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
Yes, that’s what that means. If you measured the mass of 6.022 x 10^23 nitrogen atoms, it’d come out to (roughly) 14 grams.
Mol, without the e, is a named quantity, like “dozen”.
When you say you have a mol of carbon atoms, that’s like saying you have a dozen carbon atoms. Well, the number is a lot more than 12, but it works the same way. As you say, it makes the masses easier to talk about because the mass of a dozen nitrogen atoms would still be very, very small.
Normal units of measures don’t work on all scenarios. You don’t measure human height in miles. Instead, you’d use feet and inches.
Similarly, we won’t measure distance in astronomy in miles. Instead, we introduce larger units like light year, parsecond, etc.
In chemistry, we encounter large numbers when we’re measuring number of atoms or molecules in a sample. Rather than use million billion trillions, etc, we went ahead and defined a large number called the mole. It’s simply equal to 6.023×10^23.
we know the mass of electrons/protons/neutrons
we know how many of each (on average) are in a Nitrogen atom
We know there are 6.022×10^23 to a mole.
the rest is just multiplication. averageMass*1 Mole=mass of 1 mole of the thing
Yep, you have it right.
The molar mass is defined as the mass of one mole of your stuff.
It’s directly linked to the number of nucleons, because the original definition was “as much atoms as there are in 12g of Carbon 12”, which is for all intent is equivalent to 1g per nucleon.
Nitrogen has an atomic weight of 14 (7 protons, 7 neutrons) in it’s most common isotope.
6.022 x 10^23 nitrogen atoms weighs 14 grams.
If you had some hydrogen, with an atomic weight of 1 (1 proton no neutrons), 6.022 x 10^23 hydrogen atoms would weigh 1 gram.
Why do you need to know this?
Well, let’s imagine you have 1kg of hydrogen you want to burn with oxygen. How much oxygen do you need? Well you need 2 moles of hydrogen for every mole of oxygen (because you need two hydrogen atoms for every atom of oxygen).
You have 1000/1=1000 moles of hydrogen, so you need 500 moles of oxygen. Oxygen has an atomic weight of 16 so you need 500×16=8000 grams, or 8kg.
But what if we wanted to burn an isotope of hydrogen; tritium. 1 proton, two neutrons, atomic weight 3.
You have 1000/3=333.3 moles of tritium, so you need 166.7 moles of oxygen. 166.7×16=2666.4, or 2.666kg.
1 mole is the amount of amu (atomic mass units) in a gram.
Nitrogen has a mass number of 14.0067u, so one mole of nitrogen atoms has a mass of exactly 14.0067g
Nitrogen is a diatomic molecule, so we really find it as N2, so a mole of N2 has a mass of 28.0134g
You’re right that we use it because a single atom or molecule is too small to work with, but for practical experiments, not for calculations. Or math works at all scales, but we can’t physically work at such small scales.
>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?
Yes.
The number at the bottom of a element period box is the atomic mass.
1 mol of element = that elements atomic mass.
1 mol of compound = sum of the atomic masses of its elements.
The reason we use moles is because atoms stay the same when they form molecules, but they form in whole number ratios. So take water, H2O. So two hydrogen atoms (with an average mass around 1 atomic mass unit each) and one oxygen atom (with an average mass around 16 atomic mass units). So the oxygen is heavier than the hydrogen, but regardless one atom will bond with two whole atoms. So when we scale it up to a reasonable size, there are over trillions of atoms involved, but the ratio is still 1:2. So we use 6^e23 as a constant, and say that amount of atoms of any element is now represented as 1. Now they’re sorta in gram ranges, that’s it. So one mole of something, is also 6^e23 individual atoms of that thing. To make water, you need 2 moles of hydrogen, for every 1 mole of oxygen, to not have a remainder. Its just easier to write and think about than 6^e23 : 2(6^e23).
Because the atoms are not all the same weight, we need more constants, the average atomic masses of atoms, to convert the unit moles to mass in grams.
Short story, mole is just a unit. Like a dozen. You can count anything in moles. 1 apple, 10 apples, a dozen apples, a mole of apples. If you wanted to know what an apple or mass of apples weighed, you just need the average mass of an apple. 1 apple time the mass of one apple, 10 apples times the mass of one apple, a dozen apples times the mass of one apple, a mole of apples times the mass of one apple.
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