Chapter 4 Key

4.1.  An equation is balanced when the same number of each element is represented on the reactant and product sides. Equations must be balanced to accurately reflect the law of conservation of matter.

 

4.3.

(a)  PCl₅(s) + H₂O(l) → POCl₃(l) + 2 HCl(aq)

(b)  3 Cu(s) + 8 HNO₃(aq) → 3 Cu(NO₃)₂(aq) + 4 H₂O(l) + 2 NO(g)

(c)  H₂(g) + I₂(s) → 2 HI(s) 

(d)  4 Fe(s) + 3 O₂(g) → 2 Fe₂O₃(s) 

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

(f)  (NH₄)₂Cr₂O₇(s) → Cr₂O₃(s) + N₂(g) + 4 H₂O(g)

(g)  P₄(s) + 6 Cl₂(g) → 4 PCl₃(l)

(h)  PtCl₄(s) → Pt(s) + 2 Cl₂(g)

 

4.5.

(a)  CaCO₃(s) → CaO(s) + CO₂(g)

(b)  2 C₄H₁₀(g) + 13 O₂(g) → 8 CO₂(g) + 10 H₂O(g)

(c)  MgCl₂(aq) + 2 NaOH(aq) → Mg(OH)₂(s) + 2 NaCl(aq)

(d)  2 H₂O(g) + 2 Na(s) → 2 NaOH(s) + H₂(g)

 

4.7.

(a)  Ba(NO₃)₂, KClO₃

(b)  2 KClO₃(s) → 2 KCl(s) + 3 O₂(g)

(c)  2 Ba(NO₃)₂(s) → 2 BaO(s) + 2 N₂(g) + 5 O₂(g)

(d)  2 Mg(s) + O₂(g) → 2 MgO(s)

 

4.9.

(a)  4 HF(aq) + SiO₂(s) → SiF₄(g) + 2 H₂O(l)

(b)  2 Na⁺(aq) + 2 F⁻(aq) + Ca²⁺(aq) + 2 Cl⁻(aq) → CaF₂(s) + 2 Na⁺(aq) + 2 Cl⁻(aq) (complete)

 

4.11.

(a)  2 K⁺(aq) + C₂O₄²⁻(aq) + Ba²⁺(aq) + 2 OH⁻(aq) → 2 K⁺(aq)+ 2 OH⁻(aq) + BaC₂O₄(s) (complete)

(b)  Pb²⁺(aq) + 2 NO₃⁻(aq) + 2 H⁺(aq) + SO₄²⁻(aq) → PbSO₄(s) + 2 H⁺(aq)+ 2 NO₃⁻(aq) (complete)

(c)  CaCO₃(s) + 2 H⁺(aq) + SO₄²⁻(aq) → CaSO₄(s) + CO₂(g)+ H₂O(l) (complete)

4.13.  (a)  0.435 mol Na,  0.217 mol Cl₂,  15.4 g Cl₂ (b)  0.005780 mol HgO,  2.890 × 10⁻³ mol O₂,  9.248 × 10⁻² g O₂ (c)  8.00 mol NaNO₃,  6.8 × 10² g NaNO₃ (d)  1665 mol CO₂,  73.3 kg CO₂ (e)  18.86 mol CuO,  2.330 kg CuCO₃ (f)  0.4580 mol C₂H₄Br₂,  86.05 g C₂H₄Br₂

 

4.15.  (a)  0.0686 mol Mg,  1.67 g Mg (b) 2.701 × 10⁻³ mol O₂,  0.08644 g O₂ (c)  6.43 mol MgCO₃,  542 g MgCO₃ (d)  768 mol H₂O,  13.8 kg H₂O (e)  16.31 mol BaO₂,  2762 g BaO₂ (f)  0.207 mol C₂H₄,  5.81 g C₂H₄

 

4.17.

(a)  volume HCl solution → mol HCl → molGaCl₃

(b)  1.25 mol GaCl₃,  2.2 × 10² g GaCl₃

 

4.19.  (a)  5.337 × 10²² molecules (b)  10.41 g Zn(CN)₂

 

4.21.  SiO₂ + 3 C → SiC + 2 CO, 4.50 kg SiO₂

 

4.23.  5.00 × 10³ kg

 

4.25.  1.28 × 10⁵ g CO₂

 

4.27.  161.4 mL KI solution

 

4.29.  176 g TiO₂

 

4.31.  The limiting reactant is Cl₂.

 

4.33.  Percent yield = 31%

 

4.35.  g CCl₄ → mol CCl₄ → mol CCl₂F₂ → g CCl₂F₂; percent yield = 48.3%

 

4.37.  percent yield = 91.3%

 

4.39.  Convert mass of ethanol to moles of ethanol; relate the moles of ethanol to the moles of ether produced using the stoichiometry of the balanced equation. Convert moles of ether to grams; divide the actual grams of ether (determined through the density) by the theoretical mass to determine the percent yield; 87.6%

 

4.41.  The conversion needed is mol Cr → mol H₃PO₄. Then compare the amount of Cr to the amount of acid present. Cr is the limiting reactant.

 

4.43.  Na₂C₂O₄ is the limiting reactant. percent yield = 86.56%

 

4.45.  Only four molecules can be made.

 

4.47.  This amount cannot be weighted by ordinary balances and is worthless.

 

4.49.  3.4 × 10⁻³ M H₂SO₄

 

4.51.  9.6 × 10⁻³ M Cl⁻

 

4.53.  22.4%

 

4.55.  The empirical formula is BH₃. The molecular formula is B₂H₆.

 

4.57.  49.6 mL

 

4.59.  13.64 mL

 

4.61.  0.0122 M

 

4.63.  34.99 mL KOH

 

4.65.  The empirical formula is WCl₄.

 

4A.2.  (a)  oxidation-reduction (addition) (b)  acid-base (neutralization) (c)  oxidation-reduction (combustion)

 

4A.4.  It is an oxidation-reduction reaction because the oxidation state of the silver changes during the reaction.

 

4A.6.  (a)  H +1,  P +5,  O −2 (b) Al +3,  H +1,  O −2 (c) Se +4,  O −2 (d) K +1,  N +3,  O −2 (e) In +3,  S −2 (f) P +3,  O −2

 

4A.8.  (a)  acid-base (b)  oxidation-reduction:  Na is oxidized, H⁺ is reduced (c)  oxidation-reduction:  Mg is oxidized, Cl₂ is reduced (d)  acid-base (e)   oxidation-reduction:  P³⁻ is oxidized, O₂ is reduced (f)  acid-base

 

4A.10.

(a)  2 HCl(g) + Ca(OH)₂(s) → CaCl₂(s) + 2 H₂O(l)

(b)  Sr(OH)₂(aq) + 2 HNO₃(aq) → Sr(NO₃)₂(aq) + 2 H₂O(l)

 

4A.12.

(a)  2 Al(s) + 3 F₂(g) → 2 AlF₃(s)

(b)  2 Al(s) + 3 CuBr₂(aq) → 3 Cu(s) + 2 AlBr₃(aq)

(c)  P₄(s) + 5 O₂(g) → P₄O₁₀(s)

(d)  Ca(s) + 2 H₂O(l) → Ca(OH)₂(aq) + H₂(g)

 

4A.14.

(a)  Mg(OH)₂(s) + 2 HClO₄(aq) → Mg²⁺(aq) + 2 ClO₄​⁻(aq) + 2 H₂O(l) 

(b)  SO₃(g) + 2 H₂O(l) → H₃O⁺(aq) + HSO₄​⁻(aq) (a solution of H₂SO₄)

(c)  SrO(s) + H₂SO₄(l) → SrSO₄(s) + H₂O

 

4A.16.  H₂(g) + F₂(g) → 2 HF(g)

 

4A.18.  2 NaBr(aq) + Cl₂(g) → 2 NaCl(aq) + Br₂(l)

 

4A.20.  2 LiOH(aq) + CO₂(g) → Li₂CO₃(aq) + H₂O(l)

 

4A.22.

(a)  Ca(OH)₂(s) + H₂S(g) → CaS(s) + 2 H₂O(l)

(b)  Na₂CO₃(aq) + H₂S(g) → Na₂S(aq) + CO₂(g) + H₂O(l)

 

4A.24.

(a)  step 1 N₂(g) + 3 H₂(g) → 2 NH₃(g)

    step 2 NH₃(g) + HNO₃(aq) → NH₄NO₃(aq) → NH₄NO₃(s) (afterdrying)

(b)  H₂(g) + Br₂(l) → 2 HBr(g)

(c)  Zn(s) + S(s) → ZnS(s) and ZnS(s) + 2 HCl(aq) → ZnCl₂(aq) + H₂S(g)

 

4A.26.

(a)  Sn⁴⁺(aq) + 2 e⁻ → Sn²⁺(aq)

(b)  Ag(NH₃)²⁺(aq) + e⁻ → Ag(s) + 2 NH₃(aq)

(c)  Hg₂Cl₂(s) + 2 e⁻ → 2 Hg(l) + 2 Cl⁻(aq) 

(d)  2 H₂O(l) → O₂(g) + 4 H⁺(aq) + 4 e⁻

(e)  6 H₂O(l) + 2 IO₃​⁻(aq) + 10 e⁻ → I₂(s) + 12 OH⁻(aq)

(f)  H₂O(l) + SO₃​²⁻(aq) → SO₄​²⁻(aq) + 2 H⁺(aq) + 2 e⁻

(g)  8 H⁺(aq) + MnO₄​⁻(aq) + 5 e⁻ → Mn²⁺(aq) + 4 H₂O(l)

(h)  Cl⁻(aq) + 6 OH⁻(aq) → ClO₃​⁻(aq) + 3 H₂O(l) + 6 e⁻

 

4A.28.

(a)  Sn²⁺(aq) + 2 Cu²⁺(aq) → Sn⁴⁺(aq) + 2 Cu⁺(aq)

(b)  H₂S(g) + Hg₂​²⁺(aq) + 2 H₂O(l) → 2 Hg(l) + S(_s) + 2 H₃O⁺(aq)

(c)  5 CN⁻(aq) + 2 ClO₂(aq) + 3 H₂O(l) → 5 CNO⁻(aq) + 2 Cl⁻(aq) + 2 H₃O⁺(aq)

(d)  Fe²⁺(aq) + Ce⁴⁺(aq) → Fe³⁺(aq) + Ce³⁺(aq)

(e)  2 HBrO(aq) + 2 H₂O(l) → 2 H₃O⁺(aq) + 2 Br⁻(aq) + O₂(g)

 

4A.30.

(a)  2 MnO₄​⁻(aq) + 3 NO₂​⁻(aq) + H₂O(l) → 2 MnO₂(s) + 3 NO₃​⁻(aq) + 2 OH⁻(aq)

(b)  3 MnO₄​²⁻(aq) + 2 H₂O(l) → 2 MnO₄​⁻(aq) + 4 OH⁻(aq) + MnO₂(s) (in base)

(c)  Br₂(l) + SO₂(g) + 2 H₂O(l) → 4 H⁺(aq) + 2 Br⁻(aq) + SO₄​²⁻(aq)