Module 7 Intro

Module 7—Chemical Analysis

Module Introduction

In Module 6 you learned to use the stoichiometric method to predict the quantities of the reactants and products involved in a chemical reaction. In this module you will continue to apply your ability to analyze chemical systems using mathematical relationships.

Is it possible to predict the amount of product that would result if you were given defined quantities of each reactant? You will perform a titration, which is a standard laboratory technique used for chemical analysis. You will then use the results from your titration to communicate information to other students about the substance tested.

Think about the following questions as you complete this module:

• How is stoichiometry used in the design of a chemical system?
• How is stoichiometry used in the analysis of a chemical system?

Module 7—Chemical Analysis

Big Picture

In Module 6 you explored one of the greatest achievements of humans—the ability to explore space. As you found in your study, successful space travel depends heavily on life-support systems. Many of these systems are developed using stoichiometric principles.

As you will see in this module, the careful planning and design of life-support systems must involve a knowledge of chemical systems and the quantities of substances involved.

Even if you are not planning to travel into space anytime soon, you may have concerns about the food space travellers eat or the environment in which they live. Quantitative techniques are used to monitor the nutritional content of foods and the concentration of toxic substances present in the environment.

In this module you will apply your knowledge of stoichiometry and explore how stoichiometry is used in the design and analysis of a variety of chemical systems.

Module 7—Chemical Analysis

In This Module

Lesson 1—Limiting Reagents

The focus of this lesson is to learn how to apply your knowledge of stoichiometry to determine which reactant will be the first to deplete during a chemical reaction. Understanding the calculations used to determine the limiting reagent can be applied to a variety of situations, including specifying the quantities of reactants that should be used in a laboratory procedure that you design and determining the necessary quantities of chemicals used in a life-support system for a spacecraft.

• How can limiting reagents be used to predict the amount of product for a chemical process?

Lesson 2—Titration Analysis

In this lesson you will learn about titration, which is a process used to determine the quantity of substance in a test sample. Although many methods can be used to determine quantity, titration is one of the most reliable and easily performed experimental procedures. You will see how your knowledge of stoichiometry can be used to analyze the data collected during a titration experiment. In addition, you will see how titration can be used to study an acid-base chemical system and other chemical systems.

• How can titration be used to calculate the quantity of solute within a solution?

Lesson 3—Titration Curves and Selecting Indicators

In Lesson 2 you performed a titration. In this lesson you will construct a graph depicting the changes in concentration of key components in a chemical reaction. This graph is called a titration curve. You will also interpret a titration curve and identify aspects of this graph that demonstrate significant features of the chemical reaction.

In Module 5 you used indicators to determine the pH of a solution, and in Lesson 2 you used an indicator to identify the endpoint of a titration reaction. In this lesson you will learn how to use your titration curve to select appropriate indicators for a titration, allowing for precise and sensitive detection of the completion of a chemical reaction.

• How are titration graphs drawn?
• How do you select an appropriate indicator for a titration?
  

Module Assessment

The assessment in this module consists of three lesson assignments and a module project (Parts 1, 2, and 3).

• Module 7: Lesson 1 Assignment
• Module 7: Lesson 2 Assignment
• Module 7: Lesson 3 Assignment
• Module Project (Part 1)—Using Stoichiometry to Save the Apollo 13 Astronauts
  
• Module Project (Part 2)—The Nature of Scientific Research and Apollo 13
  
• Module Project (Part 3)—Analytic Measurement Technology

Module 7—Chemical Analysis

Lesson 1—Limiting Reagents

Get Focused

The Apollo 13 lunar mission was one of the defining moments in the history of space exploration. On April 11, 1970, disaster struck when one of two oxygen tanks exploded, significantly reducing the amount of breathable air available to the astronauts.

Because the spacecraft was over 300 000 km from Earth at the time of the explosion, there was no choice but for the mission to complete its scheduled course.

While the amount of oxygen remaining in the one working tank was sufficient to last the duration of the mission, there was another problem. Because of the explosion, the three astronauts had to move into the lunar module, a part of the spacecraft intended for only two people. With every breath the astronauts took, they released carbon dioxide gas into the lunar module, overwhelming the capacity of the system to remove carbon dioxide from the air. Since a higher level of carbon dioxide in the air can be toxic, the challenge facing NASA engineers on the ground was to figure out a way to control the concentration of carbon dioxide in the air inside the spacecraft using materials aboard the vessel.

How did they do it?

Essential Questions

• How can limiting reagents be used to predict the amount of product for a chemical process?

Module 7: Lesson 1 Assignment

Save a copy of the Module 7: Lesson 1 Assignment to your course folder. You will receive more information about how to complete this assignment later in the lesson.

In this lesson you will also complete the first two parts of your module assessment:

• Module Assessment (Part 1)—Using Stoichiometry to Save the Apollo 13 Astronauts
  
  

• Module Assessment (Part 2)—The Nature of Scientific Research and Apollo 13

These are the first two parts of your Module Assessment. Later in the lesson you will read more about the Module Assessment. Save copies of your work in your course folder. At the end of Lesson 3, you will submit all parts of the Module Assessment to your teacher.

The other questions in this lesson are not marked by the teacher; however, you should still answer these questions. The Self-Check and Try This questions are placed in this lesson to help you review important information and build key concepts that may be applied in future lessons.

After a discussion with your teacher, you must decide what to do with the questions that are not part of your assignment. For example, you may decide to submit to your teacher the responses to Try This questions that are not marked. You should record the answers to all the questions in this lesson and place those answers in your course folder.

Module 7—Chemical Analysis

Explore

Discuss

The picture on the right shows NASA engineers hard at work after the explosion. The engineers are attempting to construct a carbon dioxide filtration system for the astronauts aboard the Apollo 13 spacecraft.

What scientific skills and attitudes do you think the scientists in this photo possess? Post your thoughts on the discussion board.

Read the postings made by other students. Add any skills and attitudes you may have overlooked to your list. You will need this list later to complete Module Assessment (Part 2)—The Nature of Scientific Research and Apollo 13. You will send your list to your teacher at the end of the lesson.

Read

Limiting and Excess Reagents

In Module 6 you learned that baking powder is a combination of sodium hydrogen carbonate (baking soda) and potassium hydrogen tartrate (cream of tartar). Although these two substances are present in stoichiometric proportions in baking powder, what would be the result if one component were in excess relative to the other component?

Recall from your study in Module 5 that an excess of the sodium hydrogen carbonate—a basic compound known to have a bitter taste—could alter the taste of the food being baked. Similarly, an excess of potassium hydrogen tartrate could leave the finished product with a different undesirable taste, or it could allow for an unexpected reaction to occur with another ingredient.

Have you considered what effect a deficiency of one component relative to another might have on the quantity of carbon dioxide produced by the reaction? A cake that doesn’t rise to its desired height or texture may have been the unfortunate result of a component in the recipe being in a limited quantity relative to the other components.

How do you use your knowledge of stoichiometry to design a reaction that will ensure that it is a complete reaction?

Read “Calculating Mass of Excess Reagents” on page 320 of your textbook. Then work through “SAMPLE problem 8.1.”

Self-Check

SC 1. Complete “Practice” question 2 on page 321 of your textbook.

Module 7—Chemical Analysis

Read

Have you ever ridden in a vehicle that ran out of gas before reaching the planned destination? A situation like this quickly reminds you that depleting one of the reactants in a chemical process causes the reaction to quit. Chemical reactions don’t have a fuel gauge like a vehicle does, so how can you use your knowledge of stoichiometry to identify the limiting reagent in a reaction?

Read “Identifying Limiting and Excess Reagents” on pages 321 to 323 of your textbook. Work through “SAMPLE problems” 8.2 and 8.3 and the “COMMUNICATION example.”

Self-Check

SC 2. 2.50 mol of propane, C3H8(g), is combusted with 12.0 mol of oxygen gas.

1. Write the balanced chemical equation.
   
   

2. Predict the limiting and excess reagents.
   
   

3. Calculate the volume of CO2(g) produced when the reaction is complete. Assume SATP conditions.

SC 3. 10.0 g of butane, C4H10(g), is combusted with 30.0 g of oxygen gas.

1. Write the balanced chemical equation.

2. Determine the number of moles of each reactant.

3. Predict the limiting and excess reagents.

4. Calculate the mass of CO2(g) produced when the reaction is complete.

SC 4. 2.00 L of methane, CH4(g), is combusted with 9.00 L of oxygen gas. Assume STP conditions.

1. Write the balanced chemical equation.
   
   

2. Determine the number of moles of each reactant.
   
   

3. Predict the limiting and excess reagents.
   
   

4. After the reaction is complete, the atmospheric conditions change. Calculate the volume of CO2(g) produced if the atmospheric pressure is now 99.0 kPa and the temperature is 19.0°C.

SC 5. A 12.0-mL sample of a 0.500-mol/L silver nitrate solution is mixed with 10.0 mL of 0.400-mol/L NaOH(aq). Calculate the mass of precipitate produced in the reaction.

Module 7—Chemical Analysis

Module 7: Lesson 1 Assignment

You will complete the Analysis questions for this lab as part of your Module 7: Lesson 1 Assignment. These questions appear in the first part of the Module 7: Lesson 1 Assignment that you saved to your course folder earlier in this lesson.

Lab: Chemical Analysis Using a Graph

Follow the lab instructions given in the Lesson 1 Assignment and answer the Analysis questions in your Lesson 1 Assignment.

Module 7: Lesson 1 Assignment

Complete the remaining questions in the Module 7: Lesson 1 Assignment. After you have completed these questions, save your work to your course folder. You will submit the Lesson 1 Assignment to your teacher at the end of the lesson.

Module 7—Chemical Analysis

Reflect and Connect

In this lesson you will develop Parts 1 and 2 of the Module Assessment. After you have completed both parts, save your work to your course folder. You will complete Part 3 of the Module Assessment later in this module. After you complete all three parts, you will submit the Module Assessment to your teacher.

Module Assessment (Part 1)—Using Stoichiometry to Save the Apollo 13 Astronauts

The solution to the problem of carbon dioxide accumulating in the Apollo 13 spacecraft required the development of a new way to use equipment already aboard the spacecraft. In the living environment of the Apollo 13 spacecraft, there was not enough LiOH(s) available to fully react with all of the CO2(g) produced by the astronauts. The ingenious design that used scrubbers intended for one part of the spacecraft to be used in another part allowed the NASA engineers to ensure the safety of the astronauts.

How did NASA determine the quantity of lithium hydroxide necessary to operate the carbon dioxide scrubber system? Was a knowledge of stoichiometry required?

The carbon dioxide scrubbers used in the Apollo missions were canisters containing lithium hydroxide. Air in the spacecraft was circulated through the cylinders, allowing a reaction between lithium hydroxide and carbon dioxide to take place.

2 LiOH(s) + CO2(g) → Li2CO3(s) + H2O(l)

Use the following information to determine the mass of lithium hydroxide necessary for the duration of the mission:

• An average adult at rest exhales 0.50 L of air with each breath and takes approximately 15 breaths per minute.
  
  

• Approximately 4.5% of exhaled air is carbon dioxide.
  
  

• Assume that conditions in the Apollo 13 lunar module were at SATP.
  
  

• The Apollo 13 mission lasted for 3.7 days after the oxygen tank exploded.
  
  

• Assume lithium hydroxide reacts completely with carbon dioxide gas.

As you develop your answer, provide details explaining how you used this information and how it impacted the answer you calculated.

Module Assessment (Part 2)—The Nature of Scientific Research and Apollo 13

Read “The Nature of Scientific Research” on pages 794 and 795 of your textbook.

1. Identify the terms and concepts listed in each of the following categories that the engineers working on the Apollo 13 mission may have utilized when developing a workable CO2 scrubber. Provide a justification for each of the terms and concepts you select.
   
   

   • Types of Studies

   • Design Factors

   • Nature of Evidence and Results

   • Reporting Research

   • STS Issues

   • Scientific Attitudes
     
     

2. In the discussion posting at the beginning of this lesson, you identified skills and attitudes NASA engineers might possess that help them do their job. Consider the final list of skills and attitudes you prepared with the list of terms and concepts identified in your answer to question 1 above. Identify and explain any correlations you see between these two lists.
   
   

3. Identify one other profession, apart from engineering, where a similar set of skills and attitudes is required. Provide a justification for your choice by considering the terms and concepts listed on pages 794 and 795 of the textbook.

Assessment

Submit the following items to your teacher:

• Module 7: Lesson 1 Assignment

• Discuss

Save copies of the following items in your course folder:

• Module Assessment (Part 1)—Using Stoichiometry to Save the Apollo 13 Astronauts
  
  

• Module Assessment (Part 2)—The Nature of Scientific Research and Apollo 13

At the end of Lesson 3, you will submit all parts of the Module Assessment to your teacher.

Module 7—Chemical Analysis

Lesson Summary

In this lesson you explored this essential question:

• How can limiting reagents be used to predict the amount of product for a chemical process?

Developing a “quick fix” to control the CO2(g) concentration in the Apollo 13 spacecraft demonstrates what must be considered when chemical systems have a limited amount of one of the reactants.

As part of your Module Assessment you used stoichiometry to calculate the mass of lithium hydroxide necessary to remove excess carbon dioxide from the air inside a spacecraft on an Apollo mission. In a situation such as space travel, making careful calculations involving necessary components is essential to ensure the safety and success of the mission.

Module 7—Chemical Analysis

Lesson 2—Titration Analysis

Get Focused

In the mid-1960s, Tang (orange drink crystals) was used by astronauts during the Gemini spaceflights. One of the reasons for using Tang on this and current space missions is that it helps mask the taste of the by-products in the water the astronauts drink. A second benefit is that Tang contains high concentrations of vitamins A and C, helping astronauts meet their daily nutritional requirements.

The nutritional information on a juice box indicates that citrus juice is a rich source of vitamin C. The average daily requirement for vitamin C is 90 mg for men and 75 mg for women. Some juice boxes indicate that the product contains 80% of the recommended daily intake for vitamin C. If the claim on the juice box is true, how much vitamin C must be present in the juice solution?

How can you verify that the quantity of vitamin C you calculated is actually present in the juice? The obvious answer is that you would have to test the juice. As a consumer, you may have wondered if you are really getting what you are paying for.

How can you test juice to determine the concentration of vitamin C in it? In this lesson you will learn about titration—a process routinely used to determine the concentration of substances in a solution.

Essential Questions

• How can titration be used to calculate the quantity of solute in a solution?

Module 7: Lesson 2 Assignment

Save a copy of the Module 7: Lesson 2 Assignment to your course folder. You will receive more information about how to complete this assignment later in the lesson.

You will also work on Module Assessment (Part 3)—Analytic Measurement Technology. This is the third part of your Module Assessment. Save a copy of your work in your course folder. At the end of Lesson 3, you will submit all parts of this the Module Assessment to your teacher.

You must decide what to do with the questions that are not marked by the teacher.

Remember that these questions provide you with the practice and feedback that you need to successfully complete this course. You should respond to all the questions and place those answers in your course folder.

Module 7—Chemical Analysis

Explore

Read

Titration Analysis

A titration is a method of analyzing a solution by adding known amounts of a standardized solution until an endpoint is produced. This laboratory procedure is used to determine the concentration of a solute in a solution being tested. In Lesson 1 you studied the limiting reagent and how it influences the predictions made using stoichiometry. A titration involves the careful addition of one reactant to another to determine the exact point where one reactant becomes excess.

Read page 328 of “8.4 Titration Analysis” in your textbook to become familiar with some of the terms used in a titration analysis.

Watch and Listen

View the video “Performing a Titration.” Pay careful attention to how the equipment is used during this procedure.

Review the bolded terms shown on page 328 of your textbook. Match each of the following terms from the video with one of the terms from your textbook.

Reading the level of the solution in the burette is an essential skill. To practise this skill, view the video a second time, pausing the video so you are able to read the solution level in the burette at the start and at the end of the trial. Compare the burette readings you made to the values stated in the video.

In the “Performing a Titration” video, you watched NaOH(aq) solution being added to an HCl(aq) acid solution until a permanent change in the colour of the bromothymol blue indicator occurred. How does the colour change for bromothymol blue signal the detection of the end of the reaction?

Recall from your study in Module 4 that bromothymol blue appears yellow in acidic solutions and blue in basic solutions. As shown in the video, a titration proceeds until an endpoint is reached. In this case, the excess NaOH(aq) added after all the acid in the sample had reacted creates a basic solution, causing the indicator to change colour.

Try This

The following data was collected during the titration shown in the “Performing a Titration” video. Use this data to determine the concentration of HCl(aq) in the sample tested.

Try This Answer

 

HCl(aq)	+	NaOH(aq)	→	H2O(l)	+	NaCl(aq)

 

         

 

 

The concentration of the HCl(aq) solution is 0.139 mol/L.

Module 7—Chemical Analysis

Read

Titrations can provide very accurate data. One means to ensure accuracy is by doing multiple trials. Multiple trials allow for selecting the most consistent trials for further analysis. One sign of consistency is obtaining a similar endpoint colour between trials.

Work through “SAMPLE problem 8.4” on page 329 of your textbook to see how titration data from multiple trials is analyzed.

After working through this sample problem, you may wonder why only three trials were required in this titration. As stated earlier, a titration is repeated until consistent results are obtained, such as endpoint colour and titrant volumes that are within 0.2 mL of each other.

Self-Check

SC 1. A 50.0-mL sample of HCl(aq) is titrated with 0.300-mol/L NaOH(aq). When the endpoint is reached, 35.0 mL of the titrant has been used. Calculate the concentration of the hydrochloric acid based on this one trial.

SC 2. A titration is performed to determine the concentration of KOH(aq) in a 40.0-mL sample. The endpoint is reached when 18.02 mL of 0.100-mol/L HNO3(aq) is added. Calculate the concentration of KOH(aq) based on this trial. If the manufacturer’s label for KOH(aq) says the concentration is 0.0480 mol/L, what is the percent difference for the experimental result?

SC 3. A 20.0-mL sample of calcium hydroxide is titrated with 0.100-mol/L hydrochloric acid until the endpoint is reached. The volume of titrant used for each trial is shown in the following table.

Using this data, calculate the concentration of the Ca(OH)2(aq).

Self-Check Answers

 

SC 1.

 

HCl(aq)	+	NaOH(aq)	→	H2O(l)	+	NaCl(aq)

 

         

 

 

The concentration of the hydrochloric acid is 0.210 mol/L.

 

SC 2.

 

HNO3(aq)	+	KOH(aq)	→	KNO3(aq)	+	H2O(l)

 

         

 

 

Based on the one trial, the concentration of KOH(aq) is 0.0451 mol/L.

 

 

SC 3.

 

Trial	1	2	3
Final Burette Reading (mL)	22.7	45.2	67.6
Initial Burette Reading (mL)	0.4	22.7	45.2
Volume of Titrant (mL)	22.3	22.5	22.4

 

The three volumes agree within 0.2 mL and are used to calculate the average volume of HCl(aq) required.

 

 

Ca(OH)2(aq)	+	2 HCl(aq)	→	CaCl2(aq)	+	2 H2O(l)

 

         

 

 

The concentration of Ca(OH)2(aq) is 0.0560 mol/L.

Module 7—Chemical Analysis

Module 7: Lesson 2 Assignment

The data from the following lab will be used to complete your Module 7: Lesson 2 Assignment.

Lab: Titration of an Acid with a Base

So far in this lesson you have observed how titrations are performed. In this activity, you will complete a virtual lab investigation where you will perform a titration and analyze the data you collect. You will use the data from this investigation to complete your Module 7: Lesson 2 Assignment.

After you complete the titration lab, use the data to calculate the concentration of the hydroiodic acid solution tested.

Retrieve the Module 7: Lesson 2 Assignment that you saved to your course folder earlier in the lesson, and record your answers under question 1.

Post a copy of your analysis to the discussion board, and review the postings of two other students. Provide comments to your classmates about the organization, clarity, and precision of their answers. Record your comments, along with your calculations, under question 2 in your Module 7: Lesson 2 Assignment. Save a copy of your Lesson 2 Assignment to your course folder.

Module 7—Chemical Analysis

Reflect and Connect

Module 7: Lesson 2 Assignment

The data from the following lab will be used to complete your Module 7: Lesson 2 Assignment.

Lab: Determining the Quantity of Vitamin C in Fruit Juice

A titration does not always have to involve an acid-base reaction. Analyze the information provided about a titration to determine the concentration of vitamin C in fruit juice.

Save the document Determining the Quantity of Vitamin C in Fruit Juice to your course folder. Use the data provided to answer the Analysis questions in your Module 7: Lesson 2 Assignment.

Save a copy of your Module 7: Lesson 2 Assignment to your course folder.

Reflect on the Big Picture

Module Assessment (Part 3)—Analytic Measurement Technology

In this lesson you learned that titration analysis is a method of determining the amount of concentration of a substance. Other techniques are also available to detect small amounts of solute. What use would such technology have in spaceflight and exploration?

Read “Case Study: Analytic Measurement Technology” on pages 337 and 338 of your textbook. Answer the “Case Study Questions” on page 338. When answering these questions, consider more than one perspective.

Read “2.1 Science and Technology in Society” on pages 44 and 45 to review information about different perspectives prior to completing your response. 

Submit a copy of your answer to your teacher and place a second copy of your answer in your course folder.

Assessment

Submit the following item to your teacher:

• Module 7: Lesson 1 Assignment

Save a copy of this item in your course folder:

• Module Assessment (Part 3)—Analytic Measurement Technology

At the end of Lesson 3, you will submit all parts of the Module Assessment to your teacher.

Module 7—Chemical Analysis

Lesson Summary

In this lesson you explored the following essential question:

• How can titration be used to calculate the quantity of solute in a solution?

You performed a titration and analyzed the data collected during a titration experiment. Titration analysis can be used to verify the concentration of a substance in a solution or commercial product. Through your work in determining the mass of vitamin C in a juice box, you learned that the techniques involved in titrations can be used in situations other than acid-base reactions.

In the next lesson you will learn more about the design of a titration experiment and why it allows for precise determination of a solute’s concentration.

Lesson Glossary

titration: a method of analyzing a solution by adding known amounts of a standardized solution until an endpoint is produced

Module 7—Chemical Analysis

Module Summary and Assessment

Module Summary

Quantitative analysis involves a variety of techniques that rely on stoichiometric relationships between substances involved in a reaction. In this module you performed a titration using an acid and a base. You also performed a titration to determine the quantity of vitamin C in fruit juice. By studying some of the considerations necessary to support a journey into space, you considered the following questions:

• How is stoichiometry used in the design of a chemical system?

• How is stoichiometry used in the analysis of a chemical system?

These questions are relevant to more than spaceflight, since the principles of stoichiometry can be applied to any process in which different components combine and form into new arrangements. Think about this the next time you are preparing sandwiches or planning a picnic for a large group of people. You may be surprised to find yourself thinking in ratios that relate the number of people attending to the number of plates required or the number of veggie burgers to be prepared.

Module Assessment

The assessment in this module consists of the following:

• Assignments for Lessons 1, 2, and 3
  
  

• Module Assessment (Part 1)—Using Stoichiometry to Save the Apollo 13 Astronauts
  
  

• Module Assessment (Part 2)—The Nature of Scientific Research and Apollo 13
  
  

• Module Assessment (Part 3)—Analytic Measurement Technology

Module 7—Chemical Analysis

Module Glossary

titration: a method of analyzing a solution by adding known amounts of a standardized solution until an endpoint is produced

titration curve: a graph of the change in pH of the system being studied as standardized solution is added