Exam #1 Flashcards
The predominant intermolecular force between molecules of I2 is ____.
a.) ionic bonds
b.) dipole-dipole interactions
c.) ion-dipole interactions
d.) dispersion forces
e.) covalent bonds
d.) dispersion forces
Which of the following substances would have the greatest dispersion forces?
a.) H2
b.) O2
c.) Cl2
d.) Br2
e.) I2
e.) I2
all the substances are nonpolar diatomic molecules, so they only exhibit dispersion forces. Let’s compare their molar masses:
H₂: 2 g/mol (Least molar mass)
O₂: 32 g/mol
Cl₂: 71 g/mol
Br₂: 160 g/mol
I₂: 254 g/mol (Highest molar mass) (greatest dispersion forces)
Which of the following has the lowest boiling point?
a.) C5H12
b.) C7H16
c.) C9H20
d.) C11H24
e.) C13H28
a.) C5H12
C₅H₁₂ (Pentane) ≈ 72 g/mol
C₇H₁₆ (Heptane) ≈ 100 g/mol
C₉H₂₀ (Nonane) ≈ 128 g/mol
C₁₁H₂₄ (Undecane) ≈ 156 g/mol
C₁₃H₂₈ (Tridecane) ≈ 184 g/mol
Since C₅H₁₂ has the lowest molar mass and the least number of electrons, it experiences the weakest dispersion forces and therefore has the lowest boiling point.
As a pure substance, which of the following could experience dipole-dipole interactions?
I. NO2
II. NH3
III. N2
a.) I and II only
b.) I and III only
c.) II and III only
d.) I, II, and III
e.) none of the above
a.) I and II only
I. NO₂
Lewis Structure: O=N-O (with one double bond and one single bond)
Shape: Bent (due to lone pairs on nitrogen)
Polarity: Polar (uneven distribution of electron density)
✅ Experiences dipole-dipole interactions
II. NH₃
Lewis Structure: N with 3 H’s and 1 lone pair on N
Shape: Trigonal pyramidal
Polarity: Polar (due to the lone pair creating an asymmetrical shape)
✅ Experiences dipole-dipole interactions
III. N₂
Lewis Structure: N≡N (triple bond between two identical atoms)
Shape: Linear and Symmetrical
Polarity: Nonpolar (no difference in electronegativity, no dipole moment)
❌ No dipole-dipole interactions (only London dispersion forces)
Which of the following would exhibit hydrogen bonding in a pure substance?
a.) HCl
b.) CH3CH3
c.) CF2H2
d.) CH3CH2OH
e.) CH3OCH3
d.) CH3CH2OH
In order to form a hydrogen bond, an H molecule must be attached to an F, O, or N molecule.
Consider the intermolecular forces present in pure samples of each of the following compounds.
CH3OCH3 and CH3COCH3. Identify the intermolecular forces that these compounds have in common.
a.) dipole-dipole forces and hydrogen bonding
b.) dispersion forces, dipole-dipole forces, and hydrogen bonding
c.) dipole-dipole forces only
d.) dispersion forces and dipole-dipole forces
e.) they have no intermolecular forces in common
d.) dispersion forces and dipole-dipole forces
CH₃OCH₃ (Dimethyl Ether)
Structure: H₃C-O-CH₃
Polarity: Polar due to the oxygen causing an uneven electron distribution.
Intermolecular Forces:
Dispersion forces (present in all molecules)
Dipole-dipole forces (due to polarity)
❌ No hydrogen bonding because there are no hydrogen atoms bonded directly to oxygen, nitrogen, or fluorine.
2. CH₃COCH₃ (Acetone)
Structure: H₃C-CO-CH₃
Polarity: Polar because of the carbonyl (C=O) group which creates a dipole moment.
Intermolecular Forces:
Dispersion forces (present in all molecules)
Dipole-dipole forces (due to the polar C=O group)
❌ No hydrogen bonding because the hydrogens are bonded to carbon, not to oxygen or nitrogen.
Based on intermolecular forces, which of the following is predicted to have the highest boiling point?
a.) CH4
b.) CH3Cl
c.) CH3OH
d.) C2H6
e.) they all have the same boiling point
c.) CH3OH
CH₃OH has hydrogen bonding, which is much stronger than the dipole-dipole forces in CH₃Cl or the dispersion forces in CH₄ and C₂H₆.
Which of the following straight-chain hydrocarbons will have the highest viscosity at 298 K?
a.) C5H12
b.) C6H14
c.) C7H16
d.) C8H18
e.) C9H20
e.) C9H20
C₉H₂₀ is the largest and heaviest molecule in this list, with the longest chain length.
It has the most electrons and the strongest London dispersion forces, leading to the greatest resistance to flow.
The longer chain also means more entanglement between molecules, further increasing viscosity.
The boiling point of liquid B is 95.5 degrees C at 1 atm (760 torr). Its vapor pressure at 73.5 degrees C is 315 torr. What is its △Hvap in kJ/mol? (1 atm = 760 torr, R = 8.314 J/mol K)
a.) 31.1 kJ/mol
b.) 12.8 kJ/mol
c.) 59.6 kJ/mol
d.) 42.5 kJ/mol
e.) 97.9 kJ/mol
d.) 42.5 kJ/mol
ln(P1/P2) = △Hvap/R(1/T2-1/T1)
In(760/315) = △vap/8.314(1/346.65-1/368.65) = 42.5 kJ/mol
What quantity of heat (in kJ) would be required to convert 15.1 g of ice to water at 0.00 degrees C? (△Hfus = 6.01 kJ/mol for water)
a.) 90.8 kJ
b.) 5.04 kJ
c.) 2.51 kJ
d.) 0.398 kJ
e.) 0.139 kJ
b.) 5.04 kJ
n=mass/molar mass
15.1 g / 18.02 g/mol = 0.838 mol
q = n*△Hfus
q=0.838 mol* 6.01 kJ/mol = 5.03 kJ
Identify table sugar (sucrose) as one of the following types of solids:
a.) ionic
b.) molecular
c.) covalent-network
d.) metallic
e.) none of the above
b.) molecular
Sucrose is a molecular solid because it consists of individual molecules held together by intermolecular forces.
a.) Ionic: Sucrose is not ionic because it does not consist of positive and negative ions.
c.) Covalent-Network: This type of solid has a continuous network of covalent bonds (e.g., diamond or quartz), which sucrose does not have.
d.) Metallic: Sucrose does not consist of metal atoms or a sea of delocalized electrons.
e.) None of the above: Incorrect because sucrose clearly fits as a molecular solid.
Based only on intermolecular forces, which of the following would be the least soluble in CH3OH?
a.) CH3CH2CH2CH3
b.) H2O
c.) CH3CH2OCH2CH3
d.) CH3CH2OH
e.) all are equally soluble
a.) CH3CH2CH2CH3
“like dissolves like”
a is the only nonpolar molecule in these options.
The ions formed when Sr(C2H3O2)2 dissociates in water are:
a.) Sr2+, C4-, H+, and O2-
b. Sr+ and C2HO2 2-
c.) Sr2+ and C2H3O2-
d.) Sr2+ and C2H)2 2-
e.) no ions form as Sr(C2H3O2)2 does not dissociate
c.) Sr2+ and C2H3O2-
a.) Sr²⁺, C⁴⁻, H⁺, and O²⁻ – These ions are not formed from acetate dissociation.
b.) Sr⁺ and C₂HO₂²⁻ – Sr⁺ is not a stable ion for strontium, and C₂HO₂²⁻ is not a correct ion form.
d.) Sr²⁺ and C₂H)₂²⁻ – C₂H)₂²⁻ is not a recognized ion.
e.) No ions form – This is incorrect because Sr(C₂H₃O₂)₂ is ionic and does dissociate in water.
Which of the following is not a strong electrolyte?
a.) LiOH
b.) HNO3
c.) KBr
d.) NH4Cl
e.) HNO2
e.) HNO2
Strong electrolytes dissociate completely: LiOH, HNO₃, KBr, NH₄Cl
HNO₂ is a weak acid and only partially dissociates, making it a weak electrolyte.
Which of the following is the correct dissociation equation for Li2CO3?
a.) Li+(aq) + CO32- (aq) → Li2CO2(s)
b.) Li2CO3(s) → 2 Li+(aq) + CO3 2-(aq)
c.) Li2CO3(s) → Li+(aq) + CO3 2-(aq)
d.) Li2CO3(s) → Li+(aq) + C4-(aq) + 3O2-(aq)
e.) none of the above
b.) Li2CO3(s) → 2 Li+(aq) + CO3 2-(aq)
Li₂CO₃ (Lithium carbonate) is an ionic compound composed of:
Li⁺ (Lithium ions)
CO₃²⁻ (Carbonate ions)
When it dissolves in water, it dissociates completely into its ions.
At a particular temperature, the solubility of H2 in water is 0.140 M when the partial pressure is 1.20 atm. What partial pressure (in atm) of H2 would give a solubility of 2.05 M?
a.) 0.117 atm
b.) 0.0569 atm
c.) 0.239 atm
d.) 14.6 atm
e.) 17.6 atm
e.) 17.6 atm
C1/P1=C2/P2
P2=(1.20 atm) * (2.05 M/0.140M)
17.57 atm
A 83.5 g sample of nonelectrolyte is dissolved in 250.1 g of water. The solution is determined to have a boiling point of 102.3 degrees C. What is the molar mass of the compound? (Kb for water is 0.510 degrees C/m).
a.) 451 g.mol
b.) 4.51 g/mol
c.) 74 g/mol
d.) 334 g/mol
e.) 250 g/mol
c.) 74 g/mol
ΔTb=Kb*m
m= ΔTb/Kb
2.3/0.510 = 4.51 m
m = moles of solute / kg of solvent
4.51*0.2501 kg = 1.13 m
molar mass = mass of solute / moles of solute
83.5/1.13 = 73.9 g/m or 74 g/mol
Two volatile substances are mixed with one another so that substance A has a mole fraction of 0.73. Given the information below, what is the vapor pressure of the solution in torr?
A = 42.5 torr
B = 210 torr
a.) 180 torr
b.) 44 torr
c.) 99 tor
d.) 140 torr
e.) 88 torr
e.) 88 torr
(XaP^0A)+(XBP^0B) = P solution
If mol fraction of A is 0.73 then B is 0.27.
(0.7342.5) = 31.025 torr
(0.27210) = 56.7 torr
31.025+56.7 = 88 torr
The percent by mass of ethanol (MM = 46.07 g/mol) in an aqueous solution is 16.9%. What is the molality of the ethanol solution?
a.) 83.1 m
b.) 46.1 m
c.) 4.41 m
d.) 2.16 m
e.) 1.03 m
c.) 4.41 m
m = moles of solute / kilograms of solvent
mass of water = 100g - 16.9g = 83.1g
83.1g = 0.0831kg
moles of ethanol = mass / molar mass
16.9g / 46.07 g/mol = 0.367 mol
m = moles of solute / kg of solvent
0.367 mol / 0.0831kg = 4.41 m
What is the osmotic pressure, in atm, of a 0.201 M solution of MgCl2 at 37 degrees C? (assume complete dissociation). (R=0.0821 L atm/mol K)
a.) 15.3 atm
b.) 0.603 atm
c.) 310 atm
d.) 2.01 atm
e.) 5.1 atm
a.) 15.3 atm
Π=i⋅M⋅R⋅T
find van’t hoff factor
MgCl2 = 3
convert C to K
37+273.15 - 310.15 K
Π = 3 * 0.201 * 0.0821 * 310.15
15.3 atm
A solution is made using 90.1g of dimethyl ether (MM = 46.07 g/mol) and 110g of methanol (MM = 32.04 g/mol). What is the molality of the dimethyl ether in the solution?
a.) 0.117 atm
b.) 36.1 m
c.) 1.96 m
d.) 17.8 m
e.) 1.73 m
d.) 17.8 m
m = moles of solute / kg of solvent
moles of solute = 90.1/46.07 = 1.96 mol
kg of solvent = 110g/1000 = 0.110 kg
1.96 mol / 0.110 kg = 17.8 m
What is the freezing point, in C, of a solution made with 1.31 mol of CHCl3 in 530.0g of CCl4 (Kf=29.8 C/m), normal freezing point, Tf = -22.9 C)?
a.) 2.47C
b.) -96.6C
c.) 73.7C
d.) -73.7C
e.) -22.9C
b.) -96.6C
ΔTf =i⋅K f⋅m
m=moles of solute / kg of solvent
1.31 mol / 0.5300 kg = 2.47 m
ΔTf = (1)(29.8)(2.47) = 73.7C
Tf = T^0f -ΔTf
-22.9-73.7 = -96.6C
What is the molarity of ions in a 0.620 solution of Ca(OH)2 assuming that the compound dissociates completely?
a.) 1.86 M
b.) 1.24 M
c.) 2.48 M
d.) 0.207 M
e.) 0.310 M
a.) 1.86 M
Write the dissociation equation:
Ca(OH)2 —> Ca(aq) + 2OH(aq)
so, 1 mol of Ca and 2 mol of OH
Ca= 10.620 = 0.620 mol
OH= 00.620 = 1.24 mol
0.620 mol + 1.24 mol = 1.86 mol
A solution is made using 300.0 mL of acetone (density 0.7845) and 877.3 mL of water (density 1.000). What is the mass percent of acetone?
a.) 26.83%
b.) 73.17%
c.) 21.16 %
d.) 78.64%
e.) 15.19%
c.) 21.16%
mass percent = mass of solute / total mass of solution * 100
m=vd
acetone: 300.0 mL * 0.7845g/mL =235.35 g
water: 877.3 mL * 1.00g/mL =877.3 g
235.35 g + 877.3 g =1,112.65 g
235.35g / 1112.65 g =0.212 * 100 = 21.16%
Which of the following is an example of a colloid?
a.) milk
b.) coffee
c.) soda
d.) saltwater
e.) none of the above
a.) milk
Colloids are heterogeneous mixtures in which:
• Small particles are dispersed throughout another substance.
• These particles are larger than molecules but too small to settle out or be filtered easily.
• They exhibit the Tyndall effect – they scatter light when a beam passes through.
