The Mole - We can also calculate the mass of a mole of...

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Once we know the mass of a sample we can use the mass of the atoms or molecules in the sample to determine  how many atoms or molecules are in the sample. How many  12 C  atoms are in a 1.00 kg block of pure  12 C  isotope? Obviously atoms and molecules are not a convenient unit of measure when we're working with macroscopic  ( i.e. , human size) objects. For this reason chemist define a new unit of measure called  the mole . 1 mole is defined as the number of carbon atoms in exactly 12.000000 grams of pure  12 C . From our definition of the atomic mass unit we get 1 mole = 6.0220943 x 10 23  chemical units The number 6.0220943 x 10 23  is called  Avagadro's number . How many moles are in a 1.00 kg block of pure  12 C  isotope? Of course we know a 1.00 kg block of naturally occuring carbon will contain a mixture of  12 C 13 C , and even  some  14 C  isotopes. So the number of moles of carbon atoms in a 1.00 kg block of naturally occuring carbon is
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Unformatted text preview: We can also calculate the mass of a mole of molecules. What is the mass of a mole of methane ( CH 4 ) molecules? mass of 1 mole of C is 12.011 g mass of 4 moles of H is 4 X 1.00g mass of 1 mole of CH 4 is 16.043 g In other words the molecular weight of CH 4 is 16.043g. Molecular weight = the mass in grams of 1 mole of a molecule. For ionic compounds, which do not exist as individual molecules we use the term Formula weight Formula weight = The mass in grams of 1 mole of the chemical formula. What is the formula weight of CaCO 3 ? mass of 1 mole of Ca is 40.08 g mass of 1 mole of C is 12.011 g mass of 3 moles of O is 3 X 15.999 g Formula weight of CaCO 3 is 100.09 g Let's look at another example. How many hydrogen atoms are there in 2.50 g of NH 3 ?...
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The Mole - We can also calculate the mass of a mole of...

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