Year 7 Science · Unit 2 · Lesson 16
Challenge Worksheet
Learning Goals
What if…?
Scenario
Air is a homogeneous mixture of gases. Currently, nitrogen makes up about 78% of air, oxygen about 21%, and the rest is argon and traces of carbon dioxide. Scientists have long known that plants need nitrogen from the soil (usually fixed by bacteria) rather than directly from air, because the N₂ molecule is very stable. Imagine a future technology that could easily and cheaply convert all of the nitrogen in air into oxygen — so that air became roughly 99% oxygen and less than 1% nitrogen. Some people argue this would be wonderful: humans and animals would breathe more easily and need less lung capacity. Would it really be an improvement?
Using what you know about mixtures and the composition of air from this lesson, predict and explain what would happen in this scenario. Consider at least TWO different consequences — one ecological and one medical or physical. Use scientific terms in your answer.
1. The scenario above changes the proportions of gases in the air mixture. Using what you know about mixtures, explain why changing the proportions of components in a mixture is possible, but would NOT be possible if air were a compound.
2. Nitrogen makes up 78% of air but is not used directly by most organisms during breathing. A student claims: "Nitrogen in air is useless — we should replace it with more oxygen." Using evidence from the lesson about why mixtures have their particular compositions, evaluate this claim. Is it good science?
Wrap Up
In one sentence, what was the main idea of this lesson?