Chapter 3A-Stoichiometry TAVSS

# Chapter 3A-Stoichiometry TAVSS - CHEM 161-2007 CHAPTER 3A...

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Unformatted text preview: CHEM 161-2007 CHAPTER 3A – STOICHIOMETRY: CHEMICAL CALCULATIONS PRACTICE PROBLEMS DR. ED TAVSS • Atoms, ions, moles and molecular wts. • Empir. & molec. formulas 1 ATOMS, IONS, MOLES AND MOLECULAR WTS. 5 Chem 161-2006 Exam I Hill, Petrucci et al., 4 th edition Chapter 3 – Stoichiometry: Chemical Calculations Atoms, ions, moles and molecular weights How many oxygen atoms are there in 2.25 moles of BaSO 4 ? A. 9.00 B. 2.41 × 10 24 C . 5.42 × 10 24 D. 1.35 × 10 24 E. 3.39 × 10 23 2.25 mol x (6.022 x 10 23 molecules/mol) x (4 oxygen atoms/molecule) = 5.42 x 10 24 atoms O. C 7 Chem 161-2005 Exam I Zumdahl 6 th edition Chapter 3A Atoms, ions, moles and molecular weights What is the % N (by mass) in ammonium nitrate? A. 17.5% B. 21.2% C. 53.8% D. 22.2% E . 35.0% NH 4 NO 3 = 14.01 + (4 x 1.008) + 14.01 + (3 x 16.00) = 80.05 ((2 x 14.01)/80.05) x 100 = 35.00% 2 3 Chem 161-2005 Final exam Chapter 3 - Stoichiometry Moles and molecular weights A 0.0567 g sample of a compound contains 5.865 x 10 19 molecules. What is the molar mass of this compound? A. 128 B. 256 C. 384 D. 452 E . 582 Compound 0.0567 g 5.865 x 10 19 molecules ?MW Plan: molecules → moles → MW 5.865 x 10 19 molecules x (1 mol/(6.022 x 10 23 molecules)) = 9.739 x 10-5 moles 0.0567 g/(9.739 x 10-5 moles) = 582 g/mol 3 27 Chem 161-2005 Final exam Chapter 3 - Stoichiometry Moles and molecular weights Which one of the following is true regarding the mass of one molecule of H 2 O? A. B. C. D . E. MW H 2 O = 18.02 g/mol (18.02 g/mol)/(6.022 x 10 23 molecules/mol) = 2.99 x 10-23 g/molecule The mass in amu’s is the same as the mass per mole, except that since it is the mass per atom, it is described as amu’s rather than grams. Hence the mass of 1 atom of H 2 O is 18.02 amu’s (whereas the mass of 1 mol of H 2 O is 18.02 g). 4 46 Chem 161-2005 Final exam Chapter 3 - Stoichiometry Moles and molecular weights How many molecules of H 2 are required to make 0.44 g of propane, C 3 H 8 (g)? A. 6.02 x 10-23 molecules B . 2.4 x 10 22 molecules C. 6.0 x 10 21 molecules D. 2.4 x 10 25 molecules E. 3.0 x 10 22 molecules H 2 + C → C 3 H 8 4H 2 + 3C → C 3 H 8 0.44g Plan: g C3H8 → mol C3H8 → mol H2 → molecules H2 0.44g x (1 mol/44.11g) x (4 mol H 2 /mol C 3 H 8 ) x (6.022 x 10 23 molecules H 2 /mol H 2 ) = 2.40 x 10 22 molecules of H 2 50 Chem 161-2005 Final exam Chapter 3 - Stoichiometry Moles and molecular weights What mass of sodium sulfate will contain 5.00 x 10 22 oxygen atoms? A. 12.5 g B. 16.2 g C. 8.39 g D. 3.26 g E . 2.95 g Na 2 SO 4 1 mol Na 2 SO 4 = 4 mol O Plan: atoms O → moles O → moles Na2SO4 → g Na2SO4 5.00 x 10 22 O atoms x (1 mol O/6.022 x 10 23 O atoms) x (1 mol Na 2 SO 4 /4 mol O atom) x 142.05 g/mol = 2.95g Na 2 SO 4 5 12 Chem 161-2005 Exam I Zumdahl 6 th edition Chapter 3A Atoms, ions, moles and molecular weights How many sulfur atoms are there in 0.566g of Na 2 S 2 O 3 ?...
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## This note was uploaded on 07/17/2010 for the course 160 162 taught by Professor Kimmel during the Spring '10 term at Rutgers.

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Chapter 3A-Stoichiometry TAVSS - CHEM 161-2007 CHAPTER 3A...

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