The Mole

Sample Test

Name: __________________

All questions are to be answered on this test paper. The value of each question is given in brackets. Show all formulas, units, calculations, and significant digits. Full credit will not be given for work which is incomplete. Good Luck!

Note: For your information, Avogadro's number is 6.02 x 1023 particles. (It is rumored that Mrs. Avogadro actually did the counting!)

1. Calculate the molar mass (gram formula mass) of (NH₄)₃PO₄. (4)

2.a. Calculate the approximate mass of one molecule of CO₂. (44.01 g/mol) (3)

b. How many times heavier is a molecule of CO₂ (44.01 g/mol) than a molecule of H₂ (2.02 g/mol)? (3)

c. Suppose that a gold (196.97 g/mol) ring has a mass of 39.4 grams. Approximately how many gold atoms are in this ring? (4)

d. What is the mass of 3.01 x 1024 molecules of water (18.02 g/mol)? (3)

3. Convert each of the following to moles: (3 ea.) Show work, units, and sig. figs.!

a. 100 g of Fe₂O₃ (159.70 g/mol)

b. 15.000 kg of NaCl (58.44 g/mol)

c. 5.00 x 1012 g of NH₃ (17.04 g/mol)

4. Convert each of the following to mass: (3 ea.) Show formula, units, and sig. figs. !

a. 0.200 mol of Ca(OH)₂ (74.01 g/mol)

b. 0.040 mol of K2Cr2O7 (294.20 g/mol)

c. 1.2 mol of CuSO₄ * 5 H₂O (249.71 g/mol)

5. Calculate the percent composition of CuS (95.61 g/mol). (The atomic molar mass of copper is 63.55 g/mol and that of sulfur is 32.06 g/mol) (4)

b. Copper metal is found naturally as the ore, CuS. For every metric ton (1000 kg) of copper (II) sulfide taken from the ground, what mass of copper (to the nearest kg) can be recovered? (2)

6. In the lab, a sample of calcium metal with a mass of 1.296 grams was heated in oxygen gas to form the compound calcium oxide. In this reaction the calcium combined with the oxygen in the air.

calcium +	oxygen		calcium oxide
1.296 g	?		1.813 g

As you can see above, the mass of calcium oxide formed was 1.813 grams

a. From the data above, calculate the percent composition of calcium oxide. (4)

b. Use your calculations in (a), to show that the empirical formula for calcium oxide is CaO. (4)

7. Given the following percent composition, calculate the empirical formula: (4)

Cu = 88.82%

O = 11.18%

8. Make this statement true by simply inserting the correct numbers into the spaces provided. Use the proper number of significant figures. (4)

1.00 mol of (NH₄)₂CO₃ has _________ moles of Nitrogen atoms, ________ moles of Hydrogen atoms, ________ moles of Carbons atoms, and ________ moles of Oxygen atoms.

9. The following data was collected to find the formula of a hydrate, just like we did in the lab:

• mass of crucible and cover = 33.09 g
• mass of crucible, cover and hydrate = 37.93 g
• mass of crucible, cover, and anhydrous salt = 35.79 g
• mass of 1 mole of anhydrous salt , ZnSO₄ = 161.44 g/mol
• mass of 1 mole of water = 18.02 g/mol

Show all work, including all units. Use significant figures correctly.

1. Calculate the mass of hydrate used. (1)

2. Calculate the mass of anhydrous salt produced. (1)

3. Calculate the mass of water removed. (1)

4. Calculate the moles of anhydrous salt produced. (2)

5. Calculate the moles of water removed. (2)

6. Ratio: moles of water/moles of anhydrous salt

a. unreduced ratio : _________ : _________ (1)

b. reduced ratio : _________ : _________ (1)

7. Simplest formula for hydrate: _____________________ (1)