Reactions, Moles & Composition — Chapter quiz · Physical Science: Chemistry, Grade 11

Account for atoms, charge, particle counts, and measured composition.

Problem 1

What type of reaction is 2Mg + O₂ → 2MgO?
  1. synthesis
  2. decomposition
  3. single replacement
  4. double replacement
Answer and explanation

synthesis

Two elements combine into a single compound (A + B → AB), which is synthesis.

Problem 2

Which equation is a double-replacement reaction?
  1. Zn + 2HCl → ZnCl₂ + H₂
  2. AgNO₃ + NaCl → AgCl + NaNO₃
  3. 2Mg + O₂ → 2MgO
  4. 2H₂O → 2H₂ + O₂
Answer and explanation

AgNO₃ + NaCl → AgCl + NaNO₃

Two compounds swap partners (AB + CD → AD + CB), forming a silver chloride precipitate — double replacement.

Problem 3

Balance the rusting of iron: 4Fe + ___O₂ → 2Fe₂O₃. What coefficient belongs in front of O₂?
Answer and explanation

3

2Fe₂O₃ contains 6 oxygen atoms, and 3O₂ supplies 6, so the coefficient is 3 (iron: 4 = 2 × 2).

Problem 4

Which set of coefficients balances ___Al + ___O₂ → ___Al₂O₃?
  1. 1, 1, 1
  2. 2, 3, 1
  3. 4, 3, 2
  4. 2, 1, 2
Answer and explanation

4, 3, 2

4Al + 3O₂ → 2Al₂O₃ gives 4 Al and 6 O on each side.

Problem 5

Calculate the molar mass of calcium carbonate, CaCO₃. (Ca = 40.08, C = 12.01, O = 16.00 g/mol.)
Answer and explanation

100.09 g/mol

40.08 + 12.01 + 3(16.00) = 40.08 + 12.01 + 48.00 = 100.09 g/mol.

Problem 6

How many moles are in 200.18 g of calcium carbonate? (Molar mass CaCO₃ = 100.09 g/mol.)
Answer and explanation

2 mol

moles = 200.18 g ÷ 100.09 g/mol = 2.00 mol.

Problem 7

One mole of any substance contains how many representative particles?
  1. 1.00 × 10⁶
  2. 3.00 × 10⁸
  3. 1.602 × 10⁻¹⁹
  4. 6.022 × 10²³
Answer and explanation

6.022 × 10²³

One mole is Avogadro's number of particles, 6.022 × 10²³.

Problem 8

Explain the following claim and supply a valid example or counterexample: Reaction categories overlap, and ion swapping alone does not guarantee reaction.
Answer and explanation

A newly formed solid plus a balanced net ionic model; exclude existing suspended material as an alternative. Reaction categories overlap, and ion swapping alone does not guarantee reaction.

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: A student writes an exchange equation for two clear ionic solutions and predicts a solid solely because the equation is balanced. Explain the missing evidence and give two quantities that still must balance.
Answer and explanation

Balance atoms of each element and total charge. A precipitate prediction also needs appropriate solubility/concentration evidence under the conditions; balanced pattern matching alone does not establish a separate solid phase.

Balance atoms of each element and total charge. A precipitate prediction also needs appropriate solubility/concentration evidence under the conditions; balanced pattern matching alone does not establish a separate solid phase.

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

Explain the following claim and supply a valid example or counterexample: Never change formula subscripts to balance an equation.
Answer and explanation

C₃H₈+5O₂→3CO₂+4H₂O; three C, eight H, and ten O are conserved. Never change formula subscripts to balance an equation.

Response criteria

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

Problem 11

Independent chapter check: Balance C₃H₈ + O₂ → CO₂ + H₂O using the smallest whole-number coefficients, then show the atom counts.
Answer and explanation

C₃H₈ +5O₂ →3CO₂ +4H₂O. Counts are C:3, H:8, O:10 on each side. Formula subscripts remain unchanged.

C₃H₈ +5O₂ →3CO₂ +4H₂O. Counts are C:3, H:8, O:10 on each side. Formula subscripts remain unchanged.

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 12

Explain the following claim and supply a valid example or counterexample: A mole counts entities; it is not a fixed number of grams.
Answer and explanation

Molar mass 18 g/mol, so 36/18=2 mol; identify molecules as the counted entities. A mole counts entities; it is not a fixed number of grams.

Response criteria

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

Problem 13

Independent chapter check: Using Mₘ(CO₂)=44.0 g/mol and Nₐ≈6.022×10²³ mol⁻¹, find moles, molecules and moles of oxygen atoms in 22.0 g CO₂.
Answer and explanation

n=22.0/44.0=0.500 mol CO₂. Molecules≈3.01×10²³. Each has two O atoms, giving 1.00 mol O atoms. Keep the entity labels through every conversion.

n=22.0/44.0=0.500 mol CO₂. Molecules≈3.01×10²³. Each has two O atoms, giving 1.00 mol O atoms. Keep the entity labels through every conversion.

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 14

Simplify C₄H₈ to its empirical formula.
Answer and explanation

CH₂: divide both subscripts by 4.

Response criteria

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

Problem 15

Ratios are 1.0 C:1.5 O. What simplest integers result?
Answer and explanation

Multiply both by 2 to obtain C₂O₃, provided the measured composition supports that ratio.

Response criteria

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

Problem 16

Independent chapter check: A selected oxide sample has 70.0 g Fe and 30.0 g O. Use Fe=56.0 and O=16.0 g/mol to find the simplest formula. State one assumption.
Answer and explanation

Amounts are 1.25 mol Fe and 1.875 mol O, ratio 1:1.5, hence Fe₂O₃. Assume the analyzed sample is one oxide accounted for by those elements and the input precision supports that ratio.

Amounts are 1.25 mol Fe and 1.875 mol O, ratio 1:1.5, hence Fe₂O₃. Assume the analyzed sample is one oxide accounted for by those elements and the input precision supports that ratio.

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 17

Check charge balance in Ag⁺+Cl⁻→AgCl(s).
Answer and explanation

+1−1 = 0 equals the neutral product charge.

Response criteria

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

Problem 18

Which generally dissolves: a nitrate salt or a calcium carbonate solid?
Answer and explanation

Nitrate salts generally dissolve; calcium carbonate is poorly soluble under the simple rule set.

Response criteria

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

Problem 19

Independent chapter check: Write the net ionic equation when suitable aqueous BaCl₂ and Na₂SO₄ produce BaSO₄(s). Name spectators and verify charge. This is a supplied-species exercise, not a home experiment.
Answer and explanation

Ba²⁺(aq)+SO₄²⁻(aq)→BaSO₄(s). Na⁺ and Cl⁻ are spectators in the selected account. One Ba and one sulfate group are conserved and total charge is zero on each side.

Ba²⁺(aq)+SO₄²⁻(aq)→BaSO₄(s). Na⁺ and Cl⁻ are spectators in the selected account. One Ba and one sulfate group are conserved and total charge is zero on each side.

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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