Hey guys. I’m struggling to understand the concept of moles, and was hoping someone could explain it a lot easier than in previous posts. I understand that a mole of something means that there is 6.022 x 10\^23 of that something (similar to the idea of 1 dozen = 12 things), but I don’t quite understand when for example 1 mole of Nitrogen is 14g.
If 1 mole of nitrogen means that there is 6.022 x 10\^23 nitrogen atoms, how does 1 mole of nitrogen equal 14g? Is it saying that 6.022 x 10\^23 nitrogen atoms (1 mole of nitrogen) is equal to 14g, since the mass of a nitrogen atom (single nitrogen atom) would be super small, and so we use moles to convert it into a reasonable mass for easier calculations e.g. 14g?
Hope that wasn’t too confusing :S
Thanks everyone! 🙂
In: Chemistry
Atoms are small. Atoms are really very very small indeed. For any useful quantity of a substance, you need a very large number of atoms to do anything useful. When we started out with chemistry, we didn’t have a good way to measure how small or how much mass a single atom had. To get around the problem of dealing with such tiny things, we came up with the idea of a mole.
A mole is simply a specific large number of a thing. You can have a mole of people, or a mole of cars. Even a [mole of moles](https://what-if.xkcd.com/4/). By careful study of chemistry, we could work out how different elements interact, and so work out how much a mole of each type of element weighs, and other properties about them. In time, as our ability to measure things got better, we became able to actually put a specific numerical value to what a mole is, and got 6.022×10^23 (Avogardro’s number).
Basically a mole is “enough atoms that I have a useful amount of the stuff”.
Watch this https://youtu.be/Z_TjGRPPR9Q?si=HRHz9qyHyRQ8FStm Steve mould explains it in a very easy and intuitive way IMO
This is exactly what it means.
Moles are just a way to not have absurdly high numbers during calculations
>since the mass of a nitrogen atom (single nitrogen atom) would be super small, and so we use moles to convert it into a reasonable mass for easier calculations e.g. 14g?
Kind of the other way around. We use mass as an approximation for 1 mole of a particular element, because counting 6.022 × 10^(23) would be incredibly time consuming and very, *very* expensive.
Think of it like this. Imagine you sell bulk hardware wholesale to hardware retailers. A customer has placed an order for two hundred fifty thousand (250k) M10 hex nuts. They want the nuts delivered in boxes of 1,000.
As the seller, you have to decide how you’ll go about this. Counting out 250 boxes of 1,000 nuts per box would take a ridiculous amount of labor if you had people do it. You could invest in expensive machinery that automatically counts the nuts, but there is a much cheaper way.
You count out 1,000 nuts one time, then you weigh them. Since all the nuts weigh pretty much the same, 1,000 nuts should weigh the same every time.
So you count out 1,000 nuts, weigh them, and you find that the weight is 11.5 kg. Now you can simply package up the nuts at 11.5 kg per box and you know that you’ll be pretty darn close to 250k nuts when you’re done.
When working with moles of atoms, we do the same thing. We know that 6.022 × 10^(23) nitrogen atoms weighs around 14g, so if we need 1 mole of nitrogen, we just weigh out 14g and call it close enough.
But why would we need a mole of something instead of simply saying we need 14g of something? Sometimes working by quantity is easier to understand than working by mass. For example, if you want to make the molecule H2O, you need two hydrogen and one oxygen. You know the *quantity* of each element required, not the mass. You could calculate the mass, but it’s easier to just work with the quantities directly until you’re done with the math, then convert to mass at the end. Just like when someone orders 250k M10 nuts instead of ordering 2,875 kg of M10 nuts. Sometimes we need to work in quantities, not mass. That’s where the mole is handy.
To add some background here, an interesting question is why and how we know the number in detail.
Imagine you do chemistry without knowing Avogadros number. You can figure out the relative weights of different atoms/molecules, and calculate with that, and do that for the entire periodic table. Perhaps define the lightest one as 1 unit of atomic world mass.
But all your recipes will be in one measure of this, two measures of that. How can you find out how many of the tiny things there is in one gram?
There are ofc strategies, Google the early methods, it is an interesting read. But a ton of chemistry was done without knowing avogadros number.
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Using your example of a dozen: a dozen chicken eggs have a weight in grams. A dozen quail eggs also have a weight in grams. They are different weights, but we can agree that there are a dozen of each thing.
A dozen atoms is not really enough to weigh in those units, so instead we use a much larger type of group called a mole. A mole of chicken eggs would have a different weight than a mole of quail eggs. A mole of nitrogen is a particular number of nitrogen atoms, and they also have a unique weight.
Atoms are billiard balls. To make water, you need two balls of hydrogen and a ball of oxygen (we’ll ignore diatomic molecules for convenience). But an oxygen ball (atom) is quite a lot heavier than a hydrogen ball (atom). So to get the 2:1 ratio, we need 2 moles of hydrogen atoms and 1 mole of oxygen atoms.
Since we’re not going to faff around making a single molecule of water, we’ll arbitrarily make 6.022 x 10^23 atoms of water. That means we need 2 x 1 = 2 g of hydrogen atoms, and 16 g of oxygen atoms.
The 6.022 x 10^23 number is just a weird number that makes the atomic weights come to nice values in grams. If we were working in pounds (god forbid) instead of grams we’d have a different arbitrary number but the principle remains.
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If every watermellon weighed exactly 1 pound you could put an unknown number on a scale and count them that way. If you have 1000 pounds that means you have 1000 watermelons.
Apples are lighter than watermellons, so you might want to ask “well, if I had 1000 apples how different would that weight be” and you could figure that out. If you know every apple weighs half as much as a watermellon you would know that 1000 apples is 500 pounds or that you need 2000 apples to weigh the same as 1000 watermellons.
It’s basically that. but counting atoms is really hard so instead of a good round number like 1000, it’s a big silly number that happens to be how many carbon-12 atoms are in an ounce. But you would use it the same way as 1 pound watermellons and knowing 1000 must weigh 1000 pounds. But with a bigger crazier number to talk about something way too small. It’s for figuring out how many bananas you’d need on a truck to weigh the same as watermellons or how much a truck would weigh if you replaced every watermellon with a babana. Once you know the weight of one banana you could answer that.
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