CHAPTER 10 HW - CHEM 1, G-Chem Inicholschem1.weebly.com/.../2/4/9/12497207/chem1_ch10hw.pdfPage 1 CHAPTER 10 HW Name: Lab: MW 11-2 MW 2-5 INTERMOLECULAR FORCES1 1.) In each, identify

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CHAPTER 10 HW

Name: Lab: MW 11-2 MW 2-5

INTERMOLECULAR FORCES1

1.) In each, identify the intermolecular force pointed to by an arrow.

IMF

2.) Elemental nitrogen (N2) can exist in the liquid state, and is used by dermatologists to freeze off warts and skin tags (at 1 atm its highest temperature is –196 ˚C). In the pure liquid phase, N2 molecules are held together through intermolecular forces. Identify the IMF pointed to by an arrow.

3.) Genetic information is housed in DNA, which has a double helical structure. The strands of DNA are held together through intermolecular forces (IMFs). In the portion of a DNA strand shown below, which connects the nucleic bases cytosine and guanine, identify the IMF pointed to by the arrow.

1 Q1a) Dipole-dipole force, b) London dispersion force (LDF), c) Hydrogen bond; Q2) LDF; Q3) Hydrogen bond.

H Cl

H Cl HCC

HH

H

HH

HCC

HH

H

HH

HN

OH

NO

Cytosine

NCN

CC C

N

O

Guanine

NC N

CCC

NC

NO

N

HH

H

HH

HH

H

N NN N

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4.) For each, sketch the intermolecular forces present in the pure liquid phase.

Draw a second identical molecule to the first, and show how they interact through the strongest possible intermolecular force. Use dashed lines to show the IMF, and identify it.

HBr NH3 HF

Drawing

IMF

H2CO O2 CH3OH

Drawing

IMF

5.) What is the strongest type of intermolecular force present in the liquid state of each of the following?

a. Xe c. H2O

b. CO d. H2S

BOILING POINT2

6.) Phosphorus, arsenic (As), and antimony (Sb) are in the same family of the periodic table. Explain why the boiling point increases from PH3 (–88 ˚C) < AsH3 (–62 ˚C) < SbH3 (–17 ˚C).

2 Q4a) See complete solutions for drawings, Dipole-dipole force, b) NH3, hydrogen bond, c) HF, Hydrogen bond, d) H2CO, dipole-dipole force, e) LDF, f) Hydrogen bond; Q5a) LDF, b) Dipole-dipole force, c) Hydrogen bond, d) Dipole-dipole force; Q6) As molar mass increases, strength of LDF also increases.

H BrH N

H

H H F

HC

H

O

O O H C

H

H

OH

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7.) Butane (C4H10) is a common fuel used in lighters (e.g. butane torches) and has a boiling point of –0.5 ˚C. Acetone (C3H6O) is used as nail polish remover and has a boiling point of 56.1 ˚C.

a. Is each material a liquid or gas at room temperature? Butane: _________ Acetone: ________

b. Use specific intermolecular forces to explain why acetone has a higher boiling point than butane.

8.) In each pair, decide which has the higher boiling point. Then use specific intermolecular forces to explain each answer.

a. Ar vs. HCl

b. C5H12 vs. C6H14

9.) In each pair, decide which has the higher heat of vaporization (DHvap). Then use specific intermolecular forces to explain each answer.3

a. HF vs. HCl

b. Cl2 vs. ICl

3 Q7a) Butane is gas, acetone is liquid, b) Acetone has dip-dip forces while butane has LDF, acetone has stronger IMF; Q8a) HCl, HCl has dip-dip forces (stronger) while Ar has LDF, b) C6H14, as it has higher MM so stronger LDF; Q9a) HF, HF can H-bond, HCl has dip-dip forces, b) ICl, ICl has dip-dip forces, while Cl2 has LDF.

H C

H

H

C

H

H

C

H

H

C

H

H

H CC

C

O

H

H

H

HH H

butane acetone

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10.) SiH4 has a heat of vaporization (DHvap) of 12.10 kJ/mol. Should the DHvap of CH4 be higher or lower than 12.10 kJ/mol? Explain your answer.

11.) Water has a relatively high boiling point for its molecular size because it forms hydrogen bonds. Which is not a reason why water forms especially strong intermolecular forces? (Multiple choice.)

a. There is a large d+ on each H atom in water. b. The O–H bond is very polar. c. The H atom is very small, allowing for close contact of partial charges between water

molecules. d. The O–H covalent bonds are very strong.

LIQUID PROPERTIES4

12.) Mercury atoms forms strong metallic bonds. Knowing this, explain why liquid mercury spilled from an old thermometer does not spread into a thin layer, but instead forms spherical droplets. Use a discussion of intermolecular forces to explain this preferred shape.

13.) Some shampoos use stearyl alcohol (C18H38O) and cetyl alcohol (C16H34O) as thickeners (and for other purposes). Explain why these compounds cause a solution to become highly viscous.

4 Q10) CH4 lower DHvap, SiH4 has higher MM and stronger LDF; Q11) D; Q12) Fewer strong Hg-Hg connections on the surface, so a substance tries to minimize its surface area (as sphere); Q13) Long molecules become entangled in one another.

H CH

HCH

HCH

HCH

HCH

HCH

HCH

HCH

HCH

HCH

HCH

HCH

HCH

HCH

HCH

HCH

HO H

cetyl alcohol

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14.) Multiple choice:5

A water droplet falling and rebounding from a pool of water was captured by a high speed camera, and is shown below. The shape of the water droplet is best explained by ...

a. Water’s surface tension b. Capillary action c. Water’s viscosity d. Water’s low boiling point

Blood hemoglobin is routinely measured in a doctor’s office by a finger prick and withdrawal of a sample of blood into a small glass tube. The blood moves into the glass tube because of ...

a. Blood’s surface tension b. Capillary action c. Blood’s viscosity d. Blood pressure

(Follow-up) On the molecular level, blood moves into the glass tube because ...

a. The water molecules in blood are attracted to the glass through strong intermolecular forces b. The water molecules in blood strongly hydrogen bond to each other c. A portion of the water molecules in blood have a high kinetic energy d. The water molecules vaporize into the tube

Corn syrup is made by treating corn starch with acid and enzymes to break down starch into glucose, which is why corn syrup is sometimes referred to as glucose syrup. Considering the structure of glucose (C6H12O6) shown below, corn syrup is a viscous liquid because the glucose molecules ...

a. Have multiple oxygen atoms b. Minimize their surface area by staying

connected to one another c. Are strongly attracted to the plastic container

through hydrogen bonding d. Hydrogen bond to each other at multiple sites,

making it difficult for them to slide past one another

5 Q14a) A, b) B, c) A, d) D.

C

CC

C

CO C

O

H H

HH

HO

HO

H OH

OH

HH

H

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VAPOR PRESSURE6

15.) Dichloromethane (CH2Cl2) is a solvent sometimes used to decaffeinate coffee beans. It is a liquid at room temperature, and has a vapor pressure of 330 mmHg at 20 ˚C. Should its vapor pressure be higher or lower than 330 mHg at 30 ˚C? Explain why.

16.) Which graph (A–D) correctly depicts the relationship between vapor pressure and temperature?

17.) Which has the lowest vapor pressure at 25 ˚C in each set?

a. Cl2, Br2, I2 c.

b. H2O, CH4, H2

18.) The following graph compares vapor pressure to temperature for 3 compounds: carbon disulfide, ethanol, and heptane. Based on the graph, which compound has the lower boiling point? Briefly explain your answer.

6 Q15) Greater than 330 mmHg, greater percentage of molecules have enough energy to break IMFs; Q16) C; Q17a) I2, b) H2O, c) Middle structure; Q18) CS2 as it has the highest vapor pressure (due to weaker IMFs) at any temperature.

Temp (˚C) Vap

or p

ress

ure

(mm

Hg)

CC

C

O

H

H

H

HH H

CC

CH

H

H

HH H

H H

CC

OHH

HH

H H

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19.) The following temperature and vapor pressure data was collected for benzene (C6H6).

T (˚C) Vapor Pressure, Pvap, (mmHg)

1/T (1/K) ln Pvap

7.6 40.

26.1 100. 0.003342 4.61

60.6 400. 0.002996 5.99

80.1 760. 0.002831 6.63

a. Using the data, what is the normal boiling point of benzene (in ˚C)?

b. Calculate the inverse Kelvin temperature and natural log of the vapor pressure for the first data point (7.6 ˚C, 40. mmHg). Enter these values into the table above.

c. Using the plot of inverse Kelvin temperature and ln Pvap (including the slope and y-intercept data), calculate the heat of vaporization (DHvap) of benzene in kJ/mol.

20.) Temperature and vapor pressure data are collected for alcohol (ethanol) and a graph is plotted with the natural log of the vapor pressure on the y-axis and inverse Kelvin temperature on the x-axis. The graph produces a straight line which has a slope of –5142 and y-intercept of 21.28. Use the graphical data to determine the heat of vaporization of alcohol in kJ/mol.

21.) Estimate the normal boiling point of ether and ethanol (in Kelvin) from the graph of vapor pressure versus temperature.7

Normal b.p. ether:

Normal b.p. ethanol:

7 Q19a) 80.1 ˚C, where Pvap = 760 mmHg, b) 1/T = 0.003562, ln Pvap = 3.7, c) 33.49 kJ/mol; Q20) 42.75 kJ/mol; Q3) Bp ether = ~310 K, Bp ethanol = ~350 K.

m = –4027 b = 18.04

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22.) The vapor pressure of ammonia (NH3) is 2.00 atm at –18.7 ˚C and 20.00 atm at 50.1 ˚C. Calculate the heat of vaporization (in kJ/mol) of NH3.8

23.) The city of Denver, Colorado is nicknamed the Mile High City, as its official elevation is 5280 ft (or 1 mile) above sea level. Water boils at 95.0 ˚C in Denver. Knowing that water has a normal boiling point of 100.0 ˚C and a DHvap of 40.7 kJ/mol, what is the atmospheric pressure in Denver (in torr)?

8 Q22) 22.8 kJ/mol; Q23) 640 torr.

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24.) Carbon disulfide (CS2) has a similar Lewis structure to carbon dioxide (CO2), but has different properties. CS2 is a liquid at room temperature, while CO2 is a gas, and CS2 is highly flammable while CO2 is not.9

a. Using specific intermolecular forces, explain why CS2 is a liquid at room temperature while CO2 is a gas.

b. A compound’s flammability is partially dependent on its vapor pressure, as vapors are what burn, not liquids. If insufficient vapors are present, a compound will not ignite. The minimum vapor pressure of CS2 that a match can ignite is 11.3 mmHg (this is the “flash point”). At what temperature (in ˚C) does this occur? CS2 has a DHvap of 28.7 kJ/mol and a normal boiling point of 46.5 ˚C.

25.) A pressure cooker (kitchen appliance) is a pot with a tight seal, allowing pressure to build. Most have a setting of 15 psi, which means the pressure is 15 psi (~1 atm) above atmospheric pressure (therefore a total pressure of ~2 atm at sea-level). At sea-level, water boils at ~119 ˚C inside a pressure cooker, and therefore food cooks more quickly. Explain why water boils at a higher temperature at 2 atm compared to 1 atm.

9 Q24a) CS2 has a higher boiling point (greater MM so stronger LDF) b) –43 ̊ C; Q25) Boiling occurs when vapor pressure matches atmospheric pressure; a higher temp is needed to produce a vapor pressure of 2 atm..

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MULTIPLE PHASE CHANGES10

26.) A beaker of water is set atop a hotplate and brought to a boil. Although energy is continually supplied via the hotplate, explain why the temperature remains at 100 ˚C while water remains in the beaker.

27.) Calculate the heat energy (q) associated with each transformation.

a. 150.0 g of ice at 0.0 ˚C is melted into water at 0.0 ˚C. q=?

b. 150.0 g of water at 0.0 ˚C is frozen into ice at 0.0 ˚C.

c. 150.0 g of water at 75.0 ˚C is completely boiled (turned to 100.0 ˚C steam).

28.) Calculate the amount of energy (as heat) needed to convert 5.00 g of water at 20.0 ˚C into steam at 115.0 ˚C.

10 Q26) Energy is used to break IMF, none left to increase motion and temp; Q27a) 50.1 kJ, b) –50.1 kJ, c) 355 kJ; Q28) 13.1 kJ.

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29.) A sample of sodium metal (0.250 g) is dropped into a mixture of 50.0 g water and 50.0 g ice, both at 0 ˚C. The sodium reacts with the water through the following equation, releasing energy as shown by the change in enthalpy. When the reaction is complete, has the ice melted or not? Show calculations to support your answer.

2 Na (s) + 2 H2O (l) → 2 NaOH (aq) + H2 (g) DH˚ = –368 kJ

PHASE DIAGRAMS11

30.) For the following phase diagram,

a. Identify the phase(s) present at each point.

A: ____________________

B: ____________________

C: ____________________

D: ____________________

E: ____________________

F: ____________________

G: ____________________

H: ____________________

b. Where is the triple point? ________

c. Where is the critical point? ________

d. On the diagram, label the normal melting point and normal boiling point.

11 Q29) –2.00 kJ is released, but it takes 16.7 kJ to melt the ice. The ice won’t melt; Q30a) A: solid, B: liquid, C: gas, D: s, g, E: s, l, g, F: l, g, G: l, g, H: supercritical fluid, b) E, c) G, d) where P =1 atm, T-mp = dashed line to left, T-bp = dashed line to right.

Temperature

Pres

sure

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31.) The following is a phase diagram of “Compound X”. 12 Although phase diagrams are often not to scale, assume this diagram is to scale.

a. If Compound X was at room temperature in a lab at Butte College, in what phase(s) would it exist? ____________________

b. Which process would occur if its temperature was increased, without changing pressure?

A: It would boil. B: It would condense. C: It would melt. D: It would freeze. E: It would sublime. F: It would deposit.

c. On the diagram, mark the following locations with a dot and letter:

Mark “A” anywhere Compound X exists only as a liquid.

Mark “B” anywhere Compound X is freezing.

Mark “C” anywhere Compound X exists as a supercritical fluid.

32.) The following heating curve and phase diagram are of two different substances. Use each to estimate the following physical properties.

a. Melting point: __________ b. Boiling point: __________

c. Normal melting point: __________ d. Normal boiling point: __________

33.) Butane (C4H10) is a gas at room temperature, but can be converted to a liquid if...

a. It is heated to a very high temperature. b. A high enough pressure is applied. c. Intermolecular forces are broken. d. X-rays are shined on it.

12 Q31a) Solid, b) E, sublime, c) See complete solutions; Q32a) 20 ˚C, b) 120 ˚C, c) 170 K, d) 260 K; Q33) B.

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CRYSTALLINE SOLIDS13

34.) Polonium (Z = 84) is a highly reactive metal with no stable isotopes, and is used as a radioactive heat source for satellites and the Moon rovers. Polonium crystallizes with a simple cubic unit cell. Calculate the following:

a. The number of polonium atoms in one unit cell.

b. The packing efficiency for the metal, to 3 significant figures.

c. The percentage of space unoccupied by polonium atoms in the metal (to 3 SFs).

d. The length of one edge of the unit cell (length ‘l’) in picometers (pm). The radius of a polonium atom is 169 pm (where 1 × 1012 pm = 1 m).

35.) Nickel metal crystallizes with a face-centered cubic unit cell. The radius of a nickel atom is 124 pm. What is the length of one edge of the unit cell of nickel (length ‘l’) in pm?

13 Q34a) 1 Po atom, b) 52.4%, c) 47.6%, d) 338 pm; Q35) 351 pm.

length l

length l

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36.) Silver metal crystallizes with a face-centered cubic unit cell. The edge of the unit cell (length ‘l’) is 407 pm. What is the radius of a silver atom in picometers? 14

37.) Calculate the packing efficiency (to 3 SFs) of the atoms in a face-centered cubic unit cell.

38.) Sodium metal crystallizes with a body-centered cubic unit cell. Calculate the number of Na atoms in the unit cell, and the coordination number of the sodium.

39.) Copper metal crystallizes with a face-centered cubic unit cell. What is the coordination number of the copper?

40.) Sodium bromide crystallizes in the same manner as NaCl. Describe the unit cell of NaBr, including the type of unit cell (simple cubic, face-centered cubic, or body-centered cubic) and location of the cations and anions. Sketch one face of the unit cell.

14 Q36) 144 pm; Q37) 74.0%; Q38) 2 Na atoms, CN = 8; Q39) CN=12; Q40) Face-centered cubic, Br– ions on edges and faces, Na+ in cracks, See complete solutions for drawing.

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41.) Multiple choice:15

The unit cell with the highest coordination number is:

a. Simple cubic b. Body-centered cubic c. Face-centered cubic

Pure gold is 24 K (24 karat), but gold-silver alloys are much more commonly encountered in jewelry. 18 K “yellow” gold contains 75% Au, 12.5% Ag, and 12.5 % Cu. As the gold, silver, and copper atoms replace each other in the crystal lattice, 18 K gold is considered a ...

a. Substitutional alloy b. Interstitial alloy c. Ionic solid d. Covalent molecule

Cesium chloride forms the following unit cell, with a Cs+ ion at the middle of the unit cell shown and Cl– ions on the corners. Which is NOT true about this unit cell?

a. The Cl– ions form a simple cubic unit cell b. The unit cell is body-centered cubic c. The coordination number of the Cs+ ion is 8 d. The Cl– ions do not touch each other

Which is NOT true about the “electron sea model” to describe metallic bonding?

a. Valence electrons are shared by all metal atoms b. Valence electrons are stationary around each metal nucleus c. The metal nuclei form cations which attract the sea of valence electrons d. The model explains how metals conduct electricity and heat.

Quartz (SiO2) is classified as a(n)…

a. Ionic solid b. Molecular solid c. Network solid d. Metallic solid

Which solid should have the highest melting point?

a. C6H12O6 b. H2O c. H2C2O4 d. KBr

15 Q41a) C, face-centered cubic, b) A, substitutional alloy, c) B, not bcc, d) B, valence not static, e) C, network solid, f) D, KBr.