CLEP Chemistry Practice 2026 practice questions and answers. Tap an option to test yourself — you'll see the correct answer and a plain-English explanation for every question. Free, no login.
Q11Which of the following distinctively characterizes a superoxide?
✓ Correct answer: A. Oxygen has an oxidation state of -1/2
Answer: Oxygen has an oxidation state of -1/2 In superoxides, such as KO_2 and NaO_2, oxygen exhibits an oxidation state of -1/2, which is different from its usual -2 state. This unique oxidation state allows superoxides to participate in oxidation-reduction reactions differently from peroxides and other oxygen compounds.
Q12Why does adding antifreeze to a car's radiator benefit the vehicle's cooling system?
✓ Correct answer: E. It will lower the freezing point and raise the boiling point of the coolant
Adding antifreeze to a car's radiator lowers the freezing point and raises the boiling point of the coolant. This is a colligative property, wherein adding a solute (antifreeze) to a solvent (water) affects its physical properties like freezing and boiling points. This makes the coolant more effective at preventing the engine from overheating or freezing in different weather conditions.
Q13Under which condition is Boyle's Law not applicable?
✓ Correct answer: A. When temperature is not constant
Answer: When temperature is not constant Boyle's Law states that there is an inverse proportional relationship between Volume and Pressure $$\left( V_1 P_1 = V_2 P_2 \right)$$, provided that Temperature and the amount of gas (n) are held constant. It does not matter what type of gas is involved, and it does not matter if there multiple different gas species.
Q14In the context of the Ideal Gas Law, what is a possible unit for the volume of a gas?
✓ Correct answer: D. liters (L)
Answer: liters (L) According to the Ideal Gas Law ($$PV = nRT$$), volume is typically measured in liters (L) when using standard units. The ideal gas constant R is consistent with units of pressure in atmospheres (atm), volume in liters (L), amount of substance in moles (mol), and temperature in kelvin (K).
Q15A semi-permeable membrane encloses a gas mixture containing 5% helium and 95% nitrogen. This membrane is placed into an external gas mixture containing 2% helium and 98% nitrogen. What will happen now? Analyze the probabilities of gas transfer through the semi-permeable membrane based on the percentages provided.
✓ Correct answer: E. Helium will flow from the outer gas mixture into the membrane-enclosed space
Answer: Helium will flow from the outer gas mixture into the membrane-enclosed space. This problem is about the behavior of gases and partial pressures: helium can traverse the membrane, but nitrogen cannot. There is a partial pressure gradient to balance the concentration of helium on either side of the membrane, so helium flows into the area of higher concentration to balance the pressures. Notably, gas transfer via a semi-permeable membrane does not care about the types of gases on either side of the membrane. The membrane may reach an equilibrium with completely different types of gases inside and outside of the membrane.
Q16Analyze the table below to determine which phases of matter are generally incompressible. Phase Compressibility Solid Incompressible Liquid Incompressible Gas Compressible Plasma Compressible
✓ Correct answer: B. Solid and Liquid
Answer: Solid and Liquid. Solids and liquids are generally incompressible compared to gases and plasmas, which are compressible phases of matter.
Q17All other conditions held equal, which of the following changes would increase the vapor pressure of a liquid?
✓ Correct answer: C. Increased temperature
Answer: Increased temperature Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid phase. At higher temperatures, molecules have more kinetic energy, which allows more molecules to escape from the liquid to the vapor phase, thus increasing the vapor pressure.
Q18You place a solid piece of paraffin wax into a heating apparatus and gradually increase the temperature while recording the temperature and time. The wax transitions from a solid to a liquid and then to a gas. The resulting graph shows both flat and upward-sloping lines. At which part of the graph does the 'heat of fusion' for paraffin wax occur?
✓ Correct answer: C. The first flat segment
Answer: The first flat segment. When paraffin wax absorbs heat to transition from solid to liquid, its temperature does not change during the phase change. This is represented by the first flat segment on the graph. The second flat segment represents the heat of vaporization as the wax changes from liquid to gas.
Q19Consider this reaction: Cu + S -> CuS. How has the oxidation state of sulfur changed?
✓ Correct answer: B. Decreased by 2
Answer: Decreased by 2 On the left side of the equation, both elements are in their neutral, unbonded states and therefore have oxidation states of 0. Therefore, the right side of the equation must also have a net oxidation state of 0. We know that copper sulfide is really composed of the copper ion (Cu$$^{2+}$$) and sulfide ion (S$$^{2-}$$), so sulfur's oxidation state is -2 and has therefore decreased by 2 overall.
Q20In general, the highest lattice energy is associated with:
✓ Correct answer: B. Small ionic radii and high ionic charges
Answer: Small ionic radii and high ionic charges Lattice energy is the energy released when ions form a solid lattice. Higher lattice energies are associated with stronger electrostatic forces between ions. These forces are strongest when the ions have high charges and are close together, resulting in smaller ionic radii.
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Theory