Science is not just about discovering facts — it is about building arguments that stand up to scrutiny. In this lesson, you will learn to construct, evaluate and communicate scientific arguments using evidence, reasoning and the language of chemistry.
A social media post claims: "Natural chemicals are always safer than synthetic chemicals. You should only use organic cleaning products."
Write down your answers before reading on:
Building arguments that hold up
A scientific argument is like a three-legged stool. Remove any leg, and it falls over.
The claim is your answer to the question. It must be specific, testable and stated clearly. A weak claim is vague: "Temperature matters." A strong claim is precise: "Increasing the temperature of hydrochloric acid from 20°C to 40°C doubles the rate of its reaction with magnesium ribbon."
Evidence is the data that supports your claim. It can come from experiments, observations, published studies or reliable databases. Good evidence is:
Reasoning is the bridge between evidence and claim. It explains why the evidence supports the claim using scientific principles. For example: "The data show that the reaction at 40°C produced 48 mL of gas in 30 seconds compared to 24 mL at 20°C. This supports the claim because, according to collision theory, higher temperature increases particle speed and collision frequency, leading to more successful reactions per second."
Not all information is created equal
In the age of social media and AI-generated content, evaluating sources is an essential scientific skill. When you encounter a claim about chemistry, ask these questions:
Is the author a qualified scientist? Do they work for a university, a government agency, an industry group or an advocacy organisation? Sources from peer-reviewed journals, universities and government science agencies (like CSIRO in Australia) are generally more reliable than unverified social media posts.
Does the source provide actual data, methods and references? Or does it rely on anecdotes, emotions or unsupported assertions? A reliable source tells you how the evidence was collected so you can judge its validity.
Funding bias: A study funded by a company may favour that company's products.
Confirmation bias: People tend to seek evidence that supports what they already believe.
Publication bias: Studies with positive results are more likely to be published than those with negative results.
Peer review means other experts in the field have checked the work before publication. While not perfect, peer review catches many errors and biases. Websites, blogs and social media posts are usually not peer-reviewed.
Bringing it all together
A depth study is your opportunity to investigate a chemistry question that interests you. It combines all the Working Scientifically skills you have developed: questioning, planning, conducting, analysing and communicating.
Pick a question that is:
Your plan should include:
Communicate your depth study using the CER framework. State your claim clearly, present your evidence in tables and graphs, and explain your reasoning using the chemical principles you have learned. Use scientific terminology accurately and acknowledge any limitations in your method.
"If a scientist says it, it must be true." No — scientists can be wrong, biased or working with incomplete data. Science is a process of testing and refinement, not a collection of absolute truths.
"Natural always means safe and synthetic always means dangerous." No — many natural substances are toxic (e.g., botulinum toxin, arsenic), and many synthetic substances are safe and beneficial (e.g., purified water treatment chemicals, medical drugs).
The Commonwealth Scientific and Industrial Research Organisation (CSIRO) is Australia's national science agency. CSIRO researchers conduct peer-reviewed studies on topics from bushfire chemistry to marine plastics. When CSIRO publishes findings, the data has been reviewed by independent experts, making it a highly reliable source for Australian scientific evidence.
In contrast, claims made in advertising — such as "our cleaning product is 100% chemical-free" — should be treated with scepticism. All matter is made of chemicals, including water and air. Understanding chemistry helps you spot misleading claims and demand better evidence.
Aboriginal and Torres Strait Islander knowledge systems also use evidence-based reasoning built from generations of observation and testing on Country. This knowledge is validated through its successful application over thousands of years and deserves respectful recognition in scientific discourse.
1. In the claim-evidence-reasoning framework, what does the reasoning do?
2. Which of the following is the MOST reliable source for scientific information about climate change?
3. A newspaper reports: "Study shows organic pesticides are safer than synthetic ones." The study was funded by an organic farming association. What is the main concern?
4. Which statement BEST demonstrates scientific reasoning?
5. A student concludes their depth study with: "My results prove that catalysts always make reactions go faster." What is the main problem with this statement?
1. Explain the difference between claim, evidence and reasoning in a scientific argument. Use a simple chemistry example to illustrate each component. 4 MARKS
2. You are researching whether biodegradable plastic bags are better for the environment than conventional plastic bags. Describe TWO factors you would consider when evaluating sources for this topic, and explain why each factor matters. 4 MARKS
3. A celebrity posts on social media: "I only use chemical-free products because chemicals are dangerous." Analyse this statement using your chemistry knowledge. Identify at least TWO scientific errors or logical flaws in the claim, and explain how you would respond using evidence-based reasoning. 4 MARKS
Go back to your Think First answer. Has your understanding changed?
C — Reasoning explains the logical and scientific connection between the evidence and the claim. It uses scientific principles to show why the evidence supports the conclusion.
B — Peer-reviewed articles in scientific journals are the most reliable because they have been checked by independent experts for methodology, accuracy and bias.
D — Funding bias is a real concern. The funder may influence study design, data interpretation or publication decisions to favour their interests. This does not automatically make the study wrong, but it means extra scrutiny is needed.
A — Scientific reasoning connects observations to theory. Option A explains the faster reaction by referring to collision theory — particles move faster and collide more frequently at higher temperatures. The other options rely on authority, procedure or emotion rather than scientific principles.
C — A single investigation cannot prove a universal claim. The student tested specific catalysts under specific conditions. The conclusion should be more cautious: "My results suggest that [specific catalyst] increases the rate of [specific reaction] under these conditions."
Model answer: A claim is a testable statement that answers a question. For example: "Increasing the concentration of acid increases the rate of reaction with magnesium." Evidence is the data that supports or refutes the claim. For example: "At 1.0 mol/L acid, 45 mL of gas was produced in 60 seconds; at 0.5 mol/L, only 22 mL was produced." Reasoning is the explanation of why the evidence supports the claim using scientific theory. For example: "This supports the claim because collision theory states that higher concentration means more particles per unit volume, leading to more frequent collisions and therefore a faster reaction."
Model answer: Factor 1: Whether the source is peer-reviewed. Peer-reviewed studies have been checked by independent experts, making them more reliable than blog posts or company websites. This matters because unreviewed claims may contain errors or bias. Factor 2: Whether the source declares funding or conflicts of interest. A study funded by a biodegradable bag company may be biased toward showing those bags are better. This matters because financial interests can influence study design and interpretation, so evidence from independent sources is more trustworthy.
Model answer: Error 1: "Chemical-free" is scientifically meaningless — all matter is made of chemicals, including water, air and every natural substance. The celebrity is confusing "chemical" with "synthetic" or "toxic." Error 2: The claim that "chemicals are dangerous" is an overgeneralisation. Whether a substance is dangerous depends on dose, context and exposure, not on whether it is natural or synthetic. Water is essential for life but can be fatal in excessive amounts. Evidence-based response: I would ask the celebrity to define "chemical" and provide evidence for which specific chemicals they are concerned about, at what doses, and from what sources. I would explain that scientific evaluation requires comparing specific substances under specific conditions, not making blanket statements about all chemicals.
Blast through bad science! Spot weak claims, identify reliable sources and build bulletproof arguments in this fast-paced challenge.
Tick when you have finished all activities and checked your answers.