Year 10 Science · Unit 2 · Lesson 17
Challenge Worksheet
Learning Goals
Find the mistake
A student wrote this answer
"Soap cleans because it dissolves grease in water, soap is basically just a detergent solvent that mixes everything together. You add soap to water, the soap molecules spread out, and they pull the grease into the water because soap is soluble in both. This is why you need warm water, it helps the soap dissolve faster. The reaction between soap and grease is a standard dissolution, like salt dissolving in water."
1. Identify at least two specific scientific errors in the student's answer. Be precise about what is wrong.
2. Write a corrected explanation of how soap actually removes grease. Your answer should include: (a) the structure of a soap molecule, (b) why it can interact with both water and grease, (c) what "saponification" means and how soap is made.
3. The student says warm water "helps the soap dissolve faster." Is this explanation correct, incomplete, or misleading for why warm water improves cleaning? Explain what is actually happening chemically.
1. Your liver contains enzymes that break down ethanol into acetaldehyde and then into acetate. Identify the reaction type for each step and explain why this sequence of enzyme-catalysed reactions is important for removing alcohol from your bloodstream.
2. Concrete production involves two separate reactions: (1) thermal decomposition of limestone (CaCO₃ → CaO + CO₂) and (2) an exothermic setting reaction (CaO + H₂O → Ca(OH)₂). Using your knowledge of reaction rates, explain why concrete can feel warm to the touch while setting, and why this exothermic step is useful in construction.
Wrap Up
In one sentence, explain why calling soap "a solvent" misrepresents the actual chemistry of how soap interacts with grease and water.