Science · Chemistry
Chapter 1: Matter and Measurement
One question sorts almost everything.
Carbon monoxide and carbon dioxide are both made of nothing but carbon and oxygen. A few thousand parts per million of carbon monoxide can kill within hours, yet every breath you exhale is about 4% carbon dioxide.
If both are only carbon and oxygen, why is one a poison and the other in every breath?
Make your guess to turn the page.
Still to come: 10 pages · Lab · Words to Know · What We Learned · 4 questions · Explain It in Writing · Open Questions
The idea this lesson is working on — Students picture a compound as its elements stirred together, so they expect it to keep a little of each. The book sets that against CO and CO₂, against salt, and against the lab, where a magnet that recovers 20 g of iron from a mixture recovers 0 g after the reaction. Ask: can this be separated by a physical method, and is its composition fixed? The idea to reach is that a compound is a new substance.
One question sorts almost everything — Can it be separated by physical means? If yes it is a mixture; if no it is a pure substance. Then ask whether it can be broken down chemically: if no, it is an element; if yes, a compound. The limits page names the exceptions worth knowing: nonstoichiometric solids such as wüstite, Fe(1−x)O, and azeotropes such as 95.6% ethanol.
A note on the lab — The simulation draws the reacted state as one undivided "new substance" and its note speaks of iron and salt; iron does not actually react with sodium chloride. The classic real pair is iron and sulfur, which form iron sulfide when heated, and a magnet no longer lifts the product. The book describes the switch only as "a reaction that bonds the contents into a new compound".