Year 8 Science · Unit 2 · Lesson 18
Challenge Worksheet
Learning Goals
Find the mistake
A student wrote this answer
"Hydrogen is very dangerous and flammable. Oxygen helps things burn. So water (H₂O) should be extremely flammable and dangerous. In fact, water and hydrogen peroxide (H₂O₂) should be basically the same, they have the same atoms. The only difference is one extra oxygen atom, which would make hydrogen peroxide slightly more flammable than water."
1. Identify at least three distinct mistakes in the student's answer. List each error clearly.
2. For each mistake you identified, write the correct chemistry. Make sure to explain why the student's reasoning fails, not just what the correct answer is.
3. Explain why this kind of mistake, assuming a compound's properties can be predicted from its elements, is so easy to make, and what the correct way of thinking is.
1. Using the examples from this lesson (NaCl, H₂O, Fe₂O₃, CO₂), evaluate the following statement: "Chemistry is the science of creating entirely new substances from existing ones." To what extent does the evidence from this lesson support this claim? Are there any limitations to this statement?
2. Hydrogen peroxide (H₂O₂) and water (H₂O) contain the same two elements but are very different substances: H₂O₂ is a strong oxidising agent used to bleach hair and disinfect wounds, while H₂O is stable and safe to drink. Using the core idea from this lesson, explain how two compounds made from exactly the same elements can have such dramatically different properties.
Wrap Up
In one sentence, what was the main idea of this lesson?