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Chapter 3a as handout

Chapter 3a as handout - Mass Relationships in Chemical...

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1 Mass Relationships in Chemical Reactions Chapter 3 How many grams does a hydrogen atom weigh? 3.1 1.673532579731 × 10 -24 g or 1.673532579731 × 10 -27 kg (SI) A more convenient way to express the mass of an atom is using atomic mass units (very small!). John Dalton originally set the mass of 1 H to 1 amu. (On the current scale 1 H = 1.008 amu) By definition: 1 atom 12 C “weighs” 12 amu On this scale: 1 H = 1.008 amu 7 Li = 7.016 amu 16 O = 16.00 amu 23 Na = 22.99 amu Atomic mass is the mass of an atom in atomic mass units (amu) where: 1 amu = 1.66053886 × 10 -27 kg 3.1

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2 Natural lithium is: 7.42% 6 Li (6.015 amu) 92.58% 7 Li (7.016 amu) 7.42 x 6.015 + 92.58 x 7.016 100 = 6.941 amu 3.1 Average atomic mass of lithium: Average atomic mass (6.941 amu) The mole (mol) is the amount of a substance that contains as many atoms or molecules as there are atoms in exactly 12.00 grams of 12 C 3.2 1 mol = N A = 6.0221367 x 10 23 Avogadro’s number ( N A )
3 Molar mass is the mass of 1 mole of in grams eggs shoes atoms 1 12 C atom = 12.00 amu 1 mole 12 C atoms = 6.022 x 10 23 atoms = 12.00 g 1 mole 7 Li atoms = 7.016 g 1 mole lithium atoms = 6.941 g 1 amu = 1 g/mol atomic mass (amu) = molar mass (grams) 3.2

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Chapter 3a as handout - Mass Relationships in Chemical...

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