Unified Exam — Chemistry (Armenia)

What is the ground-state electron configuration of the chromium atom (24_Cr)?

• A1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵ 4s¹ ([Ar] 3d⁵ 4s¹)
• B1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁴ 4s² ([Ar] 3d⁴ 4s²)
• C1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶ ([Ar] 3d⁶)
• D1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 4p⁴

Which of the following molecules has a non-polar (zero dipole moment) linear molecular geometry despite containing polar covalent bonds?

• ACO2 (Carbon dioxide)
• BH2O (Water)
• CSO2 (Sulfur dioxide)
• DNH3 (Ammonia)

In the reaction 2NO(g) + O2(g) <=> 2NO2(g) + Q (exothermic), which change will shift the chemical equilibrium toward the formation of more products (to the right)?

• AIncreasing the pressure or decreasing the temperature
• BDecreasing the pressure or increasing the temperature
• CAdding a catalyst
• DRemoving NO(g) from the reaction vessel

What is the oxidation state of sulfur in sodium thiosulfate (Na2S2O3)?

• A+2
• B+4
• C+6
• D+2.5

What is the pH of a 0.005 M aqueous solution of barium hydroxide (Ba(OH)2), assuming complete electrolytic dissociation at 25°C?

• A12.0
• B11.7
• C2.0
• D11.0

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

• ANH4Cl (Ammonium chloride)
• BNa2CO3 (Sodium carbonate)
• CK2SO4 (Potassium sulfate)
• DCH3COONa (Sodium acetate)

Which gas is evolved when concentrated nitric acid (HNO3) reacts with metallic copper (Cu)?

• ANO2 (Nitrogen dioxide, brown pungent gas)
• BH2 (Hydrogen)
• CN2O (Nitrous oxide)
• DNH3 (Ammonia)

Which of the following oxides is amphoteric (capable of reacting with both strong acids and strong bases)?

• AAl2O3 (Aluminum oxide)
• BCaO (Calcium oxide - basic)
• CSO3 (Sulfur trioxide - acidic)
• DCO (Carbon monoxide - neutral/non-salt forming)

What is the qualitative test reagent and characteristic observation used to identify sulfate ions (SO4²⁻) in an aqueous solution?

• AAddition of BaCl2 solution, forming a white precipitate (BaSO4) insoluble in concentrated…
• BAddition of AgNO3 solution, forming a yellow precipitate
• CAddition of NaOH solution, forming a blue precipitate
• DAddition of HCl solution, evolving a gas with rotten-egg odor

What is the primary organic product obtained from the catalytic hydration of propene (CH3-CH=CH2 + H2O) in the presence of sulfuric acid according to Markovnikov's rule?

• APropan-2-ol (Isopropanol / CH3-CH(OH)-CH3)
• BPropan-1-ol (1-Propanol / CH3-CH2-CH2-OH)
• CPropanal (CH3-CH2-CHO)
• DPropanoic acid (CH3-CH2-COOH)

Which of the following organic compounds will give a positive silver mirror test (Tollens' reagent: [Ag(NH3)2]OH)?

• AEthanal (Acetaldehyde / CH3CHO)
• BAcetone (Propanone / CH3COCH3)
• CEthanol (CH3CH2OH)
• DEthyl acetate (CH3COOCH2CH3)

What is the systematic IUPAC name of the compound with structural formula (CH3)2CH-CH(CH3)-CH2-CH3?

• A2,3-dimethylpentane
• B3,4-dimethylpentane
• C2-isopropylbutane
• D2,3-dimethylhexane

What type of chemical bond links individual amino acid residues together in a primary polypeptide protein chain?

• APeptide bond (Amide linkage: -CO-NH-)
• BGlycosidic bond
• CPhosphodiester bond
• DEster bond

How many grams of sodium hydroxide (NaOH, molar mass M = 40 g/mol) are required to prepare 500 mL (0.50 L) of a 0.20 M aqueous solution?

• A4.0 g
• B8.0 g
• C2.0 g
• D20.0 g

What volume of hydrogen gas (H2, at STP: 22.4 L/mol) is evolved when 5.4 g of metallic aluminum (Al, M = 27 g/mol) completely reacts with excess hydrochloric acid (2Al + 6HCl -> 2AlCl3 + 3H2)?

• A6.72 L
• B4.48 L
• C2.24 L
• D13.44 L

What is the mass percentage of oxygen in pure calcium carbonate (CaCO3, atomic masses: Ca = 40, C = 12, O = 16)?

• A48%
• B40%
• C12%
• D16%

In the balanced redox equation: 2KMnO4 + 10FeSO4 + 8H2SO4 -> K2SO4 + 2MnSO4 + 5Fe2(SO4)3 + 8H2O, what is the stoichiometric ratio of oxidizing agent to reducing agent?

• A1 : 5 (2 KMnO4 to 10 FeSO4)
• B5 : 1
• C2 : 8
• D1 : 1

What is the hybridization of the carbon atoms in ethyne (acetylene, H-C#C-H)?

• Asp
• Bsp²
• Csp³
• Dsp³d

Which of the following halogen elements is the strongest oxidizing agent in its standard state?

• AF2 (Fluorine)
• BCl2 (Chlorine)
• CBr2 (Bromine)
• DI2 (Iodine)

What product is formed when phenol (C6H5OH) reacts with excess bromine water (3Br2)?

• A2,4,6-tribromophenol (white precipitate)
• B4-bromophenol
• C2-bromophenol
• DBromobenzene

How many structural (constitutional) isomers exist for the alkane with molecular formula C5H12?

• A3 (pentane, 2-methylbutane, 2,2-dimethylpropane)
• B4
• C2
• D5

What is the equilibrium constant expression Kc for the heterogeneous reaction: CaCO3(s) <=> CaO(s) + CO2(g)?

• AKc = [CO2]
• BKc = [CaO][CO2] / [CaCO3]
• CKc = [CO2] / [CaCO3]
• DKc = 1 / [CO2]

Which of the following metals CANNOT displace hydrogen gas (H2) from dilute hydrochloric acid (HCl)?

• ACu (Copper - positive standard reduction potential E° = +0.34 V)
• BZn (Zinc - E° = -0.76 V)
• CFe (Iron - E° = -0.44 V)
• DMg (Magnesium - E° = -2.37 V)

What is the molar concentration (molarity, M) of a 98% (by mass) sulfuric acid solution (H2SO4, M = 98 g/mol) with a density of rho = 1.84 g/mL (1840 g/L)?

• A18.4 M
• B9.8 M
• C1.84 M
• D36.8 M

What functional group is characteristic of carboxylic acids?

• A-COOH (Carboxyl group)
• B-CHO (Aldehyde / Formyl group)
• C-OH (Hydroxyl group)
• D-COOCH3 (Ester group)

When 100 g of a 20% by mass NaCl solution is mixed with 300 g of a 10% by mass NaCl solution, what is the mass percentage of NaCl in the resulting mixture?

• A12.5%
• B15.0%
• C10.0%
• D17.5%

What is the product of catalytic dehydrogenation of ethanol (CH3CH2OH) over a hot copper catalyst at 300°C?

• AEthanal (Acetaldehyde / CH3CHO) and H2
• BEthene (Ethylene / C2H4) and H2O
• CAcetic acid (CH3COOH)
• DDiethyl ether (CH3CH2-O-CH2CH3)

Which of the following compounds is an allotrope of elemental carbon containing sp²-hybridized carbon atoms arranged in a flat hexagonal lattice with delocalized pi-electrons?

• AGraphite (and Graphene)
• BDiamond (sp³ tetrahedral network)
• CCarborundum (Silicon carbide / SiC)
• DMethane

What gas is produced at the cathode during the electrolysis of an aqueous solution of sodium chloride (NaCl) with inert graphite electrodes?

• AH2 (Hydrogen gas)
• BCl2 (Chlorine gas)
• CO2 (Oxygen gas)
• DNa (Sodium metal)

What is the empirical formula of a hydrocarbon containing 85.7% carbon and 14.3% hydrogen by mass (atomic masses: C = 12, H = 1)?

• ACH2
• BCH
• CCH3
• DC2H5

What is the primary organic product of the reaction between acetic acid (CH3COOH) and ethanol (C2H5OH) in the presence of concentrated H2SO4 catalyst (esterification)?

• AEthyl acetate (CH3COOC2H5) and water
• BDiethyl ether and water
• CAcetone and methane
• DEthanal and acetic anhydride

Which of the following substances contains ionic chemical bonding?

• AKCl (Potassium chloride)
• BHCl (Hydrogen chloride gas - polar covalent)
• CCH4 (Methane - nonpolar covalent)
• DCl2 (Chlorine gas - pure covalent)

How many moles of oxygen gas (O2) are required for the complete stoichiometric combustion of 2.0 moles of propane (C3H8 + 5O2 -> 3CO2 + 4H2O)?

• A10.0 moles
• B5.0 moles
• C6.0 moles
• D8.0 moles

Which of the following organic functional groups possesses basic properties and can form salts with mineral acids (e.g., forming hydrochlorides)?

• A-NH2 (Amino group / Amines)
• B-COOH (Carboxyl group)
• C-OH (Hydroxyl group)
• D-NO2 (Nitro group)

What is the total number of sigma (sigma) and pi (pi) bonds in one molecule of benzene (C6H6)?

• A12 sigma bonds and 3 pi bonds
• B6 sigma bonds and 6 pi bonds
• C12 sigma bonds and 6 pi bonds
• D6 sigma bonds and 3 pi bonds

Which of the following compounds reacts with sodium hydrogen carbonate (NaHCO3) to evolve carbon dioxide (CO2) gas?

• AAcetic acid (CH3COOH)
• BPhenol (C6H5OH)
• CEthanol (C2H5OH)
• DEthyl acetate (CH3COOC2H5)

What is the molar mass of glucose (C6H12O6, atomic masses: C = 12, H = 1, O = 16)?

• A180 g/mol
• B342 g/mol
• C164 g/mol
• D120 g/mol

What is the volume of CO2 gas (at STP) produced by the thermal decomposition of 20.0 g of pure calcium carbonate (CaCO3 -> CaO + CO2, M(CaCO3) = 100 g/mol)?

• A4.48 L
• B2.24 L
• C22.4 L
• D8.96 L

Which of the following polymers is obtained by the addition polymerization of tetrafluoroethene (CF2=CF2)?

• ATeflon (Polytetrafluoroethylene / PTFE)
• BPolyethylene
• CPolystyrene
• DNylon-6,6

What is the catalyst used in the industrial Haber-Bosch process for ammonia synthesis (N2 + 3H2 <=> 2NH3)?

• AFinely divided Iron (Fe) with Al2O3 and K2O promoters
• BPlatinum (Pt)
• CVanadium pentoxide (V2O5)
• DNickel (Ni)

What is the concentration of hydronium ions [H3O⁺] in a solution with pH = 3.0 at 25°C?

• A1.0 * 10^-3 M
• B3.0 * 10^-3 M
• C1.0 * 10^-11 M
• D1.0 * 10^3 M

Which of the following organic pairs represents functional group isomers (ֆունկցիոնալ իզոմերներ)?

• AEthanol (CH3CH2OH) and Dimethyl ether (CH3-O-CH3)
• BPropan-1-ol and Propan-2-ol (position isomers)
• CPentane and 2-methylbutane (chain isomers)
• DCis-but-2-ene and Trans-but-2-ene (geometric isomers)

What is the standard heat of reaction Delta_H° for the combustion of methane: CH4(g) + 2O2(g) -> CO2(g) + 2H2O(l), given standard heats of formation Delta_H_f°: CH4 = -75 kJ/mol, CO2 = -394 kJ/mol, H2O(l) = -286 kJ/mol?

• A-891 kJ/mol
• B-966 kJ/mol
• C-605 kJ/mol
• D+891 kJ/mol

What is the primary organic product when benzene reacts with a mixture of concentrated nitric acid and sulfuric acid (nitration)?

• ANitrobenzene (C6H5NO2)
• BAniline (C6H5NH2)
• CBenzenesulfonic acid (C6H5SO3H)
• DPhenol (C6H5OH)

What is the name of the chemical process in which vegetable oils (unsaturated liquid triglycerides) are converted into solid fats (margarine)?

• ACatalytic hydrogenation (addition of H2 across C=C double bonds)
• BSaponification (alkaline hydrolysis)
• CEsterification
• DDecarboxylation

Which of the following nitrogen oxides is commonly called 'laughing gas' and is used as an anesthetic in medicine?

• AN2O (Dinitrogen monoxide / Nitrous oxide)
• BNO (Nitric oxide)
• CNO2 (Nitrogen dioxide)
• DN2O4 (Dinitrogen tetroxide)

What is the theoretical mass of iron (Fe, M = 56 g/mol) obtained by the complete aluminothermic reduction of 160 g of iron(III) oxide (Fe2O3 + 2Al -> Al2O3 + 2Fe, M(Fe2O3) = 160 g/mol)?

• A112 g
• B56 g
• C224 g
• D80 g

Which of the following carbohydrates is a non-reducing disaccharide that does NOT react with Fehling's or Tollens' solution?

• ASucrose (Table sugar / Cane sugar)
• BGlucose (Monosaccharide with free aldehyde group)
• CMaltose (Reducing disaccharide)
• DLactose (Reducing milk sugar)