chem 101 - term exam ii - b (1)

7/23/2019 Chem 101 - Term Exam II - b (1)

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CHEM 101 SAMPLE TE2.doc 1 Roy Jensen21 Apr 06

CHEM 101:SAMPLETerm Exam II

___________________ _______________________________DATE NAME

All answers are to be given in the space provided and, if necessary, on the back of the page with a linkin the original answer space (see ). In calculations, show all your work, including units. Circle the

final answerand write it using a permanent instrument; answers given otherwise cannot be disputed.

No other resources are permitted during this exam. Calculators are permitted but must not haveinformation stored in their memories.

Only one person at a time is permitted to use the washroom. No one may use the washroom once

someone leaves permanently.

1. Define or explain each of the following: (10)

a) van der Waal forces

b) solute

c) delocalized bonding

d) homonuclear diatomic

e) concurrent chemical reaction

____100


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2. For each of the following molecules: (15)

i) Draw the most-likely Lewis structure, showing all reasonable resonance structures.

ii) Assign formal charges to all the atoms.

iii) Identify the hybridization (Valence Bond theory) of the central atom.

iv) Identify the electron-group and molecular geometries of the central atom.

v) State whether or not the entity has a dipole.

a) N2H2

b) IF3

c) CO32


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3. For one of the molecules in Q. 2, draw the valence bond representation of the molecule. (5)

4. Explain the interatomic interactions that control the three regions in the bonding profile. (10)

Internuclear Distance

PotentialEnergy


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5. a) In the following molecular orbital diagram: identify the molecular orbitals, fill in the

molecular orbital diagram for C2, and give two characteristics of C2. (10)

2s

2p

b) What ion of C2is expected to have the strongest bond? Explain. (5)


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6. Arrange the following molecules in order of increasingboiling point. Identify the dominant

intermolecular interactions in each molecule. (10)

Compound Ordering Intermolecular interactions

N2H4

PH3

LiF

O2

7. How many grams of dichloromethane are formed when starting with 112 g CH4 and 675 g

Cl2? Each of the following reactions has a 92 % yield. (15)

CH4+ Cl2 CH3Cl + HCl

CH3Cl + Cl2 CH2Cl2+ HCl


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8. A 2.05 g sample of an iron aluminum alloy is dissolved in excess hydrochloric acid,

producing 0.112 g of hydrogen gas. What is the mass percent composition of the alloy? (20)


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Answers

1. a) any of the intermolecular bonding forces (induced dipole, dipole, H-bonding)

b) entities in solution present in minor amounts

c) bonding between more than two atoms; shown by resonance (failure of the Lewis model)

d) a diatomic molecule where both atoms are the same: H2, C2, N2, O2, F2, etc.

e) reactions that occur at the same time; generally reduce the yield of the desired product

2. a) N2H2is trigonal planar (sp2hybridized) with a double bond between the nitrogen atoms

b) IF3 is trigonal bipyramidal (sp3d hybridized), molecular geom: T-shaped

(you work out the structure and formal charges)

c) CO32

is trigonal planar (sp2hybridized) with three equivalent resonance structures

3. see notes

4. internuclear and core-electron repulsion

bound atoms at optimal interaction distance

separated atoms with no interaction

5. see notes for MO diagram; diamagnetic, b.o. = 2

6. O2(induced dipole), PH3(dipole), N2H2(H-bonding), LiF (ionic)

7. CH4is limiting reagent. Yield = 504 g CH2Cl2

8. Fe = 75.0 % by mass

chem 101 - term exam ii - b (1)

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