You go to the store and buy a dozen eggs. How many eggs is this? The answer is obvious, twelve. Bakers have a different idea. They want to encourage the purchase of bread and roles in bulk, and want people to think there is an extra one to be eaten, so a bakers dozen in thirteen. Potters have other problems. If you need 12 plates, then you need to start with more than 12. A potter's dozen is 15, but one will crack, one will be underfired, and on one the glaze won't work right.

Chemists have their own problem. Atoms and most molecules are too small to be seen and weigh too little to sense on most scales. Even microscopes can't see them. In order to work with atoms chemists need to deal with them in groups, large groups. Consequently a chemists dozen is a very large number.

A chemist's dozen of molecules common ceramic materials can be held in the hands. With Whiting, a chemists dozen molecules of whiting (Calcium Carbonate) weighs 100 grams. about a quarter pound. How many atoms are in a chemists dozen? Well its a good thing that chemists don't need to individually count the atoms because it would take a long time.

A chemists dozen, in order to make sure we understand that it is not 12 or even close to twelve is called a mol. One molof atoms is 609000000000000000000000 atoms. Its a good thing that we don't have to count them either. We don't even have to memorize the number. But it is helpful to think of a mol as a chemists dozen, a convenient count of identical molecules.

If you have a plain salami sandwich; one piece of lettuce, four pieces of salami, and and two slices of bread and you were a chef, you might right a formula for a plain salami sandwich as: B2L1S2? . If you wanted me, your assistant chef, to make up a bakers dozen of these sandwiches when I came to work in the morning you might right me a note.

Louis When you get in please make: 13B2L1S2

Thankyou kindly, The Chef

For these BakersDozen? of sandwiches I would need

- 26 pieces of bread
- 13 pieces if lettuce
- 52 pieces of salami

or

- 2 Bakers dozen bread slices
- 1 Bakers dozen Lettuce leaves
- 4 Bakers dozen salami slices.

Whiting or calcium carbonate has the formula CaCO3?. That is there is one atom of calcium, one atom of carbon and 3 atoms of oxygen in every whiting molecule. So every Chemist's dozen or mol of whiting contains, one mole of calcium one mol of carbon and 3 moles of oxygen.

A mol of calcium weights | =40 grams | 40 grams | |

A mole of carbon weights | =12 grams | 12 grams | |

A mole of oxygen weighs | =16 grams | three of these weights | 48 grams |

Total | 100 grams |

So a mol is just a way to count atoms or molecules. Now a mole of each of the elements weights a different amount. Hydrogen is the lightest element and a mol of it weighs just 1 gram. A mole of carbon weighs about 12 grams per mol. A mol of Oxygen weighs about 16 grams. The gram molecular weigh of calcium is 40. That is a mol of calcium weighs 40 grams. They are just different ways of saying the same thing.

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Page last modified on September 23, 2011, at 11:26 PM