MDCAT 2013 Chemistry Solved MCQs with Explanations | Questions 45-102 Entry Test Preparation
Q.45 In the below reaction the nucleophile which attacks on the carbon atom of acid is: CH₃COOH + PCl₅ → CH₃COCl + POCl₃ + HCl A) OH⁻ B) P C) Cl⁻ D) H⁻
Answer: C) Cl⁻ Explanation: In the reaction of carboxylic acids with PCl₅, the mechanism involves initial protonation and formation of a mixed anhydride-like intermediate, but ultimately, chloride ion (Cl⁻ from PCl₅ dissociation or intermediate) acts as the nucleophile attacking the carbonyl carbon to replace OH with Cl, forming the acid chloride.
Q.46 When ethanoyl chloride (CH₃COCl) reacts with methylamine (CH₃NH₂), an amide is formed. What is the structure of the amide formed? A) CH₃C(O)NH₂ B) CH₃CH₂C(O)NHCH₃ C) CH₃C(O)NHCH₃ D) CH₃C(O)NHCH₃ (wait, options seem duplicated; standard is N-methylacetamide)
Answer: C) CH₃C(O)NHCH₃ (or correctly written as CH₃CONHCH₃) Explanation: Ethanoyl chloride (acetyl chloride, CH₃COCl) undergoes nucleophilic acyl substitution with methylamine (CH₃NH₂), losing HCl and forming the secondary amide N-methylethanamide (CH₃CONHCH₃).
Q.47 Organic compound containing both amine and carboxyl group is known as A) Amino acid B) Fatty acid C) Saccharide D) Amide
Answer: A) Amino acid Explanation: Amino acids have both -NH₂ (amine) and -COOH (carboxyl) groups in the same molecule.
Q.48 Alanine is an amino acid which shows neutral effect on litmus paper, the formula of alanine may be A) H₂N-CH(CH₃)-COOH B) H₂N-CH₂-CH₂-COOH C) HOOC-CH₂-CH(NH₂)-COOH D) H₂N-(CH₂)₃-CH(NH₂)-COOH (approx.)
Answer: A) H₂N-CH(CH₃)-COOH Explanation: Alanine is 2-aminopropanoic acid, H₂N-CH(CH₃)-COOH, with non-ionizable side chain (methyl), so neutral.
Q.49 Which of the following structures is not an alpha amino acid? A) H₃C-CH(NH₂)-COOH B) H₂N-CH₂-CH₂-CH₂-CH₂-COOH C) HO-CH₂-CH(NH₂)-COOH D) (some other)
Answer: B) H₂N-CH₂-CH₂-CH₂-CH₂-COOH (5-aminopentanoic acid, gamma/delta amino acid) Explanation: Alpha amino acids have NH₂ and COOH on the same carbon (α-carbon). Option B has them separated by four carbons.
Q.50 The skeletal formula of dipeptide formed between aspartic acid and phenylalanine is given below: HOOC-CH(NH₂)-CH₂-C(O)-NH-CH(CH₂C₆H₅)-COOH (approx. representation; note: original had OCH₃ but likely typo for side chains). How many functional groups are present in its formula? A) 1 B) 2 C) 3 D) 4
Answer: D) 4 (or C) 3 depending on counting; but typically 4: two COOH, one NH₂, one amide) Explanation: Dipeptide has free -NH₂, two -COOH (from Asp side + terminal), one peptide bond (-CONH-), but functional groups usually count distinct types: amino, carboxyl (×2), amide → often 3-4; standard answer leans toward 4 including side chain carboxyl.
Q.51 In basic conditions, amino acid exists in which of the following forms? A) ⁺H₃N-CH₂-COOH B) H₂N-CH₂-COOH C) ⁺H₃N-CH₂-COO⁻ D) H₂N-CH₂-COO⁻
Answer: D) H₂N-CH₂-COO⁻ Explanation: In basic medium (high pH), both acidic groups deprotonate: carboxylic acid → COO⁻ and ammonium → NH₂.
Q.52 Structure of dipeptide is H₂N-CH₂-C(O)-NH-CH(CH₃)-COOH. This is called: A) Glycyl glycine B) Alaninyl alanine C) Glycyl alanine D) Alaninyl glycine
Answer: C) Glycyl alanine Explanation: First amino acid (glycine: H₂N-CH₂-) contributes "glycyl", second (alanine: -CH(CH₃)-COOH) contributes "alanine".
Q.53 The principle energy storage carbohydrate in animals is A) Glucose B) Starch C) Protein D) Glycogen
Answer: D) Glycogen Explanation: Glycogen is the storage form of glucose in animals (liver/muscles).
Q.54 Starch is a polymer of A) β-D-glucose B) α-D-glucose C) γ-D-glucose D) α-L-glucose
Answer: B) α-D-glucose Explanation: Starch consists of α-1,4 and α-1,6 glycosidic linkages of D-glucose.
Q.55 The reaction between fats and caustic soda is called A) Hydrogenolysis B) Fermentation C) Esterification D) Saponification
Answer: D) Saponification Explanation: Alkaline hydrolysis of esters (fats/triglycerides) produces soap and glycerol.
Q.56 Adipic acid and hexamethylene diamine both of which have _________ carbon atoms: A) Seven B) Eight C) Six D) Four
Answer: C) Six Explanation: Adipic acid HOOC-(CH₂)₄-COOH (6C), hexamethylenediamine H₂N-(CH₂)₆-NH₂ (6C in chain).
Q.57 Lactose is a sugar present in milk. It is an example of A) Disaccharides B) Monosaccharides C) Polysaccharides D) Starch
Answer: A) Disaccharides Explanation: Lactose = glucose + galactose.
Q.58 Macromolecules are described as large molecules built up from small repeating units called: A) Monomers B) Isomers C) Metamers D) Tautomers
Answer: A) Monomers
Q.59 The increase in concentration of oxidizing agents in smog like H₂O₂, HNO₃, PAN and ozone in the air is called A) Carbonated smog B) Photochemical smog C) Nitrated smog D) Sulphonated smog
Answer: B) Photochemical smog
Q.60 Which is the metal, whose elevated concentration is harmful for fish as it clogs the gills thus causing suffocation? A) Sodium B) Lead C) Zinc D) Aluminium
Answer: D) Aluminium Explanation: Al³⁺ in acidic water hydrolyzes and precipitates on fish gills.
Q.61 An organic compound has empirical formula C₃H₃O, if molar mass of compound is 110.15 gmol⁻¹. The molecular formula of this organic compound is (A of C=12, H=1.008, O=16) A) C₆H₆O₂ B) C₉H₉O₃ C) C₃H₃O D) C₆H₆O₃
Answer: A) C₆H₆O₂ Explanation: Empirical mass = 12×3 + 1×3 + 16 = 55. n = 110.15 / 55 ≈ 2 → (C₃H₃O)₂ = C₆H₆O₂.
Q.62 When 8 grams (4 moles) of H₂ react with 2 moles of O₂, how many moles of water will be formed? A) Five B) Four C) Six D) Three
Answer: B) Four (from 2H₂ + O₂ → 2H₂O; 2 moles O₂ make 4 moles H₂O)
Q.63 The number of molecules in 22.4 dm³ of H₂ gas at 0 °C and 1 atm are A) 60.2 × 10²³ B) 6.02 × 10²² C) 6.02 × 10²⁵ D) 6.02 × 10²² (duplicated)
Answer: B) 6.02 × 10²² (1 mole at STP = 22.4 L = 6.02 × 10²³, but wait—standard is 6.02 × 10²³; likely typo in options, correct is 6.02 × 10²³ for 1 mole).
Q.64 Correct order of boiling points of the given liquid is A) H₂O > HF > HCl > NH₃ B) HF > H₂O > HCl > NH₃ C) H₂O > HF > NH₃ > HCl D) HF > H₂O > NH₃ > HCl
Answer: C) H₂O > HF > NH₃ > HCl Explanation: Hydrogen bonding strength: H₂O (2 H-bonds) > HF (strong but fewer) > NH₃ (weaker) > HCl (dipole-dipole only).
Q.65 The relative energies of 4s, 4p and 3d orbitals are in the order A) 3d < 4p < 4s B) 4s < 3d < 4p C) 4p < 4s < 3d D) 4p < 3d < 4s
Answer: B) 4s < 3d < 4p (for multi-electron atoms, filling order 4s before 3d, but energy 4s lower than 3d).
Q.66 With increase in the value of Principal Quantum Number ‘n’, the shape of the s-orbitals remains the same although their sizes A) Decrease B) Increase C) Remain the same D) May or may not remain the same
Answer: B) Increase
Q.67 The angle between unhybridized p-orbital and three sp² hybrid orbitals of each carbon atom in ether is: A) 120° B) 90° C) 109.5° D) 180°
Answer: B) 90° (p-orbital perpendicular to sp² plane).
Q.68 In ‘H-F’ bond electronegativity difference is ‘1.9’. What is the type of this bond? A) Polar covalent bond B) Non-polar covalent bond C) Pi (π) bond D) Co-ordinate covalent bond
Answer: A) Polar covalent bond (ΔEN 1.9 → polar covalent).
Q.69 ‘∆H’ will be given a negative sign in A) Exothermic reactions B) Decomposition reactions C) Dissociation reaction D) Endothermic reactions
Answer: A) Exothermic reactions
Q.70 Lattice energy of an ionic crystal is the enthalpy of A) Combustion B) Dissolution C) Dissociation D) Formation
Answer: C) Dissociation (energy released when gaseous ions form crystal, but often defined as energy for separation).
Q.71 As number of solute particles increases, freezing point of the solution: A) Remains the same B) Increases C) First increases, then decreases D) Decreases
Answer: D) Decreases (colligative property: depression).
Q.72 Boiling point constants help us to determine A) Molar masses B) Volumes C) Pressures D) Masses
Answer: A) Molar masses (ebullioscopy).
Q.73 In electrolysis of aqueous CuCl₂, the metal deposited at cathode is A) Sodium B) Aluminium C) Lead D) Copper
Answer: D) Copper (Cu²⁺ reduced preferentially).
Q.74 In MgCl₂, the oxidation state of ‘Cl’ is A) Zero B) +2 C) -2 D) -1
Answer: D) -1
Q.75 Formation of NH₃ is reversible and exothermic process, what will happen on cooling? A) More reactant will form B) More N₂ will be formed C) More H₂ will be formed D) More product (NH₃) will be formed
Answer: D) More product (NH₃) will be formed (Le Chatelier: decrease T favors exothermic direction).
Q.76 A buffer solution is that which resists/minimizes the change in A) pOH B) pH C) pKa D) pKb
Answer: B) pH
Q.77 In some reactions, a product formed acts as a catalyst. The phenomenon is called A) Negative Catalysis B) Activation of Catalyst C) Heterogeneous catalysis D) Autocatalysis
Answer: D) Autocatalysis
Q.78 The reaction rate in forward direction decreases with the passage of time because A) Concentration of reactants decrease B) Concentration of product decreases C) The order of reaction changes D) Temperature of the system changes
Answer: A) Concentration of reactants decrease
Q.79 Which one remains same along a period? A) Atomic radius B) Melting point C) Number of shells (orbits) D) Electrical conductivity
Answer: C) Number of shells (orbits)
Q.80 More the ionization energy of an element: A) More the electropositivity B) More the reducing power C) Less the metallic character D) Bigger the atomic radius
Answer: C) Less the metallic character
Q.81 Alkaline earth metal hydroxides decompose on heating. Which of the following reactions is a correct representation of this decomposition? A) M(OH)₂(s) → MO(s) + H₂O(l) B) MOH(s) → M₂O(s) + H₂O(l) C) 2MOH₂(s) → 2MO(s) + H₂(l) D) 4MOH(s) → 4M(s) + 2H₂O(l) + O₂
Answer: A) M(OH)₂(s) → MO(s) + H₂O(l)
Q.82 Carbon has the unique ability to form long chains by bonding with other carbon atoms. This property of self-linking in carbon is known as: A) Condensation B) Polymerization C) Cyclization D) Catenation
Answer: D) Catenation
Q.83 Oxidation state of ‘Mn’ in KMnO₄, K₂MnO₄, MnO₂ and MnSO₄ is in the order: A) +7, +6, +2, +4 B) +7, +6, +4, +2 C) +6, +7, +2, +4 D) +4, +6, +7, +2
Answer: B) +7, +6, +4, +2
Q.84 Which pair of transition elements shows abnormal electronic configuration? A) Sc and Zn B) Cu and Sc C) Zn and Cu D) Cu and Cr
Answer: D) Cu and Cr (Cr: [Ar] 4s¹3d⁵, Cu: [Ar] 4s¹3d¹⁰).
Q.85 The acid rain water has pH: A) Below 5 B) 7 C) Between 5 and 7 D) Between 7 and 14
Answer: A) Below 5 (typically <5.6).
Q.86 In Contact Process for manufacturing sulphuric acid, Sulphur trioxide (SO₃) is not absorbed in water because A) The reaction does not go to completion B) The reaction is quite slow C) The reaction is highly exothermic D) SO₃ is insoluble in water
Answer: C) The reaction is highly exothermic (forms fog/mist).
Q.87 In modern Haber Process Plants, the temperature maintained during the process is A) 670 – 770 K (400 °C – 500 °C) B) 270 – 370 K (0 °C – 100 °C) C) 370 – 470 K (100 °C – 200 °C) D) 570 – 600 K (300 °C – 380 °C)
Answer: A) 670 – 770 K (400 °C – 500 °C)
Q.88 In the Haber process for manufacturing of ammonia, Nitrogen is taken from A) Proteins occurring in living bodies B) Ammonium salts obtained industrially C) Air D) Minerals containing nitrates
Answer: C) Air
Q.89 Ethene on polymerization, gives the product polyethene. This reaction may be called as A) Addition B) Condensation C) Substitution D) Pyrolysis
Answer: A) Addition
Q.90 In the following, which one is free radical? A) Cl⁻ B) Cl⁺ C) Cl₂ D) Cl•
Answer: D) Cl• (Cl o represents Cl• free radical).
Q.91 The introduction of C + O R group in benzene is called A) Acylation B) Carbonyl reduction C) Alkylation D) Formylation
Answer: A) Acylation (Friedel-Crafts acylation for -COR).
Q.92 The alkaline hydrolysis of bromoethane shown below gives alcohol as the product: CH₃CH₂Br → CH₃CH₂OH. The reagent and the condition used in this reaction may be: A) H₂O at room temperature B) Ethanol, heat C) KOH in alcohol D) Dilute NaOH(aq) warm
Answer: D) Dilute NaOH(aq) warm (SN2 hydrolysis).
Q.93 In the reaction of ethene with bromine the intermediate formed is A) H₂C=CH₂Br⁺ B) H₂C-CH₂Br⁻ C) H₂C-CH₂⁺ Br⁻ (bridged bromonium ion) D) H₂C=CHBr
Answer: C) bridged bromonium ion (cyclic intermediate).
Q.94 In substitution reactions, dihaloalkane or secondary halogenoalkane give / show: A) SN1 Mechanism B) SN2 Mechanism C) Both E1 and E2 D) Both SN1 and SN2
Answer: D) Both SN1 and SN2 (secondary can do both depending on conditions).
Q.95 The dehydration of ethyl alcohol with concentrated H₂SO₄ at 140°C gives: A) Ethene B) Diethyl ether C) Alcohol D) Carboxylic acid
Answer: B) Diethyl ether (at 140°C intermolecular, at 170°C ethene).
Q.96 Ethanol can be converted in to ethanoic acid by: A) Oxidation B) Fermentation C) Hydration D) Hydrogenation
Answer: A) Oxidation
Q.97 The following structure is of: R-C(OH)R-R A) Secondary alcohol B) Primary alcohol C) Tertiary alcohol D) Carboxylic acid
Answer: C) Tertiary alcohol (three R groups on carbon with OH).
Q.98 When ethanol is warmed with ethanoic acid in the presence of strong acid catalyst, an ester ethyl ethanoate is formed. CH₃CH₂OH + CH₃CO₂H → CH₃CO₂CH₂CH₃. During this reaction: A) Alcohol is reduced B) O-H bond in ethanol is broken C) O-H bond in ethanoic acid is broken D) Acid is oxidized
Answer: B) O-H bond in ethanol is broken (alcohol acts as nucleophile attacking protonated carbonyl; O-H in alcohol breaks in esterification).
Q.99 Primary alcohols normally give us aldehydes when oxidized in the presence of Na₂Cr₂O₇, what the product will be, when the secondary alcohols are oxidized in same conditions? A) Alkenes B) Alkynes C) Alkyl halides D) Ketones
Answer: D) Ketones
Q.100 Formaldehyde reacts with HCN (NaCN + HCl) to give a compound: A) CH₃-CH(OH)-CN B) CH₃-CH(OH)-CH₃ CN (wait, incomplete; standard cyanohydrin) C) HO-CH₂-CN D) CH₃-C(O)-CN
Answer: C) HO-CH₂-CN (formaldehyde cyanohydrin: HCHO + HCN → HO-CH₂-CN).
Q.101 Iodoform test will not be positive with: A) CH₃CH₂C(O)CH₂CH₃ B) CH₃CH₂C(O)CH₃ C) C₂H₅OH D) CH₃CHO
Answer: A) CH₃CH₂C(O)CH₂CH₃ (no CH₃C(O)- or CH₃CH(OH)- group).
Q.102 When CH₃-CH₂-OH is oxidized in the presence of K₂Cr₂O₇ and H₂SO₄, the product formed is A) CH₃COOH B) CH₃COCH₃ C) HCHO D) CH₃COOCH₃
Answer: A) CH₃COOH (primary alcohol → carboxylic acid with strong oxidation)
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