Download Week 8 – Intermolecular Forces

Week 8 – Intermolecular Forces
NO CALCULATORS MAY BE USED FOR THESE QUESTIONS
Questions 1-3 refer to the following list.
(A) Cu
(B) PH3
(C) C
(D) SO2
(E) O2
1. Contains instantaneous dipole moments.
2. Forms covalent network solids.
3. Exists as a lattice structure held together by delocalized electrons.
4. Sodium chloride is least soluble in which of the following liquids?
(A) NH3
(B) H2O
(C) C6H6
(D) C2H5OH
(E) CH3COOH
5. Methanol, CH3OH, has a higher boiling point than ethene, C2H4. Which of the following statements
best accounts for this difference?
(A) Methanol exhibits stronger London (dispersion) forces than ethene.
(B) Methanol is a covalent network solid and ethane is not.
(C) Methanol has a higher density than ethane.
(D) Methanol exhibits dipole to dipole forces and ethane does not.
(E) Methanol exhibits hydrogen bonding and ethane cannot.
6. Which of the following substances exhibits the greatest dipole moment?
(A) CO
(B) HF
(C) CH4
(D) PH3
(E) F2
7. Which of the following substances is a nonpolar molecule that contains polar bonds?
(A) Cl2
(B) CHF3
(C) HF
(D) NH3
(E) CO2
Week 8 – Intermolecular Forces
8. Which of the following substances would be expected to exhibit the highest melting point?
(A) F2
(B) Cl2
(C) Br2
(D) I2
(E) N2
Substance
Acetaldehyde
Methyl isobutyl ketone
Benzene
Ethanol
Propanol
Equilibrium Vapor Pressure (mmHg)
740
19.95
75
43.7
18.0
9. Based on the data in the table provided above, which of the following liquid substances has the weakest
intermolecular forces?
(A) Acetaldehyde
(B) Methyl isobutyl ketone
(C) Benzene
(D) Ethanol
(E) Propanol
Ion
Mg2+
Ca2+
Sr2+
Ionic Radius (pm)
86
114
132
10. Based on the data in the table above, which of the following correctly predicts the relative strength of
attraction of Mg2+, Ca2+, and Sr2+ ions to water molecules in a solution, from strongest to weakest, and
provides the correct reason?
(A) Mg2+ > Ca2+ > Sr2+ because smaller ions have a stronger coulombic attraction to the water molecules
(B) Mg2+ > Ca2+ > Sr2+ because the smaller ions experience a stronger nuclear charge
(C) Mg2+ > Ca2+ > Sr2+ because the smaller ions experience greater electronegativity
(D) Sr2+ > Ca2+ > Mg2+ because larger ions have more instantaneous dipoles or are more polarizable
(E) Sr2+ > Ca2+ > Mg2+ because the larger ions have greater shielding
Week 8 – Intermolecular Forces
11. In the diagram above, which of the following arrows identifies the hydrogen bonding in ammonia?
(A) A
(B) B
(C) C
(D) D
(E) E
12. Lewis electron-dot diagrams of CO2 and NO2- are given above. The molecular geometry and polarity of
the two substances are
(A) The same because the molecular formulas are similar.
(B) The same because each exhibits pi bonding.
(C) The same because both molecules are linear.
(D) Different because the lone pair of electrons on the N atom make it the negative end of a dipole.
(E) Different because N has a greater number of electron domains (regions of electron density)
surrounding it as compared to C.
13. Which of the following solid compounds requires heat to break the lattice energy in order to melt?
(A) CCl4
(B) CaCl2
(C) BrCl
(D) PCl3
(E) Cl2O
Week 8 – Intermolecular Forces
14. The diagrams above show molecules of Cl2 and Br2 drawn to the same scale. Which of the following is
the best explanation for Cl2 being a gas at room temperature as opposed to liquid Br2?
(A) Liquid bromine is a network covalent substance, whereas gaseous chlorine is a London dispersion
forces gas.
(B) The covalent bonding between Br2 is weaker than those in the Cl2 molecules.
(C) The bond length of Br2 is longer as opposed to the shorter bond lengths of Cl2.
(D) Br2 molecules have electron clouds that are more polarizable than those of Cl2 molecules, therefore
the London dispersion forces are stronger in liquid Br2.
(E) Cl2 has a greater electronegativity than Br2, therefore they have stronger dipole to dipole attractions.
15. What is the best reason for H2O having a higher boiling point as compared to H2S?
(A) H2O is polar whereas H2S is nonpolar
(B) H2O exhibits hydrogen bonding whereas H2S exhibits London (dispersion) forces
(C) H2O exhibits hydrogen bonding whereas H2S exhibits dipole to dipole interactions
(D) H2O is a liquid whereas H2S is a gas
(E) H2S is more polarizable due to the greater amount of electrons
16. Of the following pure substances, which has the highest melting point?
(A) SiO2
(B) S8
(C) I2
(D) SO2
(E) C6H6
17. Iron, Fe, can be made into an alloy by mixing other elements such as carbon (C) or Manganese (Mn). If
the same mole fraction of C and Mn are introduced separately into samples of Fe, which of the
following is the best explanation for the Fe-C alloy being harder than the Fe-Mn alloy?
(A) C is a nonmetal whereas Mn is a metal.
(B) C atoms are smaller than Mn atoms, therefore they interfere more with the displacement of atoms in
the alloy.
(C) Mn atoms are less polarizable than the C atoms, therefore Mn has weaker intermolecular forces.
(D) C atoms have a higher melting point than Mn atoms.
(E) Mn atoms have similar metallic forces to the Fe, therefore the properties do not change much when
made into an alloy.
Week 8 – Intermolecular Forces
18. Based on the data in the tables above, which of the following statements provides the best prediction for
the melting point of NaBr?
(A) NaBr will have a higher melting point than MgO because the energy required to transfer electrons is
larger in NaBr than in MgO.
(B) NaBr will have a higher melting point than MgO because the ions are spaced further apart.
(C) NaBr will have a melting point in between that of NaF and MgO because the ionic character of the
bonds in NaBr is in between that of NaF and MgO.
(D) NaBr will have a lower melting point than NaF because the coulombic attractions are weaker in
NaBr than in NaF.
(E) NaBr will have a lower melting point than MgO due to the lower covalent character of the bonds in
NaBr.
Compound
decane
2-bromobutane
Molecular Formula
C10H22
C4H9Br
Molar Mass (g/mole)
142
137
Boiling Point (°C)
174
91
19. According to the data table above, the two molecules represented above have comparable molar masses
and yet extremely different boiling points. Which of the following statements best helps to explain this
data?
(A) The C-Br bond of 2-bromobutane has smaller bond energy compared to the C-H bonds of decane.
(B) The C-Br bond of 2-bromobutane is more polar than the C-H bonds of decane.
(C) The carbon chains are longer in decane than they are in 2-bromobutane.
(D) The carbon chains are farther apart in a sample of decane than they are in 2-bromobutane.
(E) The decane molecule contains covalent network bonds which take more energy to break.
20. Semiconductors are materials that have a degree of electrical conductivity between a metal and an
insulator. Silicon crystals are semiconductors that increase in conductivity when a small fraction of Si
atoms are replaced by those of a different element. Which reason best accounts for this property
change?
(A) Ge atoms experience greater shielding than Si atoms.
(B) P atoms introduce additional mobile positive charges.
(C) P atoms introduce additional mobile negative charges.
(D) C atoms introduce hardness to the material.
(E) Ge atoms have more electrons than Si atoms.