You’re probably teaching the mole and Avogadro’s number all wrong

August 29, 2022
Categories: AP | Avogadro | Moles

Honestly, the likelihood is that you’re doing just that! Wasting precious time on a concept that the kids will mostly never be able to understand, and moreover one that’s of virtually no practical use to them.

Huge amounts of time and handwringing are spent on attempting to get chemistry students to grasp the concept of the mole, or perhaps more accurately, to grasp the concept of Avogadro’s number. One of the things that chemistry teachers often say at the beginning of this topic is that, “Avogadro’s number is so large that it’s impossible for you to even imagine a number that big”. And you know what? They’re right, it IS IMPOSSIBLE! However, they then start to weave intricate and elaborate analogies involving all of the grains of sand in the world, all of the stars in the universe, or all of the blades of grass on the planet, and none of these things makes any sense or means a damn thing to anyone either! The odd thing is that we’ve already identified the fact that it’s just not possible to grasp the reality of this number. So what’s the solution?

The solution is that you don’t need a solution. It’s sufficient to say that atoms are so tiny that you can’t get your head around how tiny they are, and that because of they’re so tiny, that in order to get a reasonable mass of those atoms you need so many of them that you also cannot get your head around how many you actually need.

Here’s the thing. NONE of the the things that students are asked to do with moles in any context in any test, any quiz or any exam, actually revolves around an understanding of the conceptual idea behind the vast magnitude of Avogadro’s number. The mole questions only revolve around calculation moles via mass/Molar Mass, and the conversion factor that 1 mole of anything has 6.02 x 1023 particles in it. Referring to the equally opaque idea of “counting by weighing”, or by using totally abstract analogies in an attempt to describe a totally abstract thing, are each pointless in terms of any practical ability to answer the chemistry questions these kids will come across. The time is wasted, the struggle is in vain. The mole can be taught mechanically, with no need for a deep, conceptual understanding, and more importantly, any attempt to acquire that deeper understanding is in most cases, actually impeding students.

There is no distinction made on exams between kids that “get” the conceptual idea, and kids that don’t, as long as they can calculate the number of moles present, and apply a conversion factor to that number in order to get the number of particles. The intellectual wrestle with grains of sand is about as fruitful an exercise as well, wrestling with grains of sand. I suggest that you stop attempting it.

1 Comment

  1. Dan Reid

    Weighing by mass is a giant time suck!

    Reply

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