Moldova Bacalaureat — Chemistry (Chimie)

A neutral atom of chlorine-37 contains 17 protons. Which combination of subatomic particles is present in the nucleus and electron cloud of this isotope?

• A17 protons, 17 neutrons, and 20 electrons
• B17 protons, 20 neutrons, and 17 electrons
• C20 protons, 17 neutrons, and 17 electrons
• D17 protons, 37 neutrons, and 17 electrons

Which set of quantum numbers (n, l, m_l, m_s) is permissible for an electron occupying a 3p atomic orbital?

• An = 3, l = 0, m_l = 0, m_s = +1/2
• Bn = 3, l = 2, m_l = -1, m_s = -1/2
• Cn = 3, l = 1, m_l = -1, m_s = +1/2
• Dn = 2, l = 1, m_l = +1, m_s = -1/2

According to Hund's rule and the Pauli exclusion principle, how are the valence electrons distributed in the ground-state nitrogen atom (Z = 7)?

• AThree unpaired electrons with parallel spins occupying three separate 2p orbitals (2p_x^1…
• BOne paired electron pair in 2p_x and one single electron in 2p_y, leaving 2p_z completely…
• CThree electrons paired up in the 2s subshell with opposite spins, leaving the 2p subshell…
• DFive equivalent electrons distributed equally across all five degenerate 2d orbitals

How do first ionization energy and atomic radius generally vary across Period 3 of the periodic table from sodium (Na) to argon (Ar)?

• AFirst ionization energy decreases and atomic radius decreases
• BFirst ionization energy decreases and atomic radius increases
• CFirst ionization energy increases and atomic radius increases
• DFirst ionization energy generally increases and atomic radius decreases

Which of the following halogen elements possesses the highest Pauling electronegativity?

• AChlorine (Cl)
• BFluorine (F)
• CBromine (Br)
• DIodine (I)

Which of the following substances contains exclusively non-polar covalent bonds in its chemical structure?

• ANitrogen gas (N2)
• BHydrogen chloride (HCl)
• CPotassium chloride (KCl)
• DWater (H2O)

Why does water (H2O, boiling point 100 °C) have a drastically higher boiling point than hydrogen sulfide (H2S, boiling point -60 °C), despite H2S having a greater molecular mass?

• AH2S contains stronger covalent bonds within the molecule that prevent vaporization
• BWater molecules are held together by metallic bonds between hydrogen atoms
• CIntermolecular hydrogen bonding between H2O molecules is significantly stronger than the…
• DLiquid H2S forms an ionic network lattice that decomposes below room temperature

Why does granulated zinc react with 1.0 M hydrochloric acid at a significantly faster rate than an equal mass of a solid zinc block at the same temperature?

• AGranulated zinc has a lower activation energy for the reaction than a zinc block
• BGranulated zinc exposes a much larger surface area, increasing the frequency of effective…
• CGranulated zinc shifts the chemical equilibrium position further toward the products
• DGranulated zinc increases the rate constant k by acting as an autocatalyst

Which of the following elements exhibits an anomalous ground-state electron configuration characterized by a half-filled d subshell?

• AChromium (Z = 24), [Ar] 3d^5 4s^1
• BVanadium (Z = 23), [Ar] 3d^3 4s^2
• CManganese (Z = 25), [Ar] 3d^5 4s^2
• DIron (Z = 26), [Ar] 3d^6 4s^2

According to the Valence Shell Electron Pair Repulsion (VSEPR) theory, what are the electron domain geometry, molecular geometry, and approximate bond angle of the ammonia molecule (NH3)?

• ATrigonal planar electron geometry, trigonal planar molecular geometry, 120°
• BTetrahedral electron geometry, tetrahedral molecular geometry, 109.5°
• CTetrahedral electron geometry, trigonal pyramidal molecular geometry, ~107°
• DT-shaped electron geometry, trigonal pyramidal molecular geometry, 90°

Which statement correctly describes the formation of the coordinate (dative) covalent bond in the ammonium cation (NH4+)?

• ABoth the nitrogen atom and the incoming proton contribute one electron to form the fourth…
• BThe nitrogen atom donates an unshared electron pair into the vacant 1s orbital of a hydro…
• CA hydride ion (H-) donates two electrons into an empty 2p orbital of the nitrogen atom
• DThe bond is purely ionic and arises from electrostatic attraction between NH3+ and H-

Which set correctly pairs each central atom with its orbital hybridization state in the gaseous molecules BeCl2, BF3, and CH4?

• ABeCl2: sp3; BF3: sp2; CH4: sp
• BBeCl2: sp2; BF3: sp3; CH4: sp
• CBeCl2: sp; BF3: sp; CH4: sp3
• DBeCl2: sp; BF3: sp2; CH4: sp3

A chemical reaction follows the rate law v = k[A]^2[B]. If the concentration of reactant A is doubled while the concentration of reactant B is halved, how does the initial reaction rate change?

• AThe rate increases by a factor of 2
• BThe rate increases by a factor of 4
• CThe rate remains completely unchanged
• DThe rate decreases by a factor of 2

According to the Van 't Hoff rule, a reaction has a temperature coefficient γ = 3. By what factor will the reaction rate increase if the temperature is raised from 20 °C to 50 °C?

• A9 times
• B81 times
• C27 times
• D3 times

How does the addition of a positive catalyst accelerate a reversible chemical reaction without affecting the final equilibrium yield?

• AIt provides an alternative reaction pathway with a lower activation energy, increasing fo…
• BIt provides an alternative reaction mechanism with a lower activation energy, acceleratin…
• CIt increases the enthalpy change of the reaction (ΔH), thereby supplying thermal energy t…
• DIt shifts the position of equilibrium toward the products by increasing the equilibrium c…

What is the correct equilibrium constant expression (Kc) for the thermal decomposition of limestone: CaCO3(s) ⇌ CaO(s) + CO2(g)?

• AKc = [CaO][CO2] / [CaCO3]
• BKc = [CaCO3] / ([CaO][CO2])
• CKc = [CaO] / [CaCO3]
• DKc = [CO2]

For the Haber synthesis of ammonia: N2(g) + 3H2(g) ⇌ 2NH3(g) (ΔH° = -92.4 kJ/mol), which set of conditions will shift the equilibrium position to maximize the equilibrium yield of ammonia?

• AIncreasing the total pressure and decreasing the temperature
• BDecreasing the total pressure and increasing the temperature
• CIncreasing the total pressure and increasing the temperature
• DAdding an inert gas (He) at constant volume and increasing the temperature

Consider the equilibrium: N2O4(g) (colorless) ⇌ 2NO2(g) (red-brown) with ΔH° = +57.2 kJ/mol. What visible change occurs when the closed reaction vessel is immersed in an ice-water bath?

• AThe gas mixture turns an intense dark brown because NO2 formation is favored at low tempe…
• BThe color remains identical because phase changes do not affect gas color
• CThe gas mixture becomes lighter (pale yellow or nearly colorless) as the equilibrium shif…
• DA black precipitate of elemental nitrogen forms immediately on the vessel walls

Which of the following substances has a standard molar enthalpy of formation (ΔH_f°) equal to exactly zero at 298.15 K and 101.3 kPa?

• AO3(g, ozone)
• BO2(g, dioxygen)
• CH2O(l, liquid water)
• DCO2(g, carbon dioxide)

Given the following thermochemical equations: (1) C(graphite) + O2(g) → CO2(g) ΔH°_1 = -393.5 kJ (2) CO(g) + 1/2 O2(g) → CO2(g) ΔH°_2 = -283.0 kJ What is the standard enthalpy of reaction (ΔH°) for the partial oxidation of carbon to carbon monoxide: C(graphite) + 1/2 O2(g) → CO(g)?

• A-676.5 kJ
• B+110.5 kJ
• C-283.0 kJ
• D-110.5 kJ

The standard enthalpy of combustion of liquid ethanol (C2H5OH, molar mass M = 46.07 g/mol) is ΔH°_c = -1367 kJ/mol. How much heat is released upon the complete combustion of 23.03 g of pure ethanol in excess oxygen?

• A683.5 kJ
• B1367 kJ
• C2734 kJ
• D341.8 kJ

In a 2.0 L rigid reaction container, 0.40 mol of H2(g) and 0.40 mol of I2(g) are heated to 448 °C. At equilibrium, 0.60 mol of HI(g) is formed according to: H2(g) + I2(g) ⇌ 2HI(g). What is the value of the equilibrium constant Kc at this temperature?

• A12
• B9.0
• C36
• D0.11

A reversible reaction A + B ⇌ C has a forward activation energy E_a(forward) = 85 kJ/mol and an enthalpy of reaction ΔH = -45 kJ/mol. What is the activation energy of the reverse reaction, E_a(reverse)?

• A40 kJ/mol
• B130 kJ/mol
• C-40 kJ/mol
• D85 kJ/mol

Why does oxygen (Z = 8, 1314 kJ/mol) have a slightly lower first ionization energy than nitrogen (Z = 7, 1402 kJ/mol), despite oxygen having a higher nuclear charge?

• ANitrogen's 2p electrons experience greater shielding from core 1s electrons than oxygen's
• BOxygen has a smaller atomic radius, which decreases electrostatic nuclear attraction
• COxygen's valence electron is in a 3s orbital rather than a 2p orbital
• DOxygen has a paired electron in one of its 2p orbitals (2p_x^2 2p_y^1 2p_z^1), where elec…

Which of the following oxides is classified as amphoteric, reacting with both strong aqueous acids and strong bases?

• ACalcium oxide (CaO)
• BAluminum oxide (Al2O3)
• CSulfur trioxide (SO3)
• DCarbon monoxide (CO)

When a small piece of metallic sodium is dropped into a beaker containing distilled water and phenolphthalein indicator, what observations and products are obtained?

• ASodium darts rapidly across the water surface, effervesces releasing hydrogen gas (H2), a…
• BSodium sinks to the bottom, releases oxygen gas (O2), and the solution remains colorless
• CSodium dissolves slowly without gas evolution, producing sodium hydride (NaH) and turning…
• DSodium violently precipitates sodium oxide (Na2O) powder while releasing nitrogen gas

Chlorine water is added to a colorless aqueous solution of potassium iodide (KI) in the presence of cyclohexane. What occurs and why?

• ANo reaction occurs because iodide is more reactive and electronegative than chlorine
• BA white precipitate of potassium chlorate (KClO3) forms at the bottom of the tube
• CChlorine oxidizes iodide to elemental iodine (I2), which extracts into the organic cycloh…
• DPotassium chloride precipitates and toxic hydrogen iodide gas is violently evolved

Which of the following compounds is classified as a weak electrolyte in dilute aqueous solution?

• AHydrochloric acid (HCl)
• BPotassium hydroxide (KOH)
• CSodium nitrate (NaNO3)
• DAcetic acid (CH3COOH)

What is the pH of an aqueous solution at 25 °C in which the hydroxide ion concentration is [OH-] = 1.0 × 10^-4 mol/L?

• A10
• B4
• C7
• D14

Which reagent is used in analytical chemistry to identify sulfate ions (SO4^2-) in solution by forming a white precipitate insoluble in dilute hydrochloric acid?

• ASilver nitrate (AgNO3)
• BSodium hydroxide (NaOH)
• CBarium chloride (BaCl2)
• DPotassium permanganate (KMnO4)

In the electrochemical corrosion (rusting) of iron exposed to moist air, what reaction occurs at the anodic areas of the iron surface?

• AO2 + 2H2O + 4e- → 4OH-
• BFe^3+ + 3e- → Fe
• C2H+ + 2e- → H2
• DFe → Fe^2+ + 2e-

When excess concentrated aqueous sodium hydroxide is added dropwise to a solution of zinc chloride (ZnCl2), what sequence of changes is observed?

• AA white gelatinous precipitate forms initially, which redissolves in excess NaOH to give…
• BA white precipitate forms and remains completely insoluble regardless of the amount of Na…
• CA brown gas is evolved and metallic zinc precipitates as a dark grey powder
• DA deep royal blue solution forms immediately with no precipitate at any stage

Which statement accurately contrasts the structures and properties of the two main allotropes of elemental phosphorus: white phosphorus and red phosphorus?

• AWhite phosphorus is a giant covalent network insoluble in organic solvents, whereas red p…
• BWhite phosphorus has an electrical conductivity comparable to graphite, whereas red phosp…
• CWhite phosphorus consists of discrete tetrahedral P4 molecules and is highly toxic and sp…
• DWhite phosphorus is formed by ionic P^3+ and P^3- units, whereas red phosphorus forms met…

What gas is primarily evolved when metallic copper reacts with concentrated nitric acid (~68% HNO3) versus dilute nitric acid (~30% HNO3)?

• AHydrogen gas (H2) with concentrated HNO3, and oxygen gas (O2) with dilute HNO3
• BReddish-brown nitrogen dioxide (NO2) with concentrated HNO3, and colorless nitric oxide (…
• CColorless nitric oxide (NO) with concentrated HNO3, and reddish-brown nitrogen dioxide (N…
• DAmmonia gas (NH3) with concentrated HNO3, and dinitrogen monoxide (N2O) with dilute HNO3

In the industrial Contact process for sulfuric acid manufacturing, why is sulfur trioxide (SO3) absorbed into 98% concentrated H2SO4 rather than directly into water?

• ASO3 does not react chemically with pure water at any temperature
• BDirect absorption in water reduces SO3 back to sulfur dioxide (SO2)
• CWater reacts endothermically with SO3, causing the absorption tower to freeze
• DDirect reaction with water is violently exothermic and forms a dense, unmanageable acid m…

When concentrated sulfuric acid (H2SO4) is added to table sugar (sucrose, C12H22O11), a dramatic 'sugar snake' column of porous black carbon rises. Which property of concentrated H2SO4 is responsible for this reaction?

• APowerful dehydrating agent
• BStrong reducing agent
• CVolatile monoprotic acid
• DPrecipitating agent for carbohydrates

Which of the following salts undergoes cationic hydrolysis in aqueous solution, resulting in an acidic solution (pH < 7)?

• ASodium chloride (NaCl)
• BAmmonium chloride (NH4Cl)
• CPotassium carbonate (K2CO3)
• DSodium acetate (CH3COONa)

What is the pH of a 0.0050 M barium hydroxide solution, Ba(OH)2, assuming complete electrolytic dissociation in water at 25 °C?

• A2.00
• B11.70
• C12.00
• D12.30

Which of the following pairs of chemical substances can be combined in appropriate molar ratios in water to create a buffer solution capable of resisting pH changes?

• AHydrochloric acid (HCl) and sodium chloride (NaCl)
• BSodium hydroxide (NaOH) and potassium nitrate (KNO3)
• CSulfuric acid (H2SO4) and sodium sulfate (Na2SO4)
• DAcetic acid (CH3COOH) and sodium acetate (CH3COONa)

In the balanced redox equation in acidic aqueous solution: a KMnO4 + b Na2SO3 + c H2SO4 → d MnSO4 + e Na2SO4 + f K2SO4 + g H2O What is the stoichiometric coefficient b for sodium sulfite (Na2SO3)?

• A5
• B2
• C3
• D1

Based on standard reduction potentials (E°(Zn^2+/Zn) = -0.76 V; E°(Cu^2+/Cu) = +0.34 V; E°(Ag^+/Ag) = +0.80 V), which of the following redox reactions will proceed spontaneously under standard conditions?

• ACu(s) + ZnSO4(aq) → CuSO4(aq) + Zn(s)
• B2Ag(s) + CuSO4(aq) → Ag2SO4(aq) + Cu(s)
• CZn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s)
• DCu(s) + 2HCl(aq) → CuCl2(aq) + H2(g)

In a standard Daniell galvanic cell operating at 25 °C: Zn(s) | Zn^2+(1 M) || Cu^2+(1 M) | Cu(s), which statement correctly describes the electrode processes and direction of electron flow?

• ACopper is the anode where oxidation occurs, and electrons flow through the external wire…
• BZinc is the anode where oxidation occurs, and electrons flow through the external wire fr…
• CZinc is the cathode where reduction occurs, and sulfate ions flow through the wire
• DElectrons migrate through the salt bridge from the copper compartment to the zinc compart…

What substances are produced at the cathode, anode, and remaining in aqueous solution during the industrial electrolysis of concentrated sodium chloride solution (chlor-alkali process) using inert electrodes?

• ACathode: Na(s); Anode: Cl2(g); Solution: pure water
• BCathode: O2(g); Anode: H2(g); Solution: NaCl
• CCathode: Cl2(g); Anode: H2(g); Solution: Na2O
• DCathode: H2(g); Anode: Cl2(g); Solution: NaOH(aq)

In the industrial extraction of iron in a blast furnace, what is the primary role of limestone (calcium carbonate, CaCO3) added to the charge?

• ATo act as a flux that decomposes to CaO and reacts with acidic silica impurities (SiO2) t…
• BTo serve as the primary chemical reducing agent that directly reduces hematite (Fe2O3) to…
• CTo combust directly as fuel to supply heat for the blast furnace
• DTo prevent the re-oxidation of molten iron by forming a protective layer of carbon dioxid…

An electric current of 5.0 A is passed through an aqueous copper(II) sulfate (CuSO4) solution for 1930 seconds. What mass of pure copper (molar mass M = 63.5 g/mol, Faraday constant F = 96,500 C/mol) is deposited at the cathode?

• A6.35 g
• B1.59 g
• C3.18 g
• D12.7 g

What is the pH of a 0.10 M aqueous solution of acetic acid (CH3COOH) at 25 °C, given that its acid dissociation constant is Ka = 1.8 × 10^-5?

• A1.00
• B2.87
• C4.74
• D5.74

The solubility product constant of silver chromate (Ag2CrO4) at 25 °C is K_sp = 1.1 × 10^-12. What is the molar solubility (s) of Ag2CrO4 in pure water?

• A1.05 × 10^-6 mol/L
• B5.24 × 10^-7 mol/L
• C1.10 × 10^-4 mol/L
• D6.50 × 10^-5 mol/L

How does the reduction product and number of electrons gained per permanganate ion (MnO4-) vary when potassium permanganate acts as an oxidizing agent in acidic, neutral, and strongly alkaline solutions, respectively?

• AAcidic: Mn^2+ (gains 5 e-); Neutral: MnO2 (gains 3 e-); Alkaline: MnO4^2- (gains 1 e-)
• BAcidic: MnO2 (gains 3 e-); Neutral: Mn^2+ (gains 5 e-); Alkaline: MnO4^2- (gains 1 e-)
• CAcidic: MnO4^2- (gains 1 e-); Neutral: MnO2 (gains 3 e-); Alkaline: Mn^2+ (gains 5 e-)
• DAcidic: Mn^2+ (gains 2 e-); Neutral: Mn^3+ (gains 4 e-); Alkaline: Mn (gains 7 e-)