Atoms and molecules

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The number of atoms or molecules in a mole is defined such that the mass of one mole of a substance, in grams, is exactly equal to the substance's atomic or molecular weight.

For example, the molecular weight of natural water is about 18.015, so one mole of water is about 18.015 grams.

Slide 11

Problems with moles

1. Change 2 moles of N2 to grams. (The molecular weight of N2 is 14 grams/mole)

2. Change 36 g of C-12 to moles. (The atomic weight of C-12 is 12 grams/mole)