I was looking on the [Wikipedia page](https://en.m.wikipedia.org/wiki/SI_base_unit) for all of the base SI units, and was surprised to see that mole was considered a base unit.
Why is this even a unit? Shouldn’t it be a unit-less quantity? A mole isn’t length, or time, or mass, it’s just a number. Why does it need a unit if it just represents “6×10²³ of something”?
You don’t need units to say “I have 15 pencils,” so why is the mole necessary? It seems like a mole is just a scalar.
In: 10
All SI units are scalars – they’re just convenient values. We say “meter” because saying “the length of the path travelled by light in a vacuum during a time interval of 1/299,792,458 of a second” is long and mostly useless. We could use the Planck length as our “unit” in the same sense, but we’d end up with very large measurements. So instead we picked a useful length more-or-less arbitrarily, called it a meter, and eventually created a very nitpicky science-y value for it.
The mole was picked for the same exact reason – it’s incredibly useful in chemistry for converting between “amount” and “mass,” and using “units” for that calculation is long and unwieldy. It’s not like the SI unit is required to be used in all contexts – nobody’s expecting us to go to the store to get 0.0000000000000000000002 moles of eggs. It’s just defining the unit by something fundamental, so that it can be accurately used in the particular scientific contexts that it’s useful in.
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