass. 3) Mass an EMPTY 125 mL Erlenmeyer flask. Record this mass in Table 1. 4) Add the solid sodium bicarbonate to the Erlenmeyer flask, and then slowly add the hydrochloric acid taking care to keep the reaction mixture from overflowing the flask 5) Transfer the flask and reaction mixture to a hot plate (set on 80-90° C) and wait 5 minutes, swirling occasionally. 6) When no more bubbling is observed, mass the flask and reaction products. Record this mass in Table 1. You can pour this reaction mixture down the drain. Table 1. Mass data for calibration experiment Mass (g Mass NaHCO3 2.080 9 Mass EMPTY 25 ml graduated cylinder 50.252 9 Mass graduated cylinder with ~ 25 mL HCI 75. 349.9 Mass EMPTY 125 mL Erlenmeyer Flask 78. 8599 Mass Erlenmeyer flask and reaction products. 104.359 g 1) Calculate mass of HC1 using the Table 1 data (subtract the mass of the empty cylinder from the combined mass of the cylinder and acid). 2) Calculate total mass reactants and flask using the Table I data (add the mass of the da.. fa.- M.TICO
acid to the mass on the arnog anu ine mass of ine empty uassky. 3) Write the total (measured) mass of the reaction products and flask here. 4) Calculate the mass difference (reactant mass - product mass) = 5) Convert this mass difference into mols CO₂ (molar mass = 44.0 g) = 6) Calculate mols NaHCO3 using the Table 1 data (molar mass=84.0 g) = 7) Calculate a % difference between the two mol amounts (met CO2-met NaHCO3) % difference= mal NaHCO3 x 100 Analysis: (5) and (6) above should be the same number (% difference should be 0). How well did the experimental method work? Can you think of any sources of error? Part B2. Analyzing an antacid tablet. Repeat the experiment with an antacid tablet instead of NaHCO3. Record your data in Table 2. Table 2. Mass data for evaluating antacid tablet Mass (g) Mass antacid tablet 3. 204 9 Mass EMPTY 25 mL graduated cylinder 50.291 g Mass graduated cylinder with - 25 mL HCI 75.269 9 Mass EMPTY 125 mL Erlenmeyer Flask 89.7179 Mass Erlenmeyer flask and reaction nrdinate 117.0149
teacol provuueன் Mass active ingredient (NaHCO3) from product label 1916 mg (1.9169) B1) Calculate mass of HCl using Table 2 data = B2) Calculate total mass of reactants and flask using Table 2 data = B3) Write the total mass of products and flask here. B4) Calculate mass difference (reactant mass - product mass) = B5) Convert mass difference into mols CO2 (molar mass= 44.0 g) = (Note: mols CO₂ = mols NaHCO3 because the coefficients of the balanced chemical equation are all 1) B6) Calculate the experimental mass of NaHCO3 (molar mass= = 84.0 g) = Analysis: 1) Calculate a % difference between your experimental mass of NaHCO3 and that listed on the product label. % difference = (experimental mazz-label mass) label mass x 100 2). What specifically in your experiment accounts for the calculated percent difference?