Rucete ✏ AP Chemistry In a Nutshell
8. Solutions — Practice Questions
This chapter introduces the principles of solutions, including solubility, solution types, and concentration units.
(Multiple Choice — Click to Reveal Answer)
1. The solubility of cadmium chloride, CdCl₂, is 140 g per 100 mL of solution. What is the molar solubility of a saturated solution of CdCl₂?
(A) 0.765 M
(B) 1.31 M
(C) 7.64 M
(D) 12.61 M
Answer
(C) — Convert grams to moles and divide by volume in liters to find molarity.
2. Which of the following represents the most dilute solution if ● represents the solvent and ○ represents the solute?
(A) ●●●●●
(B) ●●○○○
(C) ●●●○
(D) ○○○●
Answer
(C) — Dilute solutions contain much more solvent than solute.
3. To make a solution, 3.45 mol of C₆H₁₃Cl and 1.26 mol of C₅H₁₂ are mixed. Which of the following is needed, but not readily available, to calculate the molarity?
(A) The density of the solution
(B) The densities of C₆H₁₃Cl and C₅H₁₂
(C) The temperature
(D) The molar masses of C₆H₁₃Cl and C₅H₁₂
Answer
(A) — Molarity requires volume; density helps convert mass to volume.
4. If a solute dissolves in an endothermic process:
(A) Hydrogen bonds must exist between solvent and solute
(B) The entropy of the solution must be greater than that of its pure components
(C) The entropy of the solution is not a factor
(D) Strong ion-dipole forces must exist in the solution
Answer
(B) — A positive entropy change helps drive endothermic dissolutions.
5. Which of the following concentration values changes as the temperature of a solution changes?
(A) Mole fraction
(B) Molarity
(C) Molality
(D) Mass percent
Answer
(B) — Molarity depends on volume, which changes with temperature.
6. When algae decay in a pond, what factor contributes to a decrease in oxygen levels?
(A) Decreasing salinity
(B) Increasing acidity
(C) Increasing temperature
(D) Increasing surface tension
Answer
(C) — Higher temperatures reduce oxygen solubility in water.
7. Which of the following is the best representation of a solution?
(A) All solvent
(B) Mostly solvent, few solute
(C) Equal solute and solvent
(D) Mostly solute
Answer
(B) — Solutions typically have much more solvent than solute.
8. What is the correct process to make 0.500 L of a 1.0 M glucose solution? (Molar mass = 180.1 g/mol)
(A) Dissolve 180.1 g in 1.00 kg water
(B) Dissolve 90.0 g in enough water to make 0.500 L
(C) Dissolve 90.0 g in 0.500 kg water
(D) Dissolve 90.0 g in 0.500 L water
Answer
(B) — Always dissolve and then dilute to the final volume.
9. When KCl dissolves and the solution feels cold, it means:
(A) Entropy increase overcomes unfavorable enthalpy
(B) KCl is insoluble
(C) Entropy decreases
(D) Boiling point is below 100°C
Answer
(A) — Energy is absorbed, but entropy drives the process.
10. Which of the following best explains why solubility of gases in liquids decreases with temperature?
(A) Gases expand when cooled
(B) Solids become gases at high temperature
(C) Gases escape more easily at higher kinetic energy
(D) Liquids are less dense at high temperatures
Answer
(C) — As temperature increases, gas molecules have more kinetic energy and escape from solution.
11. What is a supersaturated solution?
(A) Contains more solute than theoretically possible
(B) Contains no solute
(C) Is always dilute
(D) Contains equal solute and solvent
Answer
(A) — Supersaturated solutions are metastable and contain excess solute.
12. Which factor increases the *rate* of dissolution of a solid solute in water?
(A) Decreasing temperature
(B) Decreasing surface area
(C) Stirring
(D) Using cold water
Answer
(C) — Stirring increases solvent-solute interaction, speeding up dissolution.
13. What term describes a substance that dissolves but does not ionize in water?
(A) Strong electrolyte
(B) Weak electrolyte
(C) Nonelectrolyte
(D) Hydrophobic compound
Answer
(C) — Nonelectrolytes dissolve but do not form ions, e.g., sugar.
14. Which of the following is most likely a strong electrolyte?
(A) Glucose
(B) NaCl
(C) Ethanol
(D) HF
Answer
(B) — NaCl is a soluble ionic compound that dissociates completely.
15. What is the molarity of a solution prepared by dissolving 25.0 g of MgCl₂ (molar mass = 95.2 g/mol) in 450 mL of solution?
(A) 0.27 M
(B) 0.58 M
(C) 0.73 M
(D) 1.20 M
Answer
(C) — Moles = 25.0 / 95.2 = 0.2625 mol; M = 0.2625 / 0.450 L = 0.583 → ~0.58 M.
16. Which of the following best explains why ionic compounds dissolve in water?
(A) London forces
(B) Dipole-dipole interactions
(C) Ion-dipole interactions
(D) Hydrogen bonding
Answer
(C) — Water’s polarity allows strong ion-dipole interactions with ions.
17. Which of the following is NOT a unit of concentration?
(A) Molality
(B) Molarity
(C) Mole fraction
(D) Atomic mass unit
Answer
(D) — Atomic mass unit is not a concentration unit.
18. What happens to the entropy when NaCl dissolves in water?
(A) Entropy decreases
(B) Entropy remains the same
(C) Entropy increases
(D) Depends on the solvent
Answer
(C) — Dissolving increases disorder (entropy) as ions disperse in water.
19. Which property applies to weak electrolytes?
(A) Complete ionization
(B) High electrical conductivity
(C) Partial ionization
(D) No ion formation
Answer
(C) — Weak electrolytes partially ionize in water, e.g., HF, CH₃COOH.
20. A solution has 2 mol of NaCl in 500 mL of solution. What is its molarity?
(A) 0.5 M
(B) 1.0 M
(C) 2.0 M
(D) 4.0 M
Answer
(D) — M = 2 mol / 0.5 L = 4 M.
21. Which solution conducts electricity the best?
(A) Pure water
(B) Sugar water
(C) Salt water
(D) Ethanol in water
Answer
(C) — Salt water contains free ions from NaCl, making it a strong conductor.
22. Which gas will be most soluble in water at low temperature and high pressure?
(A) CO₂
(B) CH₄
(C) He
(D) H₂
Answer
(A) — CO₂ is relatively soluble; low temperature and high pressure favor solubility (Henry’s Law).
23. What is the unit of the Henry's Law constant k when using mol/L for solubility and atm for pressure?
(A) mol·atm/L
(B) mol/L·atm
(C) L/mol·atm
(D) atm/mol
Answer
(B) — Rearranged from S = kP → k = S/P, units: mol/L·atm.
24. Which of the following best explains the meaning of a “saturated” solution?
(A) The solute is completely reacted
(B) No solute is dissolved
(C) Solute and solvent are equal in mass
(D) Maximum amount of solute is dissolved at equilibrium
Answer
(D) — A saturated solution is in equilibrium with undissolved solute.
25. Which action would *not* affect the *rate* of dissolution?
(A) Stirring
(B) Heating
(C) Increasing surface area
(D) Changing the solvent’s polarity
Answer
(D) — Polarity affects solubility, not the rate of dissolution.
26. Which factor does *not* affect the solubility of a solid in water?
(A) Temperature
(B) Stirring
(C) Surface area
(D) Atmospheric pressure
Answer
(D) — Pressure has negligible effect on solid solubility in liquids.
27. Which of the following compounds is a weak electrolyte?
(A) NaOH
(B) HCl
(C) CH₃COOH
(D) CaCl₂
Answer
(C) — Acetic acid (CH₃COOH) is a weak acid and only partially ionizes.
28. Which of the following will increase both the *rate* and *amount* of sugar dissolved in water?
(A) Stirring
(B) Heating
(C) Grinding
(D) All of the above
Answer
(D) — All these factors speed dissolution; heating can also increase solubility.
29. What will happen to a supersaturated solution if a seed crystal is added?
(A) Nothing
(B) It will dilute
(C) Excess solute will precipitate
(D) All solute will dissolve
Answer
(C) — Supersaturated solutions are unstable; crystallization is triggered by disturbance.
30. Which of the following increases the entropy of a system the most?
(A) Dissolving a gas in a liquid
(B) Dissolving a solid in a liquid
(C) Condensation
(D) Freezing
Answer
(B) — Solids become dispersed when dissolved, greatly increasing entropy.
31. A student dissolves 5.8 g of KCl in enough water to make 250.0 mL of solution. What is the molarity? (Molar mass = 74.5 g/mol)
(A) 0.290 M
(B) 0.312 M
(C) 0.333 M
(D) 0.400 M
Answer
(C) — Moles = 5.8/74.5 ≈ 0.0779; M = 0.0779 / 0.250 L ≈ 0.312 M.
32. Which statement about molality is true?
(A) Depends on volume of solution
(B) Is temperature-dependent
(C) Is moles of solute per kilogram of solvent
(D) Changes with pressure
Answer
(C) — Molality = moles of solute / kg of solvent; it is independent of temperature.
33. Which solution has the highest boiling point elevation?
(A) 0.1 M glucose
(B) 0.1 M NaCl
(C) 0.2 M NaCl
(D) 0.2 M glucose
Answer
(C) — NaCl dissociates into 2 ions; 0.2 M provides the highest total particle concentration.
34. What is the effect of adding salt to ice water?
(A) Freezing point increases
(B) Boiling point decreases
(C) Freezing point decreases
(D) Ice melts slower
Answer
(C) — Adding solute lowers the freezing point (freezing point depression).
35. Which solution would have the *lowest* vapor pressure?
(A) Pure water
(B) 0.1 M glucose
(C) 0.1 M NaCl
(D) 0.2 M NaCl
Answer
(D) — More solute particles reduce vapor pressure more (Raoult’s Law).
36. Define “solute”.
Answer
A solute is the substance that is dissolved in a solvent to form a solution.
37. What is a “saturated” solution?
Answer
A saturated solution contains the maximum amount of solute that can dissolve at a given temperature.
38. Why do ionic compounds conduct electricity in aqueous solutions?
Answer
Because they dissociate into free ions that can move and carry electric current.
39. What is the unit for molarity?
Answer
Moles of solute per liter of solution (mol/L).
40. Describe a nonelectrolyte.
Answer
A nonelectrolyte dissolves in water but does not produce ions or conduct electricity.
41. What does Henry’s Law relate?
Answer
It relates the solubility of a gas to its partial pressure above the liquid.
42. Give one reason why temperature affects gas solubility.
Answer
Higher temperatures give gas molecules more energy to escape the liquid, decreasing solubility.
43. What happens to entropy when a solid dissolves?
Answer
Entropy increases because the particles become more disordered.
44. Define molality.
Answer
Molality is the number of moles of solute per kilogram of solvent.
45. What is the main difference between weak and strong electrolytes?
Answer
Strong electrolytes completely ionize in water; weak electrolytes only partially ionize.
46. Why does increasing surface area speed up dissolution?
Answer
More surface area allows more contact between solute and solvent molecules.
47. Name one example of a weak acid.
Answer
Acetic acid (CH₃COOH).
48. What is meant by “aqueous” solution?
Answer
A solution where water is the solvent.
49. What kind of particles are formed when HCl is dissolved in water?
Answer
H⁺ and Cl⁻ ions.
50. How would you prepare 1.0 L of 0.5 M NaCl solution?
Answer
Dissolve 29.25 g of NaCl in water and add more water until the total volume is 1.0 L.