AP®ChemistryCollege BoardExam QuestionsUnit 4: Chemical ReactionsStoichiometry

Stoichiometry (College Board AP® Chemistry)

Exam Questions

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Stoichiometry

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Stoichiometry

1
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When heated, anhydrous magnesium nitrate, Mg(NO3)2, will decompose into magnesium oxide and a mixture of gases shown in the following equation.

2Mg(NO3)2 (s) → 2MgO (s) + 4NO2 (g) + O2 (g)

1.48 g of anhydrous magnesium nitrate is heated until no further reaction takes place.

What mass of nitrogen dioxide is produced?

  • 0.92 g

  • 0.46 g

  • 1.48 g

  • 1.84 g

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2
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6.00 g of calcium carbonate (molar mass = 100.09 gmol-1) decomposes to produce 2.73 g of calcium oxide (molar mass = 56.08 gmol-1), according to the following equation.

CaCO3 (s)  → CaO(s) + CO2(g)

What is the percentage yield of calcium oxide?

  • 18%

  • 81%

  • 90%

  • 0.81%

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3
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In the reaction

H2 (g) + Cl2 (g) → 2HCl (g)

how many moles of which chemicals will remain when 1.5 moles of chlorine reacts with 2.0 moles of hydrogen?

  • 3.5 mol of HCl

  • 1.5 mol of HCl  and 0.5 mol of H2

  • 2.0 mol of HCl  and 0.5 mol of Cl2

  • 3.0 mol of HCl and 0.5 mol of H2

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4
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The neutralization of magnesium carbonate proceeds as follows.

MgCO3 (s) + 2HCl (aq) → MgCl2 (aq) + H2O (l) + CO2 (g) 

How many liters of CO2 are produced when 13.6 g of magnesium carbonate reacts completely with excess hydrochloric acid at STP?

  • 3.61 L

  • 7.22 L

  • 69.4 L

  • 138 L

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5
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In the following combustion reaction, 0.60 g of magnesium is burned with 0.60 L of oxygen at STP, what is the limiting reactant?

2Mg + O2 → 2MgO

  • Mg

  • MgO

  • O2

  • There is no limiting reactant.

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6
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A 25.00 mL aliquot of hydrochloric acid was titrated with 0.225 M NaOH solution. It took 36.20 mL of sodium hydroxide to neutralize the hydrochloric acid. What was the molarity of the hydrochloric acid?

  • 1.55 x 10-4 M

  • 3.26 x 10-4 M

  • 0.155 M

  • 0.326 M

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7
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A sample of sodium hydroxide is dissolved in 250 mL of distilled water. 25.0 mL of this solution requires 15.0 mL of 2.00 M sulfuric acid to achieve complete neutralization.

2NaOH + H2SO4 → Na2SO4 + 2H2O

What is the mass of sodium hydroxide dissolved in 250 mL of distilled water? 

  • 1.20 g

  • 12.0 g

  • 2.40 g

  • 24.0 g

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8
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Sodium reacts with water in the equation below.

2Na (s)  +  2H2O (l)  →  2NaOH (aq)  +  H2 (g)

Which mass of sodium reacts with water to produce 960 mL of hydrogen gas at 1 atm and 20 oC?

  • 1.152 g

  • 1.84 g

  • 18.1 g

  • 0.918 g

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9
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100 mL of a potassium carbonate solution, Na2CO3 (aq), of unknown concentration is reacted with excess calcium chloride solution, CaCl2 (aq).

Na2CO3 (aq) + CaCl2 (aq) → 2NaCl (aq) + CaCO3 (s)

The resulting calcium carbonate precipitate, CaCO3 (s), is filtered and dried. The following data is recorded.

Mass of filter paper

0.77 g

Mass of filter paper + CaCO3 precipitate

1.94 g

What is the molarity of the Na2CO3 (aq) solution?

  • 0.0117 M

  • 0.0769 M

  • 0.117 M

  • 0.194 M

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10
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2N2​O (g) → 2N2 (g) + O2 (g)

At 600 oC, nitrous oxide decomposes according to the reaction represented above. The reaction is completed at a constant temperature of 800 K in a rigid vessel. The N2O (g) is initially present in the vessel at a pressure of 1.50 atm.

What is the final pressure in the vessel after the reaction is complete?

  • 1.00 atm

  • 1.50 atm

  • 2.25 atm

  • 4.50 atm

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