Ratios and Proportions

When iron rusts the surface iron reacts with the oxygen in the atmosphere to form iron oxide (the reddish rusty stuff). This is a compound consisting of a 3 : 2 ratio of oxygen and iron atoms. If the rust contains 4320 atoms, how many iron atoms are there in the rust?

Solution: 1728 atoms

Sketch:

We use the two facts: oxygen + iron = 4320 and oxygen : iron = 3 : 2. The ratio gives:

oxygen = 1.5 iron

1.5 iron + iron = 4320
2.5 iron = 4320
iron = 1728.

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Developed by

Shodor
in cooperation with the Department of Chemistry,
The University of North Carolina at Chapel Hill

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Solution: 1728 atoms Sketch:

Solution: 1728 atoms

Sketch: