Unit 2 – Area of Study 2: How are chemicals measured and analysed?
Unit 2 – Area of Study 2: How are chemicals measured and analysed?
Outcome 2
On completion of this unit the student should be able to calculate solution concentrations and predict solubilities, use volumetric analysis and instrumental techniques to analyse for acids, bases and salts, and apply stoichiometry to calculate chemical quantities.
Examples of learning activities
Key knowledge: Measuring solubility and concentration
- Refer to the infographic, A Traveller's Guide to Tap Water and discuss the factors that make water ‘safe’ to drink; who determines what makes water ‘safe’ to drink?
- Determine qualitatively the solubility of a variety of solid, liquid and gaseous solutes in water; write equations for substances dissolving in water.
- Controlled experiment: In groups each with one of the research questions below, formulate hypotheses, design and perform experiments and reports on your chosen research question:
- Can a saturated solution of sodium chloride dissolve any Epsom salts?
- Can a saturated solution of sugar dissolve any Epsom salts?
- Can a saturated solution of Epsom salts dissolve any sodium chloride?
- Can a saturated solution of Epsom salts dissolve any sugar?
- Can a saturated solution of sodium chloride dissolve any sugar?
- Can a saturated solution of sugar dissolve any sodium chloride?
- How does solubility vary with temperature?
- How does solubility vary with the atomic mass of the solute?
- How does solubility vary with the polarity of the solute?
- Prepare ionic substances by precipitation; for example, copper(II) hydroxide, copper(II) hydroxide, barium sulfate, silver chloride.
- Prepare precipitates representing football club colours.
- Use solubility rules to predict the outcomes of precipitation reactions and experimentally test the predictions; write ‘full’ and ionic equations for precipitation reactions that occur.
- Design a procedure to identify an unknown salt dissolved in a water sample.
- Examine the ingredients list of chemicals and foods for which solution quantities are provided. Convert between given units and alternate units of concentration; for example %(m/m), %(m/v), %(v/v), ppm and ppb, g L-1 and mg L-1.
- Product, process or system development: Adapt a scale such as Mohs Scale of Hardness to develop a solubility scale.
- Classification and identification: Collect, individually, an empty package of processed food that contains salt or sugar; calculate total amount of salt or sugar for the product contained in the package; produce a class display to show increasing salt or sugar content for the food products.
- Use a multimeter to compare the total amount of electrolytes in various drinks; for example, tap water, mineral water, fruit juices, soft drinks, and sports drinks. Research and provide a brief report on the function of electrolytes in the human body.
- Controlled experiment: Design and perform an investigation to determine the types of contaminants that alum can coagulate in water, whether there are optimal concentrations of alum that should be added to coagulate contaminants in a water sample, or how effectively alum can inactivate microbes in a contaminated water sample.
- Fieldwork: Visit a water treatment plant; summarise the physical processes and chemical reactions involved in purifying the water.
Key knowledge: Analysis for acids and bases
- Product, process or system development: Make sherbet to investigate an acid-base reaction. This involves thinking proportionally by scaling quantities.
- Explain why acids should be added to water, rather than adding water to acids, when diluting acids or when undertaking acid-base experiments.
- Perform dilutions of different solutions and calculate quantities at each dilution stage.
- Prepare a standard solution of anhydrous sodium carbonate and use it to standardise a solution of hydrochloric acid.
- Controlled experiment: Perform an acid-base titration and use volume–volume stoichiometry to calculate the concentration of an acid or base in a water sample.
- Investigate the action of antacids by comparing the effectiveness of different antacids in the market. In groups, each allocated a different antacid, summarise the active ingredients and side effects of your allocated antacid. Each group performs an acid-base titration (for example, using methyl orange indicator and 0.5 M HCl) to calculate the average volume of acid neutralised per gram (or per mL) of antacid.
- Product, process or system development: Formulate an effective antacid to neutralise a given volume of acid, trialling different proportions of common active ingredients found in commercial antacids (i.e. aluminium hydroxide, calcium carbonate, sodium bicarbonate, magnesium carbonate and magnesium hydroxide). Discuss other factors that need to be considered in antacid formulations apart from effectiveness in neutralising acids.
- Simulation: Run a titration screen experiment on a computer or tablet. Carry out astrong acid versus strong base titration (or any combination of strong and weak acid-base titrations). On this site it is also possible to run aredox titration experiment(although this relates more directly to content in Unit 4 Area of Study 2) for further practise in understanding and skills, in order to become more confident and familiar with the procedures in the laboratory.
- Participate in the RACI Victorian State Titration Competition.
- Analyse and evaluate data from titrations in terms of accuracy and precision.
- Investigate the acid content in different soft drinks by using a titration procedure.
- Controlled experiment: Investigate the effect of acid rain on the growth of seedlings or leaves by simulating acid rain (mix water with vinegar or lemon juice) and using a spray bottle to spray 10 fast-growing seedlings (for example, radish, soybeans, marigold) with the solution daily for a week and comparing the growth of the seedlings with 10 other seedlings of the same type that are sprayed with distilled or tap water. Monitor the state of the seedlings, recording both qualitative and quantitative effects in logbooks. Extend the experiment to compare effects on metals and chalk or eggshells; discuss how experimental variables were controlled in the investigations.
- Literature review: Research the issue of acid sulfate soils.
Key knowledge: Measuring gases
- Modelling: Design a flow chart or other representations to show unit conversions for, and relationships between, pressure, volume and temperature of gases.
- Use the Keeling Curve to explore changes in carbon dioxide levels in Earth’s atmosphere over time.
- Use statistics from the Bureau of Meteorology to plot trends on global concentration of carbon dioxide, air temperature or sea surface temperature; comment on the observed trends in graphs.
- Simulation: Use an interactive applet to investigate how the global warming potential (GWP) of greenhouse gases is related to the infrared portion of the electromagnetic spectrum, because different greenhouse gases absorb in different parts of the infrared spectrum. An activity on modelling GWP of greenhouse gases can be found in Part 2 of this Climate change chemistry lessons resource from Beyond Benign (US).
- Literature review: Compare the Global Warming Potentials for greenhouse gases CO2, CH4, and H2O; explain why the differences occur.
- Use a gas syringe to collect and measure the gas evolved in a chemical reaction; plot your results as a volume-time graph.
- Determine the relationship between p and V when the pressure on a gas sealed in a syringe is increased.
- Complete stoichiometric exercises requiring the calculation of a combination of an amount of solids, liquids, gases, solution concentrations or volumes, and the volume, temperature and pressure of gases (including consideration of quantities in excess in chemical reactions).
- Case study: Investigate the basic chemical principles of recent innovative techniques being trialled to directly remove CO2 from the atmosphere,using Direct Air Capture.
- Literature review: Investigate why the solubility of oxygen in water is limited, but its presence in thehydrosphere is important for living species.
Key knowledge: Analysis for salts
- Discuss the rationale for why what is considered ‘safe’ drinking water varies for different chemical pollutants (or more specifically, what the different concentration limits are, and why).
- Classification and identification: Use local examples of the management of chemical contaminants in each of the categories of salts, organic compounds and acids or bases.
- Describe two sampling protocols and identify how they would contribute to accuracy, precision, repeatability, reproducibility and / or validity of water analysis results.
- Classification and identification: Perform an experiment to determine the water of a hydrated salt to distinguish between the terms, ‘hydrates’, ‘water of hydration’, ‘efflorescence’, ‘deliquescence’ and ‘hygroscopic’.
- Undertake a water quality analysis for samples of water; for example, combine laboratory ‘wet’ and instrumental techniques with online calculators such as that at the Water Research Centre in Dallas, Texas, USA, which calculates water quality based on nine indicators (in order of decreasing significance: dissolved oxygen, fecal coliform, pH, biochemical oxygen demand, temperature change, total phosphate, nitrates, turbidity, total solids).
- Discuss the principles of colorimetry including the relationship between concentration and absorption; use secondary colorimetry data to construct a calibration curve and determine the concentration of an ingredient in a consumer product.
- Perform an instrumental analysis of a coloured species in solution; for example, compare the phosphate content of various fertilisers or washing powders; investigate why phosphates pose problems in waterways and how these problems are resolved.
- Literature review: Bottled water is sometimes fortified with various vitamins and nutrients. Investigate and produce a short report to explain the purpose of the additives and how the amounts that are added are determined.
- Case study: Refer to the Australian Government Initiative, Water Quality Australia,and discuss why salinity is an issue for the quality of water or soil. Also refer to the Murray-Darling Basin issue. Summarise strategies for managing salinity.
- Classification and identification: Investigate the applicability of Benford’s Law, also called the first-digit law (in lists of numbers from many everyday sources of large datasets, the leading digit is distributed in a specific, predictable way: 1 = 30.1%, 2 = 17.6%, 3 = 12.5%, 4 = 9.7%, 5 = 7.9%, 6 = 6.7%, 7 = 5.8%, 8 = 5.1%, 9 = 4.6%), to chemical data. For example, refer to global water quality data such as those at GEMStat or data obtained from state or local water authorities.
Respond to a chemistry-based issue in society; for example ‘Would you drink recycled water? (see Detailed example)
Detailed example
Responding to a chemistry-based issue in society: would you drink recycled water?
Aim
To communicate a justified response to a social issue involving chemistry concepts through participation in a Question & Answer panel discussion.
Introduction
Teacher poses the question, ‘Would you drink recycled water?’ as a summative learning task following learning activities related to measurements of solubility and concentrations, chemical analysis or a class excursion to a water treatment plant. The focus of this activity is on students being able to consider the nature of evidence, distinguish between facts and opinion, and synthesise arguments to communicate a response to a chemistry-related social issue.
Teachers could organise the class so that students work in groups to form a number of different Q&A panels where each student takes on the role of a different stakeholder, or use a jigsaw approach to create one class Q&A panel with each panelist having a team of ‘researchers’ to assist in the development of panel arguments.
Students role-play a Q&A panel discussion to examine the arguments for and against using recycled water as a source of drinking water. Each student will assume the role of one stakeholder, or become part of the stakeholder’s research team, and become part of the panel discussion. Following the panel discussion each student provides an individual response to the question ‘Would you drink recycled water?’ by producing a public communication in an agreed format; for example, newspaper article, infographic or TV advertisement. The communication must include referenced qualitative and quantitative data, distinction between identified facts and opinions presented in the Q&A panel discussion, and a justified personal stance on the question.
Science skills
Teachers should identify and inform students of the relevant key science skills embedded in the task.
Preparation
- Prior learning experiences related to water sampling techniques, measurement of solubility and concentration, and analytical techniques used to analyse for salts, organic compounds, and acids and bases.
- Prior consideration of validity, facts and opinions; for example, students have discussed sources of reliable information related to the following chemistry-based information:
- Drinking water, also known as potable water or improved drinking water, is defined as water that is safe enough for drinking and food preparation.
- Globally, in 2020, 74% of people used safely managed water services (improved source accessible on premises, available when needed and free of contamination) compared with 70% in 2015.
- Students should have discussed examples of ‘effective’ and ‘ineffective’ oral and written communication techniques and practices.
- Students become panel members who represent stakeholder interests (students select the names of stakeholders at random ‘from a hat’); for example, local resident with young family, mayor, local water authority representative, analytical chemist, site worker from company contracted to carry out water treatment, medical professional, local producer of carbonated water, meteorologist, and environmental activist.
- Students should have access to ‘fact sheets’ or authoritative sites related to water treatment and drinking water specifications; for example, excerpts from the Australian Drinking Water Guidelines, the World Health Organization’s guidelines for drinking water quality, and comparisons of drinking water standards around the world, such as those provided by the Safe Drinking Water Foundation (SDWF).
Health, safety and ethical notes
- Students should be respectful of others and their opinions at all times.
- Students should be reminded that this activity is simply a role-play and the comments made do not necessary reflect the attitudes of the individual speakers.
Procedure
Lessons 1 and 2: In these lessons students consider general information about the process of treating water to make it potable, including statutory requirements for water to be classified as ‘drinkable’; put themselves in the role of one stakeholder and present their position; construct a question they would like addressed by a discussion panel; and prepare possible responses to these questions from their perspective as one stakeholder. Some time out of class may also be required for students to complete background research. Students:
- Read through the ‘fact sheets’ or websites relating to water treatment and water quality.
- Note in the logbook major points of interest.
- Select at random the name of a stakeholder relevant to the issue.
- Spend 10 minutes brainstorming the likely perspective of the stakeholder towards the issue. Students may discuss their ideas with peers and the teacher. Students need to consider the biases (feelings, opinions, prejudices) that their stakeholder may have for this issue and write these into the logbook.
- Present a 20-second oral summary of the stakeholder to the class, for example: ‘My name is X and I am the mayor of this town where it is proposed that we supplement our drinking water supplies with treated water, since we often need to apply water restrictions due to low water reserves in our dam. The majority of my constituents are against the proposal since there are concerns that the treated water will still contain microbes or chemicals that may threaten human health and that treated water could never exactly replicate the quality of rain water or the water in our dams.’
- On a slip of paper, construct one question that they would like addressed by someone relating to this case study. Students may suggest which stakeholder they would like to primarily respond to their question. The question should be well thought out so as to give maximum insight into different perspectives in considering the issue. Students may use the following list of question terms to assist them:
List 1: Who / What / Where / When / Why / How…?
List 2: …would / could / should / is / are / might / will / was / were…?
Submit the question to the teacher, who will collate (perhaps by photocopying all slips onto a single sheet of paper) and distribute them to the relevant discussion panel.
- Now working with the other members of the panel, discuss the questions that have been submitted and write notes in the logbook detailing the response to these questions from the perspective of a stakeholder. Include as much scientific data as possible in the responses. Students may need to conduct additional Internet research to develop responses.
Lesson 3: In this lesson students role-play the perspective of one stakeholder as part of a panel discussion. They may use any notes already written in the logbook and may also make additional notes in the logbook during the class.
Lesson 4: In this lesson students provide an individual response to the question ‘Would you drink recycled water?’ by producing a public communication in an agreed format; for example, newspaper article, infographic or TV advertisement. At the end of the lesson they submit a draft of their response. They may use any notes from the logbook.
The communication must include referenced qualitative and quantitative data, distinction between identified facts and opinions presented in the Q&A panel discussion, and a justified personal stance on the question.
The media communication should identify / highlight:
- a likely target audience
- specific scientific concept(s) being communicated
- distinction between fact and opinion
- scientific data used to justify position of the stakeholder.
Students will be assessed with respect to:
- accuracy of scientific information
- clarity of explanations
- appropriateness for purpose and audience.
