AP Chemistry Compounds 2015-09-14 www.njctl.org Slide 3 / 126 - - PDF document

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AP Chemistry

Compounds

2015-09-14 www.njctl.org

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Table of Contents: Compounds Pt. B

· States of Matter · Molecular Geometry

Click on the topic to go to that section

· Introduction to Solubility · Intermolecular Forces

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Molecular Geometry

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Slide 4 / 126 Molecular Shapes

Molecules are three dimensional objects. Their shapes affect their properties. In order to determine the shape of a molecule we use Valence-Shell Electron-Pair Repulsion theory (VSEPR). According to VSEPR theory, the molecules will adopt a shape/geometry that will reduce the repulsion between the bonded electrons; the electrons want to be as far apart as possible.

Slide 5 / 126 VSEPR Numbers

VSEPR theory assigns a 3-digit code to each molecular shape. To determine this code we must first sketch the Lewis structure.

• 1. The first digit of the VSEPR number is

the total number of electron-domains around the central atom. That means the total number of bonds and lone

• pairs. Note: Double and triple bonds only

count as 1 electron domain. 3 6

O O O

3

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Molecular Shape and VSEPR Theory

Electron Domain Geometries

"AB" Designation (# of bonds) # of unbonded pairs of electrons on "A" atom Shape Bond Angles Example

AB2 linear 180 AB3 trigonal planar 120 AB4 tetrahedral 109.5 AB5 trigonal bypyramidal 90, 120, 180 AB6

• ctahedral

90, 180

**Note: Pi bonds act with the sigma bonds to contribute to the repulsions that result in the molecular shape, however they do not act as a separate constituent around the "A" atom.

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1 What is the electron domain geometry of CH

4?

A

linear

B

trigonal planar

C

tetrahedral

D

• ctahedral

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1 What is the electron domain geometry of CH

4?

A

linear

B

trigonal planar

C

tetrahedral

D

• ctahedral

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Answer C

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2 What is the EDG of H 2O?

A

linear

B

trigonal planar

C

tetrahedral

D

• ctahedral

H H O Slide 9 / 126

2 What is the EDG of H 2O?

A

linear

B

trigonal planar

C

tetrahedral

D

• ctahedral

H H O

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Answer C

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3 What is the EDG of CO2?

A

linear

B

trigonal planar

C

trigonal bipyramidal

D

• ctahedral

C O O

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3 What is the EDG of CO2?

A

linear

B

trigonal planar

C

trigonal bipyramidal

D

• ctahedral

C O O

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Answer B

Slide 10 (Answer) / 126 VSEPR Numbers

• 2. The second digit of the VSEPR

number is the total number

• f bonding-domains around the

central atom. That means the number

• f single, double or triple bonds.

Remember, double and triple bonds

• nly count as 1 domain.

3 3 6 4

O O O

3 2

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4

Students type their answers here

3 3 0 6 4 2

O O O

3 2 1

VSEPR Numbers

• 3. The third digit of the VSEPR number

is the total number of lone pairs around the central atom. You can check your work - the first digit is always equal to the sum of the second and third. What are the shapes of BH3, XeF4, and O3?

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4

Students type their answers here

3 3 0 6 4 2

O O O

3 2 1

VSEPR Numbers

• 3. The third digit of the VSEPR number

is the total number of lone pairs around the central atom. You can check your work - the first digit is always equal to the sum of the second and third. What are the shapes of BH3, XeF4, and O3?

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Answer BH

3 - Trigonal Planar

XeF

4 - Square Planar

O

3 - Bent

117

Slide 12 (Answer) / 126 Molecular Geometry

The molecular geometry of a molecule is the shape formed by the bonded atoms. Lone pairs may play a role by decreasing the angle between bonded elements. This occurs because lone pairs generate a greater force of repulsion.

Click here to view a PhET simulation

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I

NF 3 Practice

Elements Bonds & Electrons

Cl H C O N S F Xe B

Draw a Lewis Structure and determine the electron domain geometry (EDG) and the molecular geometry (MG). For Ions

+ -

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I

NF 3 Practice

Elements Bonds & Electrons

Cl H C O N S F Xe B

Draw a Lewis Structure and determine the electron domain geometry (EDG) and the molecular geometry (MG). For Ions

+ -

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Answer

N F F F

4 3 1 EDG: tetrahedral MG: trigonal pyramidal

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I

SiF 4 Practice

Elements Bonds & Electrons

Cl H C O N S F Xe B

Draw a Lewis Structure and determine the electron domain geometry (EDG) and the molecular geometry (MG).

Si

For Ions

+ -

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I

SiF 4 Practice

Elements Bonds & Electrons

Cl H C O N S F Xe B

Draw a Lewis Structure and determine the electron domain geometry (EDG) and the molecular geometry (MG).

Si

For Ions

+ -

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Answer

4 4 0 EDG: tetrahedral MG: tetrahedral

F Si F F F

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I

IF5 Practice

Elements Bonds & Electrons

Cl H C O N S F Xe B

Draw a Lewis Structure and determine the electron domain geometry (EDG) and the molecular geometry (MG).

Si

For Ions

+ -

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I

IF5 Practice

Elements Bonds & Electrons

Cl H C O N S F Xe B

Draw a Lewis Structure and determine the electron domain geometry (EDG) and the molecular geometry (MG).

Si

For Ions

+ -

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Answer

6 5 1 EDG: octahedral MG: square pyramidal

F F I F F F

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I

NO 2- Practice

Elements Bonds & Electrons

Cl H C O N S F Xe B

Draw a Lewis Structure and determine the electron domain geometry (EDG) and the molecular geometry (MG).

Si

For Ions

+ -

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I

NO 2- Practice

Elements Bonds & Electrons

Cl H C O N S F Xe B

Draw a Lewis Structure and determine the electron domain geometry (EDG) and the molecular geometry (MG).

Si

For Ions

+ -

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Answer

3 2 1 EDG: trigonal planar MG: bent

N O O

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5 Which of the following would have a see-saw shape? A I only B II only C III only D I and II only

• I. XeO2F2
• II. IBr3
• III. SeH2

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5 Which of the following would have a see-saw shape? A I only B II only C III only D I and II only

• I. XeO2F2
• II. IBr3
• III. SeH2

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Answer A

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6 Which of the following is ranked properly from largest to smallest bond angles within the molecule? A II only B III only C II and III only D I, II, and III

• I. CH4, PCl3, SF5
• II. XeF2, H2O, XeF4
• III. NO3-, NO2-, CH4

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6 Which of the following is ranked properly from largest to smallest bond angles within the molecule? A II only B III only C II and III only D I, II, and III

• I. CH4, PCl3, SF5
• II. XeF2, H2O, XeF4
• III. NO3-, NO2-, CH4

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Answer D

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7 Which of the following does NOT have a bent shape? A BeCl2 B SeH2 C SCl2 D OH2

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7 Which of the following does NOT have a bent shape? A BeCl2 B SeH2 C SCl2 D OH2

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Answer A

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8 Which of the following has a planar shape? A C2H4 B PH3 C SiH4 D PF5

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8 Which of the following has a planar shape? A C2H4 B PH3 C SiH4 D PF5

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Answer A

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9 Which of the following contribute to the shape of the molecule? A Only the number of bonded e- pairs around atom B Only the number of un-bonded and bonded e- pairs around the atom C Only the atomic radii of atoms D Only the atomic radii and bonded e- pairs around the atom

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9 Which of the following contribute to the shape of the molecule? A Only the number of bonded e- pairs around atom B Only the number of un-bonded and bonded e- pairs around the atom C Only the atomic radii of atoms D Only the atomic radii and bonded e- pairs around the atom

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Answer B

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10 Which of the following is TRUE regarding the effect of substitution of un-bonded pairs of electrons in place of bonded pairs of electrons on the molecular shape? A The bond angle increases due to the decreased repulsions B The bond angle decreases due to the decreased repulsions C The bond angle decreases due to the increased repulsions D The bond angle increased due to the increased repulsions

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10 Which of the following is TRUE regarding the effect of substitution of un-bonded pairs of electrons in place of bonded pairs of electrons on the molecular shape? A The bond angle increases due to the decreased repulsions B The bond angle decreases due to the decreased repulsions C The bond angle decreases due to the increased repulsions D The bond angle increased due to the increased repulsions

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Answer C

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11 Which of the following would be the correct shape of the BF3 molecule? A bent B trigonal planar C trigonal pyramidal D see-saw

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11 Which of the following would be the correct shape of the BF3 molecule? A bent B trigonal planar C trigonal pyramidal D see-saw

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Answer B

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Slide 25 / 126 Slide 25 (Answer) / 126 Molecular Polarity

Two factors contribute to the polarity of a molecule: Polarity of bonds Polar bonds are necessary for a molecule to be polar but do not guarantee polarity. Symmetry To be polar a molecule must be asymmetrical to ensure an uneven distribution of electrons. Molecules in which the electrons are not evenly distributed experience a dipole moment when in an electric field and are said to be polar.

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Molecular Polarity

Asymmetrical Shapes Bent, Trigonal pyramidal, T-Shape, See-saw, Square pyramidal Asymmetry and polarity can also result from a heterogenous group of atoms attached to the central atom thereby creating asymmetrical differences in electronegativity. CHCl3 is a classic example.

• +

Certain shapes are asymmetrical in nature due to unbonded electrons and can, therefore, result in polar molecules.

Slide 27 / 126 Molecular Polarity

H2O H2S

S H H

Both molecules are asymmetrical and exhibit a dipole moment but water's dipole moment is significantly higher than hydrogen sulfide due to the greater electronegativity difference between O and H.

Dipole moment = 1.85 D Dipole moment = 0.97 D

If the molecule is asymmetrical, the more polar the bonds, the more polar the molecule

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13 Which of the following molecules would have the highest dipole moment? A NH3 B PH3 C BF3 D CH4

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13 Which of the following molecules would have the highest dipole moment? A NH3 B PH3 C BF3 D CH4

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Answer A

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14 Which of the following molecules would be expected to have the highest dipole moment? A BeCl2 B CO2 C HCN D H2S

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14 Which of the following molecules would be expected to have the highest dipole moment? A BeCl2 B CO2 C HCN D H2S

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Answer C

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15 Which of the following is TRUE regarding molecular polarity? A Polar molecules must be asymmetrical and have polar bonds B Polar molecules must have polar bonds and can be symmetrical or asymmetrical C Polar molecules cannot have polar bonds D Polar molecules do not require polar bonds but do require asymmetry

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15 Which of the following is TRUE regarding molecular polarity? A Polar molecules must be asymmetrical and have polar bonds B Polar molecules must have polar bonds and can be symmetrical or asymmetrical C Polar molecules cannot have polar bonds D Polar molecules do not require polar bonds but do require asymmetry

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Answer A

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16 Which of the following explains the low dipole moment of CCl4 (0.0 D)? A There is a small electronegativity difference between C and Cl B The bonds are non-polar C The molecule is symmetrical D The atoms in the molecule are small E The IR spectra for the molecule has few peaks

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16 Which of the following explains the low dipole moment of CCl4 (0.0 D)? A There is a small electronegativity difference between C and Cl B The bonds are non-polar C The molecule is symmetrical D The atoms in the molecule are small E The IR spectra for the molecule has few peaks

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Answer C

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Intermolecular Forces

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Slide 33 / 126 Intermolecular Forces

INTRAMOLECULAR INTERMOLECULAR attractive forces within a molecule attractive forces between different molecules

*Note: Intermolecular forces are much weaker than intramolecular forces due to the greater distance between charges which diminishes the Coulombic attractions.

Covalent bonds are intramolecular forces. The properties of a substance also depend on intermolecular forces (IMFs). IMFs exist between neighboring molecules as opposed to intramolecular forces which exist inside molecules.

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London Dispersion Forces

London dispersion forces occur between all molecules and are caused by the temporary polarization of molecules due to the random positions of electrons

e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e-

• +

Normal Polarized

e- e- e- e- e- e- e- e-

• +

e- e- e- e- e- e- e- e-

• +

These polarized molecules then form attractions called London dispersion forces. London Dispersion Force There are essentially two types of IMFs: London Dispersion Forces and Dipole-Dipole Forces.

Slide 35 / 126 London Dispersion Forces

Iodine (I2) Flourine (F2) 106 electrons 18 electrons MP = 113.7 C, solid @ 25 C MP = -219.7 C, gas @ 25 C The surface area of the molecule also influences the ability of "LDF's" to form. The greater the surface area, the greater the "LDF's", all else being equal. The greater the number of electrons in the molecule, the greater the polarization and the stronger the London dispersion forces will be.

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17 The indicated interaction pointed to by arrow is an intermolecular force. True False

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17 The indicated interaction pointed to by arrow is an intermolecular force. True False

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Answer False

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18 Which of the following is TRUE regarding intra and inter molecular forces? A Intra are stronger due to decreased coulombic attractions B Intra are stronger due to increased coulombic attractions C Inter are stronger due to decreased coulombic attractions D Inter are stronger due to increased coulombic attractions

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18 Which of the following is TRUE regarding intra and inter molecular forces? A Intra are stronger due to decreased coulombic attractions B Intra are stronger due to increased coulombic attractions C Inter are stronger due to decreased coulombic attractions D Inter are stronger due to increased coulombic attractions

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Answer B

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19 Which of the following would experience the greatest London dispersion forces between molecules? A CO2 B Br2 C H2 D CH4

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19 Which of the following would experience the greatest London dispersion forces between molecules? A CO2 B Br2 C H2 D CH4

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Answer B

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20 Which of the following solids would require the least energy to sublimate (change from a solid to a gas)? A C3H8(s) B O2(s) C CH4(s) D Ar(s)

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20 Which of the following solids would require the least energy to sublimate (change from a solid to a gas)? A C3H8(s) B O2(s) C CH4(s) D Ar(s)

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Answer C

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21 Butane (C4H10) can exist as one of two isomers: isobutane and n-butane shown to the right. The melting points of isobutane and n-butane are -160 C and

• 140 C respectively. Which of the

following BEST explains why? A Isobutane is more polarized due to having fewer electrons B n-butane is more polarized due to having more electrons C Isobutane and n-butane have equal numbers of electrons but isobutane has less surface area D Isobutane and n-butane have equal numbers of electrons but n-butane has more surface area

isobutane n-butane

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21 Butane (C4H10) can exist as one of two isomers: isobutane and n-butane shown to the right. The melting points of isobutane and n-butane are -160 C and

• 140 C respectively. Which of the

following BEST explains why? A Isobutane is more polarized due to having fewer electrons B n-butane is more polarized due to having more electrons C Isobutane and n-butane have equal numbers of electrons but isobutane has less surface area D Isobutane and n-butane have equal numbers of electrons but n-butane has more surface area

isobutane n-butane

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Answer D

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Dipole-Dipole Forces

Attractions between opposite poles of polar molecules. The more polar the molecule, the greater the charges, which results in stronger Coulombic attractions.

H Cl + - H Cl + - dipole-dipole force

H F + - H F + -

dipole-dipole force

MP = -85 C MP =19 C

less polar more polar Unlike "LDF's", Dipole-Dipole forces exist only between molecules with permanent dipoles and are therefore stronger than "LDF's" bond for bond.

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Only F, O, and N are electronegative enough to generate the high positive charge on H to necessary to create a hydrogen bond with a neighboring F, O, or N.

F F

Hydrogen Bonds

Hydrogen Bonds

Hydrogen bonds are a special type of dipole-dipole force that is generated between the highly electropositive H on a molecule and a highly electronegative atom on a neighboring molecule.

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N H O H-Bond R O R Hydrogen bonding stabilizes the secondary structure of proteins

Intermolecular Forces

Hydrogen bonds play an important role in polymers both synthetic (plastics) and natural (proteins).

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Substance # of e- Strength of LDF's H-Bonds? Boiling Point (1 atm) H2Te 106 High No

• 2.2 C

H2Se 70 Medium No

• 41.3 C

H2S 34 Low No

• 60.0 C

H2O 20 Very low Yes 100.0 C

Intermolecular Forces

Hydrogen bonds create unexpectedly high melting and boiling points.

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22 Which of the following would have dipole-dipole intermolecular forces? A Br2 B CH4 C CH3F D CF4

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22 Which of the following would have dipole-dipole intermolecular forces? A Br2 B CH4 C CH3F D CF4

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Answer C

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23 In which of the following substances would hydrogen bonding be found between molecules? A HCl B CH3F C CH3NH2 D CH3COCH3

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23 In which of the following substances would hydrogen bonding be found between molecules? A HCl B CH3F C CH3NH2 D CH3COCH3

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Answer C

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24 The indicated bond is a hydrogen bond. True False

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24 The indicated bond is a hydrogen bond. True False

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Answer False

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25 Which of the following arrows points to a hydrogen bond in the molecule below? A B C D E

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25 Which of the following arrows points to a hydrogen bond in the molecule below? A B C D E

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Answer E

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Substance LDF Rank H-Bonds DDF Rank MP @1 atm BP @ 1 atm Heat of Vaporization H2O 3 Yes 1 0 C 100 C 40.6 kJ/mol I2 1 No 3 114 C 184 C 41.6 kJ/mol CH3COCH3 2 No 2

• 95 C

56 C 29 kJ/mol

*When comparing properties of molecular compounds, first determine if the molecule is polar. If it is, dipole-dipole forces will be part of the

• discussion. If not, LDF's will be the only intermolecular force to consider.

Intermolecular Forces

When evaluating properties such as boiling point, one must consider the forces present in each substance. Although LDF's are in general weaker than dipole-dipole forces (DDF's), large non-polar molecules can have higher boiling points than smaller polar molecules, even those with hydrogen bonding.

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26 Which of the following best explains why ammonia (NH3) has a higher boiling point than methane (CH4)? A Ammonia is non-polar and methane is polar B Ammonia can form hydrogen bonds while methane cannot C Ammonia has greater london dispersion forces D Ammonia can form london dispersion forces while methane cannot

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26 Which of the following best explains why ammonia (NH3) has a higher boiling point than methane (CH4)? A Ammonia is non-polar and methane is polar B Ammonia can form hydrogen bonds while methane cannot C Ammonia has greater london dispersion forces D Ammonia can form london dispersion forces while methane cannot

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Answer B

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27 Which of the following best explains how carbon tetrabromide has a higher boiling point than water? A CBr4 is more polar and can form stronger dipole - dipole forces B CBr4 can form chlorine bonds which are stronger than hydrogen bonds C CBr4 has greater London dispersion forces due to the larger electronegativity differences D CBr4 has greater London dispersion forces due to the greater polarizability of the molecule

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27 Which of the following best explains how carbon tetrabromide has a higher boiling point than water? A CBr4 is more polar and can form stronger dipole - dipole forces B CBr4 can form chlorine bonds which are stronger than hydrogen bonds C CBr4 has greater London dispersion forces due to the larger electronegativity differences D CBr4 has greater London dispersion forces due to the greater polarizability of the molecule

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Answer D

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28 Which of the following would be expected to have the highest heat of vaporization? A H2 B Kr C PH3 D CO2

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28 Which of the following would be expected to have the highest heat of vaporization? A H2 B Kr C PH3 D CO2

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Answer C

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29 Which of the following would have the lowest boiling point? A HI B I2 C Br2 D F2

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29 Which of the following would have the lowest boiling point? A HI B I2 C Br2 D F2

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Answer D

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30 Which of the following would correctly rank the following from highest to lowest boiling point? A NH3 > PH3 > CCl4 B CCl4 > NH3 > PH3 C PH3 > NH3 > CCl4 D NH3 > CCl4 > PH3

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30 Which of the following would correctly rank the following from highest to lowest boiling point? A NH3 > PH3 > CCl4 B CCl4 > NH3 > PH3 C PH3 > NH3 > CCl4 D NH3 > CCl4 > PH3

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Answer B

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States of Matter

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Solids, Liquids, and Gases

Property Solid Liquid Gas Compressibility Very Low Very Low High Density High High Low Viscosity Very High Medium Very Low Potential Energy Low Medium High

Note: Water is unique in that its liquid state is more dense than the solid state.

Recall that viscosity is the resistance to flow. The weaker the particle interactions, the lower the viscosity. The properties of each state differ from each other considerably.

Slide 57 / 126 Solids, Liquids, and Gases

Electrical Conductivity of NaCl NaCl(s) = Non-conductive NaCl(l) = Conductive Density of H2O H2O(l) @ 0 C = 999 g/L H2O(g) @ 0 C = 0.804 g/L Viscosity of H2O H2O (l) @100 C = 0.664 u H2O (g) @100 C = 0.011 u The properties of a material will vary depending on its state.

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31

Students type their answers here

Solids, Liquids, and Gases

Why is the viscosity of water is so much less in the gas state?

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31

Students type their answers here

Solids, Liquids, and Gases

Why is the viscosity of water is so much less in the gas state?

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Answer

The Coulombic attractions are much weaker so the molecules demonstrate very little resistance to the sheering forces that cause molecules to flow past one another.

Slide 59 (Answer) / 126 Solids

Recall the properties of various solids. Solid

Melting Point Conductivity Malleability

Metallic High Yes High Ionic High As a liquid Low Covalent Network Very High Some Low Molecular Low No Low

Slide 60 / 126 Liquids

Hydraulic systems take advantage of a liquids ability to take the shape of its container and low compressibility to exert a force. Liquids distinguish themselves from the solid phase by the ability to flow due to diminished coulombic attractions between particles.

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Liquids

H2O CH3COCH3 C6H6 Types of attractions weak LDF's, H- Bonds medium LDF's, weak DDF's Strong LDF's Viscosity (m Pa*s) 0.892 0.308 0.602 Comparing three molecular liquids

*Note: Recall LDF stands for London Dispersion Forces

The viscosity of a liquid is influenced by the strength of the Coulombic attractions between particles.

Slide 62 / 126 Liquids

For instance a 0W-40 oil indicates that the oil will stay thicker (higher viscosity) at both 0C and 100 C than does

• il rated as 5W-30.

The viscosity of a motor oil is critical to correct engine

• performance. Engine oil

ratings indicate the resistance to flow at 0C and at 100 C. If the oil gets too thin, it will not lubricate adequately and goodbye engine!

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32 Which of the following is NOT true regarding the liquid state? A It is significantly more compressible than the solid state B The viscosity is less than the solid state C The density is less than the solid state for most materials D The Coulombic attractions are weaker than in the solid state

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32 Which of the following is NOT true regarding the liquid state? A It is significantly more compressible than the solid state B The viscosity is less than the solid state C The density is less than the solid state for most materials D The Coulombic attractions are weaker than in the solid state

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Answer A

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33 Which of the following is TRUE regarding viscosity? A The stronger the coulombic attractions, the lower the viscosity B The higher the temperature, the higher the viscosity C Solids have lower viscosities than liquids D A substance with a low viscosity will flow easier than one with a high viscosity

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33 Which of the following is TRUE regarding viscosity? A The stronger the coulombic attractions, the lower the viscosity B The higher the temperature, the higher the viscosity C Solids have lower viscosities than liquids D A substance with a low viscosity will flow easier than one with a high viscosity

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Answer D

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34 Which of the following liquids would be expected to have the highest viscosity? A CH3COCH3 B C6H14 C C4H10 D CH3CH2CH2OH

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34 Which of the following liquids would be expected to have the highest viscosity? A CH3COCH3 B C6H14 C C4H10 D CH3CH2CH2OH

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Answer D

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35 Which of the following make gases unsuitable to use in hydraulics? A They are too viscous B The Coulombic attractions are too strong C The gas state is too compressible D The gas state cannot flow

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35 Which of the following make gases unsuitable to use in hydraulics? A They are too viscous B The Coulombic attractions are too strong C The gas state is too compressible D The gas state cannot flow

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Answer C

Slide 67 (Answer) / 126 Kinetic Molecular Theory of Gases

Assumption 1: Gas molecules occupy a negligible volume of their container. So... the volume of a gas is assumed to be equal to the volume

• f the container.

Gas molecules

Slide 68 / 126 Kinetic Molecular Theory of Gases

Assumption 2: Gas molecules are in constant motion and routinely collide with each other and with the walls of the container thus exerting a pressure whose magnitude depends on the frequency and forcefulness of these collisions.

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Assumption 3: Each gas molecule does not experience any Coulombic attractions from the other gas molecules or container and therefore do not "stick" to each other, resulting in collisions that are perfectly elastic. Note: These assumptions are based on "ideal" gases. Real gases do not behave exactly this way but it gives us a theoretical framework for discussing the properties of gases.

Kinetic Molecular Theory of Gases Slide 70 / 126

36 Which of the following is a correct assumption of the kinetic molecular theory of gases? A Gases do not collide with each other B Gases collide but lose energy with every collision C Gases experience weak coulombic attractions between molecules D A gas occupies a neglible volume of their container

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36 Which of the following is a correct assumption of the kinetic molecular theory of gases? A Gases do not collide with each other B Gases collide but lose energy with every collision C Gases experience weak coulombic attractions between molecules D A gas occupies a neglible volume of their container

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Answer D

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37 Which of the follow is NOT true regarding the difference between gases and the liquid and/or solid states? A The volume of gas is fixed while the liquid changes volume to fill its container. B In terms of Coulombic forces: solids > liquids > gases C Gas particles are in constant motion while liquid and solid particles are relatively fixed. D In terms of distance between particles: solids < liquids < gases

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37 Which of the follow is NOT true regarding the difference between gases and the liquid and/or solid states? A The volume of gas is fixed while the liquid changes volume to fill its container. B In terms of Coulombic forces: solids > liquids > gases C Gas particles are in constant motion while liquid and solid particles are relatively fixed. D In terms of distance between particles: solids < liquids < gases

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Answer A

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38 Kinetic Molecular Theory (KMT) is used to describe the behavior of... A All gases B Ideal gases C Real gases D Noble gases

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38 Kinetic Molecular Theory (KMT) is used to describe the behavior of... A All gases B Ideal gases C Real gases D Noble gases

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Answer B

Slide 73 (Answer) / 126 Basic Gas Laws

At a given temperature, the gas molecules possess a wide range of kinetic

• energies. This is

known as the Boltzmann distribution. The higher the temperature, the greater the speed of the gases, the greater the kinetic energy.

*Note: Even at low temperatures, some of the gas molecules have as much energy as the average energy of the gas molecules at a much higher temperature. # of gas molecules Molecular speeds Temperatures

The temperature of a gas is equivalent to the average kinetic energy of the gas molecules

Slide 74 / 126 Basic Gas Laws

The higher the temperature, the greater the speed and kinetic energy of the molecules thereby increasing BOTH the frequency and force of each collision thereby increasing the pressure. P T (K) The greater the number

• f moles of a gas, the

greater the frequency of collisions and the higher the pressure. P moles The pressure of a gas is directly proportional to the Kelvin temperature and the number of moles.

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Basic Gas Laws

As the volume increases, the collisions become less numerous and the pressure decreases. less collisions more collisions Pressure Volume The pressure of a gas is inversely proportional to the volume.

Slide 76 / 126 Basic Gas Laws

As the temperature increases, the volume must expand against a constant pressure. V T (K) As the number of moles are increased, the volume will expand against a constant pressure. V moles The volume of a gas is directly proportional to the Kelvin temperature and the number of moles.

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39 Which of the following influence the pressure of an ideal gas? A The frequency of collisions B The frequency and force of collisions C The force of collisions D Neither the frequency or force of collisions

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39 Which of the following influence the pressure of an ideal gas? A The frequency of collisions B The frequency and force of collisions C The force of collisions D Neither the frequency or force of collisions

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Answer B

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40 Which of the following would be TRUE when a gas condenses? A It will become more compressible B It will become less dense C The coulombic attractions will decrease D The potential energy of the molecules will decrease

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40 Which of the following would be TRUE when a gas condenses? A It will become more compressible B It will become less dense C The coulombic attractions will decrease D The potential energy of the molecules will decrease

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Answer D

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41 Which of the following is NOT TRUE regarding a gas? A All N2 gas molecules will have the same kinetic energy at a given temperature B The volume of a gas is directly related to it's temperature (in Kelvin) C If the Kelvin temperature of a gas is doubled, the pressure will double all else being constant D Collisions between gas molecules are elastic

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41 Which of the following is NOT TRUE regarding a gas? A All N2 gas molecules will have the same kinetic energy at a given temperature B The volume of a gas is directly related to it's temperature (in Kelvin) C If the Kelvin temperature of a gas is doubled, the pressure will double all else being constant D Collisions between gas molecules are elastic

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Answer A

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42 A gas in a rigid container registers a pressure of 3.2 atm at 0 C. If the temperature is cooled to -20 C, which of the following would be TRUE? A The volume of the container will decrease. B The inter-molecular distances will increase C The average kinetic energy of the gas molecules will increase D The frequency of collisions will decrease E None of these

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42 A gas in a rigid container registers a pressure of 3.2 atm at 0 C. If the temperature is cooled to -20 C, which of the following would be TRUE? A The volume of the container will decrease. B The inter-molecular distances will increase C The average kinetic energy of the gas molecules will increase D The frequency of collisions will decrease E None of these

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Answer D

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43 Which of the following in NOT true about increasing the pressure on a gas in a sealed container? A Increasing the pressure will cause the temperature to increase B With enough pressure the gas will condense to a liquid C Increasing the pressure will cause the volume to decrease D Increasing the pressure will decrease the number of moles of gas in the chamber

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43 Which of the following in NOT true about increasing the pressure on a gas in a sealed container? A Increasing the pressure will cause the temperature to increase B With enough pressure the gas will condense to a liquid C Increasing the pressure will cause the volume to decrease D Increasing the pressure will decrease the number of moles of gas in the chamber

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Answer D

Slide 82 (Answer) / 126

Basic Gas Laws

Example: What would be the effect on the volume of a gas if the pressure were doubled and the temperature were increased from 10 C to 20 C? SOLUTION V and P are inversely related, V and T are directly related Since P doubled, volume will decrease by factor of two. Since K temperature increased by 293/273, the volume will increase by 293/273. 1 L x 1 atm x 293 K = 0.52 L 2 atm 283 K The relationships between the various qualities of a gas can be used to predict the change in the pressure, volume, moles,

• r temperature of a gas.

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44 A 9 L expandable container containing a gas is heated in an isobaric manner (constant pressure) from 17 C to 117 C. What would be the new volume at 117 C?

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44 A 9 L expandable container containing a gas is heated in an isobaric manner (constant pressure) from 17 C to 117 C. What would be the new volume at 117 C?

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Answer 12 L

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45 A flexible balloon is dropped out a spaceship on Mars. Inside the spacecraft, the balloon has a pressure of 0.6 atm, a temperature of 20 C, and a volume of 18 L. What would be the new volume of the balloon if the pressure

• n Mars was 0.08 atm and the temperature was -30 C?

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45 A flexible balloon is dropped out a spaceship on Mars. Inside the spacecraft, the balloon has a pressure of 0.6 atm, a temperature of 20 C, and a volume of 18 L. What would be the new volume of the balloon if the pressure

• n Mars was 0.08 atm and the temperature was -30 C?

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Answer 112 L

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46 Density is defined as the mass of a substance per a given volume (D = m/V). Which of the following statements must be TRUE of the density of a gas? A Density is proportional to volume B Density is inversely proportional to the number of moles of the gas C Density is inversely proportional to volume D There is no relationship between density and the number of moles of the gas

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46 Density is defined as the mass of a substance per a given volume (D = m/V). Which of the following statements must be TRUE of the density of a gas? A Density is proportional to volume B Density is inversely proportional to the number of moles of the gas C Density is inversely proportional to volume D There is no relationship between density and the number of moles of the gas [This object is a pull tab]

Answer C

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47 A gas is heated from 100 K to 300 K and the pressure is dropped from 100 mbar to 50 mbar. Which of the following would be TRUE regarding the density? A The density will inrease by a factor of 3 B The density will decrease by a factor of 3 C The density will increase by a factor of 6 D The density will decrease by a factor of 6

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47 A gas is heated from 100 K to 300 K and the pressure is dropped from 100 mbar to 50 mbar. Which of the following would be TRUE regarding the density? A The density will inrease by a factor of 3 B The density will decrease by a factor of 3 C The density will increase by a factor of 6 D The density will decrease by a factor of 6

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Answer D

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48 A 0.5 mole sample of helium gas in an isobaric chamber is heated from 100 C to 300 C. What is the density of the gas at 300 C if the gas occupies a volume of 2 L at 100 C?

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48 A 0.5 mole sample of helium gas in an isobaric chamber is heated from 100 C to 300 C. What is the density of the gas at 300 C if the gas occupies a volume of 2 L at 100 C?

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Answer 0.65 g/L

Slide 88 (Answer) / 126

49 Oxygen gas has a density of 1.43 g/L @STP. Hydrogen gas has a density of 0.098 g/L @STP. To what pressure (in atm) must the hydrogen gas be raised to increase its density to be equal to that of oxygen? Assume a rigid container and isothermal compression.

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49 Oxygen gas has a density of 1.43 g/L @STP. Hydrogen gas has a density of 0.098 g/L @STP. To what pressure (in atm) must the hydrogen gas be raised to increase its density to be equal to that of oxygen? Assume a rigid container and isothermal compression.

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Answer 14.59 atm

Slide 89 (Answer) / 126 Ideal Gas Law

PV = nRT It is critical that you pay attention to units. Recall that 760 mm Hg = 1 atm = 760 torr and K = oC + 273 The ideal gas law expresses the relationships of the pressure, volume, temperature, and mole amounts of a gas as a single equation. = 8.314 J mol-1 K-1 = 0.08206 L atm mol-1 K-1 = 62.36 L torr mol-1 K-1 R (gas constant)

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50 What is the mass of a sample of argon gas @ a temperature of 15 C, a pressure of 450 mm Hg, and

• ccupying a 120 mL container?

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50 What is the mass of a sample of argon gas @ a temperature of 15 C, a pressure of 450 mm Hg, and

• ccupying a 120 mL container?

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Answer 0.12 g

Slide 91 (Answer) / 126

51 What is the volume of a 32 gram sample of O2 gas @ 0 C and 760 torr?

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51 What is the volume of a 32 gram sample of O2 gas @ 0 C and 760 torr?

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Answer 22.4 L

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52 At what temperature would a 87 gram sample of xenon gas be at 450 torr pressure and occupying a 2.5 L container?

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52 At what temperature would a 87 gram sample of xenon gas be at 450 torr pressure and occupying a 2.5 L container?

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Answer 27 K

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53 What is the density (in g/L) of a sample of chlorine gas @ 300 K and a pressure of 1.6 atm?

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53 What is the density (in g/L) of a sample of chlorine gas @ 300 K and a pressure of 1.6 atm?

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Answer 4.54 g/L

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54 A gas has a vapor density of 1.23 g/L @15 C and 1 atm pressure. What is the formula of the gas? A CH4 B CCl4 C CH3Cl D C2H6

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54 A gas has a vapor density of 1.23 g/L @15 C and 1 atm pressure. What is the formula of the gas? A CH4 B CCl4 C CH3Cl D C2H6

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Answer D

Slide 95 (Answer) / 126

55 A 22.50 gram sample of a gas in a 2.50 L container @ -4 C exerts a pressure of 4.52 atm. Identify the gas. A O2 B Ar C CO2 D NH3

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55 A 22.50 gram sample of a gas in a 2.50 L container @ -4 C exerts a pressure of 4.52 atm. Identify the gas. A O2 B Ar C CO2 D NH3

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Answer C

Slide 96 (Answer) / 126

56 Identify the gas in which a 42 gram sample occupies 33.6 L @STP. A CO2 B CH4 C O2 D N2

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56 Identify the gas in which a 42 gram sample occupies 33.6 L @STP. A CO2 B CH4 C O2 D N2

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Answer D

Slide 97 (Answer) / 126

57 A 36 gram sample of helium gas exerts a pressure of 450 mm Hg @ 10 C. What is the molar volume of the gas at these conditions?

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57 A 36 gram sample of helium gas exerts a pressure of 450 mm Hg @ 10 C. What is the molar volume of the gas at these conditions?

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Answer 39.2 L/mol

Slide 98 (Answer) / 126

58 Oxygen gas is collected by dispensing it from a gas cylinder into a previously evacuated tube. Use the data below to find the molar volume of the gas @STP.

Mass of cylinder initially = 110.400 grams Mass of cylinder after dispensing gas = 110.273 grams Volume of gas dispensed @ 15 C = 100.3 mL Pressure of gas collected @ 15 C = 763 mm Hg

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58 Oxygen gas is collected by dispensing it from a gas cylinder into a previously evacuated tube. Use the data below to find the molar volume of the gas @STP.

Mass of cylinder initially = 110.400 grams Mass of cylinder after dispensing gas = 110.273 grams Volume of gas dispensed @ 15 C = 100.3 mL Pressure of gas collected @ 15 C = 763 mm Hg

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Answer 23.8 L/mol

Slide 99 (Answer) / 126 Law of Partial Pressures

Ptot = PA + PB + PC .... Since moles and P are directly related it follows that: Ntot = NA + NB + NC .... The relationship between pressure and moles is often conveniently expressed as: PA = NA PTOT NTOT If a sample contains more than one type of gas the total pressure of the gas mixture is the sum of the components' pressures.

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59 Air is roughly 79% by mole amount nitrogen gas, 20%

• xygen by mole amount, and 1% other trace gases. What

is the partial pressure of oxygen gas in an air sample with a pressure of 745 torr?

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59 Air is roughly 79% by mole amount nitrogen gas, 20%

• xygen by mole amount, and 1% other trace gases. What

is the partial pressure of oxygen gas in an air sample with a pressure of 745 torr?

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Answer 149 torr

Slide 101 (Answer) / 126

60 A sample of butane gas (C4H10) is collected over water @

• 17C. The vapor pressure of water at this temperature is

16.4 mm Hg. What is the partial pressure of butane collected if the total pressure is 762 mm Hg?

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60 A sample of butane gas (C4H10) is collected over water @

• 17C. The vapor pressure of water at this temperature is

16.4 mm Hg. What is the partial pressure of butane collected if the total pressure is 762 mm Hg?

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Answer 745.6 mm Hg

Slide 102 (Answer) / 126

61 A sample of He, Ar, and Ne at 10 C contains 10 grams of each gas. Which of the following would be TRUE of the mixture? A There is an equal number of moles of each gas B Each gas would exert the same partial pressure C Each gas would have have the same average kinetic energy D Each gas would have equal number of molecules in the sample

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61 A sample of He, Ar, and Ne at 10 C contains 10 grams of each gas. Which of the following would be TRUE of the mixture? A There is an equal number of moles of each gas B Each gas would exert the same partial pressure C Each gas would have have the same average kinetic energy D Each gas would have equal number of molecules in the sample

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Answer C

Slide 103 (Answer) / 126

62 What is the partial pressure of hydrogen gas if a mixture containing 4 grams of H2, 16 grams of O2, and 17 grams of NH3 exerts a total pressure of 1.2 atm?

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62 What is the partial pressure of hydrogen gas if a mixture containing 4 grams of H2, 16 grams of O2, and 17 grams of NH3 exerts a total pressure of 1.2 atm?

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Answer 0.69 atm

Slide 104 (Answer) / 126

63 Examine the container below which consists of two glass flasks connected by a valve. What is the pressure of the helium gas after the valve has been opened?

valve 2 L of He @ 2atm 0.8 L of Ar @1 atm

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63 Examine the container below which consists of two glass flasks connected by a valve. What is the pressure of the helium gas after the valve has been opened?

valve 2 L of He @ 2atm 0.8 L of Ar @1 atm

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Answer 1.43 atm

Slide 105 (Answer) / 126 Graham's Law of Effusion

For gases at the same temperature... KEa = KEb ----> mava2 = mbvb2 ----> ma = vb2 mb va2 This law can be practically viewed two ways:

• 1. A gas that is twice as heavy will move 2

(1/2) or 1.41 x slower.

• 2. A gas that is twice as fast must be 2

2 or 4x lighter.

Effusion refers to the random movement of gas molecules through a small opening. The speed of a gas is inversely proportional to the square root of the mass.

Slide 106 / 126 Graham's Law of Effusion

Example: What is the molar mass of a gas that travels at four times the speed of chlorine gas? 4 x speed = 42 x lighter = 16 x lighter Cl2 = 70 g/mol divided by 16 = 4.3 g/mol Example: How much faster would helium move compared to neon? Ne is 20/4 or 5 x heavier than He so will move 5(1/2) or 2.23 x slower than He.... or He will move 2.23x faster than Ne.

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64 A container filled with 2 moles each of Ar, Ne, and NH3 is punctured creating a small hole. Which of the following would be the correct order of the gases inside the container after 2 hours have passed? A NNH3 > NNe > NAr B NAr > NNH3 > NNe C NNe > NAr > NNH3 D NAr > NNe > NNH3

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64 A container filled with 2 moles each of Ar, Ne, and NH3 is punctured creating a small hole. Which of the following would be the correct order of the gases inside the container after 2 hours have passed? A NNH3 > NNe > NAr B NAr > NNH3 > NNe C NNe > NAr > NNH3 D NAr > NNe > NNH3

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Answer D

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65 Which of the following gases will travel at approximately 2.5x the speed of Xe? A O2 B Ne C H2 D SiH4

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65 Which of the following gases will travel at approximately 2.5x the speed of Xe? A O2 B Ne C H2 D SiH4

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Answer B

Slide 109 (Answer) / 126

66 How much slower will carbon dioxide move compared to ammonia (NH3)?

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66 How much slower will carbon dioxide move compared to ammonia (NH3)?

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Answer 1.61 x slower

Slide 110 (Answer) / 126

67 Two samples of gases (oxygen and hydrogen) occupy the same amount of space at the same temperature and

• pressure. Which would NOT be true?

A Both gases have the same average kinetic energy B Both gases have the same average molecular speed C Both gas samples have the same number of molecules D The mass of each gas sample would be different

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67 Two samples of gases (oxygen and hydrogen) occupy the same amount of space at the same temperature and

• pressure. Which would NOT be true?

A Both gases have the same average kinetic energy B Both gases have the same average molecular speed C Both gas samples have the same number of molecules D The mass of each gas sample would be different

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Answer B

Slide 111 (Answer) / 126 Ideal vs. Real Gases

All gases are real and therefore do not fully conform to our assumptions of ideal gases. Real gases do occupy a very small part of their container. Therefore the volume that we measure is too large, the gas molecules are actually taking up some of the room! The larger the gas molecule, the more real and less ideal it

• behaves. For example, C3H8(g) will behave less ideal than H2(g)

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Ideal vs. Real Gases

Real gases do experience coulombic attractions/repulsions between molecules. These attractions and repulsions cause the molecules to take the scenic route and collide less frequently making the measured pressure less than the ideal. The greater the inter-molecular forces, the less ideal and more real the gas will behave.

Slide 113 / 126 Ideal vs. Real Gases

At high temperatures, the gas molecules move too fast to form Coulombic attractions making them behave more ideally. At low pressures, the volume of the container is large thereby making the molecules occupy a non-existent fraction of it making them behave more ideally. Gases behave most ideal (less real) at high temperatures and low pressures.

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68 Which of the following is TRUE regarding real gases? A I only B II only C III only D I and II only E I, II, and III

• I. Their measured pressure is less than

an ideal gas

• II. Their measured volume is higher than

that of an ideal gas

• III. They experience coulombic

attractions/repulsions

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68 Which of the following is TRUE regarding real gases? A I only B II only C III only D I and II only E I, II, and III

• I. Their measured pressure is less than

an ideal gas

• II. Their measured volume is higher than

that of an ideal gas

• III. They experience coulombic

attractions/repulsions

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Answer E

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69 Which of the following gases would behave most ideally? A CO2 B N2 C CH4 D He

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69 Which of the following gases would behave most ideally? A CO2 B N2 C CH4 D He

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Answer D

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70 Which of the following gases would behave most real? A NH3 B CO C CO2 D F2

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70 Which of the following gases would behave most real? A NH3 B CO C CO2 D F2

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Answer A

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71 Which of the following gases and set of conditions will behave most ideally? A B C D E

Gas Temperature Pressure

H2O 500 K 3 atm H2O 100 K 0.1 atm H2O 100 K 3 atm CH4 500 K 3 atm CH4 500 K 0.1 atm

Answer

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72 Which sample would have the highest number of molecules? A B C D All have the same number of molecules

Temp: 20 C 20 C 20 C Gas: N2 O2 He Pressure: 1 atm 2 atm 1 atm Volume: 5 L 5 L 5 L

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72 Which sample would have the highest number of molecules? A B C D All have the same number of molecules

Temp: 20 C 20 C 20 C Gas: N2 O2 He Pressure: 1 atm 2 atm 1 atm Volume: 5 L 5 L 5 L

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Answer B

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73 Which sample would have the fastest moving gas molecules? A B C D All gas molecules will move at the same speed at this temperature

Temp: 20 C 20 C 20 C Gas: N2 O2 He Pressure: 1 atm 2 atm 1 atm Volume: 5 L 5 L 5 L

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73 Which sample would have the fastest moving gas molecules? A B C D All gas molecules will move at the same speed at this temperature

Temp: 20 C 20 C 20 C Gas: N2 O2 He Pressure: 1 atm 2 atm 1 atm Volume: 5 L 5 L 5 L

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Answer C

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74 Which sample would would have the highest density? A B C D All would have the same density

Temp: 20 C 20 C 20 C Gas: N2 O2 He Pressure: 1 atm 2 atm 1 atm Volume: 5 L 5 L 5 L

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74 Which sample would would have the highest density? A B C D All would have the same density

Temp: 20 C 20 C 20 C Gas: N2 O2 He Pressure: 1 atm 2 atm 1 atm Volume: 5 L 5 L 5 L

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Answer B

Slide 121 (Answer) / 126

Intro to Solubility

Return to Table

• f Contents

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75

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Solubility

Intermolecular forces play a role in solubility. Water is an excellent solvent for polar solutes such as ethanol (C2H5OH), soluble ionic salts (NaCl, K3PO4, etc), or polar gases like ammonia (NH3). Why?

Slide 123 / 126

75

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Solubility

Intermolecular forces play a role in solubility. Water is an excellent solvent for polar solutes such as ethanol (C2H5OH), soluble ionic salts (NaCl, K3PO4, etc), or polar gases like ammonia (NH3). Why?

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Answer Water is a polar molecular. Its hydrogen bonds are attracted to the charges on the solute, pulling apart the polar or ionic compound and dissolving it in the water.

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76

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Application

Fat soluble vitamins dissolve best in non-polar solvents such as bile salts released from the liver. The structure for vitamin K is

• below. Do you think it is a fat soluble or water soluble vitamin?

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76

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Application

Fat soluble vitamins dissolve best in non-polar solvents such as bile salts released from the liver. The structure for vitamin K is

• below. Do you think it is a fat soluble or water soluble vitamin?

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Answer Vitamin K is mostly nonpolar, so it is fat soluble

Slide 124 (Answer) / 126 Molecular Polarity

Many pigments used to create color in paints are non-polar and require a non-polar solvent such as hexane (C6H14) to dissolve. Many molecules have non-polar and polar regions and require an "amphipathic" solvent that also shares those qualities. Acetone (CH3COCH3) is an excellent choice for these applications. Polarity influences solubility. Polar solutes are more soluble/ miscible in polar solvents and non-polar solutes are more soluble in non-polar solvents.

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77 Which of the following would be LEAST soluble in benzene (C6H6)? A C2H2 B SiH4 C I2 D CH2F2

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77 Which of the following would be LEAST soluble in benzene (C6H6)? A C2H2 B SiH4 C I2 D CH2F2

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Answer D

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