A Mole of Crows
Today is Mole Day, at least in the United States.
Chemists celebrate Mole Day on October 23rd (10/23), from 6:02 AM to 6:02 PM
The mole is a counting number, like a dozen.
One mole (also known as Avogadro's number)= 6.02214 x 10²³
Chemists use the mole to count very large numbers of very small things, like atoms and molecules.
But honestly, most people use the mole in a mechanical way, plugging it in to chemistry calculations and never really thinking about how truly massive that number is.
We're all familiar with a dozen. We have a good feel for that number, based on a lifetime of buying a dozen eggs, storing a carton in the fridge, using half a dozen eggs to make a flan.
But a mole? No way.
We actually seem to go out of our way to avoid big numbers. We make up vague names for groups of things. Like a murder of crows.
Just how many crows are in a murder, anyway?
My friend Charity Hume asked me this today. We looked it up.
It's three. You need at least three crows to make a murder. The name comes from an English folktale about three crows conspiring to eat a dead knight.
Why is the mole useful?
A mole of water is 6.02214 x 10²³ molecules of water. That's not very big at all, if you're talking mass or volume. That's why chemists use the mole, because if they used a small grouping number, like a dozen, it would be much too hard (impossible, really) to measure that on a scale or with a graduated cylinder.
1 mole of water = 2 moles of hydrogen atoms (2x1g) + 1 mole of oxygen atoms (1x16g) = 18 grams. (We show you how to calculate Molar Mass in this video)
There's a useful conversion for water: 1 mL = 1g. So if you measure 18 grams of water, that's about 18 mL.
That's about one swallow of water.
Does that help you understand how massive the number of molecules of water that is? I don't think so. Who has any understanding of the number of molecules in a swallow of water? We need something we can touch with our hands and see with our naked eye, like that dozen eggs.
How can we picture a mole?
Crows.
I propose we examine a Mole of Crows.
From beak to tail, the average American Crow measures 45 cm in length.
If we lined up a Mole of Crows on a highway, how long would that road be?
45 cm x 6.02214 x 10²³ = 270.9963 x 10²³ cm
Let's convert to km.
270.9963 x 10²³ cm x 1 km/ 100,000 cm = 2.709963 x 10²⁰ km or 270,996,300,000,000,000,000 km if it helps to see all those zeros at the end.
That road would wrap around the Earth about 6,762,228,321,896,444 times (Earth circumference = 40,075 km).
It's only about 383,000 km to the Moon. (3.83 x 10⁵ km) Too small.
It's about 1.5 x 10⁸ km to the Sun.
So you could line up a mole of crows to the Sun and back and still have a whole bunch left over.
I give up, this number is still unimaginably large.
We have a video to help you understand the mole.
Happy Mole Day, everyone.
KHH
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