ch3notes - Chapter 3 Stoichiometry: Chemical Calculations...

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©2010 Donald L. Siegel All Rights Reserved Chapter 3 Chapter 3 Stoichiometry: Chemical Calculations
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©2010 Donald L. Siegel All Rights Reserved The mole The mole W Individual atoms are in general too tiny to work with W Need a larger unit We buy eggs by the dozen Paper by the ream (about 500 sheets) Factories use the “hundred-count” Chemistry uses the mole W One mole is the number of things that is the same as the number of atoms in exactly 12g of 12 C
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©2010 Donald L. Siegel All Rights Reserved More on the mole More on the mole W If we know the relative masses of the atoms, then we know the mass of 1 mole of those atoms If one product weighs a pound, and another weighs 2 lbs, then 2000 of them weigh 1 ton and 2 tons, respectively It works the same for atoms. One mole of 12 C weighs 12g, one mole of Cu weighs 63.5g W As it happens, one mole is 6.022×10 23 things
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©2010 Donald L. Siegel All Rights Reserved Molar Mass Molar Mass W also called molar weight W Molar mass of an element is the mass of one mole of the element W Molar mass of a molecular compound is the mass of one mole of molecules of that compound W Molar mass of an ionic compound is the mass of one mole of formula units of that compound
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©2010 Donald L. Siegel All Rights Reserved Finding number of moles Finding number of moles W n=mass of substance/molar mass of substance W Example Number of moles of F in 22.5 g of F = 22.5g/19.00g mol -1 = 1.18 Number of moles of F 2 is 22.5g of F 2 = 22.5/(2×19.00) = 0.59
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©2010 Donald L. Siegel All Rights Reserved
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©2010 Donald L. Siegel All Rights Reserved Mass Percentage and Empirical Mass Percentage and Empirical Formula Formula W Empirical formula is the simplest ratio of elements in a compound W Molecular formula is the actual numbers of atoms in a molecular compound W Example CH 2 O is the empirical formula for glucose C 6 H 12 O 6 is the molecular formula W Mass percentage is another way to express the ratio
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©2010 Donald L. Siegel All Rights Reserved Determining mass Determining mass percentage percentage W The mass % of each element is determined from the mass of that element in a sample divided by the total mass W Example: an 8.00g sample of vitamin C contains 3.27g C, 0.366g H and 4.36g O % 9 . 40 % 100 00 . 8 27 . 3 % 100 % = × = × = g g sample of mass C of mass C mass 40.9% C, 4.58% H, 54.5% O
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©2010 Donald L. Siegel All Rights Reserved Determining Empirical Determining Empirical Formula Formula W The empirical formula is the simplest ratio of moles of elements in a compound W From masses or mass %s, we can determine empirical formula from masses (or %s), find moles from moles, find ratio of moles
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©2010 Donald L. Siegel All Rights
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ch3notes - Chapter 3 Stoichiometry: Chemical Calculations...

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