Chapter 11 Sample Questions PDF

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Chapter 11 – Exam-Type Questions Multiple Choice

1. Acetaldehyde (pictured to the right) is a product of the oxidation of ethanol in your liver, and is the molecule primarily responsible for hangovers. Which one of the following statements best describes the intermolecular forces experienced by a molecule of acetaldehyde in its pure liquid form and when it is dissolved in water.

O

a. Acetaldehyde is a nonpolar molecule, so it is attracted to other molecules of acetaldehyde in the pure liquid or to water only via dispersion forces. b. Acetaldehyde molecules are attracted to other molecules of acetaldehyde (in the pure liquid) and water via dispersion and dipolar forces. Since acetaldehyde does not contain any O–H bonds, it cannot form hydrogen bonds with other acetaldehyde molecules or with water molecules. c. Acetaldehyde molecules are attracted to other molecules of acetaldehyde (in the pure liquid) and water via dispersion, dipolar forces, and hydrogen bonds. Since acetaldehyde does not contain any O–H bonds, it cannot form hydrogen bonds with other acetaldehyde molecules or with water molecules. d. Acetaldehyde molecules are attracted to other molecules of acetaldehyde (in the pure liquid) and water via dipolar forces. Dispersion forces are not present. Since acetaldehyde does not contain any O–H bonds, it cannot form hydrogen bonds with other acetaldehyde molecules or with water molecules. e. In its pure liquid form, acetaldehyde molecules are attracted to each other via dispersion and dipolar forces. When dissolved in water, acetaldehyde molecules can form hydrogen bonds between the O lone pairs of acetaldehyde and the H atoms of water molecules; acetaldehyde and water molecules are also attracted to each other via dispersion and dipolar forces. 2. An unknown solid material is crystalline and has a face-centred cubic unit cell. The material has a band gap of zero and is a conductor of electricity, with conductivity decreasing as temperature increases. The unknown material is most likely which one of the following types of solids? a. b. c. d. e.

Ceramic Ionic Metal Metalloid Network covalent

H

3. Why does a meniscus form when you fill a glass pipette or burette with an aqueous solution? a. The adhesive forces between glass and water are stronger than the cohesive forces between water molecules in the liquid, allowing the liquid to rise up the sides of the glass against the force of gravity. b. The anions in the solution are attracted to the silicate cations in the glass, allowing the liquid to rise up the sides of the glass against the force of gravity. c. The water molecules in the centre of the pipette or burette are heavier, so they sink deeper than the molecules along the sides of the glassware. d. The anions and the cations in solution repel each other, forcing them to rise up the sides of the glass against the force of gravity. e. The surface tension of water collapses in thin tubing, leading to “sagging” in the middle of a burette or pipette.

4. Complete this sentence: Hexagonal close packed structure result in a packing order of (i) and atoms with a coordination number of (ii) . a. b. c. d. e.

(i) ABABAB ABABAB ABCABC ABCABC ABCABC

(ii) 12 6 6 8 12

5. Which of the following will have the highest vapour pressure at room temperature? a. b. c. d. e.

pentane, CH3CH2CH2CH2CH3 hexane, CH3CH2CH2CH2CH2CH3 heptane, CH3CH2CH2CH2CH2CH2CH3 octane, CH3CH2CH2CH2CH2CH2CH2CH3 nonane, CH3CH2CH2CH2CH2CH2CH2CH2CH3

6. When the following substances solidify, what type of solid will each one form? a. b. c. d. e.

SiO2 ionic molecular molecular network network

Rh molecular ionic molecular metallic metallic

CS2 molecular ionic network molecular network

Ba3N2 network molecular ionic ionic molecular

7. In both the liquid and solid state, formaldehyde (HCOOH) molecules form dimers which are pairs of molecules that are attracted to each other via hydrogen bonds. In each of the three dimers depicted below, two HCOOH molecules interact with each other via different orientations. The dashed lines represent hydrogen bond interactions between the two molecules. Which option(s) below show the strongest forces of attraction between two HCOOH molecules? (i) H

O

(ii) H

H

O

(iii)

H

H

O O

O

H

H

O

O

H

O

O O

O

H

H

O

H

H

a. b. c. d.

(i) (ii) (iii) Forces of attraction between the two HCOOH molecules are stronger for (ii) and (iii), and weaker for (i). e. Forces of attraction between the two HCOOH molecules are similar for (i), (ii), and (iii).

8. Which one of the following processes is endothermic? a) The formation of ice on the Red River. b) The evaporation of bath water from your body in the morning. c) The formation of new chemical bonds. d) The cooling down of an energy drink in a refrigerator. e) The chemical reaction in a "hot pack" often used to treat sore muscles.

Short Answers 9. When ionic solids dissolve in water, anions and cations dissociate from the crystal lattice. What is the strongest interactions experienced by anions and cations in aqueous solutions?

10. Aluminum has a face-centred cubic structure. Aluminum has a radius of 143 pm. What is the volume of the unit cell of aluminum in units of cm3?

11. At 1.00 atm, the boiling point of 2,3,4-trimethypentane, C8H18, is 113.47 °C, and its molar enthalpy of vaporization is 37.600 kJ mol-1. What is its vapor pressure, in units of bar, at 105.5 °C?

12. Bromine is one of only two elements that is a liquid at room temperature. The graph below shows vapour pressure data for bromine obtained from the CRC Handbook; the line of best fit has slope = –4910 K and intercept = 15.2. What are the values of enthalpy and entropy of vapourization, ΔHvap for bromine?

13. A student mixed 5.00 g (0.0594 mol) of solid cyclohexane, C6H12, (84.18 g mol–1) at its melting temperature of 6.6°C with 50.0 g (0.594 mol) of liquid cyclohexane at 50.0°C in an open yet insulated container. After thermal equilibrium was established, the temperature of the mixture was 44.5°C. The specific heat capacity of liquid cyclohexane is 1.809 J g–1 K–1, and is assumed to be constant over the temperature interval. From this information, what is the molar enthalpy of fusion, ΔHfusion, of cyclohexane?

14. You chop out a 500 g sample of ice out of the Red River when it –40°C outside, then you bring the ice sample indoors where it melts and heats up to 25°C. Assuming that Red River ice is composed of pure water, what is the total energy is absorbed by the ice sample? Water Data Density of water

1.00 g/mL

Heat capacity of ice:

2.09 J g–1 K–1

Heat capacity of liquid water:

4.18 J g–1 K–1

Heat capacity of water vapour:

2.01 J g–1 K–1

Enthalpy of fusion:

6.02 kJ mol–1

Enthalpy of vapourization:

40.7 kJ mol–1

Melting point (1 bar):

273 K

Boiling point (1 bar):

373 K

15. Strontium titanate is a mineral used in simulated diamonds. Its unit cell is provided below. What is the empirical formula for this mineral?   

Eight Sr atoms reside on the corners Six O atoms reside on the faces One Ti atom occupies the centre of the unit cell

16. A mineral that contains aluminum, copper, and chlorine atoms has the orthorhombic unit cell pictured below. What is the empirical formula for this mineral? 





Al atoms are the four smallest spheres; all of which are in face-centred positions. Cu atoms are the twelve medium-sized black spheres; eight atoms on the corners and four atoms are on the edges Cl atoms are the eight largest spheres, al of which are inside the unit cell

Long Answer

17. Silver (Ag) metal has a face-centred cubic unit cell and has a density of 10.59 g/cm3. What is the atomic radius, in pm, of a silver atom?

18. a. Indicate with an X which intermolecular force(s) must be overcome when the following pure liquids are vapourized. b. In the last column, rank the order of the boiling points for these liquids with numbers 1 – 4 where 1 has the lowest boiling point and 4 has the highest boiling point. Compound

(dipole-dipole)

(London dispersion)

Hydrogen

dipolar forces

dispersion forces

bonding

Boiling point order

O

O H2N

OH H2N

19. How much energy is required to heat 36.0 g (2.00 mol) H2O from a liquid at 65°C to a gas at 115°C? Water Data Density of water

1.00 g/mL

Heat capacity of ice:

2.09 J g–1 K–1

Heat capacity of liquid water:

4.18 J g–1 K–1

Heat capacity of water vapour:

2.01 J g–1 K–1

Enthalpy of fusion:

6.02 kJ mol–1

Enthalpy of vapourization:

40.7 kJ mol–1

Melting point (1 bar):

273 K

Boiling point (1 bar):

373 K

20. Use the phase diagram below to answer the following questions.

a. b. c. d.

Label points x, y and z in the phase diagram. At what temperature does the substance vaporize at 0.50 atm? Does the substance sublime under normal conditions? Explain. At what temperature and pressure does a supercritical fluid form?

Answers Multiple Choice 1. 2. 3. 4. 5. 6. 7. 8.

E C A A A D A B

Short Answer 9. Ion-dipole interactions 10. 6.64 x 10-23 cm3

11. 0.7819 bar 12. 40.8 kJmol-1 13. 2.60kJ mol-1 14. 261 kJ 15. SrTiO3 16. AlCuCl4 Long Answer

17. 144.1 pm 18. Compound

(dipole-dipole)

(London dispersion)

Hydrogen

dipolar forces

dispersion forces

bonding

X

X

X

X

Boiling point order

O

2

O H2N

X

X

3

1

OH H2N

X

19. 87.7 kJmol-1 20. Answers: a. X = solid; Y= liquid ; Z = gas b. 92°C

X

X

4

c. No. Explanation that shows a student understands normal conditions and how to read a phase diagram. d. T = 225°C, P = 1.25 bar...