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Public Institution Category C (Natural Sciences) - independent foundations study materials
Public Institution Category C (Natural Sciences) - independent foundations study resources

Public Institution Category C (Natural Sciences) - independent foundations practice questions

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Question 1Mechanics, fields, thermal behavior, waves and modern models

During an orbital rendezvous and docking maneuver between the Shenzhou spacecraft and the Tiangong space station, both spacecraft fire micro-thrusters in a vacuum. Which fundamental physical principle directly explains the propulsion generated by expelling reaction mass in the absence of an external medium?

  1. Law of Conservation of Momentum (动量守恒定律) Correct answer.
  2. Bernoulli's Principle (伯努利原理)
  3. Archimedes' Buoyancy Principle (阿基米德浮力定律)
  4. Coulomb's Electrostatic Law (库仑定律)

Explanation

Rocket propulsion in a vacuum operates directly on Newton's Third Law of Motion and the Law of Conservation of Momentum (动量守恒定律). In a closed system, the forward momentum gained by the spacecraft is exactly equal and opposite to the backward momentum of the expelled high-velocity exhaust gas (m_spacecraft * Delta_v = - m_gas * v_exhaust). It does not require any ambient atmospheric medium to push against.

Question 2Mechanics, fields, thermal behavior, waves and modern models

Modern fiber optic communication networks (光纤通信) transmit high-speed data pulses across continental distances. Which optical phenomenon ensures that light signals remain confined inside the fiber's core glass without leaking into the cladding?

  1. Total Internal Reflection (全反射) Correct answer.
  2. Optical Polarization (光的偏振)
  3. Diffraction of Light (光的衍射)
  4. Photoelectric Effect (光电效应)

Explanation

Optical fibers rely on Total Internal Reflection (全反射). When light travels from a core medium with a higher refractive index (n_core) toward a cladding medium with a lower refractive index (n_cladding) at an incident angle greater than the critical angle (theta > theta_c = arcsin(n_cladding / n_core)), 100% of the optical energy is reflected back into the core with zero refractive leakage.

Question 3Mechanics, fields, thermal behavior, waves and modern models

According to the Second Law of Thermodynamics and Carnot's Theorem, what is the theoretical maximum thermal efficiency (eta_max) of a heat engine operating between a high-temperature heat reservoir at 600 K (T_H) and a cooling reservoir at 300 K (T_C)?

  1. 50% Correct answer.
  2. 100%
  3. 33.3%
  4. 75%

Explanation

Carnot's theorem establishes that the maximum theoretical thermal efficiency of any heat engine operating between two thermal reservoirs at absolute temperatures T_H and T_C is given by eta_Carnot = 1 - (T_C / T_H). Substituting the values: eta = 1 - (300 K / 600 K) = 1 - 0.50 = 0.50 (50%). No real heat engine can exceed this limit due to irreversible entropy generation.

Question 4Mechanics, fields, thermal behavior, waves and modern models

High-speed maglev trains and electromagnetic braking systems utilize non-contact eddy current brakes (电涡流制动). When a conductive non-magnetic copper/aluminum plate moves through a stationary magnetic field, braking forces arise primarily because:

  1. Induced eddy currents generate magnetic fields that oppose the relative motion per Lenz's Law (楞次定律) Correct answer.
  2. The plate develops static electrical charge that attracts the permanent magnet poles
  3. Frictional contact between air molecules and magnetic flux lines converts kinetic energy into thermal energy
  4. The magnetic field alters the nuclear structure of copper atoms, creating permanent ferromagnetism

Explanation

As the conductive metal plate moves across a magnetic field, the changing magnetic flux induces circulating electrical currents (eddy currents / 涡流) within the metal per Faraday's Law. According to Lenz's Law (楞次定律), these induced currents generate their own magnetic field that exerts a Lorentz force opposing the relative motion between the conductor and the magnetic field, smoothly converting mechanical kinetic energy into Joule heating without mechanical friction.

Question 5Mechanics, fields, thermal behavior, waves and modern models

When a material transitions into a Superconducting state below its critical temperature (T_c), it exhibits both zero electrical resistance and the Meissner Effect (迈斯纳效应). What is the physical definition of the Meissner effect?

  1. The expulsion of magnetic flux from the bulk when a material enters the superconducting state, subject to field, geometry, and penetration-depth limits Correct answer.
  2. The spontaneous generation of high-voltage alternating current without external excitation
  3. The complete absorption and trapping of all surrounding thermal infrared radiation
  4. The irreversible conversion of metallic crystalline lattices into amorphous glass

Explanation

The Meissner-Ochsenfeld effect is the expulsion of magnetic flux from the superconducting bulk as the material is cooled below its critical temperature. In an ideal weak-field description the bulk field approaches zero apart from a surface penetration depth; geometry, critical fields, flux pinning, and the mixed state of type-II superconductors qualify the simplified statement.

Question 6Cells, biomolecules, heredity and metabolism

According to Mitchell's Chemiosmotic Hypothesis (化学渗透假说), what directly drives the catalytic synthesis of ATP by ATP Synthase in both mitochondrial oxidative phosphorylation and chloroplast photophosphorylation?

  1. An electrochemical transmembrane proton gradient (质子电化学梯度 / 质子动势) Correct answer.
  2. Direct mechanical collision between glucose molecules and the cell nucleus
  3. The spontaneous hydrolytic cleavage of nuclear DNA phosphodiester bonds
  4. Electrostatic repulsion between sodium and potassium ions in the cytoplasm

Explanation

Peter Mitchell's chemiosmotic hypothesis explains that the electron transport chain pumps protons (H+) across a biological membrane (mitochondrial inner membrane or chloroplast thylakoid membrane), creating a proton concentration gradient and electrical potential difference (proton-motive force). Protons flow back down this electrochemical gradient through the F0 channel of ATP Synthase, driving the rotational mechanical catalysis that phosphorylates ADP into ATP.

Question 7Cells, biomolecules, heredity and metabolism

In the CRISPR-Cas9 genome editing system widely used in molecular biology, what determines the specific genomic site where the Cas9 endonuclease introduces a double-strand break (DSB)?

  1. Base-pairing complementarity between the single guide RNA (sgRNA) spacer and target DNA, adjacent to a Protospacer Adjacent Motif (PAM) Correct answer.
  2. Random non-specific electrostatic adhesion to histone protein tails
  3. Restriction endonuclease recognition sequences of exactly 6 base pairs without any RNA involvement
  4. Temperature-dependent thermal denaturation of DNA telomere repeats

Explanation

CRISPR-Cas9 target specificity is governed by a synthetic single guide RNA (sgRNA). A 20-nucleotide spacer sequence on the sgRNA hybridizes via Watson-Crick base pairing to the complementary genomic target DNA strand immediately 5' of a 3-nucleotide Protospacer Adjacent Motif (PAM sequence, typically 5'-NGG-3' for SpCas9). Upon PAM recognition and RNA-DNA pairing, the Cas9 endonuclease domains (RuvC and HNH) cleave both DNA strands.

Question 8Cells, biomolecules, heredity and metabolism

Which property of water is most directly responsible for its ability to moderate temperature in living organisms and large bodies of water?

  1. Its low specific heat
  2. Its inability to form hydrogen bonds
  3. Its nonpolar covalent bonds
  4. Its high specific heat Correct answer.

Explanation

Water has a high specific heat because hydrogen bonds must absorb or release substantial energy before water molecules change temperature. This allows water and water-rich organisms to resist large temperature swings, helping maintain homeostasis.

Question 9Cells, biomolecules, heredity and metabolism

Which structure is found in a typical plant cell but NOT in a typical animal cell?

  1. Mitochondrion
  2. Nucleus
  3. Ribosome
  4. Cell wall made of cellulose Correct answer.

Explanation

Plant cells have a rigid cell wall composed primarily of cellulose that surrounds the plasma membrane, providing structural support. Animal cells lack a cell wall, relying on the cytoskeleton and extracellular matrix instead.

Question 10Cells, biomolecules, heredity and metabolism

An enzyme lowers the activation energy of a reaction. Which statement best describes how this affects the reaction?

  1. It increases the reaction rate without being consumed in the reaction Correct answer.
  2. It changes the overall free-energy difference between reactants and products
  3. It supplies the energy needed to make an endergonic reaction exergonic
  4. It permanently binds to the product to stop the reaction

Explanation

Enzymes are biological catalysts that lower activation energy, speeding up reactions without being consumed. They do not change the net free-energy difference (delta G) between reactants and products; they only make the reaction reach equilibrium faster.

Question 11Cells, biomolecules, heredity and metabolism

Meiosis differs from mitosis in that meiosis produces

  1. Two genetically identical diploid cells
  2. One diploid cell with double the chromosomes
  3. Two haploid cells identical to the parent
  4. Four genetically varied haploid cells Correct answer.

Explanation

Meiosis consists of two divisions that produce four haploid gametes, each with half the chromosome number of the parent. Crossing over and independent assortment generate genetic variation, distinguishing meiosis from the identical-diploid products of mitosis.

Question 12Cells, biomolecules, heredity and metabolism

Which feature of the eukaryotic cell is the primary site of aerobic cellular respiration and ATP production?

  1. Mitochondrion Correct answer.
  2. Ribosome
  3. Golgi apparatus
  4. Lysosome

Explanation

The mitochondrion is the organelle where the citric acid cycle and oxidative phosphorylation occur, producing most of a cell's ATP through aerobic respiration. Its folded inner membrane (cristae) increases surface area for the electron transport chain.

Question 13Cells, biomolecules, heredity and metabolism

Which structural feature distinguishes a prokaryotic cell from a eukaryotic cell?

  1. The absence of a membrane-bound nucleus Correct answer.
  2. The presence of a plasma membrane
  3. The presence of ribosomes
  4. The presence of DNA

Explanation

Prokaryotic cells lack a membrane-bound nucleus and membrane-bound organelles; their DNA resides in a nucleoid region. Both cell types have a plasma membrane, ribosomes, and DNA, so those features do not distinguish them.

Question 14Cells, biomolecules, heredity and metabolism

During the light-dependent reactions of photosynthesis, water molecules are split. This process directly provides which of the following?

  1. Electrons and oxygen gas Correct answer.
  2. Glucose and carbon dioxide
  3. ATP from the citric acid cycle
  4. Carbon fixed into organic molecules

Explanation

In the light-dependent reactions, photolysis splits water, releasing electrons that replenish photosystem II and producing oxygen gas as a byproduct. Glucose and carbon fixation occur later in the Calvin cycle, which uses the ATP and NADPH generated by the light reactions.

Question 15Cells, biomolecules, heredity and metabolism

An enzyme lowers the activation energy of a reaction. Which statement about enzymes is correct?

  1. Enzymes are not consumed and can catalyze many reaction cycles Correct answer.
  2. Enzymes change the overall energy released by the reaction
  3. Enzymes work best at any temperature equally
  4. Enzymes permanently bind to their substrates

Explanation

Enzymes are biological catalysts that lower activation energy and are regenerated after each reaction, so a single enzyme molecule can catalyze many cycles. They do not alter the net free-energy change of the reaction, and each has an optimal temperature and pH.

Question 16Cells, biomolecules, heredity and metabolism

Which sequence correctly orders the levels of biological organization in a multicellular organism from smallest to largest?

  1. Cell, tissue, organ, organ system Correct answer.
  2. Tissue, cell, organ system, organ
  3. Organ, organ system, tissue, cell
  4. Organ system, organ, cell, tissue

Explanation

In multicellular organisms, cells group into tissues, tissues form organs, and organs work together as organ systems. This hierarchy reflects the structure-function organization emphasized in the CSET life science framework.

Question 17Cells, biomolecules, heredity and metabolism

Which of the following describes the role of the cell membrane in maintaining homeostasis?

  1. It selectively regulates the movement of substances into and out of the cell Correct answer.
  2. It synthesizes all of the cell's proteins
  3. It stores the cell's genetic information
  4. It generates ATP through respiration

Explanation

The plasma membrane is selectively permeable, controlling which substances enter and leave the cell and thereby maintaining internal homeostasis. Protein synthesis occurs at ribosomes, genetic information is stored in the nucleus, and ATP is generated in mitochondria.

Question 18Cells, biomolecules, heredity and metabolism

A red blood cell is placed in a hypertonic solution. What will most likely happen to the cell?

  1. Water will leave the cell, causing it to shrink (crenate) Correct answer.
  2. Water will enter the cell, causing it to swell and burst
  3. There will be no net movement of water
  4. Salt will be actively pumped into the cell

Explanation

In a hypertonic solution, the surrounding fluid has a higher solute concentration than the cell interior, so water moves out of the cell by osmosis. A red blood cell loses water and shrinks, a process called crenation.

Question 19Cells, biomolecules, heredity and metabolism

Which type of cellular transport requires the cell to expend energy in the form of ATP?

  1. Active transport against a concentration gradient Correct answer.
  2. Simple diffusion of oxygen across the membrane
  3. Osmosis of water through aquaporins
  4. Facilitated diffusion of glucose down its gradient

Explanation

Active transport moves substances against their concentration gradient, from low to high concentration, and therefore requires energy from ATP, as in the sodium-potassium pump. Simple diffusion, osmosis, and facilitated diffusion are passive and move substances down their gradients without ATP.

Question 20Cells, biomolecules, heredity and metabolism

In glycolysis, a glucose molecule is broken down in the cytoplasm. What are the direct products of glycolysis?

  1. Two pyruvate molecules, a net of two ATP, and two NADH Correct answer.
  2. Six carbon dioxide molecules and water
  3. Thirty-eight ATP and oxygen
  4. Glucose and lactic acid only

Explanation

Glycolysis splits one six-carbon glucose into two three-carbon pyruvate molecules, yielding a net gain of two ATP and two NADH in the cytoplasm. It does not require oxygen and precedes the citric acid cycle in aerobic respiration.

Question 21Cells, biomolecules, heredity and metabolism

Which macromolecule serves as the primary structural component of plant cell walls?

  1. Cellulose, a polysaccharide Correct answer.
  2. Cholesterol, a lipid
  3. Hemoglobin, a protein
  4. Glycogen, a polysaccharide

Explanation

Plant cell walls are made primarily of cellulose, a polysaccharide of glucose units linked by beta bonds that provide rigidity and structural support. Glycogen is an animal storage carbohydrate, cholesterol is a membrane lipid, and hemoglobin is an oxygen-transport protein.

Question 22Cells, biomolecules, heredity and metabolism

Proteins are polymers built from which type of monomer?

  1. Amino acids joined by peptide bonds Correct answer.
  2. Nucleotides joined by phosphodiester bonds
  3. Monosaccharides joined by glycosidic bonds
  4. Fatty acids joined to glycerol

Explanation

Proteins are chains of amino acids linked by peptide bonds formed through dehydration synthesis. The sequence of amino acids determines the protein's folding and function. Nucleotides build nucleic acids, monosaccharides build carbohydrates, and fatty acids with glycerol form fats.

Question 23Cells, biomolecules, heredity and metabolism

Which process produces genetically identical daughter cells for growth and repair in body tissues?

  1. Mitosis Correct answer.
  2. Meiosis
  3. Binary fission in eukaryotes
  4. Fertilization

Explanation

Mitosis divides a cell into two daughter cells with the same chromosome number and genetic content as the parent, supporting growth, tissue repair, and asexual reproduction. Meiosis produces genetically varied haploid gametes, and fertilization combines gametes.

Question 24Cells, biomolecules, heredity and metabolism

During which phase of mitosis do sister chromatids separate and move toward opposite poles of the cell?

  1. Anaphase Correct answer.
  2. Prophase
  3. Metaphase
  4. Telophase

Explanation

In anaphase, the centromeres split and sister chromatids are pulled apart by spindle fibers toward opposite poles, ensuring each daughter cell receives a complete chromosome set. Prophase condenses chromosomes, metaphase aligns them, and telophase reforms nuclei.

Question 25Cells, biomolecules, heredity and metabolism

Which of the following best explains why meiosis is important for sexually reproducing organisms?

  1. It halves the chromosome number so fertilization restores the diploid number Correct answer.
  2. It doubles the chromosome number in each gamete
  3. It produces identical clones of the parent cell
  4. It eliminates all genetic variation among offspring

Explanation

Meiosis reduces the chromosome number from diploid to haploid in gametes, so that fertilization restores the normal diploid number in offspring. It also generates genetic variation through crossing over and independent assortment.

Question 26Cells, biomolecules, heredity and metabolism

In a DNA molecule, adenine always pairs with which nitrogenous base?

  1. Thymine Correct answer.
  2. Guanine
  3. Cytosine
  4. Uracil

Explanation

According to complementary base pairing in DNA, adenine pairs with thymine via two hydrogen bonds, and guanine pairs with cytosine via three hydrogen bonds. Uracil replaces thymine only in RNA, not DNA.

Question 27Cells, biomolecules, heredity and metabolism

During DNA replication, the enzyme that adds new nucleotides to a growing strand using the template strand is

  1. DNA polymerase Correct answer.
  2. Helicase
  3. DNA ligase
  4. RNA polymerase

Explanation

DNA polymerase synthesizes new DNA by adding complementary nucleotides to the 3' end of a growing strand, reading the template in the 3' to 5' direction. Helicase unwinds the helix, ligase joins Okazaki fragments, and RNA polymerase transcribes RNA.

Question 28Cells, biomolecules, heredity and metabolism

The process of transcription produces which molecule from a DNA template?

  1. Messenger RNA (mRNA) Correct answer.
  2. A polypeptide chain
  3. A new DNA double helix
  4. A lipid bilayer

Explanation

Transcription is the synthesis of messenger RNA from a DNA template by RNA polymerase. The mRNA then carries the genetic code to ribosomes for translation into protein. Polypeptides are products of translation, not transcription.

Question 29Cells, biomolecules, heredity and metabolism

The cell theory includes all of the following principles EXCEPT:

  1. Cells arise spontaneously from nonliving matter Correct answer.
  2. All living things are composed of one or more cells
  3. The cell is the basic unit of structure and function in organisms
  4. All cells come from preexisting cells

Explanation

The cell theory states that all living things are made of cells, the cell is the basic unit of life, and all cells arise from preexisting cells. Spontaneous generation from nonliving matter was disproven and is not part of the cell theory.

Question 30Cells, biomolecules, heredity and metabolism

Which structure in plant cells contains chlorophyll and is the site of photosynthesis?

  1. Chloroplast Correct answer.
  2. Vacuole
  3. Nucleus
  4. Mitochondrion

Explanation

Chloroplasts contain chlorophyll, the green pigment that absorbs light energy, and are the site of photosynthesis in plant and algal cells. Vacuoles store materials, the nucleus houses DNA, and mitochondria carry out cellular respiration.

Question 31Cells, biomolecules, heredity and metabolism

Which of the following correctly describes the role of ATP in cells?

  1. It serves as the primary short-term energy currency that powers cellular work Correct answer.
  2. It stores long-term genetic information
  3. It forms the structural backbone of cell membranes
  4. It directly catalyzes all metabolic reactions

Explanation

Adenosine triphosphate (ATP) is the cell's main energy currency; energy released by breaking its high-energy phosphate bonds powers active transport, muscle contraction, and biosynthesis. It is continually regenerated through cellular respiration.

Question 32Cells, biomolecules, heredity and metabolism

Why is liquid water essential to life as it functions in living cells?

  1. It is a versatile solvent that dissolves many substances and supports biochemical reactions Correct answer.
  2. It cannot dissolve any ionic compounds
  3. It is chemically inert and never participates in reactions
  4. It exists only as a gas at biological temperatures

Explanation

Water's polarity makes it an excellent solvent for ions and polar molecules, allowing the biochemical reactions of metabolism to occur in solution. Water also participates directly in reactions such as hydrolysis and helps regulate temperature.

Question 33Cells, biomolecules, heredity and metabolism

Which of the following correctly distinguishes mitosis from meiosis?

  1. Mitosis produces two diploid cells; meiosis produces four haploid cells Correct answer.
  2. Mitosis produces four haploid cells; meiosis produces two diploid cells
  3. Both processes produce genetically varied gametes
  4. Both processes occur only in reproductive organs

Explanation

Mitosis produces two genetically identical diploid daughter cells used for growth and repair, while meiosis produces four genetically varied haploid cells used as gametes. Meiosis involves two divisions and includes crossing over and independent assortment.

Question 34Physical chemistry, amounts, reactions and equilibria

In the third period (Period 3: Na to Ar) of the Periodic Table of Elements, which of the following elements has the highest first ionization energy (第一电离能)?

  1. Argon (Ar) Correct answer.
  2. Sodium (Na)
  3. Chlorine (Cl)
  4. Silicon (Si)

Explanation

First ionization energy is the energy required to remove the most loosely held valence electron from an isolated gaseous atom. Across a period from left to right, effective nuclear charge increases and atomic radius contracts. Argon (Ar, atomic number 18) possesses a stable octet electron configuration (3s^2 3p^6) in its outermost shell, giving it the highest first ionization energy in Period 3.

Question 35Physical chemistry, amounts, reactions and equilibria

In commercial lithium-ion secondary batteries (锂离子电池), what is the primary function of the Solid Electrolyte Interphase (SEI膜 / 固体电解质界面膜) formed on the graphite anode surface during the initial formation cycle?

  1. Allowing selective Li+ transport while passivating the anode to prevent ongoing electrolyte decomposition Correct answer.
  2. Conducting electrons directly between the anode and cathode to eliminate external wiring
  3. Acting as a sacrificial cathode material to donate extra lithium ions during overdischarge
  4. Generating hydrogen gas to pressurize the battery casing and lower internal resistance

Explanation

The Solid Electrolyte Interphase (SEI膜) is a passivating passivation layer formed by the reduction decomposition of electrolyte components on the graphite anode during initial charging. A stable SEI layer is an electronic insulator (preventing continuous electron transfer that would consume liquid electrolyte) but a good Li+ ionic conductor, allowing reversible intercalation and de-intercalation of lithium ions while preserving battery cycle life.

Question 36Physical chemistry, amounts, reactions and equilibria

Polymers are synthesized via different reaction pathways. Which of the following polymers is produced through a step-growth Condensation Polymerization (缩聚反应) that eliminates small molecules such as water or ethylene glycol during chain growth?

  1. Polyethylene terephthalate (PET / 聚对苯二甲酸乙二醇酯) Correct answer.
  2. Polyethylene (PE / 聚乙烯)
  3. Polypropylene (PP / 聚丙烯)
  4. Polyvinyl chloride (PVC / 聚氯乙烯)

Explanation

Polyethylene terephthalate (PET) is synthesized via condensation polymerization (polycondensation) between terephthalic acid (or dimethyl terephthalate) and ethylene glycol, forming ester linkages (-COO-) while releasing water (or methanol) as a small byproduct. In contrast, PE, PP, and PVC are formed via addition polymerization (加聚反应) across carbon-carbon double bonds without generating byproducts.

Question 37Physical chemistry, amounts, reactions and equilibria

A student has 58.5 g of NaCl. Using a molar mass of 58.5 g/mol, how many moles of NaCl are present?

  1. 0.50 mol
  2. 1.00 mol Correct answer.
  3. 2.00 mol
  4. 58.5 mol

Explanation

Moles equal mass divided by molar mass: 58.5 g / 58.5 g/mol = 1.00 mol. This is a direct amount-of-substance calculation.

Question 38Physical chemistry, amounts, reactions and equilibria

What is the approximate mass percentage of hydrogen in H2O? Use H = 1 and O = 16.

  1. 5.6%
  2. 11.1% Correct answer.
  3. 22.2%
  4. 88.9%

Explanation

One mole of water has mass 18 g, of which 2 g is hydrogen. The hydrogen mass percentage is 2/18 x 100% = 11.1%.

Question 39Physical chemistry, amounts, reactions and equilibria

For the balanced reaction 2H2 + O2 -> 2H2O, what mole ratio of H2 to O2 is required?

  1. 1:1
  2. 1:2
  3. 2:1 Correct answer.
  4. 2:2

Explanation

The coefficients in a balanced equation give mole ratios. The reaction consumes 2 mol H2 for every 1 mol O2.

Question 40Physical chemistry, amounts, reactions and equilibria

For N2(g) + 3H2(g) <=> 2NH3(g), what happens to equilibrium if pressure is increased at constant temperature?

  1. It shifts toward NH3 Correct answer.
  2. It shifts toward N2 and H2
  3. It is unaffected because all species are gases
  4. It stops immediately

Explanation

Increasing pressure favors the side with fewer gas moles. The reactant side has 4 mol gas while the product side has 2 mol gas, so the equilibrium shifts toward NH3.

Question 41Physical chemistry, amounts, reactions and equilibria

What is the equilibrium constant expression for N2(g) + 3H2(g) <=> 2NH3(g)?

  1. K = [N2][H2]^3/[NH3]^2
  2. K = [NH3]^2/[N2][H2]^3 Correct answer.
  3. K = [NH3]/[N2][H2]
  4. K = [N2][H2]/[NH3]

Explanation

Products appear in the numerator and reactants in the denominator, each raised to its stoichiometric coefficient. Thus K = [NH3]^2 / ([N2][H2]^3).

Question 42Physical chemistry, amounts, reactions and equilibria

What is the pH of 0.010 mol/L HCl, assuming complete ionization?

  1. 1
  2. 2 Correct answer.
  3. 7
  4. 12

Explanation

HCl is a strong acid, so [H+] = 0.010 M = 10^-2 M. pH = -log[H+] = 2.

Question 43Physical chemistry, amounts, reactions and equilibria

For 2Al + 3Cl2 -> 2AlCl3, how many moles of Cl2 are required to react completely with 0.30 mol Al?

  1. 0.20 mol
  2. 0.30 mol
  3. 0.45 mol Correct answer.
  4. 0.60 mol

Explanation

The balanced equation requires 3 mol Cl2 for every 2 mol Al. Required Cl2 = 0.30 x 3/2 = 0.45 mol.

Question 44Physical chemistry, amounts, reactions and equilibria

For N2 + 3H2 -> 2NH3, 1.0 mol N2 is mixed with 2.0 mol H2. What is the maximum amount of NH3 that can form?

  1. 0.67 mol
  2. 1.0 mol
  3. 1.33 mol Correct answer.
  4. 2.0 mol

Explanation

Hydrogen is limiting because 1.0 mol N2 would require 3.0 mol H2, but only 2.0 mol is present. From 3 mol H2 to 2 mol NH3, 2.0 mol H2 produces 2.0 x 2/3 = 1.33 mol NH3.

Question 45Physical chemistry, amounts, reactions and equilibria

5.85 g NaCl is dissolved and diluted to 500 mL. What is the molar concentration? Use M(NaCl) = 58.5 g/mol.

  1. 0.020 mol/L
  2. 0.10 mol/L
  3. 0.20 mol/L Correct answer.
  4. 1.00 mol/L

Explanation

Moles NaCl = 5.85/58.5 = 0.100 mol. Volume is 0.500 L, so concentration = 0.100/0.500 = 0.20 mol/L.

Question 46Physical chemistry, amounts, reactions and equilibria

At standard conditions where molar gas volume is 22.4 L/mol, how many moles are in 11.2 L of O2?

  1. 0.25 mol
  2. 0.50 mol Correct answer.
  3. 1.00 mol
  4. 2.00 mol

Explanation

Moles = volume / molar volume = 11.2 L / 22.4 L/mol = 0.50 mol. The identity of the gas does not change this molar volume assumption at standard conditions.

Question 47Physical chemistry, amounts, reactions and equilibria

A compound is 40.0% C, 6.7% H, and 53.3% O by mass. Which empirical formula is most consistent with the data? Use C=12, H=1, O=16.

  1. CH2O Correct answer.
  2. C2H4O
  3. CHO2
  4. C2HO

Explanation

In 100 g, moles are C 40/12 = 3.33, H 6.7/1 = 6.7, O 53.3/16 = 3.33. Dividing by 3.33 gives about 1:2:1, so the empirical formula is CH2O.

Question 48Physical chemistry, amounts, reactions and equilibria

A reaction has a theoretical yield of 10.0 g and an actual yield of 8.0 g. What is the percent yield?

  1. 20%
  2. 80% Correct answer.
  3. 100%
  4. 125%

Explanation

Percent yield = actual yield / theoretical yield x 100% = 8.0/10.0 x 100% = 80%.

Question 49Physical chemistry, amounts, reactions and equilibria

For a reaction mixture at a given temperature, Q < K. Which direction will the reaction proceed to reach equilibrium?

  1. Forward, forming more products Correct answer.
  2. Reverse, forming more reactants
  3. No change because Q and K are unrelated
  4. Both directions stop

Explanation

If Q < K, the mixture has too few products relative to equilibrium. The net reaction proceeds forward until Q increases to K.

Question 50Physical chemistry, amounts, reactions and equilibria

For N2O4(g) <=> 2NO2(g), what is the relation between Kp and Kc?

  1. Kp = Kc(RT) Correct answer.
  2. Kp = Kc/(RT)
  3. Kp = Kc(RT)^0
  4. Kp = Kc(RT)^3

Explanation

Kp = Kc(RT)^Delta n, where Delta n = gas product moles - gas reactant moles = 2 - 1 = 1. Therefore Kp = Kc(RT).