The mole... guaranteed to blow your mind.
Orders of magnitude, estimation and analogy in Chemistry...
How do you convey to your students the scale of numbers indicated by the mole? One way is to use an analogy
I've often introduced the mole using an analogy and have used many examples over the years. Here's a selection you may want to consider...
Raindrops
We'll change this to cubic kilometres using a conversion factor...
The volume of 1 mole of raindrops will be 24 million cubic kilometres.
The estimated volume of water held by the Arctic Ocean is 18 750 000 cubic kilometres. In other words...
Money
A million is a large number at the human scale, as is a billion (a thousand million). A billionaire is reckoned to be worth over £1 000 000 000.
Elon Musk is considered to have a fortune of $942 billion according to Forbes Magazine (5) (obviously before his Facebook takeover!)
Do you think Mr Musk has a mole worth of cents? (100 cents = $1).
Even though Elon is loaded, he's a bit short in terms of the mole. His $942 billion converts to 94 200 000 000 000 cents. One mole of cents is still 6.4 billion times greater!
On the subject of money, if every person on Earth were given a share of 1 mole of UK pennies, everyone would be a billionaire (Elon would still have more money though).
Balls
Well... marbles.
They vary in size, but I'm going to set the diameter of an average marble to 13 mm (1⁄2 in). If I had a mole of marbles, how far would a single line of marbles, each touching another, stretch?
Would it...
... reach the top of Mt Everest?
... reach out to the moon?
... get as far as the Sun?
... extend to Neptune?
Here's my calculation...
Our moon is 384,400 km away but the end of our mole of marbles would be much much further (20 thousand billion times further).
Cells
The average human, according to recent estimates, is made up of 30 trillion cells. Written out as a number, that’s 30,000,000,000,000 cells - in one average human.
How many humans would there be for one mole of cells?
(Can you think of any assumptions you would need to make?)
That’s 20 billion humans - nearly 3 times the current population of the Earth (3)
Time
The age of the Universe is estimated to be around 13.7 billion years (7). In seconds, this is around...
Seconds or years, this is a very large number but is nowhere near the extent of time for a mole of seconds
A mole of seconds will be a million times greater than the age of the Universe!
I'll leave you to consider the flaws and assumptions in the calculations - it's a great way to engage students in the scientific method, orders of magnitude and estimation.
On the Web
Teaching the mole - The Science Teacher https://thescienceteacher.co.uk/understanding-the-mole/
How big is a mole? (Not the animal, the other one.) - Daniel Dulek for TedTalks
Infographics from the RSC: Introducing moles and Avogadro’s number
References
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