Stoichiometry & Yield — Chapter quiz · Physical Science: Chemistry, Grade 11

Calculate reacting amounts, identify shortages, and interpret production results.

Problem 1

For N₂ + 3H₂ → 2NH₃, how many moles of ammonia form from 6.0 mol of hydrogen with excess nitrogen?
Answer and explanation

4 mol

6.0 mol H₂ × (2 mol NH₃ ÷ 3 mol H₂) = 4.0 mol NH₃.

Problem 2

For C + O₂ → CO₂, what mass of carbon dioxide forms when 24.02 g of carbon burns completely? (C = 12.01 g/mol, CO₂ = 44.01 g/mol.)
Answer and explanation

88.02 g

24.02 g ÷ 12.01 g/mol = 2.00 mol C; ratio C:CO₂ = 1:1 gives 2.00 mol CO₂; 2.00 × 44.01 = 88.02 g.

Problem 3

A reaction has a theoretical yield of 60.0 g and an actual yield of 54.0 g. What is the percent yield?
Answer and explanation

90 %

percent yield = (54.0 ÷ 60.0) × 100% = 90%.

Problem 4

In a reaction, the limiting reactant is the one that…
  1. runs out first and caps the amount of product
  2. always has the smallest molar mass
  3. does not take part in the reaction
  4. is left over after the reaction stops
Answer and explanation

runs out first and caps the amount of product

The limiting reactant is consumed first, setting the maximum (theoretical) yield.

Problem 5

Explain the difference between theoretical yield and actual yield, and give one reason the actual yield is usually smaller.
Answer and explanation

Theoretical yield is the maximum product predicted by stoichiometry if the limiting reactant converts perfectly; actual yield is what you really collect. Actual is usually smaller because of losses such as product left on glassware, side reactions, impurities, or reactions that don't go fully to completion.

Problem 6

Explain the following claim and supply a valid example or counterexample: Coefficients give mole ratios, not mass ratios.
Answer and explanation

It requires 6 mol H₂ and can produce 6 mol H₂O if reactants are sufficient. Coefficients give mole ratios, not mass ratios.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the calculation or mechanism that supports it.
  • Include units, conditions, or limits where relevant.

Problem 7

Independent chapter check: For 2Mg+O₂→2MgO, use Mg=24.3 and MgO=40.3 g/mol. Find theoretical MgO from 4.86 g pure Mg with excess oxygen. Explain the mass increase.
Answer and explanation

4.86/24.3=0.200 mol Mg. The 1:1 ratio gives 0.200 mol MgO and 0.200×40.3=8.06 g MgO. The extra mass comes from incorporated oxygen; the complete mass account includes it.

4.86/24.3=0.200 mol Mg. The 1:1 ratio gives 0.200 mol MgO and 0.200×40.3=8.06 g MgO. The extra mass comes from incorporated oxygen; the complete mass account includes it.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the chemical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 8

Explain the following claim and supply a valid example or counterexample: The smaller initial mass is not necessarily the limiting reactant.
Answer and explanation

H₂ limits; it supports 2molNH₃ and consumes 1molN₂, leaving 1molN₂. Compare potential products, not raw amounts. The smaller initial mass is not necessarily the limiting reactant.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the calculation or mechanism that supports it.
  • Include units, conditions, or limits where relevant.

Problem 9

Independent chapter check: For N₂+3H₂→2NH₃, begin with 1.50 mol N₂ and 3.00 mol H₂. Find limiting reactant, theoretical NH₃, remaining N₂ and yield if 1.60 mol NH₃ is isolated.
Answer and explanation

H₂ limits. It uses 1.00 mol N₂, forms 2.00 mol NH₃ and leaves 0.50 mol N₂ in the complete model. Isolated yield is 1.60/2.00×100=80.0%; that number alone does not identify the cause of lost target.

H₂ limits. It uses 1.00 mol N₂, forms 2.00 mol NH₃ and leaves 0.50 mol N₂ in the complete model. Isolated yield is 1.60/2.00×100=80.0%; that number alone does not identify the cause of lost target.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the chemical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 10

Complete neutralization of .003 mol H₂SO₄ needs how many mol NaOH?
Hints

Write the relationship first; substitute with consistent units.

Answer and explanation

0.006 mol

1:2 ratio gives .006.

Problem 11

Which volume belongs in molarity after two solutions are mixed?
Answer and explanation

Use the final solution volume, not only one starting volume; add initial volumes only if the model allows it.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the calculation or mechanism that supports it.
  • Include units, conditions, or limits where relevant.

Problem 12

Independent chapter check: Mix 10.0 mL of 0.200 M AgNO₃ with 15.0 mL of 0.100 M NaCl. Assume complete AgCl precipitation and additive volumes. Find limiting ion, AgCl moles and remaining Ag⁺ concentration.
Answer and explanation

Ag⁺ starts at 0.00200 mol and Cl⁻ at 0.00150 mol, so chloride limits. AgCl forms 0.00150 mol; remaining Ag⁺ is 0.00050 mol in 0.0250 L, or 0.0200 M under the stated model.

Ag⁺ starts at 0.00200 mol and Cl⁻ at 0.00150 mol, so chloride limits. AgCl forms 0.00150 mol; remaining Ag⁺ is 0.00050 mol in 0.0250 L, or 0.0200 M under the stated model.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the chemical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

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