Name: ______ANSWER KEY______Date: ______Period: ______

Moles, Moles and More Moles – Unit 4 Quiz Review

Comparing atomic mass to molar mass

  • The molar mass is the mass of 6.02 x 1023 atoms.
  • Numerically the atomic mass and the molar mass are [the same, different] (circle one)
  • For example the atomic mass of sodium is 22.99 AND the molar mass of sodium is 22.99.
  • Both numbers come from the periodic table.
  • Quantitatively the atomic mass and the molar mass are[the same, different] (circle one)
  • For example the atomic mass is the mass of 1 atom and has units of amu.
  • The molar mass is the mass of 6.02 x 1023atoms and has units of g/mol.

Molar Mass Practice Problems – REMEMBER this is addition…sig figs are to place value!!!

Determine the molar mass of the following using your periodic table. Remember, the units are g/mol.

1. Li2. Ca3. Al4. Cl25. O2

6.94g/mol40.08g/mol26.98g/mol70.90g/mol32.00g/mol

6. KCl7. MgI28. CCl49. Al2O310. SiO2

74.55g/mol278.11g/mol153.81g/mol101.96g/mol60.09g/mol

11. H212. CO213. Na2CO314. H2O15. NH3

2.02 g/mol44.01 g/mol57.99 g/mol18.02 g/mol17.04 g/mol

16. Cu17. Ne18. Phosphorus19. C6H12O6

63.55 g/mol20.18 g/mol30.97 g/mol180.18 g/mol

Chemical Quantities - CONVERTING BETWEEN MASS, MOLES AND PARTICLES

  • When converting from grams to moles OR from moles to grams you use the molar massof the element or compound. You can tell because the conversion factor has units of g/mol.
  • When converting from moles to molecules OR molecules to moles you use Avogadro’s number which is equal to 6.02 x 1023. You can tell because the conversion factor has units of particles/mole.
  • When converting from atoms to moleculesORmolecules to atoms you use the chemical formula which tells how many atoms are in one molecule.

20. Calculate the # of atoms in 25g Ni - 2.6 x 1023 Ni atoms

  1. How many moles is 4.54 x 1022 molecules of H2O?.0754 moles H2O
  1. How many grams are in 2.8 mol of H2?5.6 g H2
  1. How many molecules of NH3 are in 5.0 moles of NH3? 3.0 x 1024NH3 molecules
  2. What is the number of moles in 125g of sodium carbonate (Na2CO3)?1.18 mol Na2CO3
  1. How many moles of copper is 127.1 g of copper?2.000 moles Cu
  1. How many atoms of phosphorous are there in 90.0 g of phosphorous?1.75 x 1024P atoms
  1. What is the mass of 1.74 x 1024 Ne atoms? 58.3 g Ne
  1. How many atoms are there is 36g glucose ( C6H12O6)?2.9 x 1024 atoms
  1. How many O atoms are in 12g of CO2? 3.3 x 1023 O atoms

% Composition & Empirical Formulas

Show all work, units, and round correctly.

  1. Determine the empirical formula for a compound containing: 63.50% Ag, 8.25% N, and 28.25% O.

63.5 % Ag  63.5 g Ag x 1 mol = 0.5887 mol = 1

107.87 g 0.5887

8.25 % N  8.25 g N x 1 mol = 0.589 mol = 1

14.007 g 0.5887

28.25 % O  28.25 g O x 1 mol = 1.766 mol = 3

16 0.5887

AgNO3

  1. Determine the percent composition of each element in a chemical sample that contains: 21.49 g Na, 56.15 g C, 9.43 g H, 74.81 g O, and 13.11 g N.

% Na = 21.49 g Na x 100 = 12.28 % Na% O = 74.81 g O x 100 = 42.75% O

174.99 g total 174.99 g total

% C = 56.15 g C x 100 = 32.09 % C% N = 13.11 g N x 100 = 7.492 % N

174.99 g total 174.99 g total

% H = 9.43 g H x 100 = 5.39 % H

174.99 g total

  1. Determine the empirical formula for the compound in the previous question.

12.28 g Na x 1 mol = 0.5341 mol = 1

22.99 g 0.5341

32.09 g C x 1 mol = 2.672 mol = 5

12.011 g 0.5341

5.39 g H x 1 mol = 5.34 mol = 10

1.008 g 0.5341

42.75 g O x 1 mol = 2.672 mol = 5

16 g 0.5341

7.492 g N x 1 mol = 0.5348 mol = 1

14.007 g 0.5341

NaC5H10O5N