Chem 161-2010 Chapter 3A some Tavss practice problems + solutions

# Chem 161-2010 Chapter 3A some Tavss practice problems + solutions

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Unformatted text preview: ATOMS, IONS, MOLES AND MOLECULAR WTS. 5 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 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% 1 3 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 mol g B. 256 mol g C. 384 mol g D. 452 mol g E . 582 mol g 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 27 Chapter 3 - Stoichiometry Moles and molecular weights Which one of the following is true regarding the mass of one molecule of H 2 O? Mass(amu) Mass(g) A. 18 18 B. 18 1.0 C. 1.1 x 10 25 1.1 x 10-23 D . 18 3.0 x 10-23 E. 3.0 x 10-23 18 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). 2 46 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 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 → 2Na + 1S + 4O 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 gNa 2 SO 4 /molNa 2 SO 4 = 2.95g Na 2 SO 4 3 12 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 ? A. 1.20 × 10 24 atoms B. 2.16 × 10 21 atoms C . 4.31 × 10 21 atoms D. 0.00716 atoms E. 2 atoms MW Na 2 S 2 O 3 = (2 x 22.99) + (2 x 32.06) + (3 x 16.00) = 158.1 g/mol 0.566 g x (1 mol/158.1 g) x (6.022 x 10 23 molecules Na 2 S 2 O 3 /mol Na 2 S 2 O 3 ) x (2 atoms S/molecule Na 2 S 2 O 3 ) = 4.31 x 10 21 atoms of sulfur 21 Zumdahl 6 th edition Chapter 3 Atoms, ions, moles and molecular weights...
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## This document was uploaded on 11/02/2011 for the course GEN CHEM 162 at Rutgers.

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Chem 161-2010 Chapter 3A some Tavss practice problems + solutions

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