Limiting Reagent Lab Procedure

Limiting Reagent Complete the Prelab page before coming to lab! Since the majority of the lab will be graded from the formal lab report, only certain portions of the lab report in this handout will be graded. The pre-lab portion will count for 10 points, the calculations in the lab notebook and the drawings in the beakers on page 4 will count for 6 points, and the post-lab questions will count for 9 points. (Post-lab questions will NOT be graded in the formal lab report, therefore you need to answer them on page 6 of this handout.) The remaining 75 points will come from your formal lab report. Procedure: SAFETY PRECAUTIONS: Caution: Lead(II) nitrate, Pb(NO3)2, is toxic. DO NOT INHALE ANY Pb(NO3)2 POWDER! Avoid contact with skin, eyes, and clothing. If the solid or solution contacts your skin, rinse completely with water immediately. Caution: Lead(II) iodide, PbI2, is toxic. DO NOT INHALE ANY PbI2 POWDER! Avoid contact with skin, eyes, and clothing. If the solid or solution contacts your skin, rinse completely with water immediately. LAB NOTEBOOK: Before beginning the experiment, prepare a data table to record the following data for all six trials: initial volume of KI(aq), final volume of KI(aq), total volume of KI(aq), initial, final, and total volume of Pb(NO3)2(aq). Therefore the data table should have seven columns and seven rows accounting for headings. Directly above or below the data table, label a space to record the exact concentrations of KI(aq) and Pb(NO3)2(aq). 1. Prepare a hot water bath by adding about 250 mL of water to the 400 mL beaker. Set the hot plate at 5 (a temperature of about 80 – 85oC), and place the beaker on the hot plate. Make sure the water does NOT boil. 2. Clean and number six medium-sized test tubes. In each, add the following amounts of 0.500 M potassium iodide to the six test tubes: 1mL, 2mL, 3mL, 4mL, 5mL, and 6mL. Record the exact volume initially in the buret and the exact volume after adding about each volume listed in the Lab Notebook. (The difference between these values is the volume delivered or total volume.) Also record the exact molarity from the reagent bottle in the Lab Notebook. 3. Now add about 2 mL of 0.500 M lead(II) nitrate to each test tube. Record the exact volume initially in the buret and the exact volume after adding in the Lab Notebook. Also record the exact molarity from the reagent bottle in the Lab Notebook. 4. Place each test tube in the Vortex (set to Auto/Touch; adjust the dial to a low-medium setting) for about 5 – 10 seconds. Once all six solutions have been thoroughly mixed, place them in the hot water bath for about 10 – 15 minutes. (If the test tubes start making popping sounds, move them around in the beaker and adjust the heat setting on the hot plate. This is caused by bubbles popping below the test tubes. This can be a safety issue if a test tube breaks.) 5. After the precipitates have settled to the bottom of the test tubes, remove them from the hot water bath. Remove the test tubes from the hot water bath. Leave the hot water bath on the hot plate but turn the hot plate off. Let the precipitates continue to settle at room temperature for about 5 minutes. If sparkly precipitate is seen in the supernatant solution, you may reheat those test tubes to get the precipitate to resettle at the bottom. 6. LAB NOTEBOOK: Record your observations of the reactants, the products before vortexing, products after vortexing, and before and after heating in your Lab Notebook. Have your instructor initial your observations after your precipitates have completely settled to the bottom. Then draw and label (trial 1, 2, etc..) six test tubes, similar to the ones on the prelab page, in your lab notebook. Draw the actual amount of precipitant formed in each test tube after heating. DO NOT throw your solutions out. You need them for step 8. 7. LAB NOTEBOOK: Write and balance the chemical equation for the reaction in your notebook. Also identify the precipitate in this reaction. Calculate the theoretical mass of the precipitate in each trial. You MUST show these calculations in your lab notebook. (For purposes of time constraints in lab, you may use any shortcuts you find after you finish the first set of calculations. Detailed calculations will not be graded in your lab notebook.) Determine the limiting reagent and the reagent in excess for each trial. Be sure to label each trial’s calculation and results. Results will be graded in your lab notebook! 8. Now test each supernatant (the solution above the precipitate) for the ions present in solution using a different disposable pipet for each to transfer a small amount of the solution from each trial to 2 different clean test tubes. Add more KI solution to the first new test tube and Pb(NO3)2 to the second. Record your observations in the Supernatant Test Data Table on page 5, and answer the Supernatant Tests questions to interpret your results. 9. Complete the Data Page and Postlab Questions, pages 4 – 6. Use the Format for Formal Lab Report found on the CHM151LL Week 12 website to help you write your Formal Report. Combine your work in the following order to submit the following week: Formal Lab Report, yellow copies of your Lab Notebook, Prelab Page (page 3), Data Page and Supernatant Tests (pages 4 & 5), and Post Lab Questions (page 6). Limiting Reagent: Lab Report Name: ________________________ Partners: _______________________ Section Number: ________________ PRELAB PAGE: Complete this page before coming to lab! 1. Betty Smith is making little stick figure donkeys for her daughter’s birthday party. Each donkey needs one head, one body, two ears, and four legs. How many donkeys can she make with 18 heads, 20 bodies, 39 ears and 74 legs? ________________ Draw one. The limiting body part is ___________________. The body parts in excess are ________________________________________________. How many of each excess piece will be leftover? 2. Calculate the mass of precipitate that can be produced when 1.03 mL of 0.500 M potassium iodide reacts with 2.03 mL of 0.500 M lead (II) nitrate. Indicate the limiting reagent and the reagent in excess. (The balanced chemical equation is the one used in this lab.) Theoretical mass of precipitate (how much can be produced): _________________________. The limiting reagent is ___________________. The reagent in excess is ________________. 3. In the test tubes on the left, predict and draw the amount of precipitate produced in lab as the volume of potassium iodide increases with each trial. The first one has been done for you. In the beaker on the right, draw what the solution from the calculation above will look like. (Hint: Think about the pictures from the Ionic Solubility Lab.) DATA: Summary Table Trial 1 2 3 4 5 6 Volume of KI(aq) Volume of Pb(NO3)2(aq) Theoretical mass of precipitate Limiting reagent Reagent in excess Using your calculation results, draw the resulting solution for each trial showing the precipitant and the excess reagent in the beakers below. Trial 1 Trial 2 Trial 3 Trial 4 Trial 5 Trial 6 Questions and Answers Were your prelab predictions of the amount of precipitate formed correct? Explain why or why not. Explain why the amount of precipitate “levels off” using your calculations as a reference. Supernatant Tests 1. If you predict that lead(II) nitrate is the limiting reagent and potassium iodide is in excess: a. What ions are present in the solution above the precipitate? _______________ (Draw the precipitate and excess ions in the beaker to the right.) b. What would happen if you added KI(aq) to the solution? c. What would happen if you added Pb(NO3)2(aq) to the solution? 2. If you predict that potassium iodide is the limiting reagent and lead(II) nitrate is in excess: a. What ions are present in the solution above the precipitate? _______________ (Draw the precipitate and excess ions in the beaker to the right.) b. What would happen if you added KI(aq) to the solution? c. What would happen if you added Pb(NO3)2(aq) to the solution? Supernatant Test Data Table Trial 1 Predicted reagent in excess Observation after adding KI Observation after adding Pb(NO3)2 2 3 4 5 6 Post Lab Questions Consider the reaction, N2(g) + 3H2(g) Æ 2NH3(g). The picture to the right represents a mixture of N2(g) and H2(g) just before reaction occurs. (Smaller lighter spheres are hydrogen molecules, and larger darker spheres are nitrogen molecules.) What is the limiting reactant and how much of the excess reactant remains after the reaction is complete? Write the balanced chemical equation for the formation of water from hydrogen and oxygen gas. How many water molecules can be made from 500 H2 molecules and 500 O2 molecules? (Show your calculation.) Consider the following reaction: Δ V2O5(s) + 2NaOH(l) ⎯⎯ → 2NaVO3(s) + red solid colorless liquid yellow solid H2O(g) colorless gas When the red solid is mixed with the colorless liquid and heated, the mixture starts to give off a gas and change color. When the reaction has stopped, the result is a dry, yellow solid containing small, red particles. Which substance is the limiting reactant? Explain how you determined this. In lab, you are asked to carry out the reaction between NaOH and H2SO4. You are given 32.00 mL of 2.00M NaOH and 50.00 mL of 1.50M H2SO4. Which reagent will be the limiting reagent. Which reagent will be in excess? Explain which color of litmus paper you can use to test your prediction and what result you would get from your test.