--- title: "AP Chemistry Unit 3 Practice Test" description: "A timed AP Chemistry Unit 3 (Properties of Substances and Mixtures) practice test in the AP format, drawn from 2,330 multiple-choice questions and 119 FRQs written for the unit. The standard version takes about 60 minutes." canonical: "https://fiveable.me/ap-chem/unit-test/3" type: "unit-test" subject: "AP Chemistry" unit: "Unit 3" --- # AP Chemistry Unit 3 Practice Test ## Overview A timed AP Chemistry Unit 3 (Properties of Substances and Mixtures) practice test in the AP format, drawn from 2,330 multiple-choice questions and 119 FRQs written for the unit. The standard version takes about 60 minutes. ## Test Format - 20 Multiple Choice Questions (30 minutes) - 1 FRQ – FRQ 1 – Long Answer (15 minutes) - 1 FRQ – FRQ 4 – Short Answer (15 minutes) ## Unit FRQs by Type - [FRQ 1 – Long Answer](/ap-chem/frqs/frq-1?unit=3): 10 questions - [FRQ 2 – Long Answer](/ap-chem/frqs/frq-2?unit=3): 8 questions - [FRQ 3 – Long Answer](/ap-chem/frqs/frq-3?unit=3): 7 questions - [FRQ 4 – Short Answer](/ap-chem/frqs/frq-4?unit=3): 33 questions - [FRQ 5 – Short Answer](/ap-chem/frqs/frq-5?unit=3): 30 questions - [FRQ 6 – Short Answer](/ap-chem/frqs/frq-6?unit=3): 17 questions - [FRQ 7 – Short Answer](/ap-chem/frqs/frq-7?unit=3): 14 questions ## Practice Questions ### Question 1 The Henry's law constant for oxygen gas ($O_2$) in water at $25^\circ C$ is $1.3 \times 10^{-3}$ mol/(L·atm). Calculate the concentration of dissolved $O_2$ in a solution at equilibrium with air where the partial pressure of $O_2$ is 0.21 atm. - (A) $2.7 \times 10^{-4}$ M - (B) $6.2 \times 10^{-3}$ M - (C) $1.6 \times 10^{2}$ M - (D) $2.7 \times 10^{-3}$ M **Answer: (A)** Applying Henry's Law ($C = kP$) requires multiplying the constant ($1.3 \times 10^{-3}$) by the pressure (0.21). The result is $2.7 \times 10^{-4}$ M, limited to two significant figures by the given values. ### Question 2 Potassium nitrate ($KNO_3$) has a solubility of 85.0 g per 100.0 g of water at $50^\circ C$ and 32.0 g per 100.0 g of water at $20^\circ C$. A student prepares a saturated solution using 50.0 g of water at $50^\circ C$ and then cools it to $20^\circ C$. What mass of $KNO_3$ will precipitate? - (A) 26.5 g - (B) 16.0 g - (C) 53.0 g - (D) 58.5 g **Answer: (A)** Calculating the precipitate requires determining the mass dissolved at $50^\circ C$ (42.5 g) and $20^\circ C$ (16.0 g) scaled to 50.0 g of water, then finding the difference (42.5 g - 16.0 g = 26.5 g). ### Question 3 At $20^\circ C$, the solubility of sucrose ($C_{12}H_{22}O_{11}$, molar mass 342.3 g/mol) is 204 g per 100. mL of solution. What is the molarity of a saturated sucrose solution at this temperature? - (A) 5.96 M - (B) 0.596 M - (C) 1.68 M - (D) 16.8 M **Answer: (A)** Calculating molarity requires converting mass to moles (204 g / 342.3 g/mol = 0.596 mol) and dividing by volume in liters (0.596 mol / 0.100 L = 5.96 M). ### Question 4 The solubility of ammonium chloride ($NH_4Cl$) at $20^\circ C$ is 37.0 g per 100.0 g of water. If a student dissolves 12.0 g of $NH_4Cl$ in 50.0 g of water at $20^\circ C$, how much additional $NH_4Cl$ is required to saturate the solution? - (A) 6.5 g - (B) 18.5 g - (C) 25.0 g - (D) 30.5 g **Answer: (A)** Calculating the required addition involves finding the saturation limit for 50.0 g of water (18.5 g) and subtracting the amount already dissolved (18.5 g - 12.0 g = 6.5 g). ### Question 5 A student measures the electrical conductivity of distilled water to confirm that the covalent bonds do not allow for significant ion formation. The beaker used contains traces of dried sodium chloride (NaCl) from a previous experiment. Which of the following best explains how this source of error affects the experimental result and the conclusion about the bonding in water? - (A) Conductivity will be higher than expected, leading to the incorrect conclusion that the bonds in water have significant ionic character. - (B) Conductivity will be higher than expected, leading to the incorrect conclusion that water molecules dissociate into ions more readily than they actually do. - (C) Conductivity will be higher than expected, leading to the incorrect conclusion that the covalent bonds in water are polar enough to conduct electricity without forming ions. - (D) Conductivity will be higher than expected, leading to the incorrect conclusion that water contains dissolved salts that form ionic bonds with water molecules. **Answer: (A)** Connecting the presence of ionic impurities to increased conductivity allows for the prediction of a false positive result. The residual ions dissociate in the water, allowing charge to flow, which contradicts the expected result for a covalent compound and leads to the misidentification of the bond type. ### Question 6 A calibration plot of absorbance versus concentration for a solute obeys Beer's Law, passing through the origin and the point (0.20 M, 0.60). An unknown solution of the same solute has an absorbance of 0.30. What is the concentration of the unknown? - (A) 0.10 M - (B) 0.20 M - (C) 0.30 M - (D) 0.60 M **Answer: (A)** Using the linear relationship identified from the graph, the slope is 0.60/0.20 = 3.0. An absorbance of 0.30 corresponds to a concentration of 0.30 / 3.0 = 0.10 M. ### Question 7 A student reacts a $$5.00$$ g sample of a copper-zinc alloy with excess hydrochloric acid. Zinc reacts to form hydrogen gas, but copper does not. To calculate the mass percent of zinc in the alloy using the ideal gas law, which set of quantities must be measured? - (A) The volume of hydrogen gas, the barometric pressure, and the temperature - (B) The volume of hydrogen gas, the barometric pressure, and the acid volume - (C) The volume of hydrogen gas, the acid concentration, and the temperature - (D) The mass of the chloride salt, the acid concentration, and the temperature **Answer: (A)** Connecting the ideal gas law ($$PV=nRT$$) to stoichiometry requires determining the moles of gas produced. This requires measuring the gas volume, pressure (adjusted for water vapor if applicable), and temperature to solve for $$n$$, which then relates to the mass of zinc. ### Question 8 A chemist has a commercially available aqueous solution of sulfuric acid ($$H_2SO_4$$) with a known mass percent of $$98\%$$. To calculate the molarity of this solution, which additional quantity must be known? - (A) The density of the solution in grams per milliliter - (B) The density of the solvent in grams per milliliter - (C) The molar mass of the solvent in grams per mole - (D) The total volume of the solution in milliliters **Answer: (A)** Converting mass percent (mass solute/mass solution) to molarity (moles solute/volume solution) requires bridging mass and volume. The density of the solution provides the necessary conversion factor between the mass of the solution and its volume. ### Question 9 A rigid container holds a mixture of helium ($$He$$) and neon ($$Ne$$) gases, with 4 $$He$$ atoms and 12 $$Ne$$ atoms in the container. If the total pressure is measured as 4.0 atm, which description correctly links the particulate model to the partial pressures? - (A) The $$He$$ atoms represent 25% of the particles, corresponding to a partial pressure of 1.0 atm. - (B) The $$He$$ atoms represent 25% of the particles, corresponding to a partial pressure of 3.0 atm. - (C) The $$Ne$$ atoms represent 75% of the particles, corresponding to a partial pressure of 1.0 atm. - (D) The $$Ne$$ atoms represent 75% of the particles, corresponding to a partial pressure of 4.0 atm. **Answer: (A)** Calculating the mole fraction from particle counts ($$4/16 = 0.25$$) allows for the determination of partial pressure. Since partial pressure is proportional to mole fraction, $$0.25 \times 4.0$$ atm equals 1.0 atm. ### Question 10 A student views a particulate model of a sodium chloride ($$NaCl$$) solution showing 5 $$Na^+$$ ions and 5 $$Cl^-$$ ions in a specific volume. A second model of a calcium chloride ($$CaCl_2$$) solution shows 5 $$Ca^{2+}$$ ions and 10 $$Cl^-$$ ions in the same volume. Which statement correctly compares the macroscopic molarity of chloride ions? - (A) The chloride ion molarity in the $$CaCl_2$$ solution is double that of the $$NaCl$$ solution because the particle count is twice as high. - (B) The chloride ion molarity in the $$CaCl_2$$ solution is half that of the $$NaCl$$ solution because calcium ions are larger. - (C) The chloride ion molarity is the same in both solutions because the number of cations is identical. - (D) The chloride ion molarity depends on the mass of the ions, so the $$NaCl$$ solution has a higher concentration. **Answer: (A)** Comparing the particle counts in equal volumes directly reveals the concentration relationship. With 10 $$Cl^-$$ ions versus 5 $$Cl^-$$ ions, the molarity of chloride in the second solution is exactly double. ## Review the Unit - [3.1 Intermolecular and Interparticle Forces](/ap-chem/unit-3/intermolecular-forces/study-guide/aq9pSoNJoW70eCdben01) - [3.2 Properties of Solids](/ap-chem/unit-3/properties-solids/study-guide/0lW4bHW7ksIahDb0zW9v) - [3.3 Solids, Liquids, and Gases](/ap-chem/unit-3/solids-liquids-gases/study-guide/uNMmoAyjJQkL63ysUrJC) - [3.4 Ideal Gas Law](/ap-chem/unit-3/ideal-gas-law/study-guide/XINb2AUU6e3c1rGlhBXg) - [3.5 Kinetic Molecular Theory](/ap-chem/unit-3/kinetic-molecular-theory-gases/study-guide/nBJY7t92TEJmGXm9HHTU) - [3.6 Deviation from Ideal Gas Law](/ap-chem/unit-3/deviation-ideal-gas-law/study-guide/8FjXF3vZolkQTXL0mCkm) - [3.7 Solutions and Mixtures](/ap-chem/unit-3/solutions-mixtures/study-guide/lmjYxgiQN5yljSWPxWUl) - [3.8 Representations of Solutions](/ap-chem/unit-3/representations-solutions/study-guide/O4uZStuqpe603GRuztjG) - [3.9 Separation of Solutions and Mixtures](/ap-chem/unit-3/separation-solutions-mixtures-chromatography/study-guide/BMXrD6AItw7ILAHui8X9) - [3.10 Solubility](/ap-chem/unit-3/solubility/study-guide/XmVywOyhrzQscHR0OYP1) - [3.11 Spectroscopy and the Electromagnetic Spectrum](/ap-chem/unit-3/spectroscopy-electromagnetic-spectrum/study-guide/Swp8nLjZFev1h1Fu9sqJ) - [3.12 Properties of Photons](/ap-chem/unit-3/photoelectric-effect/study-guide/aSateoQF56rKcT1xgLeY) - [3.13 Beer-Lambert Law ](/ap-chem/unit-3/beer-lambert-law/study-guide/smCHzraorVz6qlWW1oeB) ## Other Unit Tests - [Unit 1: Atomic Structure & Properties](/ap-chem/unit-test/1) - [Unit 2: Compound Structure and Properties](/ap-chem/unit-test/2) - [Unit 4: Chemical Reactions](/ap-chem/unit-test/4) - [Unit 5: Kinetics](/ap-chem/unit-test/5) - [Unit 6: Thermochemistry](/ap-chem/unit-test/6) - [Unit 7: Equilibrium](/ap-chem/unit-test/7) - [Unit 8: Acids & Bases](/ap-chem/unit-test/8) - [Unit 9: Thermodynamics and Electrochemistry](/ap-chem/unit-test/9) ## About This Document Canonical Fiveable pages are available as Markdown at the same path plus `.md`. - [llms.txt](https://fiveable.me/llms.txt): index of Fiveable's sections and URL patterns - [llms-full.txt](https://fiveable.me/llms-full.txt): complete subject and unit listing - [MCP server](https://fiveable.me/mcp): call Fiveable as tools instead of fetching pages (`https://fiveable.me/api/mcp`) - [MCP server for AP teachers](https://fiveable.me/mcp/teachers): a teacher's classes, assignments and AP-rubric grading (`https://fiveable.me/api/mcp/teacher`)