Why all this attention to measuring by mols? The reason's really quite simple. A mol of water, weighing 18.016 grams contains the same number of molecules as one mol of ethanol, weighing 46.068 grams. Knowing the relative number of molecules greatly simplifies the calculations for chemical and physical phenomena. The actual number of molecules in a mol is named after the scientist who first proposed the concept, Lorenzo Romano Amedeo Carlo Avogadro, conte di Quarequa e di Cerreto (1776 - 1856). The number of molecules in a mol (remember, this is a gram mole)is defined as 6.0221367 x 1023 molecules, and this is known as Avogadro's number. This number is so huge that it's difficult to comprehend, so here are a few examples for perspective:

• A mol of standard soft drink cans would cover the surface of the earth to a depth of over 200 miles.

• A mol of unpopped popcorn kernels, spread across the United States of America, would bury the country over 9 miles deep.

• If you counted atoms at the rate of 10 million per second, it would take about 2 billion years to count the atoms in one mol.

Fortunately, we don't need to remember this number as it cancels out in all the equations we'll be using. However, knowing it helps to remind us just how incredibly small atoms and molecules are.

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