Unit Planning

What follows is one of many ways to plan a unit. No one method of planning is prescribed for use. What is important is that units be planned. Through planning, the maximum benefit for the students in each classroom can be achieved. The topics can be tailored to the interests, needs, and conditions which prevail within each class. Unit planning is an important part of adapting the curriculum to the classroom.

• Scan the unit overview and the foundational objectives to become familiar with the concepts to be discussed.

• Decide on the approach to be used with that unit. Consider the Common Essential Learnings, the Dimensions of Scientific Literacy, the interests of the students in your classes and the resources available.

• Analyze the resources you have. Select activities which deal with the foundational objectives for both chemistry and the Common Essential Learnings and promote development of scientific literacy. Adapt these activities so that they suit your students, the facilities and resources available, the learning objectives, and the initiatives of Core Curriculum. Try to select activities which involve varied instructional strategies so that the different learning styles and needs of your students are accommodated.

  Consider the initiatives of the Core Curriculum. How can Gender Equity, the Indian-Métis perspective, and agriculture in the classroom be emphasized and developed through this unit?

• Plan a sequence of the activities. Make sure that the schedule is flexible enough to make best use of the opportunities for enrichment and extension which will arise as the learning progresses in the classroom.

• Develop an evaluation plan. Select evaluation instruments and techniques which match the instructional methods you have used. Consider how self- and peer evaluation can be used to enhance the students' learning. Discuss with the students how evaluation of this unit will be done.

• Create a time schedule.

Unit overview and approach

Lesson 1

Lesson 2

Lesson 3

Lesson 4

Lesson 5

Lesson 6

Lesson 7

Lesson 8

Lesson 9

Lesson 10

Unit overview and approach

This unit deals with the nature of acids and bases, the interaction of H⁺ and OH^- ions with water, and the neutralization process. This is outline is presented as one way to approach the topic of acids and bases. Modify, adapt and use parts of this unit as you see fit.

The unit will be developed as a study of acid deposition, more commonly known as acid precipitation or acid rain. The introduction of the topic to the classroom by newspaper articles highlights some of the relationships among chemistry, technology, society and the environment. Citizens must be scientifically literate to understand the source and extent of the problem and to be able to evaluate proposed solutions.

This unit, as do all units in grade 12 chemistry offers many opportunities to review and use the concepts and abilities learned during Chemistry 20 and during the preceding units of Chemistry 30. It is always good practice to assess the entry level of students and adjust the teaching to help them progress from that level to the desired standing. Concepts that are used in this unit to which students have had previous exposure are outlined below:

• the use of symbols, formulas, balanced equations for chemical reactions in all lessons
• lesson 2- solubility, chemical reactions
• lesson 3- chemical reactions, solubility, equilibrium
• lesson 4- use of mathematics, dissociation
• lesson 5-
• lesson 6- dissociation, equilibrium, stoichiometry
• lesson 7- chemical reactions, solubility
• lesson 8- solubility, chemical reactions
• lesson 9- chemical reactions

The times estimated for the lessons in this unit add to a total of 17 to 22 hours. Of this total, 8 to 10 hours can be allocated to the Acid-Base core unit, 7 to 8 hours to the Laboratory activities unit, and 3 to 4 hours (from lesson 9) to the Independent Research unit. Please note that 2 or 3 months preparation time is needed for you or the teacher-librarian to gather materials for lesson 9.

All the Common Essential Learnings can be developed and emphasized in the course of this unit. Personal and Social Values and Skills are promoted within class discussions and in the consideration of the question of how our lifestyle contributes to the production of acid deposition.

Considering the relationship between the demand for energy and the production of acid rain can lead to a discussion of individual responsibility for corporate action. Is a scientist responsible for all consequences which lead from a discovery, for only those reasonably foreseeable, or only for the direct effects? Does our desire to have gasoline cheaply available for our cars, our desire to have warm houses in winter and cool houses in summer, make us individually responsible for a related outcome - acid deposition?

This last matter links also to the Common Essential Learning of Technological Literacy, as do the measurements of the levels of acidity in rain and in lab samples, and the discussion of ways to reduce the impact of acid rain.

Independent Learning is inherent in lesson 9, where individuals or groups of students are responsible for finding answers to some questions and arguing others. Many of the activities (in lessons 1 and 2 for example) are structured to encourage Independent Learning. In these same activities are fostered the Common Essential Learning of Communication. As students discover information, devise procedures for experiments and consider issues, as well as present their reports to the class, their communication skills and abilities are enhanced.

Creative and Critical Thinking also has a strong presence in this unit. In the creation of the unit-end reports, the consideration of the reports of other groups and in the design and analysis of experimental procedures, students' reasoning and understanding is expanded. Numeracy is enhanced when students are asked to estimate, to use charts and graphs to extract information and meaning, and to apply the logic of proportionality in the stoichiometric sections of this unit.

Many of the factors of the Dimensions of Scientific Literacy can be developed within this unit. With the description of each lesson, the is a commentary on one or more of the factors of the Dimensions of Scientific Literacy which could be developed during that lesson. The description is not meant to restrict which factors are dealt with during the lesson, but simply to remind you that a consideration of the factors of scientific literacy is an important part of planning for and reflecting upon science teaching.

The same components which make the unit useful for dealing with the Common Essential Learning of Personal and Social Values and Skills also are critical for developing students' attitudes towards science and their understanding of the interrelationships among science, technology, society and the environment. The unit can be a forum for the discussion of factors D2, D3, D7, D8, D9, and D10. By looking at the unit in light of the factors of each Dimension, help in planning the approach to discussion and formulating evaluation and research questions is available. Here is an opportunity to discuss technology being controlled by society (D9), both from the point of view that publicly-held corporations are major emitters of the precursors of acid rain and that government regulatory agencies set standards for emissions. Society controls the emitters, the regulators, and is composed of people who have the power to demand that technology be developed to reduce the impact. How does the factor D8 - limitations of science and technology - interact with demands that the emissions of acid rain-causing chemicals be reduced?

Science is human/culture related (A9). With data gained (C3, D4) by monitoring the quality of air and water, we recognize that we affect our environment, we analyze both qualitatively and quantitatively (C12) how we affect that environment, extrapolate (B11, C10) to produce future scenarios, and debate (A9, C19, F6) what actions could and should be taken to make our future environment habitable. These considerations are also important in giving students a chance to examine some of the values which underlie science. The search for data and their meaning (F3), respect for logic (F5), consideration of consequence F6), valuing natural environments(F4), demand for verification (F7), and consideration of premises (F8) all have strong links to the possible activities in this unit. This unit, too, is one in which both avocation (G5) and vocation (G7) in science and science-related topics can be encouraged. By giving students a chance to develop a strong understanding of the issue both response preference (G6) and explanation preference (G8) for science can be developed. Those persons who do the basic research in this area, as well as those who take public stands and popularize the concern, can be seen here as persons who are making valuable contributions to science, technology, and to our society.

Among the key science concepts, B1- change, B2-interaction, B5- perception, B16- system, B15- model, B10- cause-effect, B11- predictability, B19- probability, B21- accuracy, B27- amplification, B28- equilibrium, B31- significance, and B32- validation could be emphasized.

Resources identified

• newspaper articles
• ideas for activities from a variety of sources, including the curriculum guide, texts, journals and other print materials
• videos
• SRC Technical Report #122 (December 1981)
• household solvents and solutions brought by students
• chemicals and equipment from the laboratory

Lesson 1 (1 hour)

Objectives

• Observe some physical and chemical characteristics of acids and bases.
• Investigate the nature of the production and use of acids and bases in our society.
• Appreciate how use of the principles of acid/base reactions has influenced our lives.
• Value the role of technology in studying acid/base reactions.

The day before you start this unit, assign reading the newspaper articles titled North of Sixty and Alberta oil sands plants may threaten Saskatchewan to your students as homework. Ask them to make brief notes on their reading. You might assign both articles to each student, or one to each member of a pair. This would depend on the time available, the reading abilities, interest levels, and motivation levels of the students, and the degree to which you wish to immerse them, figuratively speaking, in the topic. Ask them to generate a list of questions about acid rain raised by the articles, and a list of terms which must be understood to make sense of the articles.

During the first class of the unit, discuss with them what they know about acid rain, and what questions and terms they listed. If it becomes necessary, supplement the points raised in the discussion and the students' responses to the above questions with those from this list, and others you may create.

Questions

• How can an expansion of the capacity at the Syncrude plant poison Saskatchewan lakes with acid rain?
• Why are pre-Cambrian shield lakes sensitive to acid rain?
• How does acid rain kill the lakes?
• What is a lake with high tolerance for acid rain?
• What is a moderately sensitive lake?
• What does air quality monitoring have to do with acid rain?
• What are background levels of acids?
• Where do airborne sulphates and nitrates come from?
• Why is the northern environment fragile?
• How do magnesium and calcium act as buffering agents?

Terms

• nitrogen oxides
• pre-Cambrian shield
• neutral
• acid levels
• acid rain
• migration of airborne emissions
• oil sands
• sensitive lakes
• emissions
• sulphur dioxide
• pollution
• inorganic ions
• ion balance

Record on a large poster the questions and terms identified during the discussion. Use this poster for reference during the course of the unit and to help adapt and select activities.

Construct a concept map with acid rain (or acid deposition or acid deposition) as the central concept. This can be done as a class or can be assigned to groups of three or four. On the concept maps, highlight areas which involve the questions and terms generated during the class discussion.

Factors The factor A3 - holistic - could be emphasized in this lesson. The newspaper articles deal with the chemical aspects of the production of acid deposition and the interaction of the precipitation with the chemistry of the lakes in northern Saskatchewan. The precipitation has an effect on the ecology of the region. Weather systems move the pollutants from their source to where they are deposited. An understanding of aspects of chemistry, biology and meteorology are needed to understand the production, distribution and impact of acid deposition.

Factor D8 - limitations of science and technology - could be discussed in the context of Syncrude spokesman David Young's comment that emissions will be reduced with expansion of the plant because of improvements in pollution control. What are these improvements? Why can't they be implemented in the current plant? Why will 265 tonnes per day still be emitted after improvements are made? Why can't all emissions be eliminated?

Evaluation The discussion of the articles, the creation of a list of questions and terms, and the development of concept maps gives the teacher a chance to informally assess the students' understandings of acids, bases and associated concepts. This information can be used in adapting and shaping the activities of the unit to be of most benefit to the students. Some planned activities may be omitted or extensively altered, others added, and the concept mapping exercise may be repeated at intervals in order to meet the needs of the students.

Concept maps are a form of student self-evaluation. Their construction gives students a chance to express their understanding and monitor the development of their thinking about the concept. It gives them a chance to discuss their ideas with their peers and compare and assess their understanding.

Lesson 2 (2 hours)

Objectives

• Identify some acids and some bases which are used in common household products.
• Observe some physical and chemical characteristics of acids and bases.
• Construct an operational definition of an acid and a base, using the characteristic properties of those substances.
• Describe the Brønsted-Lowry conceptual definition of acids and bases.
• Collect and organize data in charts and graphs.
• Interpret collected data.

As you explore the concepts in these activities, relate them to the questions and terms listed during the discussion in lesson 1. What is an acid? How can acids be produced? What is a base? How can bases be produced? These questions form the focus of the second lesson.

Use litmus paper to test various substances. These substances may include those prepared in the laboratory and those which students have brought from home. Check the substances which the students have brought from home to ensure that they are safe to use in this activity. Substances provided from the laboratory might include these chemicals, all with strengths of 0.1 mol·L^-1: HCl_(aq), CH₃COOH_(aq), NaHCO_3(aq), Na₂CO_3(aq), NH₄OH_(aq) and NaOH_(aq). CH₃COOH_(aq) and Na₂CO_3(aq) with strengths of 6.0 mol·L^-1 and 1.0 mol·L^-1 can also be used.

Regardless of source, the samples should be clearly labelled by the chemical or common name. Save what is not used of these samples in this lesson for use in lesson 3. Discuss the litmus test as an example of an operational definition: An acid is a substance which causes litmus to be red; a base is a substance which causes litmus to be blue. How can litmus be used to establish that a solution or liquid is neither acidic nor basic? Identify other properties which contribute to operational definitions of acids and bases.

Ask the students to design a procedure to discover if the pH is altered when CO_2(g) dissolves in water. When the students' designs have been discussed, have them do the activity.

Use also the activity involving SO_2(g) and car exhaust on page 156 of this guide.

Have the students make and test a base by reacting a very small piece (equivalent to 2 mm length of a toothpick) of calcium or sodium with about 5 mL water. Discuss the nature of the reaction with them so that they understand completely the need to wear goggles and follow safety precautions during this, and every other, activity. (Exercise extreme caution in reacting calcium or sodium with water - make sure that the piece is small.)

Burn a small piece of magnesium ribbon in air to illustrate the production of MgO from Mg. Distribute a small portion of magnesium oxide powder to each group. Have them mix it with water and test the mixture with litmus. The powder distributed to each group need not come from the burning process. The burning process is only to show one way that MgO_(S) is produced.

Concepts which can be reinforced or reviewed during this lesson are the use of symbols and formulas, the writing of balanced equations for chemical reactions, and solubility.

Assign for reading a section in the text which deals with characteristics of acids and bases, and the Brønsted-Lowry definition of acids and bases.

Factors Classifying (C1) and manipulative ability (E7) are two of the factors which could be emphasized during this lesson. The use of litmus paper to group chemicals according to their acidic character is part of one of the fundamental activities of science. In classification, we search for an organizing principle which can help us understand how things work. What are the common characteristics of those substances which are classified as acids? Can such a recognition help us to predict whether untested substances will be acidic? Manipulative ability is the key to producing consistent, replicable results in these activities.

Evaluation Select three lab groups and fill in the group checklist. (Distribute copies of this checklist to students at the start of the year. Inform them that in each lab activity period, two or three groups will be rated, with all group members receiving the same mark.) Also provided is a checklist which the students may use to rate your performance as you do demonstrations. In this lesson, you may distribute it for use during and after the burning of magnesium demonstration. Create written response test questions dealing with the lesson's objectives.

students' names: criteria for assessment	rating
uncluttered workspace	yes                                       no
materials for activity organized	yes           somewhat             no
entries made in journal of each group member	yes                                       no
safe practices followed notes on safety:	yes                                       no
area cleaned	yes                                       no
Was the workspace uncluttered?	yes                                       no
Were the materials for the demonstration well organized?	yes            somewhat            no
Were student tasks during the demonstration clearly explained?	yes            somewhat            no
Were safe practices followed? notes on safety:	yes                                       no
Could you see all aspects of the demonstration?	yes                                       no
Was the demonstration discussed or summarized?	yes                                       no
Was the work area cleared after the demonstration?	yes                                       no

Lesson 3 (1 hour)

Objectives

• Observe some physical and chemical characteristics of acids and bases.
• Estimate the pH of solutions, using indicator solutions and indicator papers.
• Interpret collected data.
• Observe and record carefully during experimental or investigative procedures.
• Develop and conduct investigations and research.

Investigate the relative strength of the acidic or basic properties of each substance from lesson 2, plus additional solutions if desired. Two questions students could investigate are: how fast do the bubbles form when an acidic solution is dropped onto a piece of zinc? how does mixing a drop of an acid with a drop of the base change the pH of the solution?).

Factors Do the investigations produce predictable results? Can cause and effect be identified? Understanding of these concepts (factor B11 - predictability and factor B10 - cause-effect) develops during the consideration of results from these activities. To be able to distinguish between correlation and cause is a critical ability for scientifically literate citizens. The pseudosciences base much of their argument for validity on correlation. Science is based on cause and effect relationships established by empirical investigation.

The opportunity to comment upon the importance in science of the search for data and their meaning (factor F3) is also a part of this activity.

Evaluation This is a good opportunity to stress the importance of complete, organized, and accurate recording of data from investigations. You may prefer this to be submitted in a formal lab report, or may require a journal-type notebook, but the importance of accurate records of what has been done should be stressed. Holistic rating scales or checklist can be used to rate reports or journal entries. Students should be aware of the critieria on which their work is being assessed.

Rate another two groups using the checklist introduced in lesson 2. As well, scenarios involving data from these activities could be created for use on exams. Students could be asked to interpret a series of observations and measurements dealing with the effects of an acid on an unknown substance, and make judgements about the unknown substance. Alternatively, data from the reaction between an unknown substance and a metal could be given, with interpretations requested about the acid character or strength of the substance.

Continue evaluation of the safety of the facilities and equipment.

Lesson 4 (1 hour)

Objectives

• Describe the Brønsted-Lowry conceptual definition of acids and bases.
• Identify the conjugate bases formed in acid dissociation.
• Identify the conjugate acid of any base.
• Write the equilibrium constant expression for the dissociation of water.
• Recognize the relationship between the [H⁺] and [OH^-] in an aqueous system.

Examine conceptual definitions of acids and bases, including the Brønsted-Lowry definition. Stress the importance of dissociation to release H⁺ ions which can associate with water molecules to form H₃O⁺.

Consider the dissociation of water, the value of Kw, and the role of water in acid dissociations, as well as its capability of acting as an acid. Describe litmus as a dye which is sensitive to the level of H⁺ or H₃O⁺ in a solution. If there are more H⁺ or H₃O⁺ ions than in water, litmus is red. If there are fewer H⁺ or H₃O⁺ ions than in water, litmus is blue. That the change point is equivalent to the level in water is the circumstance which allows litmus to divide substances into the groups acids and bases. Other indicators have different change points.

Demonstrate the differences in conductivity among acids. You may need to establish the relationship between conductivity and presence of ions in a solution. Appropriate acids for this demonstration are 6.0 mol·L^-1 HCl, glacial acetic acid, 1.0 mol·L^-1 HCL, 1.0 mol·L^-1 acetic acid and distilled water. Ask students to account for the difference in terms of dissociation.

Introduce the relationship between the amount of dissociation and the acidic properties of the solution.

Factors In this lesson, quantitative relationships (E13) are used to relate the concept of equilibrium (B28) to the study of acid deposition. Equilibrium is described mathematically. The theory of equilibrium can be used together with measurements from systems which were not used during the origination or the testing of the theory to help explain what is happening in the new system. This illustrates the power and the validity of the theory. It is important that students understand the power of scientific theories.

Evaluation This is a good point in this unit to use a short quiz to assess students' ability to use numbers expressed in scientific notation and to do calculations involving multiplication, division and square root using numbers in scientific notation. Extra teaching or review may have to be undertaken. Often, students who understand the principles can be invaluable in explaining them to their peers. Organizing of heterogeneous lab /working groups in your classroom promotes this interaction.

Lesson 5 (1 hour)

Objectives

• Estimate the pH of solutions, using indicator solutions and indicator papers.
• Interpret collected data.
• Discuss with peers how estimates of values are made.
• Observe and record carefully during experimental or investigative procedures.
• Develop and conduct investigations and research.

What is meant by acid level and the pH of a substance? Ask the students to recall where they have seen or heard the term pH used. (shampoos, swimming pools...) Recall how litmus was used to determine whether a substance was an acid, a base or neither.

Distribute a pH scale diagram. Identify neutral as 7 and that litmus simply places a substance on one side or the other of that line. Also distribute the list of indicators and colours or refer in a text to a list of dyes (indicators) which change colour at pH values other than 7. Discuss how these indicators could be used to estimate pH.

Supply the students with a variety of indicators. Methyl violet, methyl orange, bromothymol blue, and alizarin yellow would be an appropriate selection. Ask them to use the indicators to estimate the pH of each unknown solution. Use the substances from lesson 2.

After they have estimated the pH of the solutions, discuss the variety of levels of acidity found and the difficulty of using one indicator to estimate pH. Introduce the use of universal indicators, pH paper or pH meters to pinpoint the pH more easily.

Factors Understanding the use of indicators as boundary markers between regions of lower pH and higher pH requires them to understand the logic (F5) of how indicators work and how we do classification. The selection and use of two or more indicators to narrow the pH range in which the test solution is found requires application of logic. In addition to an appreciation that the steps must be logical, the identification of the pH of solutions by use of indicators requires problem solving (C14) and analysis (C15). Within a lab group, the estimation of a pH value from the data available may require some consensus making (C19). The use of a pH meter will make them appreciate the contributions of technology (D1) to the study of science.

Evaluation Rate two more lab groups, using the checklist introduced in lesson 2. Remind students of the importance of keeping complete records of what is done in the laboratory. Do spot checks on their notebooks or journals. If they are making measurements, ask them to consider whether there are visual observations which they can record as well. If they are making descriptive observations, ask them if there is anything they could measure. Set a date for laboratory reports or journals to be turned in for marking. Rating scales and checklists are useful for deciding upon grades. Ensure that students understand the criteria on which the marking is based.

Lesson 6 (2 hours)

Objectives

• Identify the conjugate bases formed in acid dissociation.
• Associate acid or base strength with magnitudes of K_a and K_b.
• Identify the conjugate acid of any base.
• Recognize substances which are amphiprotic (amphoteric).
• Compare the strengths of the dissociations in the dissociation series for a polyprotic acid.
• Calculate the [H⁺] in a solution.
• Express the [H⁺] as a pH value.
• Explain how a logarithmic scale differs from an arithmetic scale.
• Use information from K_a tables to calculate pH values in solutions and check results of calculations with indicators.
• Compare the nature of scientific knowledge with knowledge in other areas of study.

Review dissociation of water and acids. Relate the pH value to the level of H⁺ ions in the solution. Write equations for the dissociation of several acids. Use a K_A chart to calculate and estimate levels of acidity ( [H⁺] ) in solutions. Do calculations involving integral pH values.

Factors This lesson is important in the development of response preference (G6). The narrative report is easier for most students. Encourage them to use measurement, and mathematical analysis and manipulation of their measurements, to communicate what happens during an investigation. It is also important to stress that valid measurements can be replicated (A4). This process of replication of results is critical in establishing the validity of both results and theory. Theories must make predictions which are testable, and the tests probe those predictions.

The Proton in Chemistry, from the World of Chemistry series, is available from Media House and is a good support for this lesson.

Evaluation This lesson is a good source of problems for examinations. Distribute a mid-unit take home exam booklet to gain an idea of how students are progressing in problem solving. The exam booklet format can be produced by folding two sheets of paper in half and stapling along the fold to produce a 14 cm by 21 cm booklet of eight pages. The front cover can describe the assignment, and the problems distributed one per page. This gives students a chance to try questions similar to those which will be on the exam in a situation where they can work at their own speed and ask you or their peers for help. When all have finished, answers can be posted for the questions or they may be taken up as part of the review for the unit test.

This suggestion is adapted from an idea submitted by Elsie Eade of Moose Jaw.

Lesson 7 (4 hours)

Objectives

• State the general neutralization equation:
  acid + base salt + water
• Write equations for specific neutralization reactions, identifying the nature of each species.
• Solve mathematical problems involving data from titrations.
• Develop skill in doing titrations.
• Observe and record carefully during experimental or investigative procedures.
• Collect and organize data in charts and graphs.
• Interpret collected data.

What is neutralization? Add, by drop, some base to a sample of acid. Monitor the pH, using a pH meter, pH paper, or universal indicator in the solution. Continue adding base until the limit of your indicator or pH paper is reached. If you use dilute (0.1 mol·L^-1) HCl as the acid, a concentrated strong base such as 2.0 mol·L^-1 NaOH is appropriate. 10 mL of the HCl is a reasonable volume for this activity. Graph the approximate pH against the number of drops of base used.

Discuss the stoichiometry of neutralization. Do an activity involving a titration.

Factors A critical factor when using indicators to estimate pH values is the perception of colour. During the shift of bromothymol blue from yellow to blue, just how green the solutions is (yellowish-green or bluish-green) is a matter of perception (B5). If there is some way to measure the colour or some standard series of colour gradations to match, the estimate can be less reliant on individual perception. That is why phenolphthalein, with its change from colourless to pink at pH=8, is preferred for titration. From absence of colour to pink is an easier judgement than judging the tone of green of a titration.

Evaluation In addition to providing test problems, this activity may serve as a source for components of a performance task. Techniques appropriate for performance testing might include: reading the level of a buret; delivering a particular volume from a buret; graphing a titration curve when given data; colour matching indicators; and, using a serial dilution to produce a solution of a particular strength. A checklist of process skills which are expected to be exhibited during the performance task facilitates assessing the achievement of the student or group.

Lesson 8 (1 hour)

Objectives

• Estimate the pH of solutions, using indicator solutions and indicator papers.
• Write equations for specific neutralization reactions, identifying the nature of each species.
• Explore how knowledge about acid/base reactions has both explained existing applications and suggested new applications .
• Value the role of technology in studying acid/base reactions.

Use dilute H₂SO₄ to simulate acid rain. Why is this acid a good choice for this simulation? Write a series of equations for the reactions involved in converting the sulphur atoms in crude oil into acid rain. You might demonstrate the effect of one or two drops of concentrated H₂SO₄ on a piece of paper towel

Each group should prepare or obtain 10 mL of 1.0x10^-1 mol·L^-1 H₂SO₄. On a strip of pH paper, make a reference spot with a small drop of distilled water and another with a small drop of H₂SO₄. You might practice so that you can place small drops side by side on the paper but yet remain discrete or at least distinguishable.

To 5 mL distilled water in a 50 mL beaker, add a drop of the H₂SO₄. Mix thoroughly and place a small drop of this solution at one end of another strip of pH paper. Add another drop of H₂SO₄, mix, and place another small drop of the solution next to the first on the pH paper. Continue this process until the colour on the pH paper matches the colour of the acid reference spot. By counting the dots on the pH paper the number of drops added can be determined.

Repeat this process using 5 mL of 1.0x10^-2 mol·L^-1 NaHCO₃ instead of distilled water.

Repeat again, using 5 mL of 1.0x10^-2 mol·L^-1 Na₂CO₃ instead of distilled water.

Compare and discuss the results of all three procedures. Why can the distilled water be compared to the northern lakes of Saskatchewan, and the NaHCO₃ and Na₂CO₃ solutions to the southern lakes?.

Factors This simulation of the acid systems in Saskatchewan lakes is an attempt to link the learning from science to a concern for the natural environment (F4) and understanding of how human and natural activity influences the environment (D4). Whether the SO_2(g) comes from a volcano, a smelter or the combustion of coal, its chemistry and ecological effects are identical.

Evaluation Two more lab groups can be rated using the checklist introduced with lesson 2. A written response question on the unit examination could ask students to discuss why lakes in the pre-Cambrian region of Saskatchewan are more sensitive to the effects of acid deposition than are the lakes of southern Saskatchewan. Develop criteria for assessment of the responses. Consider sharing these criteria with the students.

Lesson 9 (3 - 5 hours)

Objectives

• Investigate the nature of the production and use of acids and bases in our society.
• Develop and conduct investigations and research.
• Understand the meaning of theory in science.
• Compare the nature of scientific knowledge with knowledge in other areas of study.
• Value the role of technology in studying acid/base reactions.

This lesson is one which would benefit greatly by some cooperative planning with the teacher-librarian. Two to three months to assemble appropriate and adequate resources for the research is not unreasonable. This is an important lesson. It shows the strong ties between chemistry, biology and geology.

Divide the class into six groups. Assign each group the task of reporting on one of the areas described below. The report should include a written report of the group's findings, a summary of this report for distribution to all class members and an oral presentation to the class. The oral presentation should be illustrated with posters, pictures, diagrams and equations for chemical reactions.

• What are the main chemical components of acid deposition? How do these substances get into the air? How does our lifestyle contribute to their presence in the air? How far can they travel from their source? What are some of the ways of preventing them from getting into the air?
• Does the pH of soil change because of acid deposition? How does the geological history of southern Saskatchewan ensure that lakes in that region are resistant to the effects of acid deposition? Why are lakes found in the pre-Cambrian bedrock region susceptible to lowered pH levels from acid deposition?
• How does the pH of lake or river water influence plant life in that medium? What specific effects of a decreased pH level are seen in aquatic plant growth? Is there the same degree of effect on all aquatic plants? How do acidic conditions cause these effects?
• What are some of the direct and the indirect effects of increased acidity on aquatic animals? How does the acid cause these effects?
• How does acid deposition affect buildings and statues of stone? Is all stone affected? Does acid deposition affect other human structures or artifacts?
• Is there a direct effect of acid deposition on the leaves and stems of terrestrial plants, or as the acidic water is picked up by the roots? Are there indirect effects on plant growth attributable to acid deposition?

The lesson is allotted three hours. Identifying, organizing, and allocating tasks, and beginning the research should take one period. The second period could be used for organizing the information discovered and starting the synthesis of this information into a report. The third class is left for the presentation of reports. Students should do about three hours work and preparation outside of class time for this lesson.

Some groups may want to view the videos Acid Rain Part 1 - What is Acid Rain and Acid Rain Part 2 - The Effects of Acid Rain, available from Media House Productions, as part of their research for their presentation.

The third video in that series, Acid Rain Part 3 - What Can We Do? is an excellent summary of the problem of acid deposition and the difficulty of finding solutions. Consider using it as a centre for a discussion to conclude lesson 9. The article "Acid aerosols a problem" could also provide a starting point for discussion.

Factors This lesson affords the chance for students to develop an explanation preference (G8) for arguments supported by theories and explanations from science. The nature of the questions posed forces them to consider the consequences of acid deposition (F6), demand verification of propositions (F7) and consider the premises (F8) of the arguments of both sides in the acid deposition debate. Social influences on science and technology (D9) will almost certainly be considered.

Evaluation During the first period of this lesson use a class discussion to decide upon the criteria with which the projects developed will be assessed. Consider using some component of peer assessment, especially in rating the oral presentations. Use this opportunity to discuss with the students why and how they are evaluated.

Lesson 10 (1 - 4 hours)

Review the concept map(s) produced during lesson 1. Revise the map(s) in accordance with the understanding of acid deposition which the students now have. Review the questions and terms that arose from the reading of the newspaper articles. Discuss the important concepts in acid-base chemistry which have been studied in this unit. Introduce any concepts which have not yet been introduced, but which are needed for an adequate understanding of this area of chemistry.

Factors Depending on what is done during this lesson, opportunities to discuss various factors will emerge. Please keep in mind that the overall goal of science in Saskatchewan classrooms is to develop scientifically literate students, as defined by the factors of the Dimensions of Scientific Literacy, and that you have the chance to do that in the context of chemistry.

Indicator	Colour at acidic end of range (lower pH)	pH values for colour change	Colour at basic end of range (higher pH)
methyl violet	yellow	0                             1.6	blue
methyl orange	red	3.2                          4.4	yellow
litmus	red	5.5                          8.0	blue
bromothymol blue	yellow	6.0                          7.6	blue
phenolphthalein	colourless	9.4                          10.6	red
alizarin yellow	yellow	10.0                        12.0	red