What is avocado constant?

Answer 1

The Avogadro number is a convenient multiplier for dealing with numbers of entities on a molecular scale, since dealing with practical amounts of a substance (say, a few grammes) would usually entail a colossal number of molecules that would be inconvenient to fully write down. Instead, one divides the number of molecules by Avogadro's number and expresses the new value in moles; moles being a shorthand, dimensionless unit for however many multiples of the avogadro number are present. The Avogadro number itself is about 6x10^23; that is, there are 6x10^23 molecules in one mole of a particular substance (it is the same number for one mole of any substance - we are counting numbers of particles; we are not currently concerned with how massive one of these particles might be). As an example, consider a 1kg lump of pure iron. The mass of one molecule of iron is slightly less than 1x10^-25 kg, so dividing by this there there would be 1x10^25 molecules of iron in that 1kg lump. It would be inconvenient to keep on writing down this number in scientific form, and also increase the likelihood of mistakes. Instead, we divide by the Avogadro number (6x10^23) to get about 16.7 - so we say there are 16.7 Moles of iron in one kilogram (there is no need to specify that this is the number of molecules; the unit of moles tells us that we are dealing in the number of particles, ie molecules, already). This is much more convenient to write down, and whereas a misspelling or pen smudge of the word "mole" would not introduce any error, miswriting "x10^25" could produce a drastic mistake. Indeed, it would be rare to find the Atomic Mass of iron given in kg per molecule; most sources would use either kg per mole (kg/mol), or atomic mass units(u). One would assume that the avocado number has the same value as the Avogadro number, since the two are so often mistaken, but presumably in reference to pieces of fruit rather than molecules. Unlike the Avogadro number this is not useful, as 6x10^23 is clearly too many avocados.