The Student Room Group

This discussion is no longer active so you won't be able to reply.Check out other Related discussions

I don't understand the mole

It's getting quite ridiculous i understand 1 mol = 6.02 * 10-23 molecules and I know the generic equations for working out certain things

But i want an understand of what i'm doing not just using generic equations that I don't understand therefore i'm taking a punt as to whether the answer is correct or not

I've looked at past papers and I can still get a good grade without knowing the mole too well but my biggest fear is that come january the paper is full of questions relating to the mole

And if I do survive January then there's the question of June 2013 and A2 2014

I've got a grasp of most things in chemistry but with the mol it's just not happening
Reply 1
so you want to know what the actual mole number is then, where it came about etc?
Reply 2
A mole is basically the amount of atoms,ions, formal units there are in a substance.

It's just a unit.
[video="youtube;XrkdZ4SGrDc"]http://www.youtube.com/watch?v=XrkdZ4SGrDc[/video]
Reply 4
Original post by diggy
It's getting quite ridiculous i understand 1 mol = 6.02 * 10-23 molecules and I know the generic equations for working out certain things

But i want an understand of what i'm doing not just using generic equations that I don't understand therefore i'm taking a punt as to whether the answer is correct or not

I've looked at past papers and I can still get a good grade without knowing the mole too well but my biggest fear is that come january the paper is full of questions relating to the mole

And if I do survive January then there's the question of June 2013 and A2 2014

I've got a grasp of most things in chemistry but with the mol it's just not happening


You have stated Avagadro's constant, which is 6.023 x 10^23 atoms.

A definition of a mole for any given substance is the amount of atoms in the subtsance relative to 12g of carbon (which is 1 mole of carbon which has 6,023 x 10^23 atoms).

An example is sulfur, we can say that 1 mole of sulfur (32g) has the same amount of atoms (6.023 x 10^23) when compared/relative to 12g of carbon-12 (Which is 6.023x 10^23 atoms).
1 mole of ANY substance contains the Avogadro constant number of particles. This is 600000000000000000000000 particles, approximately. (lots of particles)
(edited 11 years ago)
Reply 6
I might just skip the Mole my exam is in January I think I'll be fine

Posted from TSR Mobile
Reply 7
Original post by CoolRunner
You have stated Avagadro's constant, which is 6.023 x 10^23 atoms.

A definition of a mole for any given substance is the amount of atoms in the subtsance relative to 12g of carbon (which is 1 mole of carbon which has 6,023 x 10^23 atoms).

An example is sulfur, we can say that 1 mole of sulfur (32g) has the same amount of atoms (6.023 x 10^23) when compared/relative to 12g of carbon-12 (Which is 6.023x 10^23 atoms).


Don't make the OP's confusion worse with dry scientific formalisms. I'm sure he has already read that in a book and still not understood it anyway.

OP, a good way to understand moles is

we know that

Hydrogen gas + Oxygen gas -> Water gas (steam)

and from experiment we also know that 2 litres of Hydrogen gas plus 1 litre of Oxygen gas gives 2 litres of Water (steam) or in other words,

2 volumes of H2 + 1 volume of O2 -> 2 volumes of H2O (steam)

Now if molecules are really tiny then most of the volume in a container is just empty space formed by the molecules bouncing around. This means that the volume of a gas depends only on the number of gas molecules and not on the type of molecule. From this reasoning we get the rule that "Equal volumes of any two gases contain an equal number of molecules". So we can now say that

2 molecules of H2 + 1 molecule of O2 -> 2 molecules of H2O

So if we have 200 hydrogen molecules plus 100 oxygen molecules we get 200 water molecules. Unfortunately there are billions of molecules in even a gram of hydrogen so to make the numbers more manageable we group them in batches of 6.022x10^23 molecules and call it a mole.
Say you had 6g of hydrogen and 6g of oxygen. The hydrogen atom is lighter than oxygen so you will have more hydrogen atoms than you do oxygen even though there is 6g of each.

Now your told that you must add 6g of hydrogen to the 6g of oxygen to make OH groups.(bad example) You will use up all the oxygen but have some hydrogen left over as there are more atoms.

thus we use the mole. This means we can use the exact amount of hydrogen atoms needed to react with the oxygen.

As you know 1 mole is equal to 6.023x10^23. So if we have 1 mole of oxygen and 1 mole of hydrogen we will have equal amounts of each type of atom due to the mole not being independent on their masses. This will then show you that 1 mole of hydrogen will be lighter than 1 mole of oxygen.

i hope that explains it a little. :smile:
i know my example is a bad one but you get the idea :smile:
This is my knowledge on the topic, so if I have said anything wrong please correct me :smile:
Reply 9
ill give you guys an example

an 0.11 g sample of pure barium was added to 100cm3 water

Ba(s) + 2h2O(l) ----- Ba(OH)2 + H2

Calculate the volume of hydrogen produced at room temp and pressure


the bigger question is will i be able to get good grades in chemistry without fully understanding the mole
Original post by diggy
ill give you guys an example

an 0.11 g sample of pure barium was added to 100cm3 water

Ba(s) + 2h2O(l) ----- Ba(OH)2 + H2

Calculate the volume of hydrogen produced at room temp and pressure


the bigger question is will i be able to get good grades in chemistry without fully understanding the mole


Im an A2 student and I did good at As chemistry. It took me a while to grasp the idea but by June I had grasped it.
in WJEC Chemistry you only realy get define it and a few calculation questions at As level and then the calculations get harder at A2 so a basic understanding would be beneficial. However the questions asked could be a little different for each exam board.
if you started chemistry in September you will probably get it more easily as the year goes on as you study more detailed topics. :smile:

dont worry about it. One day it will just click and you'll be like how did I not understand it. :smile:
Reply 11
Original post by CoolRunner
Talking about confusing...:rolleyes:


If you found that confusing then chemistry is not for you.
Original post by S.R
If you found that confusing then chemistry is not for you.


I can't believe you missed the fact that my previous reply was obviously a rhetorical question :rolleyes:. Your ignorance astounds me! :tongue:
It's basically a conversion factor between number of atoms or molecules and grams for a given atom or molecule. So for example 32g of O2 is 6.02x10^23 atoms or 1 mole as the Mr of O2 is 32.
Original post by Helloworld_95
It's basically a conversion factor between number of atoms or molecules and grams for a given atom or molecule. So for example 32g of O2 is 6.02x10^23 atoms or 1 mole as the Mr of O2 is 32.

I may be wrong, I am usually wrong but I think you mean molecules. As each O2 molecule has two atoms :smile:
(edited 11 years ago)
Original post by Lizard cream
I may be wrong, I am usually wrong but I think you mean molecules. As each O2 molecule has two atoms :smile:


Correct, a really stupid mistake on my part.
stop wasting people times, gtfo
Original post by Lizard cream
Im an A2 student and I did good at As chemistry. It took me a while to grasp the idea but by June I had grasped it.
in WJEC Chemistry you only realy get define it and a few calculation questions at As level and then the calculations get harder at A2 so a basic understanding would be beneficial. However the questions asked could be a little different for each exam board.
if you started chemistry in September you will probably get it more easily as the year goes on as you study more detailed topics. :smile:

dont worry about it. One day it will just click and you'll be like how did I not understand it. :smile:

didn't really answer the question at all
Original post by S.R
If you found that confusing then chemistry is not for you.


way to discourage people from attempting to understand "cool runner"...

Latest