Dont worry, I also had a lot of problems withat first.
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First things first; pull out your PeriodicTable. Find the atomic weight (probably inthe top left corner.) This Atomic weight isthe weight of 1 mole of atoms of that kind. For instance look at N (Nitrogen), you will seethe atomic mass is 14.00674 grams. So that meansif you had 1 mole of nitrogen atoms, it wouldweight, 14.00674 grams.
So if you have a fraction of a mole, say forinstance, just multiply * 14.00674 grams toobtain the weight, 7.00337 grams. (I used theequation below):
Fraction of a mole * Atomic weight = weightor mass you have
Now we have to get what fraction of a mole youhave. To start, you need know that all a molemeans is you have 6.022 x 1023 atoms ofthat type. So if I tell you I have a mole ofnitrogen, then I have 6.022 x1023nitrogen atoms. That ugly number is calledAvogadro"s Constant, NA. Scientist use NAjust so they don"t have to keep writing that longnumber over and over again.
To get the fraction of a mole you have, takethe number of atoms you have, and divide it by6.022 x 1023. (Use equation below):
Number of atoms you have / 6.022 x1023 = Fraction of a mole
After you do that, plug it into the first aboveequation and that should give you your answer.
1 mole = 6.03 x 1023 particles.One mole of any element has a mass in gramsthat is equal to its atomic number, and hasexactly 6.02 x 1023 atoms - howeverbecause the atoms of each element have differentsizes and weights, then the volume that each oneoccupies is different. Also, some elements aresolids, liquids, or gases at room temperature, sothey will also occupy different volumes.
The trick to working with moles is tounderstand that you are dealing with differentunits, and you have to translate between them.We call this "units factoring" because itinvolves setting up ratios of the units andcancelling... For example: money. The smallestamount of money you can have is a penny. Youcan"t have half a penny. But you can translateevery amount of money into its equivalent numberof pennies. The standard is that 1 dollar = 100pennies. So, 10 dollars = 10 dollars x 100pennies/dollar = 1000 pennies. Similarly, half adollar = 0.5 dollar x 100 pennies/dollar = 50pennies. And, working backwards, if someonegives you 50 pennies and asks you how many dollarsyou have, you can probably do this in your head,but let"s write it out for the sake ofillustrating the point:
50 pennies x 1 dollar/100 pennies = 50/100 =0.5 dollar. It works just like this for doingmole fraction problems.
If one mole of carbon, for example, has a massof 12 grams, then 12 grams of carbon contain(12)(6.03 x 1023 ) atoms. How manyatoms are in 3 grams of carbon? Well... (3grams of carbon) x (1 mole of carbon/12 grams ) =3/12 = 1/4 of a mole of carbon.
Then... ( 1/4 of a mole) x (6.02 x1023 atoms/mole) = approximately 1.5 x1023 atoms. If you have a compoundlike H2O, then:
one mole of water contains 6.02 x1023 MOLECULES of water. But eachmolecule of water contains 2 H and 1 O atom = 3atoms, so there are approximately 1.8 x1024 atoms in a mole of water.
In having trouble with the notion of what a moleis and how to use the concept, you are not alone.Many people have problems understanding what amole is. A mole is a collective term. Just asone says, a bunch of grapes, a pride of lions, orbetter still, a dozen cookies, one could say, a"mole of atoms", or a "mole of molecules". A moleis a collection of Avogadro number of things. Thethings could be atoms or molecules.They couldalso be horses. A mole of horses would be Avogadronumber of horses (a lot actually !). Avogadronumber is 6.023 x 10(23).
A mole of H (hydrogen) atomscontains 6.023 x 10(23) H atoms. A moleof H2molecules contains 6.023 x 10(23)H2 molecules or2 moles of H atoms (since each molecules has 2atoms).
A mole of CaCO3 (calcium carbonate) hasone mole (Avogadro number) of Ca atoms, one moleof C atoms and 3 moles of O atoms.
So what isspecial about the Avogadro number. It isjust asimple multiplicative constant that relates atomicweights to the simpler, more familiar measure ofthe gram(g).
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Look up a periodic table of theelements. Under each element entry, you willusually find the atomic mass. For example,underOxygen, you find the atomic weight is 16.00. Thismeans that 16.00 g of oxygen has Avogadro numberof oxygen atoms. Carbon is 12.01. So a 12.01 gsample of carbon has Avogadro number of carbonatoms. If we take the CaCO3 example, theformula weight is the sum of the atomic masses. Wefind that for CaCO3, the formula weight is:
Ca(40.08) + C (12.01) + 3 O (16.00) = 100.1
100.1 gof CaCO3 is one mole ofCaCO3. We can prepare itby reaction, one mole of CaO weighing 56.08 g, withone mole of CO2 weighing 44.01 g. If wepreferred towork with ounces, instead of g, and wished torelated the atomic weight to ounces, then thevalue that we would chose for the Avogadro numberwould be different.