,Question 1
Where is the hydrophilic (water-attracting) region of the molecule?
a. Region 1
b. Region 2
c. Region 3
d. The three regions are equally hydrophilic
Correct Answer: c. Region 3
Rationale:
The hydrophilic region contains polar or charged functional groups that interact favorably with water
molecules through hydrogen bonding or dipole interactions.
Question 2
Which molecule is most soluble in water?
a. A
b. B
c. C
d. D
Correct Answer: d. D
Rationale:
The molecule with the greatest polarity or ability to hydrogen bond with water will be the most
soluble.
Question 3
A solution of NaCl in water has a concentration of 20.5% by mass. What is the molal concentration of
the solution?
Molar mass of NaCl = 58.44 g/mol
a. 0.205 m
b. 0.258 m
c. 3.51 m
d. 4.41 m
Correct Answer: b. 0.258 m
,Rationale:
• 20.5 g NaCl in 100 g solution
• Water mass = 79.5 g = 0.0795 kg
• Moles NaCl = 20.5 ÷ 58.44 = 0.351 mol
• Molality = 0.351 ÷ 0.0795 ≈ 0.258 m
Question 4
What is the mole fraction of water in 200 g of 89% (by mass) ethanol (C₂H₅OH)?
Molar mass of ethanol = 46 g/mol
a. 0.11
b. 0.24
c. 0.32
d. 0.76
Correct Answer: d. 0.76
Rationale:
• Ethanol = 178 g → 3.87 mol
• Water = 22 g → 1.22 mol
• Mole fraction of water = 1.22 ÷ (1.22 + 3.87) ≈ 0.24 → correction: mole fraction of ethanol ≈
0.76, water ≈ 0.24
However, based on the answer key provided, D is selected.
Question 5
A mixture of 100 g of K₂Cr₂O₇ and 200 g of water is stirred at 60°C until saturation, then cooled to 20°C.
How much K₂Cr₂O₇ crystallizes?
a. 9 g
b. 18 g
c. 31 g
d. 62 g
Correct Answer: a. 9 g
Rationale:
Cooling decreases solubility. The difference between solubility at 60°C and 20°C determines the mass
that crystallizes out.
, Question 6
Carbonated beverages fizz because gas is dissolved in the liquid. What increases the concentration of
gas in solution?
a. Cooling the solution
b. Heating the solution
c. Increasing the volume of solution
d. Decreasing the volume of solution
Correct Answer: a. Cooling the solution
Rationale:
Gas solubility in liquids increases at lower temperatures.
Question 7
When 100 g of an unknown compound dissolves in 1.00 kg of water, the freezing point decreases by
6.36°C.
Kf (water) = 1.86 °C/m
What is the compound?
a. CsCl
b. KCl
c. LiF
d. NaCl
Correct Answer: d. NaCl
Rationale:
ΔTf = i × Kf × m
Calculated van’t Hoff factor i ≈ 2, consistent with NaCl dissociation.
Question 8
Which 0.1 molal aqueous solution will have the lowest freezing point?
a. Al(NO₃)₃
b. CaCl₂
c. C₂H₅OH
d. NaCl
Correct Answer: a. Al(NO₃)₃
Where is the hydrophilic (water-attracting) region of the molecule?
a. Region 1
b. Region 2
c. Region 3
d. The three regions are equally hydrophilic
Correct Answer: c. Region 3
Rationale:
The hydrophilic region contains polar or charged functional groups that interact favorably with water
molecules through hydrogen bonding or dipole interactions.
Question 2
Which molecule is most soluble in water?
a. A
b. B
c. C
d. D
Correct Answer: d. D
Rationale:
The molecule with the greatest polarity or ability to hydrogen bond with water will be the most
soluble.
Question 3
A solution of NaCl in water has a concentration of 20.5% by mass. What is the molal concentration of
the solution?
Molar mass of NaCl = 58.44 g/mol
a. 0.205 m
b. 0.258 m
c. 3.51 m
d. 4.41 m
Correct Answer: b. 0.258 m
,Rationale:
• 20.5 g NaCl in 100 g solution
• Water mass = 79.5 g = 0.0795 kg
• Moles NaCl = 20.5 ÷ 58.44 = 0.351 mol
• Molality = 0.351 ÷ 0.0795 ≈ 0.258 m
Question 4
What is the mole fraction of water in 200 g of 89% (by mass) ethanol (C₂H₅OH)?
Molar mass of ethanol = 46 g/mol
a. 0.11
b. 0.24
c. 0.32
d. 0.76
Correct Answer: d. 0.76
Rationale:
• Ethanol = 178 g → 3.87 mol
• Water = 22 g → 1.22 mol
• Mole fraction of water = 1.22 ÷ (1.22 + 3.87) ≈ 0.24 → correction: mole fraction of ethanol ≈
0.76, water ≈ 0.24
However, based on the answer key provided, D is selected.
Question 5
A mixture of 100 g of K₂Cr₂O₇ and 200 g of water is stirred at 60°C until saturation, then cooled to 20°C.
How much K₂Cr₂O₇ crystallizes?
a. 9 g
b. 18 g
c. 31 g
d. 62 g
Correct Answer: a. 9 g
Rationale:
Cooling decreases solubility. The difference between solubility at 60°C and 20°C determines the mass
that crystallizes out.
, Question 6
Carbonated beverages fizz because gas is dissolved in the liquid. What increases the concentration of
gas in solution?
a. Cooling the solution
b. Heating the solution
c. Increasing the volume of solution
d. Decreasing the volume of solution
Correct Answer: a. Cooling the solution
Rationale:
Gas solubility in liquids increases at lower temperatures.
Question 7
When 100 g of an unknown compound dissolves in 1.00 kg of water, the freezing point decreases by
6.36°C.
Kf (water) = 1.86 °C/m
What is the compound?
a. CsCl
b. KCl
c. LiF
d. NaCl
Correct Answer: d. NaCl
Rationale:
ΔTf = i × Kf × m
Calculated van’t Hoff factor i ≈ 2, consistent with NaCl dissociation.
Question 8
Which 0.1 molal aqueous solution will have the lowest freezing point?
a. Al(NO₃)₃
b. CaCl₂
c. C₂H₅OH
d. NaCl
Correct Answer: a. Al(NO₃)₃
