23 October 23 (10-23)

 Every year on 23 October, chemists around the world celebrate Mole Day. It's an amusing association of 10-23 with the exponential part of Avogadro's Number, 6.022x10**23. This number counts the number of items in one mole of a substance. The mole is the most useful measurement unit for comparing different substances. Eighteen milliliters of water (slightly more than 3 and a half teaspoons) contains the same number of molecules of water as there are atoms in 56 grams of iron (two big nails or 56 paper clips). My tie shows many boxes from the periodic table, where the atomic weight (at the bottom of each box) reports the mass of one mole of that element. In my ethics class on Mole Day, I showed examples of moles of water, alcohol, iron, carbon, aluminum, table salt and sugar.