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# k16 - Moles and mass 1 mol = 6.022 x 1023 Chem 1A 1 mol of...

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12/1/2008 1 Chem 1A Empirical and molecular formulas Lecture 16 Moles and mass 1 mol = 6.022 x 10 23 Molar mass 1 mol of 1 amu = 1 g 1 mol of beta carotene (C 40 H 56 ) is: 40 x 12.01 + 56 x 1.008 = 536.85 g From moles to mass: Amount (moles) x 1 mol Molar mass = amount (grams) From mass to moles: Amount (grams) x Molar mass 1 mol = amount (moles) Molar Mass: How many moles in a sample How many moles of aspirin in a 50 mg sample? Aspirin (C 9 H 8 O 4 ) 9 mol C = 108.09 g 8 mol H = 8.064 g 4 mol O = 64 00 g unit factor 4 mol O = 64.00 g 1 mol aspirin = 180.16 g 0.050 g x 1 mol 180.16 g = 2.8 x 10 -4 mol Molar Mass: E.g., vitamin C How many oxygen atoms in 5.3 μ g of vitamin C? C 6 H 8 O 6 6 x 12.01 g 8 x 1.008 g 6 x 16.00 g (C) (H) (O) 1 mol = 176.12 g 5.3 x 10 -6 g x 1 mol 176.12 g = 3.0 x 10 -8 mol ascorbic acid 3.0 x 10 -8 x 6.022 x 10 23 = 1.8 x 10 16 molecules 1.8 x 10 16 x 6 = 1.1 x 10 17 oxygen atoms Molar Mass: E.g., glucose C 6 H 12 O 6 What is the molar mass of glucose? 1 mol = 180.156 g Mass of C: Mass of H: Mass of O: 6 mol x 12.01 g/mol 12 mol x 1.008 g/mol 6 mol x 16.00 g/mol = 72.06 g C = 12.096 g H = 96.00 g O 180.16 g Mass percent: definition M t f C mass of C in 1 mol compound X 100% What is the percentage of each element in a compound by mass? Mass percent of C = mass of 1 mol compound This is another way of expressing the relative amounts of different elements in a compound.

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12/1/2008 2 Mass percentages, e.g, sorbital Mass percent = mass of atom in 1 mol compound mass of 1 mol compound X 100% What are the mass percentages of the different atoms in sorbitol? C 6 H 14 O 6 Mass % O: Mass % H: Mass % C: 182.17 g 6 x 12.01 g x 100 % = 39.56 % 182.17 g 14 x 1.008 g x 100 % = 7.75 % 182.17 g 6 x 16.00 g x 100 % = 52.70 % Total = 100.01 % Mass percent, e.g., glucose C 6 H 12 O 6 Mass percent of C = 72.06 g C 180.16 g C 6 H 12 O 6 X 100% = 40.00%
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k16 - Moles and mass 1 mol = 6.022 x 1023 Chem 1A 1 mol of...

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