Moles - The bag of rice analogy

A way to get your head around moles 

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Moles ­ The bag of rice analogy
Think of moles as the number of rice in a bag of rice
n (number of moles) = Mass (g) divided by Mr (Relative molecular
mass)
So n = the number of rice
Mass = the total mass of the bag in grams
Mr = the mass of an individual grain of rice
The grains of rice represent molecules of a substance
Does it not make sense that if you divide the total mass of a bag of rice
by the mass of each grain of rice you get the number of rice?
n = m/Mr
If you multiply the number of rice (moles (n)) by the mass of each grain
of rice (Mr) you get the total mass of the bag
n x Mr = m
And finally if you divide the mass of the whole bag by the number of
grains of rice you get the weight of each grain?
m/n = Mr
Just apply this to questions like: How many moles of Oxygen (O2)
are there in 32g?
So 1 oxygen molecule is O2; the Ar (relative atomic mass) of oxygen is
16.0. As there are 2 atoms of oxygen you multiply 16 by 2 giving 32 Mr.
The mass = 32g so applying n = m/Mr gives n = 32/32 so n=1 there is
one mole of O2 in 32g
If there is anything you don't understand or would like further detail feel
free to message me through the website! Or check out the chemistry
study group and see if anyone else knows or can explain it better!
REMEMBER this is a way to think about moles NOT an answer to a
question, only use scientific terms in your exam. This is ONLY a way to
get your head around the concept. Although the equations can of course
be used in the exam.

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