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CSET Science: Chemistry study materials
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CSET Science: Chemistry practice questions

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Question 1Chemistry content domain (weight not stated in source)

Which statement correctly describes the arrangement of particles in a solid at the particle level, according to the kinetic molecular model?

  1. Particles are far apart and move rapidly in straight lines until they collide.
  2. Particles are ionized into free electrons and positive ions arranged in a lattice.
  3. Particles are closely packed in fixed positions and vibrate about those positions. Correct answer.
  4. Particles are closely packed but move freely past one another throughout the volume.

Explanation

In a solid, intermolecular forces hold particles close together in an ordered arrangement, and the particles can only vibrate about fixed average positions. This restricted motion explains why solids keep a definite shape and volume. The other descriptions apply to liquids, gases, or metals specifically.

Question 2Chemistry content domain (weight not stated in source)

A sample of a pure substance has a fixed mass and a fixed volume but takes the shape of its container. Which state of matter is described?

  1. Crystalline solid
  2. Liquid Correct answer.
  3. Gas
  4. Plasma

Explanation

A liquid has definite volume because its particles remain in contact, but it flows to match the shape of its container because the particles can slide past one another. Fixed mass applies to any closed sample and does not distinguish the states. The combination of fixed volume with variable shape is the defining feature of a liquid.

Question 3Chemistry content domain (weight not stated in source)

Which change of state is correctly paired with the energy process it involves?

  1. Condensation: a gas absorbs energy to become a liquid
  2. Sublimation: a solid releases energy to become a gas
  3. Deposition: a gas releases energy to become a solid Correct answer.
  4. Melting: a liquid absorbs energy to become a gas

Explanation

Deposition is the direct change from gas to solid, and forming the more ordered solid state releases energy to the surroundings. Each other pairing mislabels either the starting and ending states or the direction of energy flow. Sublimation and melting both require absorption of energy, while condensation releases energy.

Question 4Chemistry content domain (weight not stated in source)

A 25.0 g sample of an unknown metal absorbs 1.14 kJ of heat and its temperature rises from 22.0 °C to 72.0 °C. What is the specific heat capacity of the metal?

  1. 0.912 J/(g·°C) Correct answer.
  2. 2.28 J/(g·°C)
  3. 0.456 J/(g·°C)
  4. 1.82 J/(g·°C)

Explanation

Use q = mcΔT, so c = q/(mΔT). Convert 1.14 kJ to 1140 J and ΔT = 50.0 °C, giving c = 1140/(25.0 × 50.0) = 0.912 J/(g·°C). The result is a plausible value for a metal such as aluminum.

Question 5Chemistry content domain (weight not stated in source)

A sealed rigid container holds a gas at 300 K and 1.0 atm. If the gas is heated to 600 K, what happens to the average kinetic energy and the pressure?

  1. Average kinetic energy doubles; pressure doubles. Correct answer.
  2. Average kinetic energy doubles; pressure stays the same.
  3. Average kinetic energy stays the same; pressure doubles.
  4. Average kinetic energy quadruples; pressure quadruples.

Explanation

Average kinetic energy is proportional to absolute temperature, so doubling 300 K to 600 K doubles it. At constant volume, pressure is directly proportional to absolute temperature (Gay-Lussac's law), so the pressure also doubles to 2.0 atm.

Question 6Chemistry content domain (weight not stated in source)

Which observation provides the strongest evidence that a new substance formed in a chemical reaction rather than a physical change occurring?

  1. A solid with a different color and composition precipitated from two clear solutions. Correct answer.
  2. The liquid was stirred and its color spread evenly through the container.
  3. The mixture became warmer as the two solutions were combined.
  4. A sample was ground into a finer powder with a mortar and pestle.

Explanation

Formation of a precipitate with properties different from both reactants indicates that new substances with new compositions have formed, which is the hallmark of a chemical change. Physical changes such as dissolving, mixing, or grinding alter form but not composition. A temperature change alone can accompany physical processes like dissolving.

Question 7Chemistry content domain (weight not stated in source)

How many significant figures are in the measured value 0.004070 kg?

  1. Four Correct answer.
  2. Three
  3. Seven
  4. Six

Explanation

Leading zeros that only position the decimal point are not significant, so the three zeros before the 4 are excluded. The digits 4, 0, 7, and the trailing 0 after the 7 are significant, giving four significant figures. Trailing zeros after a decimal point are counted.

Question 8Chemistry content domain (weight not stated in source)

An atom of an element has the electron configuration 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p³. Which element is this?

  1. Nitrogen
  2. Vanadium
  3. Arsenic Correct answer.
  4. Phosphorus

Explanation

The configuration corresponds to atomic number 33 (2 + 2 + 6 + 2 + 6 + 2 + 10 + 3 = 33), which is arsenic. The 4p³ valence pattern places it in group 15, period 4. Phosphorus and nitrogen share the group but have fewer filled shells.

Question 9Chemistry content domain (weight not stated in source)

Which trend correctly describes how atomic radius changes across a period and down a group in the periodic table?

  1. Radius decreases across a period and increases down a group. Correct answer.
  2. Radius increases across a period and increases down a group.
  3. Radius decreases across a period and decreases down a group.
  4. Radius increases across a period and decreases down a group.

Explanation

Across a period, increasing nuclear charge pulls the same-shell electrons closer, so radius decreases. Down a group, electrons occupy higher principal energy levels, so the outermost electrons are farther from the nucleus and radius increases.

Question 10Chemistry content domain (weight not stated in source)

Which pair of elements would most likely form an ionic compound when combined?

  1. Two noble gases at room temperature
  2. Two nonmetals with similar electronegativities
  3. A highly electropositive metal and a highly electronegative nonmetal Correct answer.
  4. Two transition metals with nearly equal electronegativities

Explanation

Ionic bonding typically arises when a low-electronegativity metal transfers electrons to a high-electronegativity nonmetal, producing oppositely charged ions that attract electrostatically. A large electronegativity difference favors electron transfer rather than sharing. Similar electronegativities favor covalent bonding instead.

Question 11Chemistry content domain (weight not stated in source)

Why does water (H₂O) have a much higher boiling point than hydrogen sulfide (H₂S), despite sulfur being below oxygen in the same group?

  1. Hydrogen bonding between H₂O molecules requires more energy to overcome than the dipole–dipole forces in H₂S. Correct answer.
  2. H₂O molecules are linear, which allows tighter packing in the liquid.
  3. H₂S is nonpolar, so it has no intermolecular forces at all.
  4. H₂O has a larger molar mass, so London dispersion forces are stronger.

Explanation

Oxygen is highly electronegative and small, so O–H bonds are strongly polar and water forms extensive hydrogen bonds. Hydrogen bonding is much stronger than the ordinary dipole–dipole attractions available to H₂S, so more energy is needed to separate water molecules. Molar mass actually favors stronger dispersion forces in H₂S, not water.

Question 12Chemistry content domain (weight not stated in source)

Which Lewis structure feature correctly represents the bonding in the carbonate ion, CO₃²⁻?

  1. Three double bonds to carbon, with all three oxygens neutral.
  2. One triple bond and two single bonds to carbon, with all oxygens neutral.
  3. Three single bonds to carbon, with the negative charge placed on carbon.
  4. One double bond to carbon, two single bonds to oxygen, and the two single-bonded oxygens carrying the formal negative charges. Correct answer.

Explanation

Carbonate has 24 valence electrons; a valid resonance structure places one C=O double bond and two C–O single bonds, with the negative charge on the singly bonded oxygens. The three equivalent resonance forms average the bond order to about 1.33. Carbon cannot expand its octet beyond four bonds here without exceeding the electron count.

Question 13Chemistry content domain (weight not stated in source)

A molecule has the general formula AX₄ with four identical bonding pairs and no lone pairs on the central atom. What is its molecular geometry and bond angle?

  1. Trigonal pyramidal, 107°
  2. Square planar, 90°
  3. See-saw, 90° and 120°
  4. Tetrahedral, 109.5° Correct answer.

Explanation

Four bonding pairs and zero lone pairs on the central atom give electron-pair geometry and molecular geometry that are both tetrahedral, with ideal angles of about 109.5°. An example is methane, CH₄. Lone pairs would be needed to distort the shape toward pyramidal or see-saw geometries.

Question 14Chemistry content domain (weight not stated in source)

Which statement best explains why a catalyst increases the rate of a reaction without being consumed?

  1. It provides an alternative pathway with a lower activation energy, increasing the fraction of collisions that are effective. Correct answer.
  2. It increases the equilibrium constant so more product forms.
  3. It raises the activation energy so only the most energetic molecules react.
  4. It raises the temperature of the reaction mixture by releasing heat.

Explanation

A catalyst lowers the activation energy by offering a different reaction pathway, so a larger fraction of collisions has enough energy to form products, increasing the rate. The catalyst is regenerated, so it is not consumed. It does not change the equilibrium constant or the overall energy change of the reaction.

Question 15Chemistry content domain (weight not stated in source)

For the equilibrium N₂(g) + 3H₂(g) ⇌ 2NH₃(g), which change would shift the equilibrium toward more ammonia?

  1. Adding a catalyst to the mixture
  2. Decreasing the concentration of nitrogen gas
  3. Increasing the volume of the container at constant temperature
  4. Increasing the pressure by decreasing the container volume Correct answer.

Explanation

There are four moles of gas on the left and two on the right, so increasing pressure (by reducing volume) shifts the equilibrium toward the side with fewer gas molecules, producing more ammonia. Le Châtelier's principle governs this response. A catalyst affects only the rate of approach to equilibrium.

Question 16Chemistry content domain (weight not stated in source)

A solution has a hydronium ion concentration of 1.0 × 10⁻⁴ M at 25 °C. What are the pH and the hydroxide ion concentration?

  1. pH = 4 and [OH⁻] = 1.0 × 10⁻¹⁰ M Correct answer.
  2. pH = 4 and [OH⁻] = 1.0 × 10⁻⁸ M
  3. pH = 4 and [OH⁻] = 1.0 × 10⁻⁴ M
  4. pH = 10 and [OH⁻] = 1.0 × 10⁻¹⁰ M

Explanation

pH = −log(1.0 × 10⁻⁴) = 4. Using Kw = 1.0 × 10⁻¹⁴ = [H₃O⁺][OH⁻], the hydroxide concentration is 1.0 × 10⁻¹⁴ / 1.0 × 10⁻⁴ = 1.0 × 10⁻¹⁰ M. The solution is acidic, consistent with a pH below 7.

Question 17Chemistry content domain (weight not stated in source)

Which reaction is correctly classified as a Brønsted–Lowry acid–base reaction?

  1. NH₃(aq) + H₂O(l) ⇌ NH₄⁺(aq) + OH⁻(aq) Correct answer.
  2. AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq)
  3. Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g)
  4. 2H₂O₂(aq) → 2H₂O(l) + O₂(g)

Explanation

In the ammonia–water reaction, water donates a proton (acid) to ammonia, which accepts it (base), producing NH₄⁺ and OH⁻. Proton transfer between species defines a Brønsted–Lowry acid–base reaction. The other equations are a redox reaction, a precipitation reaction, and a decomposition.

Question 18Chemistry content domain (weight not stated in source)

Which of the following is an oxidation–reduction reaction?

  1. 2Na(s) + Cl₂(g) → 2NaCl(s) Correct answer.
  2. CaCO₃(s) → CaO(s) + CO₂(g)
  3. NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l)
  4. AgNO₃(aq) + KBr(aq) → AgBr(s) + KNO₃(aq)

Explanation

In the formation of sodium chloride, sodium goes from oxidation state 0 to +1 (oxidized) and chlorine from 0 to −1 (reduced), so this is a redox reaction. Oxidation-state changes are the diagnostic test. The other reactions involve no change in oxidation states.

Question 19Chemistry content domain (weight not stated in source)

In the electrolysis of molten sodium chloride, what products form at the cathode and anode, respectively?

  1. Hydrogen gas at the cathode and oxygen gas at the anode
  2. Sodium metal at the cathode and oxygen gas at the anode
  3. Chlorine gas at the cathode and sodium metal at the anode
  4. Sodium metal at the cathode and chlorine gas at the anode Correct answer.

Explanation

At the cathode, reduction occurs: Na⁺ gains electrons to form sodium metal. At the anode, oxidation occurs: Cl⁻ loses electrons to form chlorine gas. In molten NaCl no water is present, so hydrogen and oxygen cannot be produced.

Question 20Chemistry content domain (weight not stated in source)

Which statement correctly describes the first law of thermodynamics as applied to a chemical system?

  1. The total energy of the universe is constant; energy lost by the system equals energy gained by the surroundings. Correct answer.
  2. The enthalpy of a reaction depends on the reaction pathway taken.
  3. Energy can be created by an exothermic reaction and destroyed by an endothermic one.
  4. The entropy of the universe always decreases in a spontaneous process.

Explanation

The first law states that energy is conserved: ΔE_universe = 0, so energy transferred out of a system must be absorbed by the surroundings. For a reaction at constant pressure, the heat exchanged is the enthalpy change. Enthalpy is a state function and does not depend on pathway.

Question 21Chemistry content domain (weight not stated in source)

A reaction has ΔH = +58 kJ and ΔS = +175 J/K. At approximately what temperature does the reaction become spontaneous under standard conditions?

  1. About 3.0 K, above which it is spontaneous
  2. About 331 K, below which it is spontaneous
  3. The reaction is spontaneous at all temperatures because ΔS is positive
  4. About 331 K, above which it is spontaneous Correct answer.

Explanation

Spontaneity requires ΔG = ΔH − TΔS < 0. Setting ΔG = 0 gives T = ΔH/ΔS = 58,000 J / 175 J/K ≈ 331 K. Because both ΔH and ΔS are positive, the reaction becomes spontaneous above this temperature, where the TΔS term outweighs ΔH.

Question 22Chemistry content domain (weight not stated in source)

How many moles of oxygen gas are required to completely combust 4.0 moles of methane according to CH₄ + 2O₂ → CO₂ + 2H₂O?

  1. 4.0 moles
  2. 16.0 moles
  3. 8.0 moles Correct answer.
  4. 2.0 moles

Explanation

The balanced equation shows a 1:2 mole ratio of methane to oxygen. Multiplying 4.0 moles of CH₄ by 2 gives 8.0 moles of O₂. The coefficients must be balanced before applying the ratio.

Question 23Chemistry content domain (weight not stated in source)

What is the molarity of a solution prepared by dissolving 5.85 g of NaCl (molar mass 58.5 g/mol) in enough water to make 250.0 mL of solution?

  1. 0.400 M Correct answer.
  2. 1.00 M
  3. 0.100 M
  4. 0.0250 M

Explanation

Moles of NaCl = 5.85 g / 58.5 g/mol = 0.100 mol. Volume = 0.2500 L, so molarity = 0.100 mol / 0.2500 L = 0.400 M. Molarity is moles of solute per liter of solution, not per liter of solvent.

Question 24Chemistry content domain (weight not stated in source)

A sample of an ideal gas occupies 2.0 L at 300 K and 1.0 atm. If the pressure is doubled and the temperature is halved, what is the new volume?

  1. 1.0 L
  2. 0.50 L Correct answer.
  3. 2.0 L
  4. 8.0 L

Explanation

Using the combined gas law, V₂ = V₁(P₁/P₂)(T₂/T₁). Here P₂ = 2.0 atm and T₂ = 150 K, so V₂ = 2.0 × (1.0/2.0) × (150/300) = 2.0 × 0.5 × 0.5 = 0.50 L. Both changes act to reduce the volume.

Question 25Chemistry content domain (weight not stated in source)

Which set of quantum numbers is not permitted for an electron in an atom?

  1. n = 3, l = 2, m_l = −1, m_s = +½
  2. n = 2, l = 2, m_l = +1, m_s = +½ Correct answer.
  3. n = 4, l = 3, m_l = +2, m_s = +½
  4. n = 2, l = 1, m_l = 0, m_s = −½

Explanation

The angular momentum quantum number l can range only from 0 to n − 1. For n = 2, the allowed values are l = 0 and l = 1, so l = 2 is not permitted. The other sets obey all quantum-number rules.

Question 26Chemistry content domain (weight not stated in source)

A sealed flask contains a mixture of ice and liquid water at 0 °C. Heat is slowly added until all the ice just melts, and the temperature remains at 0 °C throughout. Which description of the energy change is correct?

  1. The added energy increases the average kinetic energy of the water molecules.
  2. The added energy is released again as the liquid refreezes.
  3. The added energy is stored as potential energy as hydrogen bonds between molecules are broken. Correct answer.
  4. The added energy is destroyed because the temperature does not change.

Explanation

During a phase change at constant temperature, added heat goes into overcoming intermolecular attractions rather than raising average molecular speed. Because average kinetic energy is proportional to temperature, the potential energy of the molecules increases while kinetic energy stays fixed. This is why the melting curve is flat on a heating graph.

Question 27Chemistry content domain (weight not stated in source)

A sample of a compound is decomposed and found to contain 2.0 g of calcium, 1.0 g of carbon, and 4.0 g of oxygen. What is the empirical formula of the compound? (Molar masses: Ca = 40, C = 12, O = 16 g/mol)

  1. Ca₂CO₃
  2. CaCO₂
  3. CaCO₃ Correct answer.
  4. CaC₂O

Explanation

Convert each mass to moles: Ca = 2.0/40 = 0.050 mol, C = 1.0/12 ≈ 0.083 mol, O = 4.0/16 = 0.25 mol. Dividing by the smallest value (0.050) gives a ratio of 1 : 1.67 : 5, and multiplying by three gives whole numbers 3 : 5 : 15, which reduces to CaCO₃. The mass ratio itself (2:1:4) matches the 40:12:48 ratio of calcium carbonate.

Question 28Chemistry content domain (weight not stated in source)

Which statement correctly describes how the periodic table organizes elements with respect to their electron configurations?

  1. Elements in the same period have the same number of valence electrons.
  2. Elements in the same period have identical numbers of neutrons in their nuclei.
  3. Elements in the same group have the same number of occupied electron shells.
  4. Elements in the same group have similar valence electron configurations and therefore similar chemical properties. Correct answer.

Explanation

A group is a vertical column, and its members share the same valence-shell electron pattern (for main-group elements, the same number of valence electrons). Because chemical behavior is governed largely by valence electrons, group members show similar reactivity and bonding patterns. Periods are horizontal rows, and moving across a period adds protons and electrons rather than repeating the valence configuration.

Question 29Chemistry content domain (weight not stated in source)

A gas is held in a rigid steel cylinder at 27 °C and 2.0 atm. The cylinder is then heated to 327 °C. Assuming the volume is fixed, what is the new pressure?

  1. 2.2 atm
  2. 1.0 atm
  3. 22 atm
  4. 4.0 atm Correct answer.

Explanation

Gay-Lussac's law states that at constant volume, pressure is directly proportional to absolute temperature, so P₂ = P₁(T₂/T₁). Converting to kelvin gives T₁ = 300 K and T₂ = 600 K, so the pressure doubles to 4.0 atm. Using Celsius temperatures directly would give a wrong answer because the relationship requires an absolute scale.

Question 30Chemistry content domain (weight not stated in source)

Which description correctly characterizes the bonding in a sample of solid copper metal?

  1. Copper atoms are held together by hydrogen bonds between partially positive hydrogen atoms.
  2. Electrons are transferred from copper atoms to form discrete Cu²⁺ and Cu²⁻ ions.
  3. Delocalized valence electrons are shared among a lattice of positively charged copper ions. Correct answer.
  4. Each copper atom shares one pair of electrons with a single neighboring atom in a diatomic molecule.

Explanation

Metals are modeled as a lattice of cations surrounded by a sea of delocalized valence electrons. This electron sea explains metallic properties such as electrical conductivity, malleability, and luster. There are no discrete molecules or directional shared pairs in the metallic lattice.

Question 31Chemistry content domain (weight not stated in source)

A student mixes solutions of lead(II) nitrate and potassium iodide and observes a bright yellow solid form. Which net ionic equation correctly represents the reaction?

  1. Pb²⁺(aq) + 2K⁺(aq) → PbK₂(s)
  2. Pb²⁺(aq) + 2I⁻(aq) → PbI₂(s) Correct answer.
  3. K⁺(aq) + NO₃⁻(aq) → KNO₃(s)
  4. Pb²⁺(aq) + 2NO₃⁻(aq) → Pb(NO₃)₂(s)

Explanation

In a precipitation reaction, the net ionic equation shows only the ions that combine to form the insoluble product. Lead(II) iodide is the yellow precipitate, so Pb²⁺ and I⁻ appear on the reactant side in a 1:2 ratio. Potassium and nitrate are spectator ions and are omitted from the net ionic equation.

Question 32Chemistry content domain (weight not stated in source)

According to VSEPR theory, what is the molecular geometry of the sulfur dioxide molecule, SO₂, which has two bonding pairs and one lone pair on the central sulfur atom?

  1. Bent Correct answer.
  2. Tetrahedral
  3. Trigonal planar
  4. Linear

Explanation

The electron-domain geometry for three electron domains is trigonal planar, but one domain is a lone pair. The lone pair repels the bonding pairs more strongly, so the two oxygen atoms are pushed into a bent arrangement with an angle less than 120°. Molecular geometry describes only the positions of the atoms, not the lone pair.

Question 33Chemistry content domain (weight not stated in source)

A first-order reaction has a half-life of 20 seconds. If the initial concentration of the reactant is 0.80 M, what is the concentration after 60 seconds?

  1. 0.20 M
  2. 0.05 M
  3. 0.10 M Correct answer.
  4. 0.40 M

Explanation

For a first-order reaction, each half-life reduces the concentration by half, and 60 seconds corresponds to three half-lives. Halving three times: 0.80 → 0.40 → 0.20 → 0.10 M. The half-life of a first-order reaction is independent of starting concentration, so this halving pattern applies directly.

Question 34Chemistry content domain (weight not stated in source)

Which change would increase the equilibrium concentration of product in the endothermic reaction A(g) ⇌ B(g) + C(g), for which ΔH is positive?

  1. Adding a catalyst to the reaction mixture
  2. Increasing the total pressure by compressing the system
  3. Decreasing the temperature of the system
  4. Increasing the temperature of the system Correct answer.

Explanation

Le Châtelier's principle predicts that raising the temperature favors the endothermic direction, which here is the forward reaction producing B and C. Adding heat shifts the equilibrium toward the products and increases their equilibrium concentrations. Pressure changes and catalysts do not alter the equilibrium position in the way temperature does.

Question 35Chemistry content domain (weight not stated in source)

Which solution has the highest pH at 25 °C?

  1. 0.10 M NaOH Correct answer.
  2. 0.10 M CH₃COOH (acetic acid, a weak acid)
  3. 0.10 M HCl
  4. 0.10 M NaCl

Explanation

pH measures the negative logarithm of hydronium ion concentration, so the most basic solution has the highest pH. Sodium hydroxide is a strong base that dissociates completely, giving a hydroxide concentration of 0.10 M and a pH of about 13. The other solutions are acidic or neutral and therefore have much lower pH values.

Question 36Chemistry content domain (weight not stated in source)

In the reaction Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s), which species is oxidized and which is reduced?

  1. Both Zn and Cu²⁺ are oxidized.
  2. Zn is reduced and Cu²⁺ is oxidized.
  3. Zn is oxidized and Cu²⁺ is reduced. Correct answer.
  4. Neither species changes oxidation state.

Explanation

Oxidation is a loss of electrons, and reduction is a gain of electrons. Zinc goes from oxidation state 0 to +2, losing two electrons, so it is oxidized. Copper goes from +2 to 0, gaining those electrons, so it is reduced.

Question 37Chemistry content domain (weight not stated in source)

A galvanic cell is constructed with a standard zinc electrode in Zn²⁺ solution and a standard copper electrode in Cu²⁺ solution. Given that the standard reduction potential of Zn²⁺/Zn is −0.76 V and that of Cu²⁺/Cu is +0.34 V, what is the standard cell potential?

  1. +1.10 V Correct answer.
  2. −0.42 V
  3. −1.10 V
  4. 0.42 V

Explanation

The standard cell potential is the difference between the cathode and anode reduction potentials: E°cell = E°cathode − E°anode. Copper has the higher reduction potential, so it serves as the cathode: 0.34 − (−0.76) = +1.10 V. A positive value indicates a spontaneous reaction as written.

Question 38Chemistry content domain (weight not stated in source)

Which statement correctly describes the relationship between the standard free-energy change, ΔG°, and the equilibrium constant, K, for a reaction?

  1. ΔG° is zero for every reaction at equilibrium.
  2. A reaction with K greater than 1 has a negative ΔG° and is product-favored. Correct answer.
  3. ΔG° is independent of temperature and does not affect K.
  4. A reaction with a large positive K has a large positive ΔG°.

Explanation

The relationship ΔG° = −RT ln K shows that a K greater than 1 gives a negative ΔG°, meaning the reaction is product-favored under standard conditions. A large K corresponds to a large negative ΔG°, not a positive one. ΔG° does depend on temperature through both R T and the temperature dependence of K.

Question 39Chemistry content domain (weight not stated in source)

Which set of quantum numbers correctly describes an electron in a 3p orbital?

  1. n = 3, l = 2, mₗ = 0
  2. n = 2, l = 1, mₗ = +1
  3. n = 3, l = 0, mₗ = 0
  4. n = 3, l = 1, mₗ = −1 Correct answer.

Explanation

For a 3p orbital, the principal quantum number n is 3 and the angular momentum quantum number l is 1 (s = 0, p = 1, d = 2). The magnetic quantum number mₗ can take values from −l to +l, so −1, 0, and +1 are all allowed for a p orbital. The set n = 3, l = 1, mₗ = −1 therefore satisfies all the rules.

Question 40Chemistry content domain (weight not stated in source)

Which statement correctly explains the trend in first ionization energy across Period 3 from sodium to argon?

  1. Ionization energy is constant because all Period 3 elements have the same number of shells.
  2. Ionization energy generally increases because effective nuclear charge increases while the shielding remains similar. Correct answer.
  3. Ionization energy generally decreases because atomic radius increases across the period.
  4. Ionization energy increases only because the number of neutrons increases across the period.

Explanation

Across a period, protons are added to the nucleus while electrons enter the same principal shell, so shielding changes little. The growing effective nuclear charge holds valence electrons more tightly, raising the energy required to remove one. This produces the general increase in first ionization energy from sodium to argon, with minor irregularities at group boundaries.

Question 41Chemistry content domain (weight not stated in source)

A 25.0 mL sample of hydrochloric acid is titrated to the equivalence point with 0.100 M sodium hydroxide. If 20.0 mL of the base is required, what is the molarity of the hydrochloric acid?

  1. 0.0500 M
  2. 0.0800 M Correct answer.
  3. 0.125 M
  4. 0.100 M

Explanation

At the equivalence point, moles of acid equal moles of base for a 1:1 reaction: M_acid × V_acid = M_base × V_base. Solving gives M_acid = (0.100 M × 20.0 mL) / 25.0 mL = 0.0800 M. The volumes can be used in milliliters because the units cancel in the ratio.

Question 42Chemistry content domain (weight not stated in source)

Which description correctly explains why a solution of sodium chloride in water conducts electricity while solid sodium chloride does not?

  1. Water molecules become charged when sodium chloride dissolves.
  2. In solution, ions are free to move, whereas in the solid they are locked in a fixed lattice. Correct answer.
  3. Solid sodium chloride contains no ions until it is melted or dissolved.
  4. Electrons flow through the solution as they do through a metal wire.

Explanation

Electrical conduction in an ionic solution requires mobile charge carriers. When sodium chloride dissolves, the ionic lattice breaks apart and hydrated Na⁺ and Cl⁻ ions move freely, carrying current. In the solid, ions are present but fixed in place, so they cannot migrate.

Question 43Chemistry content domain (weight not stated in source)

Which statement correctly describes how the rate of a reaction changes when the concentration of a reactant is doubled for a second-order reaction in that reactant?

  1. The rate remains unchanged.
  2. The rate doubles.
  3. The rate is halved.
  4. The rate quadruples. Correct answer.

Explanation

For a second-order dependence on a reactant, rate = k[A]², so doubling [A] multiplies the rate by 2² = 4. The exponent in the rate law gives the factor by which the rate changes when concentration changes. A doubling of rate would correspond to first-order dependence, not second-order.

Question 44Chemistry content domain (weight not stated in source)

Which pair of properties best distinguishes an ionic compound from a molecular covalent compound?

  1. Ionic compounds conduct electricity when molten, while covalent compounds generally do not. Correct answer.
  2. Ionic compounds have low melting points, while covalent network compounds have high melting points.
  3. Ionic compounds are gases at room temperature, while covalent compounds are solids.
  4. Ionic compounds share electrons between atoms, while covalent compounds transfer electrons.

Explanation

Molten ionic compounds contain mobile ions and therefore conduct electricity, whereas simple molecular covalent compounds consist of neutral molecules and do not conduct. Ionic solids also typically have high melting points due to strong electrostatic attractions. The electron-sharing versus transfer description is reversed in the last option.

Question 45Chemistry content domain (weight not stated in source)

A reaction is found to be spontaneous at all temperatures. Which combination of signs for ΔH and ΔS is consistent with this observation?

  1. ΔH positive and ΔS positive
  2. ΔH positive and ΔS negative
  3. ΔH negative and ΔS positive Correct answer.
  4. ΔH negative and ΔS negative

Explanation

Spontaneity is governed by ΔG = ΔH − TΔS, and a negative ΔG means the process is spontaneous. If ΔH is negative and ΔS is positive, both terms favor a negative ΔG at every temperature. Other sign combinations become spontaneous only above or below a certain temperature.

Question 46Chemistry content domain (weight not stated in source)

Which statement correctly describes the behavior of a buffer solution made from acetic acid and sodium acetate?

  1. It maintains a pH of exactly 7 regardless of composition.
  2. It resists pH change when small amounts of strong acid or strong base are added. Correct answer.
  3. It becomes strongly basic when a small amount of acid is added.
  4. It loses its buffering ability only when the temperature is changed.

Explanation

A buffer contains a weak acid and its conjugate base, which can neutralize added strong base or strong acid respectively. This pair of species allows the solution to resist large pH changes when small amounts of either are introduced. The buffer pH is set by the ratio of the components through the Henderson–Hasselbalch relationship, not fixed at 7.

Question 47Chemistry content domain (weight not stated in source)

How many liters of 0.50 M HCl are needed to completely neutralize 2.0 moles of NaOH according to HCl + NaOH → NaCl + H₂O?

  1. 4.0 L Correct answer.
  2. 2.0 L
  3. 1.0 L
  4. 0.50 L

Explanation

The balanced equation shows a 1:1 mole ratio between HCl and NaOH, so 2.0 moles of HCl are required. Using molarity = moles/volume, volume = 2.0 mol / 0.50 mol/L = 4.0 L. Checking units confirms the result is in liters.

Question 48Chemistry content domain (weight not stated in source)

Which statement correctly describes the difference between an orbit and an orbital in atomic theory?

  1. An orbit can hold two electrons, while an orbital can hold only one.
  2. An orbit describes the nucleus, while an orbital describes the electron cloud.
  3. An orbit is a quantum number, while an orbital is a physical path.
  4. An orbit is a fixed circular path, while an orbital is a region of space where an electron is likely to be found. Correct answer.

Explanation

The Bohr model pictured electrons in fixed circular orbits, but quantum mechanics replaced this with orbitals, which are probability distributions describing where an electron is likely to be found. An orbital is defined by a set of quantum numbers and can hold up to two electrons with opposite spins. The orbit concept is a historical model, not a quantum-mechanical description.

Question 49Chemistry content domain (weight not stated in source)

A sample of an ideal gas occupies 4.0 L at 2.0 atm and 300 K. If the gas is allowed to expand to 8.0 L while the temperature is held constant, what is the new pressure?

  1. 4.0 atm
  2. 2.0 atm
  3. 1.0 atm Correct answer.
  4. 0.50 atm

Explanation

Boyle's law states that at constant temperature, pressure and volume are inversely proportional: P₁V₁ = P₂V₂. Substituting gives (2.0 atm)(4.0 L) = P₂(8.0 L), so P₂ = 1.0 atm. Doubling the volume halves the pressure when temperature is fixed.

Question 50Chemistry content domain (weight not stated in source)

Which statement correctly accounts for the fact that the second ionization energy of magnesium is much higher than its first ionization energy?

  1. The second ionization energy is always smaller because the atom becomes more stable after losing one electron.
  2. The second electron is removed from a higher energy shell that is farther from the nucleus.
  3. The second electron is a neutron that has been converted into an electron.
  4. The second electron is removed from a positively charged ion, so it experiences a stronger effective nuclear attraction. Correct answer.

Explanation

After the first electron is removed, the remaining ion has a net positive charge, so the nucleus holds the remaining electrons more tightly. Removing a second electron therefore requires significantly more energy than removing the first. Additionally, successive electrons come from increasingly stable configurations closer to the nucleus.