Answer Key
Chem Covalent Bonding Exam Key
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University:
Cornell University -
Course:
CHEM 1150 | The Language of Chemistry Academic year:
2020
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331
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13
Author:
Clint W.
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Honors Chemistry Final Exam Review Guide
Covalent Bonding
1. Explain the difference between single, double, and triple covalent bonds including electrons shared, bond length, bond strength, AND bond dissociation energy (BDE).
* **Single:**
Shares 2e-, longest, weakest, lowest BDE
* **Double:** Shares 4e-
* **Triple:** Shares 6e-, shortest, strongest, highest BDE
2. Write the prefix corresponding to each number of atoms for naming covalent compounds.
* 1: mono
* 2: di
* 3: tri
* 4: tetra
* 5: penta
* 6: hexa
* 7: hepta
* 8: octa
* 9: nona
* 10: deca
3. Complete the table below.
| Formula | Name | Formula | Name |
|---|---|---|---|
| CO₂ | carbon dioxide | P₄O₁₀ | Diphosphorus pentoxide |
| IF₃ | iodine trifluoride | ClO₂ | Chlorine dioxide |
| P₄O₆ | tetraphosphorus hexoxide | SiF₆ | Silicon hexafluoride |
| SiI₄ | silicon tetraiodide | B₂I₄ | Boron triiodide |
| N₂O₅ | dinitrogen pentoxide | CO | Carbon monoxide |
| SF₆ | sulfur hexafluoride | B₆Si | Hexaboron monosilicide
4. Describe how one would determine the polarity of a bond.
Obtain the electronegativity values for each atom and subtract. If EN difference is
< 0.5 - nonpolar covalent, 0.5-1.7 - polar covalent, > 1.7 - ionic
5. Explain how to decide if a molecule is polar or nonpolar.
Molecular symmetry: If the molecule is symmetrical, it is nonpolar; if it is not symmetrical, then it is polar.
6. For each molecule, draw the Lewis structure, determine the VSEPR shape, bond polarity using the electronegativity values from your notes (nonpolar covalent, polar covalent, or ionic), and molecular polarity.
* PO₃³⁻: 5+3(6)+3 = 26
[Image of PO₃³⁻ Lewis structure]
VSEPR shape: Trigonal Pyramidal
Bond Polarity: 3.5 - 2.1 = 1.4 PC
Molecular Polarity: Polar
* SiO₂: 4 + 2(6) = 16
[Image of SiO₂ Lewis structure]
VSEPR shape: Linear
Bond Polarity: 3.5 - 1.7 = 1.76 Ionic
Molecular Polarity: Nonpolar
* BrF₅: 7 + 5(7) = 42
[Image of BrF₅ Lewis structure]
VSEPR shape: Square Pyramidal
Bond Polarity: 4 - 2.7 = 1.3 PC
Molecular Polarity: Polar
* N₂: 5 + 5 = 10
[Image of N₂ Lewis structure]
VSEPR shape: Linear
Bond Polarity: Nonpolar
Molecular Polarity: Nonpolar
* NH₃: 5 + 3(1) = 8
[Image of NH₃ Lewis structure]
VSEPR shape: Trigonal Pyramidal
Bond Polarity: 3.0 - 2.1 = 0.9 PC
Molecular Polarity: Polar
* GeBr₄: 4 + 4(7) = 32
[Image of GeBr₄ Lewis structure]
VSEPR shape: Tetrahedral
Bond Polarity: 2.7 - 2.0 = 0.72 PC
Molecular Polarity: Nonpolar
Intermolecular Forces & Phases
7. Describe the difference between an INTRAmolecular force and an INTERmolecular force (IMF). Which is stronger?
* **Intramolecular force:** within the molecule (the bond); stronger
* **Intermolecular force (IMF):** between molecules; much weaker
55. The solubility of lead (II) iodide is 1.2 x 10⁻³ M at 298K. Calculate Ksp for PbI₂.
PbI₂ ⇌ Pb²⁺ + 2I⁻
Ksp = [Pb²⁺][I⁻]²
= (x)(2x)²
= 4x³ = 4(1.2 x 10⁻³)³
= 6.9 x 10⁻⁹
56. Explain the common ion effect.
The lowering of the solubility of a substance because of the presence of a common ion. Ex: CaSO₄ in a 1.5 M CaCl₂ solution.
57. Given the equilibrium system below, which direction will the equilibrium shift if NaF is added to the system?
MgF₂(s) ⇌ Mg²⁺(aq) + 2F⁻(aq)
adds F⁻ to the system
58. Calculate the molar solubility of barium fluoride in a 0.15 M NaF solution. The solubility product (Ksp) constant for BaF₂ is 1.0 x 10⁻⁶.
BaF₂ ⇌ Ba²⁺ + 2F⁻
Ksp = [Ba²⁺][F⁻]²
1.0 x 10⁻⁶ = (x)(0.15 + 2x)²
0 + x 0.15 + 2x
0.15² ≈ 0.0225
1.0 x 10⁻⁶ = 0.0225x
x = 4.4 x 10⁻⁵ M
Acids & Bases
59. DESCRIBE how you can identify an acid or base according to the Brønsted-Lowry model.
Acids are H⁺ donors
Bases are H⁺ acceptors
60. Identify the Brønsted-Lowry conjugate acid-base pairs in the following equations.
a. NH₃ + H₂O ⇌ NH₄⁺ + OH⁻
B A CA CB
b. HCl + H₂O ⇌ Cl⁻ + H₃O⁺
A B CB CA
c. HC₂H₃O₂ + H₂O ⇌ H₃O⁺ + C₂H₃O₂⁻
A B CA CB
61. Boric acid (H₃BO₃) ionizes in steps. Which of the acids below is the weakest?
a. H₃BO₃ + H₂O ⇌ H₂BO₃⁻ + H₃O⁺
b. H₂BO₃⁻ + H₂O ⇌ HBO₃²⁻ + H₃O⁺
c. HBO₃²⁻ + H₂O ⇌ BO₃³⁻ + H₃O⁺
Acid Strength ↓
with negative charge
62. Label the pH scale below with neutral, acidic, and basic regions.
acidic neutral basic
0
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