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# Don't understand moles at all. watch

1. I've changed schools, and now discovered that my old chemistry teacher was terrible. I've really got to work out moles, because I'm doing AS chemistry, so they're quite important in that!

Could anyone explain, or give a link that explains the basics as simply as possible of moles/empirical formulae etc?

Thanks so much!

Joe

P.S. +rep to all that help
2. 1 mole = 6.02214179 * 10^23

It's just a number. You should be able to work it all out from there.
3. www.chemguide.co.uk is incredible

but basically... a mole is just a number of particles (6 x 10^23). molar mass is the mass of 6 x 10^23 particles of something, for example:
the mass of 6x10^23 atoms of oxygen is 16
the mass of 6x10^23 atoms of carbon is 12

and then in equations, it shows you the proportions of each substance in a reaction. so...
in C + O2 --> CO2
1 atom of carbon reacts with 1 molecule of oxygen to make 1 molecule of carbon dioxide
1 mole of carbon reacts with 1 mole of oxygen to make 1 mole of carbon dioxide

does that make any more sense?
4. Moles is basicly the amount of substance.

1 Mole is the number of carbon atoms in 12 grams (2.3 x 10^23 or somthing)

one mole 12^C has a mass of exactly 12 g

So 1 mole of Cl (RAM - 35.5) has exactly the same number of carbon atoms, cept each Cl atom wieghs more than a carbon (Clorine has a greater number of neutrons and protons than Carbon), so one mole of Cl is 35.5grams

You can also have moles of sub atomic particals, like electrons.

Why is this useful instead of weight? Because each elements wieghs diffrent, and SO DOES EACH ELEMENTS ISOTOPE.

BIG FAT EXAPMLE;
NaCl (Sodium Cloride)

One Mole of Na reacts with One mole of CL (But both weight diffrent)

Ask me if you want to know more
5. Moles = Mass/Mr
6. Moles have a unit of Mol.
So for example 0.5 Mol of a Substance.

In AS Chemistry there are a few formulas, No. of Moles = Mass/ Relative Mass (The bigger number on the periodic table)
No. of Moles = Concentration in Mol dm^-3 x Volume in Decimeters.

If you get a volume in Cm^3 you have to convert it.
I do it like this, If there are 15Cm^3 of water, there are 15x10^-3 Dm^3. (Basically stick x10^-3 on the end of the number.

Hope this helps.
7. Moles:

Definition - 1 mole is the amount of substance which contains the same number of particles (atoms, ions, molecules etc) as exactly 12 grams of carbon 12.

The number of atoms of carbon 12 is 6.022x10^23 (Avogadro's constant) - you may not require 3dp's of accuracy in the work you're doing, check with your teacher.

The relative atomic mass of an element in grams contains 6.022x10^23 atoms

The relative molecular mass of a compound in grams contains 6.022x10^23 molecules

Examples:

Relative atomic mass of Sodium = 23, there for 23 grams of sodium = 1 mole of sodium

Relative molecular mass of Caron dioxide = 44, there for 44 grams of Carbon dioxide = 1 mole.

Calculations:

moles = mass/relative molecular mass

example:

You have 66grams of CO2

moles of CO2 = 66/44
= 1.5 moles
8. avergado number is something like 6.03x10^23 blah blah

basically 1 mole the molecular mass of one substance

so 16g of oxygen is 1 mole

32g is 2moles
8g = 0.5 moles

breif but im in year ten gcse :\
9. The number of moles = mass in g / mass of 1 mole in g

A question maybe, How many moles of atoms are there in 64.2 g of sulfur, S?

To work this out, first you have to find the mass of 1 mole in g. If you look on a periodic table then the mass number should tell you the mas of 1 mole of that element. In this case the number would be 32.1

so to work out the amount of moles it would be 64.2/32.1 = 2.00 moles

hope this helps
10. everyone knows what a dozen is (i.e. 12) so my chemistry teacher used to say that a mole is just a number and you could go into a sweet shop and ask for a mole of sweets if you wanted to. the number a mole refers to in this case just happens to be the same number as molecules as you'd find in 12 grams of carbon and is used cos it has all sorts of convenient properties that helps with calculations. thats why things in chemistry are measured in moles and so when you say 0.5 moles of sodium, you're really saying a certain number of sodium atoms.
11. (Original post by M1F2R3)
Moles = Mass/Mr
lies!
moles = conc x volume!!

OP. It isnt really a hard concept. Its just a standardised measure of quantity compared to carbon12.

You don't really need to know the specific details of what it is for A level chem, only how to calculate, and use it. Its kind of like questioning what a kilo gram is.

Moles = Conc x Volume,
Moles = Mass / Mr

/it.
12. (Original post by punkrockisfreedom)
everyone knows what a dozen is (i.e. 12) so my chemistry teacher used to say that a mole is just a number and you could go into a sweet shop and ask for a mole of sweets if you wanted to.
I always found that helpful... you'd need really big pockets though.
13. mass (g) / Mr (periodic table) = moles

moles is a measure of the amount of substance

1mole of co2 is the same as 1mole of h2o (if 1 to 1 ratio)

6.022 x10 to the 23 is no. of particles in 1 mol of substance
14. Everyone knows what a dozen is (i.e. 12) so my chemistry teacher used to say that a mole is just a number and you could go into a sweet shop and ask for a mole of sweets if you wanted to.
.
(Original post by Joinedup)
I always found that helpful... you'd need really big pockets though.

If they're fruit salads at 2 per 1p, you've have to have 3.01 x 1021 GB pounds to pay for them

= 3,010,000,000,000,000,000,000 GBP

.. so you'd need a pretty big wallet as well.

Gold is currently about 26.60 GBP per gram, so if you chose to pay in gold you would need:

113,200,000,000,000,000,000 g = 113,200,000,000,000 Tonnes of pure gold..

.. but as only about 165,000 tonnes of gold have been mined since the existence of man you'd probably have to wait a while to collect it.

All in all I'd forget the sweets...
15. (Original post by charco)
If they're fruit salads at 2 per 1p, you've have to have 3.01 x 1021 GB pounds to pay for them

= 3,010,000,000,000,000,000,000 GBP

.. so you'd need a pretty big wallet as well.

Gold is currently about 26.60 GBP per gram, so if you chose to pay in gold you would need:

113,200,000,000,000,000,000 g = 113,200,000,000,000 Tonnes of pure gold..

.. but as only about 165,000 tonnes of gold have been mined since the existence of man you'd probably have to wait a while to collect it.

All in all I'd forget the sweets...
That would be 4.38 x 1011-ish fruit salads for every man, woman and child on this earth. That is, I think it's fair to say, quite a few.
16. (Original post by cpchem)
That would be 4.38 x 1011-ish fruit salads for every man, woman and child on this earth. That is, I think it's fair to say, quite a few.
If the average thickness of a fruit salad (or Black Jack) is about 0.8 mm, then everyone on earth would be able to have a pile of them 350,400 kilometers high.

Which is nearly enough to reach the moon (average 384,000 Km)

.. you'd have to borrow some more from a friend or neighbour if you wanted to do that...
17. don't worry. i got throught the whole of A-level chem without really knowing what i was doing and still managed to do alright. Ask for extra help 'cos i'm sure your teacher will help

And a mole is just a number of atoms or molecules.
this triangle thingy helped me out with my equations

18. (Original post by charco)
If the average thickness of a fruit salad (or Black Jack) is about 0.8 mm, then everyone on earth would be able to have a pile of them 350,400 kilometers high.

Which is nearly enough to reach the moon (average 384,000 Km)

.. you'd have to borrow some more from a friend or neighbour if you wanted to do that...
I think serious consideration should be given to the expansion in dental school places necessary if everyone had such a formidable stack of confectionery.

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