Stoichiometry Logs

The multiple-choice section of the AP Exam does not allow calculators. The questions are very easy to calculate without a calculator as long as you have revisited and practiced some basic math strategies. Try these multiple-choice questions without a calculator.

1.  What number of moles of O2 is needed to produce 14.2 grams of P4O10 from P (Molecular weight P4O10 = 284)

1.  0.0500 mole

2.  0.0625 mole

3.  0.125 mole

4.  0.250 mole

5.  0.500 mole

2. 3 Ag (s) + 4 HNO3 ßà 3 AgNO3 + NO (g) + 2 H2O

The reaction of silver metal and dilute nitric acid proceeds according the the equation

above. If 0.10 mole of powdered silver is added to 10. milliliters of 6.0 M nitric acid, the

number of moles of NO gas that can be formed is

a.  0.015 mole

b.  0.020 mole

c.  0.030 mole

d.  0.045 mole

e.  0.090 mole

3.  When 70. milliliter of 3.0 M Na2CO3 is added to 30. milliliters of 1.0 M NaHCO3 the resulting concentration of Na+ is

6.  2.0 M

7.  2.4 M

8.  4.0 M

9.  4.5 M

10.  7.0 M

4.  A 20.0 mL sample of 0.200 M K2CO3 solution is added to 30.0 mL of 0.400 M Ba(NO3)2 solution. Barium carbonate precipitates. The concentration of barium ion, Ba2+, in solution after reaction is

11.  0.150 M

12.  0.160 M

13.  0.200 M

14.  0.240 M

15.  0.267 M

5.  A 27.0 g sample of an unknown hydrocarbon was burned in excess oxygen to form 88.0 g of CO2 and 27.0 grams of water. What is a possible molecular formula of the hydrocarbon?

16.  CH4 c. C4H3 e. C4H10

17.  C2H2 d. C4H6

6.  The weight of H2SO4 (molecular weight = 98.1 g) in 50.0 mL of a 6.00 M solution is

  1. 3.10 g
  2. 12.0 g
  3. 29.4 g
  4. 294 g
  5. 300. g

7.  How many grams of calcium nitrate, Ca(NO3)2, contains 24 g of oxygen atoms?

  1. 164 grams
  2. 96 grams
  3. 62 grams
  4. 50. grams
  5. 41 grams

8.  The mass of element Q found in 1.00 mole of each of four different compounds is 38.0 grams, 57.0 grams, 76.0 grams, and 114 grams, respectively. A possible atomic weight of Q is

  1. 12.7
  2. 19.0
  3. 27.5
  4. 38.0
  5. 57.0

9.  How many milliliters of 11.6 M HCl must be diluted to obtain 1.0 liter of 3.0 molar HCl?

  1. 3.9 mL
  2. 35 mL
  3. 260 mL
  4. 1,000 mL
  5. 3,900 mL

10.  If 87 grams of K2SO4 (molar mass 174 grams) is dissolved in enough water to make 250 mL of solution, what are the concentrations of the potassium and the sulfate ions?

  1. 0.020 M and 0.020 M
  2. 1.0 M and 2.0 M
  3. 2.0 M and 1.0 M
  4. 2.0 M and 2.0 M
  5. 4.0 M and 2.0 M

II. Questions pertaining to Stoichiometry on the AP Exam deal mainly with empirical/molecular formulas and limiting reactants. Here are a few examples:

1. An unknown compound contains only the three elements C, H and O. A pure sample of the

compound is analyzed and found to be 65.60 percent C and 9.44 percent H by mass.

Determine the empirical formula of the compound

2. Elemental analysis of an unknown pure substance indicates that the percent composition by

mass is as follows:

Carbon – 49.02 %

Hydrogen – 2.743 %

Chlorine – 48.23 %

Determine the empirical formula for the compound.

3.  A 2.035 g organic compound containing carbon, hydrogen, and oxygen was burned in excess oxygen releasing 4.162 g of carbon dioxide and 1.291 g of water. The molecular mass of the compound is 172.0 g/mol.

  1. What is the emipirical formula?
  2. What is the molecular formula?
  3. How many grams of oxygen were used to oxidize the original 2.035 g of compound?

4.  A 8.129 gram sample of a hydrate is heated until the water of hydrations is given off. The resulting anhydrous magnesium sulfate salt weighs 3.967 g. What is the formula of the hydrate?

  1. If you were to perform this experiment, what data will be needed?
  2. What are the sources of error?

5.  A mixture of methane and ethane of mass 13.43g is completely burned in oxygen. If the total mass of carbon dioxide and water produced is 64.84 g, calculate the mass of methane in the mixture.

6.  (OPTIONAL for additional practice) Leaded gasoline contains an additive to prevent engine “knocking.” On analysis, the additive compound is found to contain carbon, hydrogen, and lead. When 51.36 g of this compound are burned in excess oxygen, 55.90 g of CO2 and 28.61 g of H2O are produced. Determine the empirical formula of the gasoline additive. Answer: PbC8H20