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CHEMICAL COMPOUNDS AND THE MOLE Chapter 7
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Formula Mass Mass of H 2 O? Formula Mass: mass of molecule, formula unit, or ion is sum of masses of all atoms represented (amu) Ca(NO 3 ) 2
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Molar Mass Definition: mass of 1 mole of compound – use molar masses of elements (g/mol) MgCl 2 (NH 4 ) 2 CrO 4 CuSO 4 * 5H 2 O
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Molar Mass in Conversions Remember flow chart from chapter 3? What is mass (g) of 3.04 mol of ammonia vapor, NH 3 ? How many moles of sodium chloride are present in 100.0 grams?
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PRACTICE MOLAR MASS Work as a group of 4. 1 st group member: 1,5,9,13,17,21 GroupII:1 2 nd group member: 2,6,10,14,18,22 Group II:2 3 rd group member: 3,7,11,15,19,23 Group II:3 4 th group member:4,8,12,16,20,24 Group II:4 Show work for each problem you complete. Explain your work to the other group members and write in their answers. HW: complete your set and 33-40.
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“Super Mole” Conversions How many molecules are in 4.15 x 10 -5 g C 6 H 12 O 6 ? How many H atoms are in 7.1 moles of C 6 H 12 O 6 ? How many formula units are in 4.5 kg Ca(OH) 2 ?
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More “Super Mole” Conversions What is the mass of H 2 SO 4, if you have 1.53 x 10 23 sulfate ions your compound? How many water molecules are present in in a 5.00 g sample of copper (II) sulfate pentahydrate?
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Percent Composition The percent by mass of each element in a compound. % = mass due to 1 element x 100 mass of whole compound
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Percent Composition What is the percent composition by mass of each element in (NH 4 ) 2 O? What percentage by mass of Al 2 (SO 4 ) 3 6H 2 O is water? Given a 25.0 gram sample of aluminum sulfate hexahydrate, how much water (g) could be driven off?
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Empirical Formula Definition: formula showing smallest whole-number mole ratio of atoms in a compound Ex: B 2 H 6 Molecular Formula BH 3 Empirical Formula Given (CH2O)x as the empirical, determine possible molecular formulas.
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Empirical Formula Calculation Given the molecular formula: reduce Given % compostion data Find grams of each element Find moles of each element Find mole ratio of atoms by dividing through by the smallest number of moles If the ratio yields a 0.33, 0.50 multiply the entire formula through to clear fractional mole amounts.
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Finding Empirical Formula Determine the empirical formula of the compound with 17.15% C, 1.44% H, and 81.41% F. (CHF 3 )x
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Finding Empirical Formula Find empirical formula of 26.56% K, 35.41% Cr, and rest O. (K 2 Cr 2 O 7 )x
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Finding Molecular Formula x(empirical formula) = molecular formula x(emp.form mass) = molec.form mass x = Molecular formula Mass Empirical formula Mass
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Finding Molecular Formula Determine molecular formula of compound with empirical formula CH and formula mass of 78.110 amu.
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Finding Molecular Formula Sample has formula mass of 34.00 amu has 0.44 g H and 6.92 g O. Find its molecular formula.
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Combustion Analysis A compound contains only carbon, hydrogen, and oxygen. Combustion of the compound yields.01068 grams of carbon dioxide and.00437 grams of water. The molar mass of the compound is 180.1 g/ mol. The sample has a total mass of.0100 grams. What are the empirical and molecular formulas of the compound?
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