Chemical Reactions Investigation Two Data Record Name: Date: 1. During this Investigation, you will analyze how changing the amounts of the reactants in a chemical reaction affects the amount of the products that are produced. By performing the experiments in the Investigation, you will answer the following questions: Focus Questions: In a chemical reaction, do the amounts of the reactants affect the amounts of products produced? How does the Law of Conservation of Matter relate to chemical reactions? Tool: Prediction You are going to study how changing the amount of the reactants affects the amount of the products of a chemical reaction. Use the Prediction tool to think of possible answers to the following questions: Are the reactants always completely used up in a chemical reaction? Student answers may vary. Does the matter making up the reactants disappear? Student answers may vary. What happens if there is more of one reactant than the other reactant? Student answers may vary. How do you know when a chemical reaction has stopped? Student answers may vary. 15
2. Materials per group: 1 triple beam balance 1 500 ml Erlenmeyer flask 1 lab scoop 1 weigh dish 6 large balloons 1 15 ml centrifuge tube 1 100 ml graduated cylinder 3.5 g of Magnesium (Mg) powder 1 400 ml beaker 350 ml of hydrochloric acid (HCl) in a beaker 1 metric ruler 1 calculator 1 stop watch 1 pair gloves per student 1 pair goggles per student 16
Background In a chemical reaction, the chemical bonds that hold the atoms of the reactants together are broken and reformed in a different arrangement to form the products. Breaking and reforming these bonds occurs when the reactants react with each other. The different arrangement of atoms can be seen by the different formulas that represent the reactants and products. When all of the reactants are consumed in a chemical reaction, they no longer exist in their original form. All the atoms originally found in the reactants can now be found in the products. The observation that all the matter of the reactants is converted into the matter of the products is referred to as the Law of Conservation of Matter. Sometimes two reactants are not present in equivalent or equal amounts. More of one reactant is present compared to the other. The reactant present in the lesser amount is completely consumed or used up in such a chemical reaction. Since none of this reactant remains, the chemical reaction must stop. When the reaction stops, only a portion of the other reactant has been consumed, meaning that some is still unreacted. In this Investigation, the following chemical reaction will take place. Mg + 2 HCl MgCl 2 + H 2 Hydrochloric Magnesium Acid Chloride Magnesium Metal 3. Procedural Toolbox During each Trial in this Investigation, you will use the following tools from the Procedural Toolbox. Triple Beam Balance Equilibration Triple Beam Balance Use and Operation Measuring Mass Using a Weigh Dish or Beaker Graphing of Independent and Dependent Variables Hydrogen gas 17
Experiment 1. Six Trials will be performed in this Investigation. The first 5 Trials will use the same mass of magnesium metal (Mg) but a different volume of hydrochloric acid (HCl). The last Trial will use a different mass of magnesium (Mg). In all Trials, the amount of one of the products, hydrogen gas, will be determined. Use Table A as a guide for the mass of magnesium (Mg) and the volume of hydrochloric needed for each Trial. Trial 1 Table A Trial Mass of Mg Volume of HCl (g) (ml) 1 0.5 2 2 0.5 15 3 0.5 50 4 0.5 75 5 0.5 100 6 1 100 1. In this Trial you will investigate the reaction of 2 ml of hydrochloric acid (HCl) with 0.5 g of magnesium. a. Use the centrifuge tube to measure 2 ml of HCl and add it to the Erlenmeyer flask. b. Use the triple beam balance, lab scoop, and weigh dish to measure 0.5g of magnesium. If you need help, read the Procedures, Triple Beam Balance Equilibration, Triple Beam Balance Use and Operation, and Measuring Mass Using a Weigh Dish or Beaker. Mass of weigh dish Mass of weigh dish and magnesium 5.0 g 5.5 g c. Blow up each balloon to stretch and then deflate it. Use the lab scoop to add the 0.5g of magnesium to a balloon. 18
d. Stretch the open end of the balloon over the mouth of the Erlenmeyer flask until it securely covers the mouth of the flask. During this step, do not allow any magnesium metal to fall into the flask. e. Use the triple beam balance to determine the total mass of the flask, hydrochloric acid (HCl), balloon, and magnesium. 2. Record: Write the mass for Before Reaction in Table B. Table B Mass of Flask, HCl, Mg and balloon (grams) Before Reaction 204 After Reaction 204 3. Making sure that the balloon does not come off the mouth of the flask, hold the balloon and shake the magnesium out of the balloon until all of it has fallen to the bottom of the flask into the hydrochloric acid (HCl). 4. Gently swirl the flask, so the magnesium stays in contact with the hydrochloric acid. After approximately 5 minutes, the production of the product, hydrogen gas (H 2 ), will have stopped. Do not remove the balloon. 5. Using the triple beam balance, determine the total mass of the flask, hydrochloric acid (HCl), balloon, and any remaining magnesium metal. 6. Record: Write the mass for After Reaction in Table B. 7. Question: What was the mass of the flask, hydrochloric acid (HCl), balloon, and magnesium metal (Mg) before the reaction? Student answers may vary. 19
8. Question: What was the mass of the flask, hydrochloric acid (HCl), balloon, and magnesium (Mg) after the reaction? Was it the same as the mass of the flask, hydrochloric acid, and magnesium before the reaction? Student answers may vary. Yes, the mass should be the same as the mass before the reaction took place. 9. Question: Do the data support the Law of Conservation of Matter? Why? Student answers will vary. Yes, the Law of Conservation of Matter was supported because the total mass of the flask, hydrochloric acid (HCl), and balloon was the same before and after the reaction. 10. To determine how much hydrogen gas (H 2 ) was produced, use the metric ruler to measure the diameter of the balloon in centimeters. The diameter is the distance across the width of the balloon. 11. Record: Enter the diameter of the balloon in Table C in the row for Trial 1. Table C is located after Trial 6 in the Student Data Record. 12. Question: What was the product of the reaction that caused the balloon to expand? (Hint: look at the chemical equation in the Background) The product of the reaction was hydrogen gas (H 2 ) 13. Question: How do you know that a chemical reaction occurred? One of the products of the reaction is hydrogen gas (H 2 ). The balloon attached to the flask expanded as it filled with the hydrogen gas (H 2 ) produced by the chemical reaction. 20
14. Question: Did any magnesium (Mg) remain after the reaction ended? Yes, some magnesium remained. 15. Discard the contents of the flask in the 400 ml beaker, and rinse the flask with water. Trial 2 1. In this Trial you will investigate the reaction of 15ml of hydrochloric acid (HCl) with 0.5g of magnesium. Tool: Prediction Use the Prediction tool to answer the following question. 2. Question: Do you think the balloon will expand to a smaller or larger diameter in Trial 2 compared to Trial 1. Explain the reason for your prediction. The balloon will expand to a greater diameter than in Trial 1. More hydrogen gas (H 2 ) will be produced because more hydrochloric acid (HCl) reactant is used. 3. Using the 100 ml graduated cylinder, measure 15ml of hydrochloric acid (HCl) and add it to the Erlenmeyer flask. 4. Use the triple beam balance, lab scoop, and weigh dish to measure 0.5g of magnesium. Add the 0.5 g of magnesium to a new balloon. 5. Stretch the open end of the balloon over the mouth of the Erlenmeyer flask until it securely covers the mouth of the flask. During this step, do not allow any magnesium to fall into the flask. 6. Making sure that the balloon does not come off the mouth of the flask, hold the balloon and shake the magnesium out of the balloon until all of it has fallen to the bottom of the flask into the hydrochloric acid. 21
7. Gently swirl the flask so the magnesium stays in contact with the hydrochloric acid. After approximately 5 minutes, the production of the hydrogen gas will have stopped. Do not remove the balloon. 8. To find out how much hydrogen was produced, use the metric ruler to measure the diameter of the balloon in centimeters. 9. Record: Enter the diameter of the balloon in Table C in the row for Trial 2. Table C is located after Trial 6 in the Student Data Record. 10. Question: How do you know that a chemical reaction occurred? One of the products of the reaction is hydrogen gas (H 2 ). The balloon attached to the flask expanded as it filled with the hydrogen gas produced by the chemical reaction. 11. Question: Did any magnesium remain after the reaction ended? Yes, some magnesium (Mg) remained. 12. Question: Why did the balloon expand to a smaller or larger diameter compared to Trial 1? More of the reactant, hydrochloric acid, was used in Trial 2 so more of the product, hydrogen gas (H 2 ), was produced. 22
Trial 3 1. In this Trial you will investigate the reaction of 50ml of hydrochloric acid (HCl) with 0.5g of magnesium. Tool: Prediction Use the Prediction tool to answer the following question. 2. Question: Do you think the balloon will expand to a smaller or larger diameter compared to Reaction 2? Explain the reason for the prediction. The balloon will expand to a greater diameter than in Trial 2. More hydrogen gas (H 2 ) will be produced because more hydrochloric acid (HCl) reactant is used. 3. Repeat the procedure used for Trial 2 using 50 ml of hydrochloric acid and 0.5g of magnesium. 4. Record: Enter the diameter of the balloon for Trail 3 in Table C. 5. Question: How do you know that a chemical reaction occurred? One of the products of the reaction is hydrogen gas. The balloon attached to the flask expanded as it filled with the hydrogen gas produced by the chemical reaction. 6. Question: Did any magnesium remain after the reaction ended? Student answers may vary. No magnesium remained. 7. Question: Did the balloon expand to a smaller or larger diameter compared to Trial 2? The balloon expanded to a greater diameter than in Trial 2. 23
Trial 4 1. In this Trial you will investigate the reaction of 75ml of hydrochloric acid with 0.5g of magnesium. Tool: Prediction Use the Prediction tool to answer the following question. 2. Question: Do you think the balloon will expand to a smaller or larger diameter compared to Trial 3. Explain the reason for your prediction. Student answers will vary. The balloon will expand to the same diameter compared to Trial 3 because all of the magnesium will be used up. 3. Repeat the procedure used for Trial 2 using 75 ml of hydrochloric acid and 0.5g of magnesium. 4. Record: Enter the diameter of the balloon for Trial 4 in Table C. 5. Question: Did any magnesium remain after the reaction ended? Student answers may vary. No magnesium remained. 6. Question: Did the balloon expand to the same diameter as in Trial 3? The balloon expanded to the same diameter as in Trial 3. 24
Trial 5 1. In this Trial you will investigate the reaction of 100ml of hydrochloric acid with 0.5g of magnesium. Tool: Prediction Use the Prediction tool to answer the following question. 2. Question: Predict whether the balloon will expand to a smaller or larger diameter compared to Trial 4. Explain the reason for your prediction. Student answers will vary. The balloon will expand to the same diameter compared to Trial 3 because all of the magnesium will be used up. 3. Repeat the procedure used for Trial 2 using 100 ml of hydrochloric acid and 0.5g of magnesium. 4. Record: Enter the diameter of the balloon for Trial 5 in Table C. 5. Question: Did any magnesium remain after the reaction ended? Student answers may vary. No magnesium remained. 6. Question: Did the balloon expand to the same diameter as in Trial 3? The balloon expanded to the same diameter as in Trial 3. 25
Trial 6 1. In this Trial you will investigate the reaction of 100ml of hydrochloric acid with 1 g of magnesium. Tool: Prediction Use the Prediction tool to answer the following question. 2. Question: Do you think the balloon will expand to a smaller or larger diameter compared to Trial 5. Explain the reason for the prediction. Student answers will vary. The balloon will expand to a larger diameter because more magnesium will be used in this trial 3. Repeat the procedure used for Trial 2 using 100 ml of hydrochloric acid and 1 g of magnesium. 4. Record: Enter the diameter of the balloon for Trial 6 in Table C. 5. Question: Did the balloon expand to a smaller or larger diameter than in Trial 5? The balloon expanded to a larger diameter than in Trial 5. Table C Trial Mass of Mg (g) Volume of HCl (ml) Diameter of Balloon (cm) Volume of Balloon (ml) 1 0.5 2 4 33.3 2 0.5 15 5.75 98.9 3 0.5 50 8.5 319.3 4 0.5 75 8.5 319.3 5 0.5 100 8.5 319.3 6 1 100 10 520 26
Analysis 1. Before the data can be analyzed, the amount of hydrogen gas that was produced as a product must be determined for each reaction. This can be done by calculating the volume of the inflated balloon for each reaction. a. Since the balloon is a sphere, use the formula for the volume of a sphere. In the following equations: π = 3.14 r = the radius of a sphere in centimeters d = the diameter of a sphere in centimeters d 3 = (d d d) The volume of a sphere = 4 π r 3 3 This can be simplified to: Volume of a sphere = 0.52 d 3 = 0.52 (d d d) b. In the space below, use the measured diameter of the balloon in each reaction to calculate the volume of H 2 gas produced. c. Enter the calculated volumes in the last column of Table C. 27
2. Graph: Use the axes below to draw a graph that compares the concentration of volume of hydrogen gas (H 2 ) that is produced to the volume of hydrochloric acid (HCl) used. Use the data from Table C to draw the graph. a. Decide what the independent variable is in the experiment. b. Decide what the dependent variable is in the experiment. c. If you need help, read the Procedure, Graphing of Independent and Dependent Variables. d. Connect the data points from Trials 1 through 5. Do not draw your line through the data point from Trial 6. 600 500 400 Volume H2 gas (ml) 300 200 100 0 0 20 40 60 80 100 120 Volume of HCl (ml) 28
3. Analyze the graph in the range of hydrochloric acid volumes between 2 and 50 ml. Question: What is the relationship between the volume of hydrochloric acid added as a reactant and the volume of hydrogen gas (H 2 ) that was produced as a product? Student answers will vary. For every increase in the volume of hydrochloric acid, the volume of hydrogen gas increases. 4. Question: In this range of hydrochloric acid volume, do you think that the hydrochloric acid or the magnesium is greater in amount? Why? (Hint: Remember that you looked into the flask after Trials 1-3 were complete to observe if any magnesium remained.) Student answers will vary. In this range of hydrochloric acid (HCl) volume, the magnesium metal (Mg) is in greater amount because magnesium metal (Mg) was observed to remain after the reactions were complete. 5. Analyze the graph in the range of hydrochloric acid (HCl) volumes between 50 and 100 ml. Question: What is the relationship between the volume of hydrochloric acid added as a reactant and the volume of hydrogen gas that was produced as a product? Student answers will vary. For every increase in the volume of hydrochloric acid used as a reactant, the volume of hydrogen gas remained the same. 6. Question: In this range of volumes of hydrochloric acid, do you think that the hydrochloric acid or the magnesium is greater in amount? Why? (Hint: Remember that you looked into the flask after Trials 3-5 were complete to observe if any magnesium remained.) Student answers will vary. In this range of hydrochloric acid volume, the hydrochloric acid is in greater amount because no magnesium was observed to remain after the reactions were complete. 29
Background Sometimes one reactant is present in a greater amount than the second reactant. The result of such a reaction is that one reactant is completely consumed and a portion of the second reactant remains unreacted. A smaller amount of the products are produced than if both reactants are present at the greater amount. The Law of Conservation of Matter is obeyed even when two reactants are not present in equivalent amounts. In such a reaction, none of the matter is lost even if only a portion of the matter of one reactant remains unreacted. 7. Question: If one of the reactants is completely consumed but some of the second reactant remains unreacted, which reactant limits the amount of products that can be produced? Why? Student answers will vary. The reactant that is completely consumed limits the amount of the products that can be produced because there is no more of that reactant left. 8. Analyze the graph in the range of hydrochloric acid volumes between 50 and 100 ml. Question: Why did the diameter of the balloon and the volume of hydrogen gas remain unchanged in this range of hydrochloric acid volumes? Student answers will vary. The magnesium was completely consumed in this range of hydrochloric acid volumes because the hydrochloric acid was present in a greater amount. 30
9. Analyze the graph for the two data points for the reactions of 0.5g of magnesium and 1g of magnesium metal with 100 ml of hydrochloric acid. Question: Compare the volume of hydrogen produced by the reactions of 0.5g and 1g of magnesium with 100 ml of hydrochloric acid. Which reaction produced a greater volume of hydrogen H 2? Student answers will vary. The reaction using 1g of magnesium produced the greater volume of hydrogen. 10. Question: Why did one reaction produce more hydrogen H 2 gas than the other? Student answers will vary. More hydrogen gas was produced in the reaction using 1g of magnesium because unreacted hydrochloric acid remained. 11. Question: In the reaction of 100 ml of hydrochloric acid and 0.5g of magnesium, which reactant was present in the lesser amount? Explain your answer. Student answers will vary. The magnesium was present in the lesser amount because the 0.5g of magnesium was used up. When a greater amount of magnesium, 1g, was added to 100 ml of hydrochloric acid, more hydrogen gas was produced suggesting that an excess of hydrochloric acid remained after the 0.5g of magnesium was used up. 12. Written below is the chemical reaction that you have been studying. Circle the two products you have observed. Mg + 2 HCl MgCl 2 + H 2 Magnesium Metal Hydrochloric Acid Magnesium Chloride Hydrogen gas 31
Tool: Conclusions At the beginning of the Investigation, you used the Prediction tool to think of possible answers to the following questions. Use the Conclusions tool to answer the questions based on your results from this Investigation. Are the reactants always completely used up in a chemical reaction? If the reactants are present in equal amounts, then each reactant will be completely used up. Does the matter making up the reactants disappear? The matter making up the reactants does not disappear, it is found in the products of the reaction. What happens if there is more of one reactant than the other reactant? If there is more of one reactant than the other reactant, then it will not be completely used up in the reaction. How do you know when a chemical reaction has stopped? No more products are produced when a chemical reaction has stopped. 32
Focus Questions: In a chemical reaction, do the amounts of the reactants affect the amounts of products produced? Student answers will vary. Reactants must be present in the reaction in equivalent amounts to produce the maximum amount of all products. How does the Law of Conservation of Matter relate to chemical reactions? Student answers will vary. No matter is lost from a chemical reaction even if the reactants are present in amounts that are not equivalent. Every atom of every reactant can be found in either the products or in reactants that are not consumed. 33