Wear on Earth
View Sequence overviewStudents will:
- model and observe chemical weathering through hands-on exploration.
- consider how human activities contribute to chemical weathering.
Students will represent their understanding as they:
- discuss the chemical weathering changes observed during modelling.
- draw diagrams of changes observed during chemical weathering investigations.
- compare and discuss the similarities and differences between real-life chemical weathering and classroom modelling.
In this lesson, assessment is formative.
Feedback might focus on:
- the claims students are making about the difference between physical and chemical weathering. Are they referring to the definitions and their evidence to make their claims? Can they give an example of where they might see the effects of chemical weathering?
- students’ descriptions of chemical weathering. Have they recognised that chemical weathering is a natural process and that human activities contribute to it?
Whole class
Class science journal (digital or hard-copy)
Demonstration copy of the pH scale Resource sheet
Demonstration copy of the Chemical weathering investigations Resource sheet
Optional: Demonstration copy of the PROE Resource sheet
Video: Chemical Weathering (0:56)
Video: Cave Formation (0:30)
Video: Jenolan Caves (0:23)
Each group
Four investigations are presented in this lesson. Complete any or all of them as appropriate for your students. See the Investigate lesson step for details of each investigation. See the Preparing for this sequence tab in the sequence overview for more information on sourcing limestone or cement for the Reaction time investigation.
Chemical weathering investigations Resource sheet (modified to include instructions of chosen investigations only). Alternatively, display an enlarged version for the whole class.
Reaction time
2 clear cups/jars
2 pieces of either limestone or cement
White vinegar
Water
Texta or label to indicate which substance in each cup
Drip drip
2 sugar cubes
Clear cup/jar
Vinegar diluted in water, using a 1:1 or 1:2 vinegar to water ratio
Dripper (syringe/eye-dropper/straw) to drip the diluted vinegar
Altered sculptures
2-5 sugar cubes or toffee (commercially available or homemade), to represent rock
Sculpting tools (popsticks/nail files/toothpicks/butter knife)
Dripper (syringe/eye-dropper/straw)
Vinegar diluted in water, using a 1:1 or 1:2 vinegar to water ratio
Optional: icing to glue together sugar cubes
Caves and sinkholes
Sugar cubes
Clay or biscuit/cracker
Clear cup/jar
Dripper (syringe/eye-dropper/straw)
Vinegar diluted in water, using a 1:1 or 1:2 vinegar to water ratio
Each student
Individual science journal (digital or hard-copy)
Optional: Demonstration copy of the PROE Resource sheet (printed as many times as needed, or students can make their own in the science journals)
Lesson
Re-orient
Recall the previous lessons, focusing on how physical weathering changes rocks and sometimes breaks them apart.
The Inquire phase allows students to cycle progressively and with increasing complexity through the key science ideas related to the core concepts. Each Inquire cycle is divided into three teaching and learning routines that allow students to systematically build their knowledge and skills in science and incorporate this into their current understanding of the world.
When designing a teaching sequence, it is important to consider the knowledge and skills that students will need in the final Act phase. Consider what the students already know and identify the steps that need to be taken to reach the level required. How could you facilitate students’ understanding at each step? What investigations could be designed to build the skills at each step?
Read more about using the LIA FrameworkIdentifying and constructing questions is the creative driver of the inquiry process. It allows students to explore what they know and how they know it. During the Inquire phase of the LIA Framework, the Question routine allows for past activities to be reviewed and to set the scene for the investigation that students will undertake. The use of effective questioning techniques can influence students’ view and interpretation of upcoming content, open them to exploration and link to their current interests and science capital.
When designing a teaching sequence, it is important to spend some time considering the mindset of students at the start of each Inquire phase. What do you want students to be thinking about, what do they already know and what is the best way for them to approach the task? What might tap into their curiosity?
Read more about using the LIA FrameworkWhat is chemical weathering?
Note for teachers
The concept and potential consequences of chemicals in the environment affecting rocks, including in the form of acid rain, are explored in this lesson. This is modelled using vinegar as a substitute for naturally occurring acids in the environment. The idea of acid rain can be alarming to students, and it is worth noting that vinegar is a stronger acid than naturally occurring acid rain. See the embedded professional learning The pH scale for more information.
Discuss if students think that rocks can wear away without a physical force, and how that might happen.
- Are there any other ways a rock can break down?
- What are chemicals? How might they change a rock?
- Everything is made of chemicals (even water). Some chemicals can cause changes in materials, including the weathering of rocks.
- Students’ responses will depend upon their prior knowledge, but it is likely most have been exposed to terminology that describes chemicals as dangerous liquids or other substances. Examples might include cleaning products, batteries and drugs, and alcohol.
- Have you heard the words ‘acidic’ or ‘acid’ before? What do you know about them?
- What natural things are acidic?
- Have you heard the terms ‘alkaline’, ‘neutral’ or ‘pH level’? What do you know about them?
- Looking at this visual image of a pH scale, what substances are you familiar with? How do you encounter them in everyday life?
- The pH scale Resource sheet provides a visual image to reference during the discussion.
- How acidic is water? Rainwater? Lemon juice? Vinegar? Soft drink?
- Is this what you expected?
- What do you think would happen if we poured something acidic over rocks?
- What about if we left a rock submerged in something acidic?
- What if we diluted the acidic substance with water? Do you think the same things would happen?
- Have you ever seen natural rocks with stripes of colour running through them? What do you think might cause those colours to appear?
- Have you seen stalactites and stalagmites inside a cave? How do you think they might form?
Pose the questions: What is chemical weathering, and how does it change rocks?
The pH scale
What is the pH scale, and what do my students need to understand about it at this year level?
The pH scale (‘potential of hydrogen’) measures how acidic or alkaline (also known as basic) a substance is.
The scale is typically depicted as ranging from 0 (the most acidic) to 14 (the most alkaline), but there are substances that fall outside this range. Substances with a pH level less than 7 are considered acidic, substances with a pH more than 7 are considered alkaline, and substances with a pH of 7 are neutral. Each step on the scale represents a value of 10, therefore, a substance with a pH level of 2 is 10 times more acidic than something with a pH level of 3.
Pure water has a pH level of 7 and is considered neutral. Clean rainwater has a pH of between 5 and 5.5, so it is naturally slightly acidic.
When rainwater combines with specific chemicals that are often by-product of human industries, namely sulfur dioxide or nitrogen oxides, the pH level can decrease to around 4. When this rainwater falls, it is called ‘acid rain’. Acid rain is actually a weaker acid than some common acidic substances such as vinegar and lemon juice, which are used regularly with little consequence. Even carbonated soft drinks are more acidic than acid rain, with a pH level of 3.
Having a basic understanding of this scale will help allay any potential fears students might develop about the concept of acid rain. Point out that typical rainwater is already slightly acidic, and that acid rain is not as acidic as other common substances.
The pH scale (‘potential of hydrogen’) measures how acidic or alkaline (also known as basic) a substance is.
The scale is typically depicted as ranging from 0 (the most acidic) to 14 (the most alkaline), but there are substances that fall outside this range. Substances with a pH level less than 7 are considered acidic, substances with a pH more than 7 are considered alkaline, and substances with a pH of 7 are neutral. Each step on the scale represents a value of 10, therefore, a substance with a pH level of 2 is 10 times more acidic than something with a pH level of 3.
Pure water has a pH level of 7 and is considered neutral. Clean rainwater has a pH of between 5 and 5.5, so it is naturally slightly acidic.
When rainwater combines with specific chemicals that are often by-product of human industries, namely sulfur dioxide or nitrogen oxides, the pH level can decrease to around 4. When this rainwater falls, it is called ‘acid rain’. Acid rain is actually a weaker acid than some common acidic substances such as vinegar and lemon juice, which are used regularly with little consequence. Even carbonated soft drinks are more acidic than acid rain, with a pH level of 3.
Having a basic understanding of this scale will help allay any potential fears students might develop about the concept of acid rain. Point out that typical rainwater is already slightly acidic, and that acid rain is not as acidic as other common substances.
The Inquire phase allows students to cycle progressively and with increasing complexity through the key science ideas related to the core concepts. Each Inquire cycle is divided into three teaching and learning routines that allow students to systematically build their knowledge and skills in science and incorporate this into their current understanding of the world.
When designing a teaching sequence, it is important to consider the knowledge and skills that students will need in the final Act phase. Consider what the students already know and identify the steps that need to be taken to reach the level required. How could you facilitate students’ understanding at each step? What investigations could be designed to build the skills at each step?
Read more about using the LIA FrameworkThe Investigate routine provides students with an opportunity to explore the key ideas of science, to plan and conduct an investigation, and to gather and record data. The investigations are designed to systematically develop content knowledge and skills through increasingly complex processes of structured inquiry, guided inquiry and open inquiry approaches. Students are encouraged to process data to identify trends and patterns and link them to the real-world context of the teaching sequence.
When designing a teaching sequence, consider the diagnostic assessment (Launch phase) that identified the alternative conceptions that students held. Are there activities that challenge these ideas and provide openings for discussion? What content knowledge and skills do students need to be able to complete the final (Act phase) task? How could you systematically build these through the investigation routines? Are there opportunities to build students’ understanding and skills in the science inquiry processes through the successive investigations?
Read more about using the LIA FrameworkA chemical reaction
Four different investigations exploring chemical weathering are outlined below. Select the investigation(s) that best suit the needs and context of your students. You may choose to do all of these investigations if adequate time and supplies are available. The instructions for each are provided on the Chemical weathering investigations Resource sheet. Modify the resource sheet to include the instructions required for the investigations you will undertake, and print or display them for teams as necessary.
Before undertaking any investigations
Introduce a formal definition of ‘chemical weathering’—the breakdown of rocks and minerals caused by non-physical changes (chemical reactions).
View and discuss the materials students will use, and how/why they are being used to model the chemical weathering process. For example:
- vinegar has a high pH level, and so exaggerates the effects of what happens when rocks/minerals are exposed to acid.
- sugar cubes can be used as a substitute for rock because breaking up the hard, compressed particles can show what happens to rocks when they come into contact with acidic substances.
Discuss/model the PROE strategy, as students will use it to record what is happening in their investigations.
- First, students make a Prediction about what they think will happen and give Reasons for why they think that, based on their prior knowledge and experiences.
- Next they undertake the investigation, discussing it with their team and writing about, drawing, or taking photos of their Observations in their science journal.
- Finally, they Explain what they think happened and why.
Allow teams time to undertake the selected investigations. The PROE template Resource sheet can be printed as many times as will be required, or students can create as many as they need in their individual science journal.
Reaction time
Students conduct an investigation into what happens to rocks when they are exposed to neutral and acidic substances (water and vinegar).
Students complete the P and R sections of a PROE, then submerge one piece of limestone/cement cement in a cup of water and the other piece in a cup of undiluted white vinegar. They record observations during the course of the day in the O section of their PROE, before leaving the limestone or cement submerged overnight. They make a final observation the following day finalise the Observations and Explanations of their PROE in their science journals.
Watch the video Chemical Weathering: Acid Rain (2:00). Discuss if students’ observations matched those in the video. Discuss the chemical reaction where carbon dioxide is produced as the acidic vinegar reacts with the limestone. Allow students time to add to or amend their explanations as needed.
Drip drip
Students conduct an investigation comparing physical weathering to non-physical (chemical) weathering, using sugar cubes and diluted vinegar.
Students ‘physically’ weather their ‘rocks’ (sugar cubes) by, for example, pressing down on the cubes with their hand or a book, or scraping two cubes against each other.
Students consider the questions: Are these smaller pieces you have created still ‘rock’ (sugar)? and What will happen when we drip acid onto the ‘rock’? They complete the P and R sections of a PROE, before dripping diluted vinegar onto the rock using a dropper or syringe. They record their Observations and Explanations in their science journals, including a response to the question How has the rock changed?
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Altered sculptures
Students make a sugar cube/toffee sculpture then observe the effects of acid rain (vinegar) dripping on their sculpture.
Supply teams with sugar cubes/toffee and sculpting tools (popsticks, nail files, toothpicks etc.) and allow time for them to create a sculpture.
If using sugar, single cube sculptures work fine or cubes can be glued together with icing if required. Encourage students to include fine details and sharp edges on their sculpture.
Once sculptures are complete, students complete the P and R sections of a PROE, before modelling the effects of acid dripped on rock by dripping diluted vinegar onto their sculpture. They record their Observations and Explanations in their science journals.
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Caves and sinkholes
Teams explore the creation of a cave or sinkhole by making a model of the Earth's surface.
Teams place a layer of ‘rock’ (sugar cubes) in a clear glass/jar and cover it with ‘topsoil’ (clay or a biscuit/cracker). They make a few holes or cracks in the ‘topsoil’ so rainwater can seep into the ‘rock’ layer.
Students complete the P and R sections of a PROE before dripping diluted vinegar onto their model of the Earth's surface. The sugar cubes (rocks) will begin to chemically weather beneath the surface layer, in a similar way to how caves and sinkholes are created. Students record their Observations and Explanations in their science journals.
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Chemical weathering
What is chemical weathering?
Students in Year 5 have not yet been introduced to chemical changes/reactions. For this reason, the term 'non-physical changes' can be used as an alternative.
Chemical weathering involves the breaking-down of rocks and minerals through chemical reactions. These changes in the chemical composition are the result of interactions between the air, water, and chemical compounds contained in the rock. For example, the mild acidity of some rainfall can cause minerals in rock to react and dissolve in the water. This is how caves such as the Jenolan Caves in New South Wales were formed.
Acid can also be released from living things, for example, the decay of organic material, or by direct secretion of acids (by lichens).
Chemical weathering continues to shape Wave Rock in Western Australia. In the wetter months, water from springs runs down the cliff face, dissolving and re-depositing chemicals in the granite, leaving red, brown, yellow and grey stains of carbonates and iron hydroxide. Wave Rock is estimated to be about 2700 million years old.
Human activities and acid rain
Weathering is a natural process, but human activities can speed it up. For example, certain kinds of air pollution increase the rate of weathering. Burning coal, natural gas, and petroleum releases chemicals such as nitrogen oxide and sulfur dioxide into the atmosphere. When these chemicals combine with sunlight and moisture, they react to form acids. They then fall back to Earth as acid rain.
Clean rainwater has a pH of between 5 and 5.5, so it is naturally slightly acidic. Acid rain has a pH of around 4. For context, common substances such as lemon juice and vinegar have a pH level of 2, and are therefore 20 times more acidic than acid rain. Even carbonated soft drinks are more acidic, with a pH level of 3.
The pH of water contributes to the weathering of limestone, marble, and other kinds of stone, with higher levels of pH accelerating this process. A visit to an old cemetery is an ideal way to see the effects of weathering from water, as it causes damage to gravestones, making names and other inscriptions difficult to read.
Students in Year 5 have not yet been introduced to chemical changes/reactions. For this reason, the term 'non-physical changes' can be used as an alternative.
Chemical weathering involves the breaking-down of rocks and minerals through chemical reactions. These changes in the chemical composition are the result of interactions between the air, water, and chemical compounds contained in the rock. For example, the mild acidity of some rainfall can cause minerals in rock to react and dissolve in the water. This is how caves such as the Jenolan Caves in New South Wales were formed.
Acid can also be released from living things, for example, the decay of organic material, or by direct secretion of acids (by lichens).
Chemical weathering continues to shape Wave Rock in Western Australia. In the wetter months, water from springs runs down the cliff face, dissolving and re-depositing chemicals in the granite, leaving red, brown, yellow and grey stains of carbonates and iron hydroxide. Wave Rock is estimated to be about 2700 million years old.
Human activities and acid rain
Weathering is a natural process, but human activities can speed it up. For example, certain kinds of air pollution increase the rate of weathering. Burning coal, natural gas, and petroleum releases chemicals such as nitrogen oxide and sulfur dioxide into the atmosphere. When these chemicals combine with sunlight and moisture, they react to form acids. They then fall back to Earth as acid rain.
Clean rainwater has a pH of between 5 and 5.5, so it is naturally slightly acidic. Acid rain has a pH of around 4. For context, common substances such as lemon juice and vinegar have a pH level of 2, and are therefore 20 times more acidic than acid rain. Even carbonated soft drinks are more acidic, with a pH level of 3.
The pH of water contributes to the weathering of limestone, marble, and other kinds of stone, with higher levels of pH accelerating this process. A visit to an old cemetery is an ideal way to see the effects of weathering from water, as it causes damage to gravestones, making names and other inscriptions difficult to read.
The Inquire phase allows students to cycle progressively and with increasing complexity through the key science ideas related to the core concepts. Each Inquire cycle is divided into three teaching and learning routines that allow students to systematically build their knowledge and skills in science and incorporate this into their current understanding of the world.
When designing a teaching sequence, it is important to consider the knowledge and skills that students will need in the final Act phase. Consider what the students already know and identify the steps that need to be taken to reach the level required. How could you facilitate students’ understanding at each step? What investigations could be designed to build the skills at each step?
Read more about using the LIA FrameworkFollowing an investigation, the Integrate routine provides time and space for data to be evaluated and insights to be synthesized. It reveals new insights, consolidates and refines representations, generalises context and broadens students’ perspectives. It allows student thinking to become visible and opens formative feedback opportunities. It may also lead to further questions being asked, allowing the Inquire phase to start again.
When designing a teaching sequence, consider the diagnostic assessment that was undertaken during the Launch phase. Consider if alternative conceptions could be used as a jumping off point to discussions. How could students represent their learning in a way that would support formative feedback opportunities? Could small summative assessment occur at different stages in the teaching sequence?
Read more about using the LIA FrameworkWhat did you observe?
In this Integrate step, guide students to link their experiences in the investigation to the processes of chemical weathering in real-life.
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Students share their observations and explanations from the investigation/s they undertook.
- What is the difference between physical/mechanical weathering and chemical weathering?
- How does acid in the environment cause rocks to weather?
- Do you think the flatter faces of rock or the sharper, pointier areas of rock weather the quickest? Why do you think that?
- Sharp/pointed/narrow sections of weather faster than large flat areas, because they are smaller and provide a greater exposure (surface area) for the acidic substances to react easily.
Further consolidate student understanding of chemical weathering by viewing videos of weathering and discussing brief explanations to suit your context. Examples include:
- Chemical weathering (0:56) – the importance of chemical weathering
- Cave formation (0:30) – limestone cave formation explanation
- Jenolan Caves (0:23) – footage to music without explanation
Discuss how students’ observations from their investigations were similar or different from what they had just viewed.
- How is this similar to our modelling? How is it different?
- Do you think chemical weathering is a rapid or slow weathering process? Why do you think that?
- Chemical weathering is usually very slow, but it can be sped up by human activities such as the burning of fossil fuels.
- How does the modelling we have seen in today’s lesson help us to learn about the Earth’s surface, and why it looks the way it does?
Optional: Use Google Maps to explore some famous Australian landscapes that are the result of chemical weathering, such as Wave Rock, WA. Wave Rock is 14m high and 110m long, and is formed by water dissolving and re-depositing chemicals in the granite as it runs down the cliff face
Reflect on the lesson
You might:
- add new words and images to the word wall or glossary.
- add to the W and H sections of the TWLH chart.
- consider how students were thinking and working like scientists during the lesson by discussing the use of models to develop their understanding of chemical weathering. Weathering, particularly of large rocks, takes place over millions of years. Modelling helps us to view the process in a reasonable timeframe. Landforms can be large and difficult to view, so modelling makes a smaller version for us to study.