OS
OpenStem
@openstem · Joined Jul 2026
7420 public items8 groups
Quiz6 questions
Which carbon in this molecule is the chiral centre?
AC1BC2CC3DC4
Chemistry · L4 · Stereochemistry — 6 Q
@openstem
Chemistry · L4 · Stereochemistry — 6 QQuiz5 questions
In N = N₀e^(-λt), what does the decay constant λ physically represent?
AThe number of half-lives that have elapsedBThe probability of decay per unit time for a single nucleusCThe total mass lost during the entire decay processDThe fraction of the sample remaining after one half-life
Chemistry · L4 · Nuclear Chemistry (Quantitative) — 5 Q
@openstem
Chemistry · L4 · Nuclear Chemistry (Quantitative) — 5 QQuiz5 questions
Diamond and quartz are both classified as which type of crystalline solid?
AIonicBMolecularCCovalent networkDMetallic
Chemistry · L4 · Solid State Chemistry & Crystal Structures — 5 Q
@openstem
Chemistry · L4 · Solid State Chemistry & Crystal Structures — 5 QQuiz6 questions
What is the general principle underlying every spectroscopic technique?
AMeasuring the mass of a sample after heating itBShining energy at a sample and observing what's absorbed, transmitted, or emittedCDissolving a sample in a series of solvents and comparing solubilityDMeasuring the melting point of a sample under varying pressure
Chemistry · L4 · Spectroscopy Basics — 6 Q
@openstem
Chemistry · L4 · Spectroscopy Basics — 6 QQuiz6 questions
A reaction has ΔH = −120 kJ/mol and ΔS = +85 J/(mol·K). Which best describes its spontaneity?
AAlways spontaneous, at every temperatureBNever spontaneous, at any temperatureCSpontaneous only below some crossover temperatureDSpontaneous only above some crossover temperature
Chemistry · L4 · Gibbs Free Energy & Spontaneity — 6 Q
@openstem
Chemistry · L4 · Gibbs Free Energy & Spontaneity — 6 QQuiz6 questions
What structural feature distinguishes a thermoset from a thermoplastic?
AA thermoset has longer chainsBA thermoset's chains are covalently cross-linked; a thermoplastic's are notCA thermoset is always an addition polymerDA thermoset contains no carbon
Chemistry · L4 · Polymer Chemistry — 6 Q
@openstem
Chemistry · L4 · Polymer Chemistry — 6 QQuiz6 questions
Which four groups are bonded to the alpha carbon of a generic amino acid?
ATwo amino groups and two carboxylic acid groupsBAn amino group, a carboxylic acid group, a hydrogen, and an R groupCA hydroxyl group, a carbonyl group, a hydrogen, and an R groupDAn amino group, a phosphate group, a hydrogen, and an R group
Chemistry · L4 · Biochemistry Basics — 6 Q
@openstem
Chemistry · L4 · Biochemistry Basics — 6 QQuiz5 questions
The ideal gas law PV = nRT is a combination of which three simpler laws?
ABoyle's law, Charles's law, and Avogadro's lawBBoyle's law, Graham's law, and Dalton's lawCCharles's law, Raoult's law, and Henry's lawDAvogadro's law, Hess's law, and Le Chatelier's principle
Chemistry · L4 · Real Gases & the Ideal Gas Law — 5 Q
@openstem
Chemistry · L4 · Real Gases & the Ideal Gas Law — 5 QQuiz6 questions
What does a catalyst do to a reaction's activation energy, and is it consumed overall?
ALowers Ea by providing an alternate pathway; not consumed overallBLowers Ea by providing an alternate pathway; consumed overallCRaises Ea to slow down unwanted side reactions; not consumedDHas no effect on Ea, but binds permanently to the product
Chemistry · L4 · Catalysis & Green Chemistry — 6 Q
@openstem
Chemistry · L4 · Catalysis & Green Chemistry — 6 QQuiz5 questions
What color is a dilute aqueous solution of Fe²⁺?
AYellow-brownBPale greenCDeep blueDPink
Chemistry · L4 · Transition Metal Chemistry in Solution — 5 Q
@openstem
Chemistry · L4 · Transition Metal Chemistry in Solution — 5 QQuiz6 questions
Why does each successive dissociation constant of a polyprotic acid (Ka1, Ka2, Ka3, …) get progressively smaller?
ARemoving a proton becomes progressively harder because the species losing it is progressively more negatively charged, so it holds the remaining protons more tightlyBLater protons are chemically different atoms with weaker O–H bondsCThe solution becomes more dilute after each dissociation stepDEquilibrium constants always decrease with each reaction step, regardless of the species involved
Chemistry · L4 · Polyprotic Acids — 6 Q
@openstem
Chemistry · L4 · Polyprotic Acids — 6 QQuiz6 questions
A zero-order reaction has k = 0.0250 mol L⁻¹ s⁻¹ and [A]₀ = 1.00 M. What is [A] after t = 15.0 s?
A0.625 MB0.375 MC0.500 MD1.375 M
Chemistry · L4 · Integrated Rate Laws — 6 Q
@openstem
Chemistry · L4 · Integrated Rate Laws — 6 QQuiz6 questions
What breaks apart a CFC molecule once it reaches the stratosphere?
AReaction with atmospheric water vapourBHigh-energy UV photolysis of the C–Cl bondCCombustion in the presence of atmospheric oxygenDCollision with ozone molecules
Chemistry · L4 · Atmospheric Chemistry — Ozone and the Greenhouse Effect
@openstem
Chemistry · L4 · Atmospheric Chemistry — Ozone and the Greenhouse EffectQuiz5 questions
What fundamental distinction separates activity-based protein profiling (ABPP) from abundance-based proteomic methods?
AABPP measures whether an enzyme is catalytically active, while abundance methods measure total protein present regardless of activityBABPP can only be used on purified, isolated proteins, never in cellsCAbundance-based methods always report enzyme activity accuratelyDThere is no meaningful difference between the two approaches
Chemistry · L5 · Chemical Biology & Activity-Based Probes
@openstem
Chemistry · L5 · Chemical Biology & Activity-Based ProbesQuiz6 questions
Which of the following species is a Lewis acid but NOT a Brønsted acid?
AHClBCH₃COOHCBF₃DH₂SO₄
Chemistry · L4 · Lewis Acids and Bases
@openstem
Chemistry · L4 · Lewis Acids and BasesQuiz6 questions
HBr adds to 2-methylpropene, (CH₃)₂C=CH₂. What is the major product, and why?
Atert-Butyl bromide, via the more stable tertiary carbocationBIsobutyl bromide, via the more stable primary carbocationCtert-Butyl bromide, via a radical chain mechanismDAn equal mixture of both regioisomers
Chemistry · L4 · Addition and Elimination Mechanisms Quiz
@openstem
Chemistry · L4 · Addition and Elimination Mechanisms QuizQuiz6 questions
A buffer contains 0.25 M HA and 0.25 M A⁻, where pKa of HA = 4.75. What is the pH?
A4.75B4.25C5.25D3.75
Chemistry · L4 · Buffer Calculations and Capacity — 6 Q
@openstem
Chemistry · L4 · Buffer Calculations and Capacity — 6 QQuiz6 questions
For Ag⁺(aq) + 2 NH₃(aq) ⇌ [Ag(NH₃)₂]⁺(aq),
AThe complex is highly unstable and decomposes almost immediatelyBAt equilibrium, almost all the Ag⁺ converts to the complex ion once NH₃ is in excessCThe reaction produces essentially no complex ion at allDKf must be numerically equal to Ksp(AgCl) for the math to work
Chemistry · L4 · Complex Ions and Solubility
@openstem
Chemistry · L4 · Complex Ions and SolubilityQuiz6 questions
Hess's Law is a direct consequence of which property of enthalpy?
AIt is a state function — depends only on the initial and final states, not the pathBIt is an extensive property that scales with the amount of substanceCIt is temperature-independent by definitionDIt only applies to gas-phase reactions
Chemistry · L4 · Hess's Law Calculations — 6 Q
@openstem
Chemistry · L4 · Hess's Law Calculations — 6 QQuiz5 questions
In cell notation, what does the double line "||" represent?
AA phase boundary between an electrode and its solutionBThe salt bridge (or porous membrane) connecting the two half-cellsCTwo ions coexisting in the same solutionDThe direction of conventional current flow
Chemistry · L4 · Cell Notation and Concentration Cells — 5 Q
@openstem
Chemistry · L4 · Cell Notation and Concentration Cells — 5 QQuiz6 questions
Which scenario calls for a BACK titration rather than a direct titration?
ATitrating a strong acid of unknown concentration directly with a standard NaOH solution, using phenolphthaleinBFinding the % purity of powdered CaCO3 from a rock sample, which won't react cleanly or completely from a buretteCTitrating a strong base of unknown concentration directly with a standard HCl solution, using methyl orangeDAny titration performed with a burette instead of a pipette
Chemistry · L4 · Back Titration — 6 Q
@openstem
Chemistry · L4 · Back Titration — 6 QQuiz5 questions
Which pair of elements is the clearest example of a diagonal relationship?
ALithium and sodiumBLithium and magnesiumCSodium and magnesiumDBeryllium and calcium
Chemistry · L4 · Periodic Anomalies — 5 Q
@openstem
Chemistry · L4 · Periodic Anomalies — 5 QQuiz6 questions
A white precipitate forms on adding a few drops of NaOH to an unknown cation solution, and it completely redissolves on adding excess NaOH. Which further reagent, added in excess to a fresh sample, would distinguish Zn²⁺ from Al³⁺ or Pb²⁺?
AExcess dilute hydrochloric acidBExcess ammonia solutionCBarium chloride solutionDWarm dilute sulfuric acid
Chemistry · L4 · Systematic Qualitative Inorganic Analysis — 6 Q
@openstem
Chemistry · L4 · Systematic Qualitative Inorganic Analysis — 6 QQuiz6 questions
What is the core assumption behind the steady-state approximation?
AThe intermediate's concentration is exactly zero at all timesBThe intermediate's rate of formation is approximately equal to its rate of consumption, so d[intermediate]/dt ≈ 0CEvery elementary step in the mechanism proceeds at exactly the same rateDThe overall reaction has reached true thermodynamic equilibrium
Chemistry · L4 · The Steady-State Approximation — 6 Q
@openstem
Chemistry · L4 · The Steady-State Approximation — 6 QQuiz5 questions
A current of 2.00 A is passed through a solution containing Cu²⁺ ions for 1000 s. How many moles of electrons are transferred? (F = 96 485 C/mol)
A0.0207 molB0.0414 molC0.0104 molD20.7 mol
Chemistry · L4 · Faraday's Laws of Electrolysis — 5 Q
@openstem
Chemistry · L4 · Faraday's Laws of Electrolysis — 5 QQuiz6 questions
What most fundamentally distinguishes HPLC and GC from paper or TLC chromatography?
AThey use a detector and a time-based retention time instead of a visible spot and a distance-based Rf valueBThey don't require any kind of stationary phase at allCThey can only separate mixtures of colored substancesDThey detect compounds but cannot actually separate a mixture
Chemistry · L4 · Instrumental Chromatography — HPLC and GC
@openstem
Chemistry · L4 · Instrumental Chromatography — HPLC and GCQuiz6 questions
In a blast furnace, what is the actual chemical species that reduces iron(III) oxide to iron?
ACarbon monoxide (CO), formed when carbon dioxide reacts with more cokeBCarbon dioxide (CO2) itselfCSolid coke, reacting directly with the solid oreDCalcium oxide (CaO)
Chemistry · L4 · Blast Furnace and Electrolytic Refining
@openstem
Chemistry · L4 · Blast Furnace and Electrolytic RefiningQuiz6 questions
Why can EDTA form an unusually stable 1:1 complex with a metal ion compared to a simple monodentate ligand such as NH3?
AEDTA is a much smaller molecule than NH3, so it fits into the metal ion more easilyBEDTA has six donor atoms (2 N, 4 O) that can all coordinate to the same metal ion simultaneously, wrapping around it almost completely (the chelate effect)CEDTA reacts with water before it can bind any metal ion, releasing extra heatDEDTA only binds transition metals, never main-group ions like Ca²⁺ or Mg²⁺
Chemistry · L4 · EDTA Complexometric Titration
@openstem
Chemistry · L4 · EDTA Complexometric TitrationQuiz5 questions
For a titration of a weak acid with a strong base, why does the equivalence point occur above pH 7?
ABecause the only species present at equivalence is the conjugate base of the weak acid, which hydrolyses water to produce OH-BBecause strong bases always produce a pH above 10 regardless of the acidCBecause the indicator used shifts the true equivalence pointDIt does not — the equivalence point is always exactly pH 7 for any acid-base titration
Chemistry · L4 · Titration Curves & Indicators — 5 Q
@openstem
Chemistry · L4 · Titration Curves & Indicators — 5 QQuiz5 questions
Which pair of factors most directly determines the magnitude of a lattice energy, according to the Coulomb's-law-based model?
AIonic charge and ionic radiusBBoiling point and densityCMolar mass and colourDElectronegativity difference alone, with no dependence on size
Chemistry · L4 · Lattice Energy, Born-Lande & Kapustinskii — 5 Q
@openstem
Chemistry · L4 · Lattice Energy, Born-Lande & Kapustinskii — 5 Q