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MTEL Chemistry practice questions

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Question 1Chemistry content knowledge

An atom of an element has the electron configuration 1s² 2s² 2p⁶ 3s² 3p⁴. In which group of the periodic table does this element belong?

  1. Group 12
  2. Group 14
  3. Group 16 Correct answer.
  4. Group 18

Explanation

The configuration ends in 3s² 3p⁴, so the atom has six valence electrons (2 + 4). Elements with six valence electrons occupy Group 16, the chalcogens. The period is three because the highest occupied shell is n = 3.

Question 2Chemistry content knowledge

Which statement correctly describes what happens when a covalent bond forms between two hydrogen atoms?

  1. The two nuclei fuse into a single nucleus with a shared electron cloud.
  2. Each atom loses an electron so that both reach a stable octet.
  3. Electron density increases between the nuclei, lowering the potential energy. Correct answer.
  4. A proton is transferred from one atom to the other, producing ions.

Explanation

A covalent bond forms when atomic orbitals overlap and electrons are shared, concentrating electron density in the region between the two nuclei. That density is attracted to both nuclei simultaneously, so the system's potential energy decreases as the bond forms.

Question 3Chemistry content knowledge

Aqueous solutions of sodium chloride and silver nitrate are mixed and a white precipitate forms. Which net ionic equation represents the reaction?

  1. Na⁺(aq) + Cl⁻(aq) → NaCl(s)
  2. Ag⁺(aq) + NO₃⁻(aq) → AgNO₃(s)
  3. Ag⁺(aq) + Cl⁻(aq) → AgCl(s) Correct answer.
  4. Na⁺(aq) + NO₃⁻(aq) → NaNO₃(s)

Explanation

The precipitate is silver chloride, formed when silver ions combine with chloride ions. Sodium and nitrate ions remain dissolved as spectator ions, so they are omitted from the net ionic equation. Silver chloride is insoluble and is written as a solid.

Question 4Chemistry content knowledge

A sample of gas occupies 2.0 L at 300 K. If the pressure is held constant and the temperature is raised to 600 K, what volume does the gas occupy?

  1. 2.0 L
  2. 1.0 L
  3. 4.0 L Correct answer.
  4. 8.0 L

Explanation

Charles's law states that volume is directly proportional to absolute temperature at constant pressure, so V₂ = V₁(T₂/T₁). Doubling the Kelvin temperature from 300 K to 600 K doubles the volume from 2.0 L to 4.0 L.

Question 5Chemistry content knowledge

Which of the following is the correct IUPAC name for the compound CH₃CH₂CH₂OH?

  1. propanone
  2. propan-1-ol Correct answer.
  3. propanoic acid
  4. propanal

Explanation

The three-carbon chain carrying an –OH group is named from propane with the suffix -ol, and the hydroxyl sits on carbon 1. The correct name is therefore propan-1-ol (1-propanol). The -al, -one, and -oic acid suffixes belong to other functional groups.

Question 6Chemistry content knowledge

Which type of radiation emitted by a radioactive nucleus carries a positive charge?

  1. Alpha particles Correct answer.
  2. Beta particles
  3. Neutrons
  4. Gamma rays

Explanation

An alpha particle is a helium nucleus consisting of two protons and two neutrons, giving it a 2+ charge. Beta particles are electrons (negative), gamma rays are uncharged photons, and neutrons are neutral.

Question 7Chemistry content knowledge

Which of the following is a homogeneous mixture?

  1. A mixture of iron filings and sulfur powder
  2. A piece of granite showing visible mineral grains
  3. A suspension of sand in water
  4. Salt water in which the dissolved salt is uniformly distributed Correct answer.

Explanation

A homogeneous mixture has a uniform composition throughout, with components not visibly distinct. Salt water is a solution in which dissolved ions are dispersed evenly at the molecular level. The other examples contain visibly separate phases or components.

Question 8Chemistry content knowledge

An atom of ³⁷Cl contains how many neutrons in its nucleus?

  1. 20 Correct answer.
  2. 37
  3. 54
  4. 17

Explanation

The mass number (37) equals the sum of protons and neutrons, and chlorine's atomic number is 17 protons. Neutrons = 37 − 17 = 20. The mass number is not the neutron count itself.

Question 9Chemistry content knowledge

A reaction has a negative enthalpy change (ΔH < 0) and a positive entropy change (ΔS > 0). Which statement about the reaction is correct?

  1. It is spontaneous only at low temperatures.
  2. It is spontaneous only at high temperatures.
  3. It is nonspontaneous at all temperatures.
  4. It is spontaneous at all temperatures. Correct answer.

Explanation

Spontaneity is governed by ΔG = ΔH − TΔS. With ΔH negative and ΔS positive, both terms favor a negative ΔG at every temperature above absolute zero, so the reaction is spontaneous throughout.

Question 10Chemistry content knowledge

A buffer is prepared from acetic acid and sodium acetate. Adding a small amount of strong base to this buffer causes which change?

  1. Acetate ions react with the hydroxide to regenerate acetic acid and water.
  2. The pH rises sharply because buffers cannot resist base addition.
  3. Acetic acid molecules neutralize the added hydroxide, forming acetate ion. Correct answer.
  4. Sodium ions precipitate as sodium hydroxide and remove hydroxide from solution.

Explanation

A buffer resists pH change because its weak acid component consumes added strong base. Acetic acid donates a proton to hydroxide, producing water and additional acetate, so the pH shifts only slightly. The conjugate base component protects against added strong acid instead.

Question 11Chemistry content knowledge

In the reaction 2KClO₃(s) → 2KCl(s) + 3O₂(g), what is the oxidation state of chlorine in KClO₃?

  1. −1
  2. 0
  3. +5 Correct answer.
  4. +7

Explanation

In chlorate, each oxygen is −2, so three oxygens contribute −6. The potassium ion is +1, so chlorine must be +5 for the formula unit to be neutral (+1 + Cl − 6 = 0).

Question 12Chemistry content knowledge

Ethanol and dimethyl ether have the same molecular formula, but pure ethanol boils at a higher temperature. Which interaction available between ethanol molecules best explains this?

  1. An ionic lattice of ethanol ions
  2. Metallic bonding between carbon atoms
  3. Covalent bonds joining separate ethanol molecules into a network
  4. Intermolecular hydrogen bonding involving O-H groups Correct answer.

Explanation

Ethanol has an O-H group and can form intermolecular hydrogen bonds with other ethanol molecules. Dimethyl ether lacks an O-H donor, so its pure liquid lacks this self-association mechanism.

Question 13Chemistry content knowledge

What is the pH of a 0.010 M solution of a strong monoprotic acid?

  1. 12.0
  2. 2.0 Correct answer.
  3. 7.0
  4. 1.0

Explanation

A strong acid dissociates completely, so [H⁺] equals the acid concentration, 0.010 M = 1.0 × 10⁻² M. pH = −log(1.0 × 10⁻²) = 2.0.

Question 14Chemistry content knowledge

A galvanic cell is constructed with a zinc anode and a copper cathode. Which process occurs at the anode?

  1. Cu²⁺ ions gain electrons and are deposited as copper metal.
  2. Zn metal is oxidized to Zn²⁺, releasing electrons into the external circuit. Correct answer.
  3. Electrons flow from the copper electrode to the zinc electrode through the wire.
  4. Zn²⁺ ions gain electrons and are deposited as zinc metal.

Explanation

Oxidation always occurs at the anode of a galvanic cell, and zinc is the more easily oxidized metal here. Zinc atoms lose electrons to form Zn²⁺, and those electrons travel through the external circuit toward the copper cathode, where reduction occurs.

Question 15Chemistry content knowledge

Which quantum number determines the overall shape of an atomic orbital (s, p, d, or f)?

  1. Angular momentum quantum number, l Correct answer.
  2. Magnetic quantum number, mₗ
  3. Spin quantum number, mₛ
  4. Principal quantum number, n

Explanation

The angular momentum quantum number l takes values from 0 to n − 1 and defines the orbital type: l = 0 is s, l = 1 is p, l = 2 is d, and l = 3 is f. These labels correspond directly to orbital shape.

Question 16Chemistry content knowledge

Which pair of coefficients correctly balances the equation __C₃H₈ + __O₂ → __CO₂ + __H₂O?

  1. 1, 10, 3, 8
  2. 2, 7, 6, 8
  3. 1, 5, 3, 4 Correct answer.
  4. 1, 4, 3, 4

Explanation

Balancing carbon gives 3 CO₂ and balancing hydrogen gives 4 H₂O. The right side then holds 6 + 4 = 10 oxygen atoms, requiring 5 O₂ molecules. The set 1, 5, 3, 4 satisfies conservation of every element.

Question 17Chemistry content knowledge

A reaction is first order with respect to reactant A. If the initial concentration of A is doubled while temperature is held constant, how does the initial rate change?

  1. It is halved.
  2. It stays the same.
  3. It doubles. Correct answer.
  4. It quadruples.

Explanation

For a first-order dependence, rate = k[A], so the rate is directly proportional to concentration. Doubling [A] doubles the rate. Quadrupling would require a second-order dependence.

Question 18Chemistry content knowledge

According to VSEPR theory, what is the molecular geometry of NH₃?

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

Explanation

Nitrogen in NH₃ has three bonding pairs and one lone pair, giving four electron domains and a tetrahedral electron-pair geometry. The lone pair compresses the bond angles, and the molecular geometry described by the atoms alone is trigonal pyramidal.

Question 19Chemistry content knowledge

Which statement best explains why the first ionization energy of magnesium is greater than that of sodium?

  1. Magnesium's outer electron is removed from a filled 3s subshell, whereas sodium's comes from a half-filled 3s subshell. Correct answer.
  2. Magnesium has a larger atomic radius, so its outer electron is held more tightly.
  3. Magnesium's valence electron is in a lower principal shell than sodium's.
  4. Magnesium has more neutrons, which increases the nuclear charge felt by outer electrons.

Explanation

Sodium loses its single 3s electron easily, leaving a stable neon-like core. Magnesium must remove an electron from a filled 3s subshell, and the added proton raises the effective nuclear charge without adding a new shell, so more energy is required.

Question 20Chemistry content knowledge

In an experiment, 0.50 mol of a nonelectrolyte is dissolved in 1.0 kg of water. If the freezing-point depression constant for water is 1.86 °C·kg/mol, what is the freezing-point depression?

  1. 3.72 °C
  2. 1.86 °C
  3. 0.93 °C Correct answer.
  4. 0.50 °C

Explanation

The freezing-point depression is ΔT = Kf × m, where molality m = 0.50 mol / 1.0 kg = 0.50 mol/kg. Multiplying 1.86 °C·kg/mol by 0.50 mol/kg gives 0.93 °C. A nonelectrolyte produces one particle per formula unit, so no van't Hoff factor is needed.

Question 21Chemistry content knowledge

Which of the following best describes the role of a catalyst in a chemical reaction?

  1. It increases the equilibrium constant of the reaction.
  2. It provides an alternative pathway with lower activation energy without being consumed. Correct answer.
  3. It increases the enthalpy change released by the reaction.
  4. It raises the activation energy so fewer collisions are effective.

Explanation

A catalyst speeds a reaction by offering a pathway with a lower activation energy, so a larger fraction of collisions has sufficient energy. It is regenerated during the reaction and does not alter the thermodynamics of the overall process.

Question 22Chemistry content knowledge

A 0.10 M solution of a weak monoprotic acid has a pH of 3.0. What is the approximate acid dissociation constant, Ka?

  1. 1.0 × 10⁻⁵ Correct answer.
  2. 1.0 × 10⁻⁷
  3. 1.0 × 10⁻¹
  4. 1.0 × 10⁻³

Explanation

A pH of 3.0 means [H⁺] = 1.0 × 10⁻³ M. For a weak acid, Ka ≈ [H⁺]²/[HA] = (1.0 × 10⁻³)² / 0.10 = 1.0 × 10⁻⁶ / 0.10 = 1.0 × 10⁻⁵. The small degree of dissociation justifies neglecting the change in acid concentration.

Question 23Chemistry content knowledge

A radioactive isotope has a half-life of 12 years. What fraction of an original sample remains after 36 years?

  1. 1/3
  2. 1/4
  3. 1/8 Correct answer.
  4. 1/16

Explanation

Thirty-six years spans three half-lives (36 ÷ 12 = 3). Each half-life halves the remaining amount, so the fraction left is (1/2)³ = 1/8.

Question 24Chemistry content knowledge

A system at equilibrium is disturbed by decreasing the volume of its container at constant temperature. According to Le Chatelier's principle, the equilibrium shifts in which direction for the reaction N₂(g) + 3H₂(g) ⇌ 2NH₃(g)?

  1. Toward the products, because fewer moles of gas are present on that side. Correct answer.
  2. No shift occurs, because volume changes do not affect gas-phase equilibria.
  3. Toward the reactants, because the forward reaction releases heat.
  4. Toward the products, because the reaction is exothermic.

Explanation

Decreasing the volume raises the partial pressures of all gases. The system relieves this increase by shifting toward the side with fewer moles of gas, which is the product side (2 mol versus 4 mol). The enthalpy change is irrelevant to a pressure or volume disturbance.

Question 25Chemistry content knowledge

Which of the following sets of quantum numbers (n, l, mₗ, mₛ) is not permitted for an electron in an atom?

  1. (2, 1, 0, +1/2)
  2. (2, 2, 1, +1/2) Correct answer.
  3. (3, 2, −2, −1/2)
  4. (1, 0, 0, +1/2)

Explanation

The angular momentum quantum number l must be less than n, so for n = 2 the only allowed values are l = 0 and l = 1. The set (2, 2, 1, +1/2) violates this rule and is therefore not permitted. The other sets satisfy all quantum number constraints.

Question 26Chemistry content knowledge

Which subatomic particle is gained or lost when a neutral atom becomes a monatomic ion?

  1. Neutron
  2. Nucleon
  3. Proton
  4. Electron Correct answer.

Explanation

Ion formation involves the transfer of electrons between atoms or from an atom to its surroundings. The number of protons defines the element and does not change during ordinary ionization, and neutrons are unaffected in chemical processes.

Question 27Chemistry content knowledge

Using Stock nomenclature, which name is correct for the compound with the formula Fe₂O₃?

  1. Iron(III) oxide Correct answer.
  2. Iron(II) oxide
  3. Iron trioxide
  4. Diiron trioxide

Explanation

Oxygen in a binary ionic compound is assigned an oxidation state of −2, so three oxide ions total −6 and each iron must be +3. The Stock system expresses this with a Roman numeral in parentheses after the metal name.

Question 28Chemistry content knowledge

Which particle is emitted when carbon-14 decays to nitrogen-14?

  1. A positron
  2. A beta particle Correct answer.
  3. An alpha particle
  4. A gamma ray

Explanation

In carbon-14 decay the atomic number rises from 6 to 7 while the mass number stays at 14, which is the signature of beta-minus emission, in which a neutron converts to a proton and an electron. An emitted electron accounts for the increased nuclear charge.

Question 29Chemistry content knowledge

A sample of matter has a fixed volume but takes the shape of its container. In which state is the sample?

  1. Liquid Correct answer.
  2. Solid
  3. Gas
  4. Plasma

Explanation

Particles in a liquid are close together, so the volume is essentially fixed, but they can move past one another, so the sample conforms to the container's shape. Solids also have fixed volume but retain their own shape.

Question 30Chemistry content knowledge

Which observation indicates that a chemical change has occurred rather than a physical change?

  1. Ice melts into liquid water
  2. A new substance with different properties forms Correct answer.
  3. Salt dissolves in water
  4. A solid is broken into smaller pieces

Explanation

A chemical change produces one or more new substances whose composition and properties differ from those of the starting materials. Changes of size, state, or dispersion leave the chemical identity unchanged.

Question 31Chemistry content knowledge

Which quantity is conserved in every balanced chemical equation?

  1. Total volume of the reactants
  2. Number of molecules
  3. Total number of atoms of each element Correct answer.
  4. Number of moles of gas

Explanation

Balancing reflects the law of conservation of mass: atoms are neither created nor destroyed, so each element must appear with the same atom count on both sides. Molecule counts and gas volumes can change as bonds rearrange.

Question 32Chemistry content knowledge

Which element has the ground-state electron configuration 1s²2s²2p⁶3s²3p¹?

  1. Silicon
  2. Sodium
  3. Aluminum Correct answer.
  4. Magnesium

Explanation

The configuration totals 13 electrons, and the neutral atom with atomic number 13 is aluminum. The final electron occupies the 3p subshell, consistent with aluminum's position in group 13.

Question 33Chemistry content knowledge

Which type of bond forms when electrons are transferred from a metal atom to a nonmetal atom?

  1. Hydrogen bond
  2. Covalent bond
  3. Ionic bond Correct answer.
  4. Metallic bond

Explanation

Ionic bonding results from the electrostatic attraction between cations and anions produced by electron transfer, typically between a metal and a nonmetal. Covalent bonds instead involve sharing electron pairs.

Question 34Chemistry content knowledge

What is the molar mass of calcium carbonate, CaCO₃? (Ca = 40.08, C = 12.01, O = 16.00)

  1. 100.09 g/mol Correct answer.
  2. 68.09 g/mol
  3. 84.09 g/mol
  4. 116.09 g/mol

Explanation

Summing the atomic masses gives 40.08 + 12.01 + 3(16.00) = 100.09 g/mol. The three oxygen atoms contribute 48.00 g/mol of that total.

Question 35Chemistry content knowledge

How many grams of NaCl are needed to prepare 250.0 mL of a 0.200 M solution? (NaCl = 58.44 g/mol)

  1. 5.84 g
  2. 2.92 g Correct answer.
  3. 11.7 g
  4. 29.2 g

Explanation

Moles needed equal 0.200 mol/L × 0.2500 L = 0.0500 mol. Multiplying by the molar mass gives 0.0500 × 58.44 = 2.92 g.

Question 36Chemistry content knowledge

In the reaction N₂(g) + 3H₂(g) ⇌ 2NH₃(g), which change shifts the equilibrium toward the products?

  1. Adding a catalyst to the mixture
  2. Removing some NH₃ as it forms Correct answer.
  3. Increasing the temperature of the system
  4. Adding argon gas at constant volume

Explanation

Removing a product lowers the reaction quotient below K, so the system responds by forming more products to restore equilibrium. Concentration changes of this kind shift the position of equilibrium without altering K.

Question 37Chemistry content knowledge

Which compound is the strongest electrolyte when dissolved in water?

  1. Acetic acid, CH₃COOH
  2. Potassium nitrate, KNO₃ Correct answer.
  3. Ethanol, C₂H₅OH
  4. Glucose, C₆H₁₂O₆

Explanation

Potassium nitrate is a soluble ionic salt that dissociates completely into ions, making it a strong electrolyte. Molecular solutes that do not ionize or that ionize only slightly conduct poorly.

Question 38Chemistry content knowledge

What volume of 0.500 M HCl is required to neutralize 25.0 mL of 0.200 M NaOH?

  1. 5.00 mL
  2. 25.0 mL
  3. 50.0 mL
  4. 10.0 mL Correct answer.

Explanation

Neutralization follows a 1:1 mole ratio, so moles of acid equal moles of base: 0.0250 L × 0.200 M = 0.00500 mol. Dividing by the acid concentration gives 0.00500 / 0.500 = 0.0100 L, or 10.0 mL.

Question 39Chemistry content knowledge

A gas occupies 2.0 L at 300 K and 1.0 atm. What volume does it occupy at 600 K if the pressure is held constant?

  1. 4.0 L Correct answer.
  2. 1.0 L
  3. 8.0 L
  4. 2.0 L

Explanation

Charles's law states that volume is directly proportional to absolute temperature at constant pressure. Doubling the temperature from 300 K to 600 K therefore doubles the volume from 2.0 L to 4.0 L.

Question 40Chemistry content knowledge

A 2.0 g sample of a hydrocarbon is burned completely, producing 6.29 g of CO₂ and 2.57 g of H₂O. What is the empirical formula of the hydrocarbon? (C = 12.01, H = 1.008, O = 16.00)

  1. CH₃
  2. C₂H₅
  3. CH₂ Correct answer.
  4. C₂H₃

Explanation

The carbon in CO₂ is 6.29 g × (12.01/44.01) = 1.716 g, or 0.1429 mol C. The hydrogen in water is 2.57 g × (2.016/18.02) = 0.2876 g, or 0.2853 mol H; the ratio H:C is about 2:1, giving CH₂.

Question 41Chemistry content knowledge

Which statement correctly describes the trend in atomic radius across a period from left to right?

  1. Radius increases because added electrons repel one another strongly
  2. Radius decreases because effective nuclear charge increases while the shell number stays constant Correct answer.
  3. Radius remains constant because the number of shells does not change
  4. Radius increases because more electron shells are added

Explanation

Across a period, protons are added to the nucleus while electrons enter the same principal shell, so the effective nuclear charge rises and pulls the electron cloud inward. The result is a smaller atomic radius from left to right.

Question 42Chemistry content knowledge

Which molecule contains a polar covalent bond but has a net dipole moment of zero?

  1. HCl
  2. CO₂ Correct answer.
  3. NH₃
  4. H₂O

Explanation

Each C=O bond in carbon dioxide is polar, but the linear geometry places the two bond dipoles in exactly opposite directions, so they cancel. The molecule is therefore nonpolar overall despite having polar bonds.

Question 43Chemistry content knowledge

What is the oxidation state of sulfur in the sulfate ion, SO₄²⁻?

  1. +6 Correct answer.
  2. −2
  3. +4
  4. +2

Explanation

Assigning oxygen −2 gives a total of −8 from the four oxygen atoms. Because the ion carries a −2 charge, sulfur must be +6 so that +6 + (−8) = −2.

Question 44Chemistry content knowledge

A reaction has an activation energy of 50 kJ/mol without a catalyst and 30 kJ/mol with a catalyst. What is the effect of the catalyst on the rate constant at a fixed temperature?

  1. It decreases the rate constant because the activation energy is lower
  2. It leaves the rate constant unchanged because ΔH is unchanged
  3. It increases the rate constant only if the reaction is exothermic
  4. It increases the rate constant because the fraction of collisions with sufficient energy rises Correct answer.

Explanation

The Arrhenius equation shows that the rate constant depends exponentially on the activation energy, so lowering the barrier from 50 to 30 kJ/mol sharply increases the fraction of collisions energetic enough to react. The catalyst does not change the enthalpy of reaction.

Question 45Chemistry content knowledge

A sample of an ideal gas occupies 5.0 L at 2.0 atm and 300 K. How many moles of gas are present? (R = 0.0821 L·atm/(mol·K))

  1. 0.20 mol
  2. 2.4 mol
  3. 0.41 mol Correct answer.
  4. 4.1 mol

Explanation

Using PV = nRT, n = PV/RT = (2.0 × 5.0)/(0.0821 × 300) = 10.0/24.63 ≈ 0.41 mol. The calculation requires absolute temperature and pressure in atmospheres.

Question 46Chemistry content knowledge

A solution is prepared by dissolving 18.0 g of glucose (molar mass 180.2 g/mol) in 500.0 g of water. What is the molality of the solution?

  1. 0.500 m
  2. 0.100 m
  3. 0.360 m
  4. 0.200 m Correct answer.

Explanation

The moles of glucose are 18.0/180.2 = 0.0999 mol, and the solvent mass is 0.5000 kg. Molality equals moles of solute per kilogram of solvent, so 0.0999/0.5000 ≈ 0.200 m.

Question 47Chemistry content knowledge

At 25 °C, Ksp for AgCl is 1.8 × 10⁻¹⁰. What is the molar solubility of AgCl in pure water at this temperature?

  1. 9.0 × 10⁻¹¹ M
  2. 3.6 × 10⁻¹⁰ M
  3. 1.3 × 10⁻⁵ M Correct answer.
  4. 1.8 × 10⁻¹⁰ M

Explanation

For AgCl, Ksp = [Ag⁺][Cl⁻] = s², so s equals the square root of 1.8 × 10⁻¹⁰, which is about 1.3 × 10⁻⁵ M. The 1:1 stoichiometry means both ion concentrations equal the molar solubility.

Question 48Chemistry content knowledge

A galvanic cell uses Ag⁺/Ag (E° = +0.80 V) and Cu²⁺/Cu (E° = +0.34 V) half-cells. What is the standard cell potential?

  1. −1.14 V
  2. +0.46 V Correct answer.
  3. +1.14 V
  4. −0.46 V

Explanation

The half-cell with the higher reduction potential, silver, is reduced at the cathode, while copper is oxidized at the anode. The standard cell potential is E°cathode − E°anode = 0.80 − 0.34 = +0.46 V.

Question 49Chemistry content knowledge

A reaction has ΔH = +58 kJ and ΔS = +176 J/K. Above approximately what temperature does the reaction become spontaneous under standard conditions?

  1. 330 K Correct answer.
  2. 0.33 K
  3. 176 K
  4. 580 K

Explanation

Spontaneity requires ΔG = ΔH − TΔS < 0, so T must exceed ΔH/ΔS. Converting entropy to kJ/K gives 0.176 kJ/K, and 58/0.176 ≈ 330 K. Above this temperature the favorable entropy term outweighs the unfavorable enthalpy term.

Question 50Chemistry content knowledge

A buffer contains 0.10 M acetic acid (Ka = 1.8 × 10⁻⁵) and 0.10 M sodium acetate. What is the pH of the buffer?

  1. 5.74
  2. 2.87
  3. 7.00
  4. 4.74 Correct answer.

Explanation

The Henderson–Hasselbalch equation gives pH = pKa + log([A⁻]/[HA]). Because the acid and conjugate base concentrations are equal, the log term is zero and pH equals pKa = −log(1.8 × 10⁻⁵) ≈ 4.74.