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# u6 - m v MOL p Chemistry Unit 6 The Mathematics of Chemical...

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Unit 6: The Mathematics of Chemical Formulas Chemistry Na2CO3 . 10 H2O p v MOL m Cu(OH)2 SO3

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# of H2O molecules # of H atoms # of O atoms 1 2 3 100 6.02 x 1023 1 2 4 16.0 g 2 6 3 100 200 2 (6.02 x 1023) 6.02 x 1023 2.0 g 18.0 g molar mass : the mass of one mole of a substance
Pb O 2 H NO3 ammonium phosphate Pb : 1 (207.2 g) = 207.2 g O : 2 (16.0 g) = 32.0 g 239.3 g H : 1 (1.0 g) = 1.0 g N: 1 (14.0 g) = 14.0 g 63.0 g O: 3 (16.0 g) = 48.0 g ( NH4 )3 PO4 H: 12 (1.0 g) = 12.0 g N: 3 (14.0 g) = 42.0 g 149.0 g P: 1 (31.0 g) = 31.0 g NH41+ PO43 O: 4 (16.0 g) = 64.0 g

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percentage composition : the mass % of each element in a compound Find % composition. Pb O 2 ( NH4 )3 PO4 % of element = g element molar mass of compound x 100 207.2 g Pb 239.2 g : = 86.6% Pb 32.0 g O 239.2 g = 13.4% O 31.2 g P 149.0 g = 20.8% P 64.0 g O 149.0 g = 43.0% O 42.0 g N 149.0 g = 28.2% N 12.0 g H 149.0 g = 8.1% H : : : : : (see calcs above)
zinc acetate Zn2+ CH3COO1– Zn ( CH3COO )2 183.4 g = 3.3% H = 34.9% O = 35.7% Zn = 26.2% C : C: 4 (12.0 g) = 48.0 g Zn : 1 (65.4 g) = 65.4 g H: 6 (1.0 g) = 6.0 g O: 4 (16.0 g) = 64.0 g 183.4 g

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“What’s your flavor of ice cream?” Finding an Empirical Formula from Experimental Data 1. Find # of g of each element. 2. Convert each g to mol. 3. Divide each “# of mol” by the smallest “# of mol.” 4. Use ratio to find formula. A compound is 45.5% yttrium and 54.5% chlorine. Find its empirical formula. YCl3 Y g 45.5 Y g 88.9 Y mol 1 Y mol 0.512 = 0.512 ÷ 1 Cl g 54.5 Cl g 35.5 Cl mol 1 Cl mol 1.535 = 0.512 ÷ 3
A ruthenium/sulfur compound is 67.7% Ru. Find its empirical formula. RuS1.5 Ru2S3 Ru g 67.7 Ru g 101.1 Ru mol 1 Ru mol 0.670 = 0.670 ÷ 1 S g 32.3 S g 32.1 S mol 1 S mol 1.006 = 0.670 ÷ 1.5

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A 17.40 g sample of a technetium/oxygen compound contains 11.07 g of Tc. Find the empirical formula.
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