Safety: Safety goggles should be worn at all times. Students should hold the balloons on the test tubes tightly while the reaction takes place.

Transcription

1 LIMITING REAGENT LAB: THE REACTION BETWEEN VINEGAR AND BAKING SODA Goal: During this lab students will gain a quantitative understanding of limiting reagents. Safety: Safety goggles should be worn at all times. Students should hold the balloons on the test tubes tightly while the reaction takes place. Procedure 1. Students need to get together in teams of four students. 2. Students need to follow the directions below: Student A: Weigh the following six amounts of baking soda (sodium bicarbonate, NaHCO 3 ): 0.18 grams, 0.35 grams, 0.52 grams, 0.70 grams, 1.00 grams, and 1.70 grams. Student B: Student C: Student D: Label the balloons 1-6. Put the six different masses of baking soda into six balloons using a small plastic funnel. Make sure the baking soda goes to the bottom of the balloon. Using the graduated cylinder, accurately measure and transfer 10.0 ml vinegar (5% acetic acid, HC 2 H 3 O 2 ) into each of the 6 test tubes. Attach the filled balloons to the mouth of the test tubes. Make sure that the contents of the balloon and test tube are not mixed. 3. Before mixing the contents of the balloons and test tubes, make a prediction about which combination will produce the greatest amount of carbon dioxide gas. Prediction: 1

2 Observations Data Analysis 1. [1 mark] What was the independent variable in this lab? 2. [1 mark] What was the dependent variable in this lab? 3. [2 mark] What variables were controlled? 4. [1 mark] Does each balloon inflate to some degree? 5. [5 marks] On excel, make a graph of the mass of CO 2 vs. balloon number on excel. Make balloon number the independent variable. 6. Use your observations and the graph to compare the degree to which each balloon inflated. i) [1 mark] What is the pattern of inflation in test tubes 1-4? ii) [1 mark] Noting that in these first four test tubes the mass of bicarbonate increases, what effect does this have on the reaction? iii) [1 mark] What is the pattern of inflation in test tube 4-6? iv) [1 mark] Noting that in last three test tubes the mass of bicarbonate is still increasing, what effect does this have on the reaction? 2

3 Post lab calculations: Answer the following questions and complete the table below. 1. [1 mark] Write the balanced molecular double displacement equation for the reaction that takes place during this lab. One of your products undergoes ad decomposition reaction. Highlight/circle the identity of the gas that inflated the balloons? 2. [1 mark] What is the true combining mole ratio of acetic acid to sodium bicarbonate for the reaction based on the balanced equation? 3. [3 marks] Find the number of moles of baking soda (NaHCO 3 ) used in each reaction: (NaHCO 3 = 84.0 g/mole). Record answers in data table. 4. [3 mark] Determine the mole ratio of sodium bicarbonate to acetic acid for each reaction. (There are 8.3 x 10-3 moles of acetic acid in 10.0 ml of acetic acid.) Record answers in data table. 5. [1 mark] How does the vinegar-bicarbonate mole ratio in the test tube #4 fit into the equation you wrote? What does this ratio mean? 6. [2 mark] Determine which reactants are limiting and which ones are in excess for all the test tubes. Write answers in the data table. 7. [1 mark] After the you have determined which chemical is the limiting reagent in each test tube reaction you can therefore determine how many moles of carbon dioxide were produced in each tube. Record your data in the table. 8. [3 marks] From the limiting reagent, find the mass of carbon dioxide produced. Show your work in the table below. 9. [3 marks] The mass of NaHCO3 increases in each of the test tube. Does this follow the inflation pattern shown in your graph? If not, how do you account for the difference? [Hint; discuss limiting reactants] 3

4 10. Consider the following reaction: Mg(s) + 2HCl(aq) MgCl 2 (aq) + H 2 (g) (a) What is the combining mole ratio of Mg to HCl? (b) Suppose this reaction is performed similarly to the acetic acid/baking soda reaction. A volume of HCl is put in the test tube and a mass of Mg metal is placed in the balloon. Hydrogen gas is produced and inflates the balloon. Which balloon will be the largest? Complete the following table: (There are mol of HCl in 10.0 ml of HCl; Mg = 24.3 g/mole). Test Tube # Mass of Mg, g Mg Volume of HCl, ml HCl Mole ratio Mg:HCl Excess Limiting

5 Test Tube # Mass of NaHCO 3 NaHCO 3 Volume of acid, ml acetic acid Mole ratio: NaHCO 3 : acetic acid Excess Limiting Maximum moles of CO 2 Maximum mass of CO g g g g g g

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