Moles and Mass
How do we know how many molecues or atoms are there in something? Obviously we can't count them. That is why we use the weighing principle. If 1 bar of chocolate weighs 5 grams, and I have a box of chocolate that weighs 25 grams, how many chocolate bars do I have inside? Well that must be (25 bars/5 grams per bar) which means 5 bars.
The same logic can be applied to chemistry. You must however learn this concept first: molar mass.
Molar mass is equivalent to how heavy one chocolate bar weigh - but in terms of elements.
What about the mass?
Firstly, elements and compounds do matter now. You now need to know their molar masses (gmol). The molar mass can be found in the Periodic Table, right under the element...it can be a decimal. We usually round it to the nearest whole number though.
That number, the molar mass of the element, represents the mass, in grams, of one mole of that particular substance.
Thus, 1 mole of
Carbon = 12g
Oxygen = O2 = 2*16 = 32g
Cobalt = 59g
Krypton = 84g
Armed with this, you can now calculate the mass of a particular mole(s) of anything!
For example:
Mass of 6 moles of water:
1 mole of water weighs: 2*(2*1)+16=18
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H2 O
6 moles: 6*18=108g
Bingo!
How about finding the number of molecues in 36 grams of water?
1) Find how many moles are there in 35 grams of water:
1 mole of water weighs 18 grams.
36/18=2 mol
2) Convert moles to molecues:
2*6.02*10^23=1.204^24 molecues
And that's how moles work!
