CHEM 120 Final Exam 5 GRADED A ACTUAL EXAM

CHEM 120 Final Exam 5 GRADED A+ (ACTUAL EXAM )

Questions and Answers (Solved)

• How many bonds can nitrogen have? Which rule or principle should be used?
• Five bonds; octet rule.
• Three bonds; octet rule.
• Three bonds; the Hund's rule.
• Five bonds; the Aufbau Principle.

Answer: B

• When two hydrogen atoms meet, they will attract to each other and form a bond

(and a H2 molecule). Why?

• Because electrons like to stay together.
• Because electrons like to be paired up.
• Because there is attraction between the electron in one hydrogen atom and the

nucleus of another hydrogen atom.

• Gravitational attraction between two atoms binds two hydrogen atoms (or any

two atoms) together into a molecule.

Answer: C

• How do you determine the number of electron domains on the central atom?

• Draw Lewis structure of the compound, then add up the numbers of lone electron

pair, single bond, double bond, and triple bond.

• The # of electron domains = the # of valence electrons
• The # of electron domains = the number of atoms the central atom is bonded to.
• The # of electron domains = the # of valence electrons divided by 2

Answer: A

• Indicate partial charges on each atom of the following two bonds: C-Br and O-N.

• Carbon has partial negative charge and bromine has partial positive charge; both

oxygen and nitrogen have no charge. 1 / 4

• Carbon has partial positive charge and bromine has partial negative charge;

oxygen has partial negative charge and nitrogen has partial positive charge.

• Carbon has partial negative charge and bromine has partial positive charge;

oxygen has partial positive charge and nitrogen has partial negative charge.

• Carbon has partial positive charge and bromine has partial negative charge;

oxygen has partial positive charge and nitrogen has partial negative charge.

Answer: B

• In which of the above structures, the nitrogen atom carries a negative formal charge?
• a
• b
• c
• d

Answer: A

• In which of the above Lewis structures, the oxygen atom carries a positive formal

charge?

• a
• b,c
• a,d
• c
• d

Answer: B

• Which of the following compounds exists?

A) CH3CH3CH3

B) (CH3) 2CCH3

C) CH3CHCH2CH3

D) (CH3)2CHCH3

Answer: D

8. Indicate hybridization of oxygen atom in the following compounds: H2O,

H2C=O, H3O+, HO-, and CO

• sp3, sp3, sp3, sp3, sp B) sp3, sp2, sp2, sp, sp
• sp3, sp2, sp3, sp3, sp D) sp, sp2, sp2, sp, sp 2 / 4

Answer: C

• Indicate hybridization of carbon in the above compounds.

• sp3, sp2, sp3, sp2
• sp3, sp2, sp2, sp2
• sp3, sp3, sp3, sp2
• sp3, sp3, sp3, sp3

Answer: A

• What is the bond angle in a perfect tetrahedron molecule like CH4? A) 120
• 0

C) 180

D) 109.5

Answer: D

• When SO3 reacts water, sulfuric acid (H2SO4) is formed. Is SO3 a BrØnst- ed-

Lowry acid?

• No, it is not a BrØnsted-Lowry acid.
• Yes, it is a BrØnsted-Lowry acid.

Answer: A

• Conjugate acid and base is a concept unique to BrØnsted-Lowry acids and bases.

Which of the pairs below are not conjugate acid and base?

• H2SO4 and SO42- b. H2CO3, CO2 c. HCl and Cl2 d. H3O+ and HO- e. HBr and Br-
• a,b,c B) a,b,c,d C) a,b D) a,b,c,d,e E) e

Answer: B

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• What is the pH value of an acidic solution with a proton molar concentra- tion

of 10^-3?

A) 0.001 B) 0.003 C) 3 D) -3

Answer: C

• Gastric acid is composed of hydrochloric acid (HCl) - a strong acid. The pH

range of gastric acid is 1.5 to 3.5 in the human stomach. If the HCl concentration is 0.5 mole/liter in John's stomach, is the pH value of his gastric acid in the normal range, too high, or too low?

• Too low B) Too high C) In the normal range.

Answer: A

• Which of the compounds below is the smallest carboxylic acid? (Some

carboxylic acids can found in Section 2.3) 58%

• Methyl alcohol (MeOH)
• Methylamine (CH3NH2)
• Acetic acid
• Formic acid

Answer: D

• Hydronium (H3O+) has a pKa of -1.7, and is the strongest acid that can exist in

water. A carboxylic acid (RCOOH) can be protonated by hydronium. So, the pKa of

RCOOH:

• must be greater than -1.7
• cannot be determined
• must be smaller than -1.7

Answer: A

• What is the molecular formula of carbonic acid? Is it a strong acid? (Section

2.2)

• H2CO3. It is a very weak acid.
• H2CO3. It is a weak acid.
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