Look at the box of fresh donuts in the picture. If you have a sweet tooth, they probably look delicious. When you go to a donut shop or to the grocery store, you typically buy donuts according to the number—a single donut, by the half-dozen, or by the dozen. That makes it easy for both the seller and the buyer. However, it would be possible to price the donuts and sell them according to mass. A jelly-filled donut would probably weigh more and thus be more expensive than a sugared or a powdered donut. Donut shops don’t do this because it would take too much time. In this chapter you will learn about different ways to measure the amount of something and the interrelationships between those measurements. You will also be introduced to one of the most important units used in chemistry, the mole.
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