MDCAT 2024 Chemistry

MDCAT 2024 Chemistry Past Paper MCQs with Answers

172 Chemistry MCQs that appeared in MDCAT 2024, arranged unit by unit in syllabus order. Tap “Show answer” under any question for the correct option and a short solution.

Fundamental Concepts of Chemistry

1.The number of moles of an element is directly proportional to the: (MDCAT 2024)

  1. mass of the element
  2. empirical formula mass
  3. molar mass of the element
  4. formula mass
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Correct answer: (a) mass of the element

$n=m/M$, and for a given element $M$ is fixed, so the number of moles follows the mass.

2.Number of moles in an element is directly proportional to: (UHS MDCAT 2024)

  1. Mass of an element
  2. Empirical formula mass
  3. Molar mass of an element
  4. Formula mass
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Correct answer: (a) Mass of an element

The number of moles is the mass divided by the fixed molar mass, so it rises with the mass.

3.The type and relative amount of each isotope in an element can be found by: (UHS MDCAT 2024)

  1. R spectroscopy
  2. U. V spectroscopy
  3. Mass Spectrometry
  4. N.M.R
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Correct answer: (c) Mass Spectrometry

A mass spectrometer separates the isotopes by mass and measures how much of each there is.

4.The atomic masses of element depend upon: (UHS MDCAT 2024)

  1. Atomic number
  2. Number of electrons
  3. Number of isopotes & their abundance
  4. None of the above
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Correct answer: (c) Number of isopotes & their abundance

The atomic mass is the weighted mean over the isotopes, so it depends on which they are and how abundant.

5.No individual atom in the sample of 1 mole of Neon has a mass of 20.18 a.m.u. because it is: (UHS MDCAT 2024)

  1. Overall mass of an isobar
  2. It is a fractional mass
  3. It is molar mass of Ne
  4. Average atomic mass of Ne
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Correct answer: (d) Average atomic mass of Ne

No single atom weighs the average; $20.18$ is the mean over the isotopes of neon.

6.What is the mass of 1 mole of calcium carbonate (CaCO3)? (KMU MDCAT 2024)

  1. 50g
  2. 75g
  3. 100g
  4. 125g
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Correct answer: (c) 100g

$40+12+48$ gives a molar mass of $100\,\mathrm{g\,mol^{-1}}$.

7.How many grams of CO2 can be produced by thermally decomposing 10 moles of ZnCO3(s)? (KMU MDCAT 2024)

  1. 320
  2. 360
  3. 400
  4. 440
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Correct answer: (d) 440

Each mole of the carbonate gives a mole of carbon dioxide, so ten moles give $440\,\mathrm{g}$.

8.How many moles of NaCl are produced from 16.5g of HCl, according to the neutralization reaction? HCl(aq) + NaOH(aq) -> NaCl(aq) + H2O(l) (KMU MDCAT 2024)

  1. 0.252
  2. 0.452
  3. 0.652
  4. 0.852
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Correct answer: (b) 0.452

$16.5/36.5$ is $0.452$ mole of the acid, and each mole gives one of the salt.

9.What mass of aluminium oxide (Al2O3) is produced from 18.5g of Al metal, when it reacts completely with oxygen gas according to the following equation? 4Al(s) + 3O2(g) → 2Al2O3(s) (KMU MDCAT 2024)

  1. 30.8g
  2. 32.6g
  3. 34.9g
  4. 36.5g
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Correct answer: (c) 34.9g

$18.5/27$ is $0.685$ mole of aluminium, half of which is $0.343$ mole of oxide, that is $34.9\,\mathrm{g}$.

10.When 4 g of magnesium was heated in excess of oxygen. Calculate the theoretical yield of magnesium oxide (MgO). (KMU MDCAT 2024)

  1. 3.7g
  2. 4.2g
  3. 5.4g
  4. 6.6g
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Correct answer: (d) 6.6g

$4\,\mathrm{g}$ is $1/6$ mole of magnesium, which gives $1/6$ mole, about $6.6\,\mathrm{g}$, of the oxide.

11.Select the greatest number of particles in the following: (NUMS MDCAT 2024)

  1. 2g of Sodium (atomic mass = 23)
  2. 2g of Hydrogen gas (atomic mass of H = 1)
  3. 2g of Nitrogen gas (atomic mass of N = 14)
  4. 2g of Carbon dioxide gas (C=12, O=16)
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Correct answer: (b) 2g of Hydrogen gas (atomic mass of H = 1)

Two grams of hydrogen is a whole mole; the others are small fractions of one.

12.Heating 24.8g of copper carbonate (CuCO3) in a crucible produced only 13.9g of copper oxide (CuO). What is the percentage yield of copper oxide? (KMU MDCAT 2024)

  1. 81.79%
  2. 83.98%
  3. 86.87%
  4. 89.68%
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Correct answer: (c) 86.87%

$24.8\,\mathrm{g}$ is $0.2$ mole, which should give $16\,\mathrm{g}$ of the oxide, and $13.9/16$ is $86.87\%$.

13.Efficiency of chemical reaction can be checked by calculating (KMU MDCAT 2024)

  1. Actual yield
  2. Theoretical yield
  3. Percentage yield
  4. Amount of the reactant unused
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Correct answer: (c) Percentage yield

The percentage yield compares what was got with what was possible, so it measures the efficiency.

14.Actual yield will reach the ideal (theoretical) value if the % yield of the reaction is, (KMU MDCAT 2024)

  1. 10%
  2. 50%
  3. 90%
  4. 100%
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Correct answer: (d) 100%

A hundred per cent yield is exactly the case where the actual yield equals the theoretical one.

15.Ca + S → CaS. If 2.0g of Calcium and 4.0g of Sulphur are available, amount of product formed: (NUMS MDCAT 2024)

  1. 4.6g
  2. 1.6g
  3. 2.6g
  4. 3.6g
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Correct answer: (d) 3.6g

$2.0\,\mathrm{g}$ is $0.05$ mole of calcium, the limiting reactant, so $0.05\times72$, that is $3.6\,\mathrm{g}$, of the sulphide is formed.

Atomic Structure

16.Which of the following sub-shell does not exist? (KMU MDCAT 2024)

  1. 1p
  2. 1s
  3. 5d
  4. 6f
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Correct answer: (a) 1p

The first shell has $l=0$ only, so there is no 1p subshell.

17.The value of 'l' for 4p orbital is: (NUMS MDCAT 2024)

  1. 0
  2. 1
  3. 2
  4. 3
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Correct answer: (b) 1

A p orbital has $l=1$ whatever its shell.

18.Choose the correct quantum numbers: (NUMS MDCAT 2024)

  1. n=3, l=2, m=0, s=+1/2
  2. n=-3, l=3, m=0, s=-1/2
  3. n=4, l=3, m=4, s=+1/2
  4. n=4, l=2, m=4, s=-1/2
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Correct answer: (a) n=3, l=2, m=0, s=+1/2

Only the first set obeys the rules: $l$ below $n$, and $m$ within $\pm l$.

19.The p orbital has: (MDCAT 2024)

  1. 2 lobes
  2. 3 lobes
  3. 4 lobes
  4. 5 lobes
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Correct answer: (a) 2 lobes

A p orbital is dumb-bell shaped, with two lobes on either side of the nucleus.

20.Which of the following electronic configurations is correct for carbon? (MDCAT 2024)

  1. $1s^22s^22p^2$
  2. $1s^22s^22p^4$
  3. $1s^22s^22p^3$
  4. $1s^22s^22p^1$
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Correct answer: (a) $1s^22s^22p^2$

Carbon has six electrons, which fill $1s$ and $2s$ and leave two in $2p$.

21.Which of the following electronic configuration is correct for carbon? (UHS MDCAT 2024)

  1. 1s22s2p3
  2. 1s22s2p4
  3. 1s22s2p2
  4. 1s22s2p1
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Correct answer: (c) 1s22s2p2

Carbon has six electrons, $1s^2 2s^2 2p^2$.

22.Which element has the electronic configuration of noble-gas notation [Kr], 5s2, 4d? (KMU MDCAT 2024)

  1. Mo
  2. Se
  3. Sr
  4. Zr
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Correct answer: (d) Zr

Zirconium is $[\mathrm{Kr}]5s^2 4d^2$.

23.The element having the electronic configuration (Kr) 5s24d8 is: (NUMS MDCAT 2024)

  1. Sr
  2. Ru
  3. Pd
  4. Zr
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Correct answer: (c) Pd

Filling to $[\mathrm{Kr}]5s^2 4d^8$ accounts for 46 electrons, which is palladium.

24.The splitting of spectral lines in magnetic field is (KMU MDCAT 2024)

  1. Aufbau principle
  2. Pauli exclusion principle
  3. Stark effect
  4. Zeeman effect
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Correct answer: (d) Zeeman effect

Splitting of spectral lines in a magnetic field is the Zeeman effect; in an electric field it is the Stark effect.

Gases

25.The intermolecular forces between the molecules of an ideal gas are: (MDCAT 2024)

  1. strong
  2. moderate
  3. weak
  4. absent
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Correct answer: (d) absent

The kinetic theory of an ideal gas assumes no attraction between the molecules at all.

26.The relationship between absolute temperature and velocities of gas molecules is given by: (NUMS MDCAT 2024)

  1. Crms = sqrt(3RT/M)
  2. PV = nRT
  3. V = sqrt(2Ek/m)
  4. PV = 1/3mNc2
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Correct answer: (a) Crms = sqrt(3RT/M)

The root mean square speed is $\sqrt{3RT/M}$.

27.760 torr is equal to ____ Pascal (KMU MDCAT 2024)

  1. 1
  2. 76
  3. 760
  4. 101325
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Correct answer: (d) 101325

One atmosphere is $760\,\mathrm{torr}$, that is $101325\,\mathrm{Pa}$.

28.A gas has volume 10dm3 at 10°C. At what temperature is volume reduced to half? (NUMS MDCAT 2024)

  1. 283K
  2. 566K
  3. 142K
  4. 373K
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Correct answer: (c) 142K

At constant pressure the volume follows the absolute temperature, so halving it halves $283\,\mathrm{K}$ to about $142\,\mathrm{K}$.

29.The correct ideal gas equation is: (MDCAT 2024)

  1. $qV=nRT$
  2. $PV=nRT$
  3. $PV=nRt$
  4. $PV^2=nRT$
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Correct answer: (b) $PV=nRT$

$PV=nRT$, with $T$ the absolute temperature.

30.Real gases show deviation from ideal behaviour at: (MDCAT 2024)

  1. low temperature and low pressure
  2. high temperature and high pressure
  3. low temperature and high pressure
  4. high temperature and low pressure
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Correct answer: (c) low temperature and high pressure

Cold, compressed molecules are close together and slow, so their own volume and their attractions both matter.

31.Intermolecular forces between molecules of ideal gas are (UHS MDCAT 2024)

  1. Strong
  2. Moderate
  3. Weak
  4. Absent
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Correct answer: (d) Absent

An ideal gas is defined as one whose molecules neither attract nor repel each other.

32.The real gases show deviation from ideal behavior at: (UHS MDCAT 2024)

  1. Low temperature and low pressure
  2. High temperature and high pressure
  3. Low temperature and high pressure
  4. High temperature and low pressure
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Correct answer: (c) Low temperature and high pressure

Cooling and compressing bring the molecules close and slow, so their attractions begin to tell.

Liquids

33.The maximum polarizability is exhibited in: (NUMS MDCAT 2024)

  1. C6H14
  2. C3H6
  3. C5H12
  4. C2H6
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Correct answer: (a) C6H14

The largest, most loosely held electron cloud is the most easily distorted, and hexane is the biggest here.

34.In order to boil water at $110^\circ$C, the external pressure should be: (MDCAT 2024)

  1. 200-760 torr
  2. 760-1200 torr
  3. 665-670 torr
  4. 660-700 torr
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Correct answer: (b) 760-1200 torr

Above $100^\circ$C the vapour pressure of water is above one atmosphere, so the external pressure must be above 760 torr.

35.The boiling point of a liquid is the temperature at which: (MDCAT 2024)

  1. the surface tension is greater than the atmospheric pressure
  2. the viscosity is less than the atmospheric pressure
  3. the vapour pressure equals the atmospheric pressure
  4. the viscosity equals the atmospheric pressure
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Correct answer: (c) the vapour pressure equals the atmospheric pressure

Bubbles can form in the bulk only once the vapour pressure has risen to the pressure above the liquid.

36.In order to boil water at 110°C, external pressure should be (UHS MDCAT 2024)

  1. 200 - 760 torr
  2. 760 - 1200 torr
  3. 665-670 torr
  4. 660-700 torr
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Correct answer: (b) 760 - 1200 torr

Water boils above $100^{\circ}\mathrm{C}$ only when the pressure on it is above one atmosphere.

37.Boiling point of a liquid is a temperature at which: (UHS MDCAT 2024)

  1. Surface tension is greater than the atmospheric pressure
  2. Viscosity is less than the atmospheric pressure
  3. Vapour pressure equals the atmospheric pressure
  4. Viscosity equals the atmospheric pressure
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Correct answer: (c) Vapour pressure equals the atmospheric pressure

A liquid boils when its vapour pressure has risen to the pressure above it.

38.Molar heat of vaporization of water is (KMU MDCAT 2024)

  1. 40.7 cal/mol
  2. 40.7 J/mol
  3. 40.7kcal/mol
  4. 40.7 kJ/mol
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Correct answer: (d) 40.7 kJ/mol

It takes $40.7\,\mathrm{kJ}$ to turn a mole of water at $100^{\circ}\mathrm{C}$ into steam.

39.Distillation under very reduced pressure is ____ distillation (KMU MDCAT 2024)

  1. Destructive
  2. Fractional
  3. Steam
  4. Vacuum
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Correct answer: (d) Vacuum

Lowering the pressure lowers the boiling point, which is how heat sensitive liquids are distilled.

40.If external pressure is reduced to half, boiling point of ethanol will be: (NUMS MDCAT 2024)

  1. Greater than 78°C
  2. Less than 78°C
  3. Equal to 78°C
  4. Reduced to half
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Correct answer: (b) Less than 78°C

A liquid boils when its vapour pressure reaches the pressure above it, so less pressure means a lower boiling point.

41.Which of the following does NOT have a tendency to form hydrogen bonding? (MDCAT 2024)

  1. water
  2. ethyl alcohol
  3. carboxylic acid
  4. hydrocarbon
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Correct answer: (d) hydrocarbon

Hydrogen bonding needs hydrogen bound to a small, strongly electronegative atom, and a hydrocarbon has none.

42.Which one of the following DO NOT have tendency to form hydrogen bonding? (UHS MDCAT 2024)

  1. Ammonia
  2. Ethyl alcohol
  3. Carboxylic acid
  4. Hydrocarbon
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Correct answer: (d) Hydrocarbon

A hydrocarbon has no hydrogen bound to nitrogen, oxygen or fluorine, so it cannot hydrogen bond.

Solids

43.Whenever crystalline solids are broken they do so along definite planes known as: (MDCAT 2024)

  1. cleavage planes
  2. refractory planes
  3. sagittal planes
  4. coronal planes
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Correct answer: (a) cleavage planes

The regular lattice parts most easily along particular planes, called cleavage planes.

44.One of the following is NOT an example of an amorphous solid: (MDCAT 2024)

  1. plastic
  2. glass
  3. glucose
  4. rubber
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Correct answer: (c) glucose

Glucose is crystalline, with a sharp melting point; the other three have no long-range order.

45.Whenever the crystalline solids are broken they do so along definite planes known as: (UHS MDCAT 2024)

  1. Cleavage planes
  2. Refractory planes
  3. Sagittal planes
  4. Coronal planes
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Correct answer: (a) Cleavage planes

A crystal splits along its cleavage planes, where the lattice forces are weakest.

46.One of the following is NOT an example of amorphous solids (UHS MDCAT 2024)

  1. Plastic
  2. Glass
  3. Glucose
  4. Rubber
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Correct answer: (c) Glucose

Glucose forms proper crystals; plastic, glass and rubber have no long range order.

47.In graphite the carbon atoms are arranged in which of the following structure? (UHS MDCAT 2024)

  1. Rhombic
  2. Hexagonal
  3. Tetragonal
  4. Trigonal
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Correct answer: (b) Hexagonal

Graphite is built of flat sheets of carbon atoms in hexagonal rings.

48.The example of metallic solid is (KMU MDCAT 2024)

  1. B
  2. C
  3. Cu
  4. Si
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Correct answer: (c) Cu

Copper is a metal; boron, carbon and silicon here form covalent solids.

49.When a crystalline substance conducts current in one direction but not through other directions of the crystal, this property is (KMU MDCAT 2024)

  1. Allotropy
  2. Anisotropy
  3. Isomorphism
  4. Polymorphism
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Correct answer: (b) Anisotropy

A property that differs with the direction taken through the crystal is anisotropy.

50.Which of the following compound have any characteristic heat of fusion except? (NUMS MDCAT 2024)

  1. NaCl
  2. Aluminium oxide
  3. Iron oxide
  4. Silicates
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Correct answer: (d) Silicates

Silicates are amorphous, so they soften over a range instead of melting at a fixed point.

51.In graphite the carbon atoms are arranged in which of the following structures? (MDCAT 2024)

  1. rhombic
  2. hexagonal
  3. tetragonal
  4. trigonal
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Correct answer: (b) hexagonal

Each layer of graphite is a sheet of hexagons of $sp^2$ carbon atoms.

52.Predict the shape of CsCl having radius ratio of 0.93: (NUMS MDCAT 2024)

  1. Tetrahedral
  2. Octahedral
  3. Body centered cubic
  4. Hexagonal
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Correct answer: (c) Body centered cubic

A radius ratio above $0.732$ gives eight-fold coordination, the caesium chloride body centred structure.

53.All of the following steps are used to calculate the lattice energy in the Born-Haber cycle EXCEPT: (MDCAT 2024)

  1. atomizing the metal
  2. ionizing the metal
  3. deionizing the metal
  4. ionizing the non-metal
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Correct answer: (c) deionizing the metal

The cycle atomizes and ionizes; there is no step that returns an ion to its atom.

54.All of the following steps are used to calculate the lattice energy in Born-Haber cycle EXCEPT (UHS MDCAT 2024)

  1. Atomizing the metal
  2. Ionizing the metal
  3. Delonlize the metal
  4. Ionlize non metal
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Correct answer: (c) Delonlize the metal

The Born-Haber cycle atomizes and ionizes the metal and adds electrons to the non-metal; nothing is de-ionized.

55.The heat of sublimation of potassium is 98kJ/mol, the heat of dissociation of bromine gas is 192.5 kJ/mol. The ionization energy of K is 414 kJ/mol. The electron affinity of Br is -334.7 kJ/mol and the heat of formation of KBr is -405.8 kJ/mol. Calculate the lattice energy of KBr. (KMU MDCAT 2024)

  1. -679.3
  2. -669.5
  3. 679.3
  4. 669.5
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Correct answer: (a) -679.3

The cycle gives $-405.8-(98+96.25+414-334.7)$, that is $-679.3\,\mathrm{kJ\,mol^{-1}}$.

Chemical Equilibrium

56.Forward reaction is the one that (KMU MDCAT 2024)

  1. Is very slow at the beginning of the reaction
  2. Reacts to form reactants
  3. Speeds up gradually and at equilibrium its rate becomes constant
  4. Takes place from left to right as given in chemical equation
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Correct answer: (d) Takes place from left to right as given in chemical equation

The forward reaction is the one written from left to right in the equation.

57.The unit of Kc for the system PCl5 ⇌ PCl3 + Cl2 is (KMU MDCAT 2024)

  1. dm³/mol
  2. mol/ dm³
  3. mol/ dm⁶
  4. mol²/dm⁶
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Correct answer: (b) mol/ dm³

One concentration term is left over in the numerator, so the unit is moles per cubic decimetre.

58.The principle which states that if a stress is applied to a system at equilibrium the system nullifies the effect of the stress as far as possible is: (MDCAT 2024)

  1. Haber's
  2. Le Chatelier's
  3. Boyle's
  4. Charles'
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Correct answer: (b) Le Chatelier's

That is Le Chatelier's principle.

59.Consider the following reaction in equilibrium and tell which chemical, when added, will change the cloudy solution into a clear solution: $\mathrm{BiCl_3+H_2O\rightleftharpoons BiOCl+2HCl}$ (MDCAT 2024)

  1. $\mathrm{BiCl_3}$
  2. $\mathrm{H_2O}$
  3. $\mathrm{BiOCl}$
  4. $\mathrm{HCl}$
Show answer

Correct answer: (d) $\mathrm{HCl}$

Added HCl drives the equilibrium back to the left, so the insoluble BiOCl that clouded the solution dissolves.

60.The principle that states that if a stress is applied to a system at equilibrium the system nullify the effect of stress as far as possible is: (UHS MDCAT 2024)

  1. Haber's
  2. Le-Chatelier
  3. Boyle's
  4. Charles'
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Correct answer: (b) Le-Chatelier

That is Le Chatelier’s principle.

61.Consider the following reaction in equilibrium and tell addition of which chemical will turn the cloudy solution into clear solution? BiCl3 + H2O <-> BiOCl + 2HCl (UHS MDCAT 2024)

  1. BiCl3
  2. H2O
  3. BiOCl
  4. HCl
Show answer

Correct answer: (d) HCl

Adding hydrochloric acid drives the equilibrium back and dissolves the white bismuth oxychloride.

62.In the production of SO3 from SO2 and Oxygen, the yield of SO3 is increased by (KMU MDCAT 2024)

  1. Adding a catalyst
  2. Adding more SO2
  3. Increasing temperature
  4. Removing oxygen
Show answer

Correct answer: (b) Adding more SO2

Adding more of a reactant drives the equilibrium towards the product.

63.The solubility of PbS at 25°C is 4.0 × 10−28. Then ionic concentration will be: (NUMS MDCAT 2024)

  1. 4x10−14
  2. 2x10−14
  3. 1x10−14
  4. 3.0x10−10
Show answer

Correct answer: (b) 2x10−14

For a one to one salt $K_{sp}=s^2$, so $s=\sqrt{4.0\times10^{-28}}$, that is $2\times10^{-14}$.

64.Select the buffer solution having highest pH: (NUMS MDCAT 2024)

  1. 0.1M CH3COOH, 0.01M CH3COO-
  2. 0.1M CH3COOH, 0.05M CH3COO-
  3. 0.1M CH3COOH, 0.10M CH3COO-
  4. 0.1M CH3COOH, 0.15M CH3COO-
Show answer

Correct answer: (d) 0.1M CH3COOH, 0.15M CH3COO-

The pH rises with the ratio of salt to acid, which is largest in the last mixture.

65.Identify the CORRECT conditions required for the maximum yield of ammonia by Haber's process: (MDCAT 2024)

  1. high pressure, low temperature and continual removal of ammonia
  2. low pressure, low temperature and continual removal of ammonia
  3. high pressure, high temperature and continual removal of ammonia
  4. high pressure, low temperature and continual addition of ammonia
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Correct answer: (a) high pressure, low temperature and continual removal of ammonia

The forward reaction is exothermic and goes with a fall in the number of moles, so pressure helps, heat hurts, and taking the ammonia out keeps pulling it forward.

66.Identify the CORRECT option required for the maximum yield of ammonia by Haber's process: (UHS MDCAT 2024)

  1. High pressure low temperature continual removal of ammonia
  2. Low pressure low temperature continual removal of ammonia
  3. High pressure high temperature continual removal of ammonia
  4. High pressure low temperature continual addition of ammonia
Show answer

Correct answer: (a) High pressure low temperature continual removal of ammonia

The forward reaction is exothermic and contracts in volume, and taking the ammonia away keeps pulling it forward.

67.Consider N2 + 3H2(g) ⇌ 2NH3(g) ΔH= -92.46kJ/mol The optimum temperature (°C), to produce ammonia is (KMU MDCAT 2024)

  1. 450
  2. 500
  3. 5000
  4. Constant temperature
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Correct answer: (a) 450

About $450^{\circ}\mathrm{C}$ is the compromise between a good yield and a workable rate.

68.What conditions should be applied to minimize the leftover reactants in Ammonia synthesis? (NUMS MDCAT 2024)

  1. 200atm, 500°C
  2. 400atm, 200°C
  3. 100atm, 400°C
  4. 200atm, 400°C
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Correct answer: (d) 200atm, 400°C

High pressure drives the contraction forward, and $400^{\circ}\mathrm{C}$ is warm enough to reach equilibrium quickly.

Reaction Kinetics

69.Identify the correct formula to calculate the rate of a reaction: (MDCAT 2024)

  1. change in concentration of substance $\div$ time taken for the change
  2. time taken for the change $\div$ change in concentration of substance
  3. time taken for the change $\div$ change in concentration $\times100$
  4. time taken for the change $\times$ change in concentration
Show answer

Correct answer: (a) change in concentration of substance $\div$ time taken for the change

Rate is the change in concentration per unit time.

70.Identify the correct formula to calculate rate of reaction: (UHS MDCAT 2024)

  1. Change in concentration of substance ÷ Time taken for the change
  2. Time taken for the change ÷ Change in concentration of substance
  3. Time taken for the change ÷ Change in concentration of substance x 100
  4. Time taken for the change x Change in concentration of substance
Show answer

Correct answer: (a) Change in concentration of substance ÷ Time taken for the change

Rate is the change in concentration divided by the time it took.

71.Formation of hydrogen gas can be increased by reacting which Zn sample with 1M HCl? (NUMS MDCAT 2024)

  1. 1g Zn Rod
  2. 1g Zn Pellets
  3. 1g Zn Ribbon
  4. 1g Zn Powder
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Correct answer: (d) 1g Zn Powder

The powder offers by far the greatest surface for the acid to attack.

72.Consider the hypothetical equation $aA+bB\to cC+dD$. Which of the following represents the correct rate equation? (MDCAT 2024)

  1. Rate $=k[A][B]$
  2. Rate $=k[A]^a[B]^b$
  3. Rate $=k[A]^a$
  4. Rate $=k[B]^b$
Show answer

Correct answer: (b) Rate $=k[A]^a[B]^b$

For an elementary step the order in each reactant is its coefficient, so the rate law carries both concentrations raised to those powers.

73.If a reaction rate does not change with concentration, then it is: (MDCAT 2024)

  1. third order
  2. second order
  3. first order
  4. zero order
Show answer

Correct answer: (d) zero order

A rate independent of concentration is $\text{rate}=k[A]^0$, which is zero order.

74.A reaction is first order with respect to A and second order with respect to B, the rate equation is (KMU MDCAT 2024)

  1. Rate = k [A]
  2. Rate = k [A][B]
  3. Rate = k [A]²[B]
  4. Rate = k [A][B]²
Show answer

Correct answer: (d) Rate = k [A][B]²

Each concentration is raised to the power of its own order.

75.6CO2 + 6H2O → sunlight → C6H12O6 + 6O2. Predict the order of reaction: (NUMS MDCAT 2024)

  1. 2nd
  2. 1st
  3. Zero
  4. 3rd
Show answer

Correct answer: (c) Zero

A photochemical reaction goes at a rate set by the light, not by the concentrations, so it is zero order.

76.Which mechanism is consistent with rate law Rate = K[NO]2[H2]? (NUMS MDCAT 2024)

  1. 2NO + H2 → N2 + H2O2 (slow), H2O2 + H2 → 2H2O (fast)
  2. NO + H2O → N2 + H2O2 (slow), H2O2 + H2 → 2H2O (fast)
  3. 2NO + 2H2 → N2O + H2 (slow), H2O + H2 → H2O2 (fast)
  4. NO + NO → N2 + O2 (slow), O2 + H2 → H2O (fast)
Show answer

Correct answer: (a) 2NO + H2 → N2 + H2O2 (slow), H2O2 + H2 → 2H2O (fast)

The rate law follows the slow step, and only the first scheme has two molecules of nitric oxide and one of hydrogen in it.

77.Which of the following is the CORRECT Arrhenius equation? (MDCAT 2024)

  1. $k=Ae^{-E_a/QT}$
  2. $k=Ae^{-E_a/RT}$
  3. $k=Ae^{-E_a/ST}$
  4. $k=Ae^{-E_a/uT}$
Show answer

Correct answer: (b) $k=Ae^{-E_a/RT}$

$k=Ae^{-E_a/RT}$, with $R$ the gas constant and $E_a$ the activation energy.

78.For a first order reaction A → B, the rate constant is 0.0458 s⁻¹. Calculate rate of the reaction if the concentration of reactant is 0.35mol dm⁻³. (KMU MDCAT 2024)

  1. 0.012 mol dm⁻³ s⁻¹
  2. 0.014 mol dm⁻³ s⁻¹
  3. 0.016 mol dm⁻³ s⁻¹
  4. 0.018 mol dm⁻³ s⁻¹
Show answer

Correct answer: (c) 0.016 mol dm⁻³ s⁻¹

Rate is $k[A]=0.0458\times0.35$, which is $0.016\,\mathrm{mol\,dm^{-3}\,s^{-1}}$.

Thermochemistry and Energetics of Chemical Reactions

79.In an exothermic reaction, the heat content of the: (MDCAT 2024)

  1. reactants and products is equal
  2. reactants is more than that of the products
  3. products is more than that of the reactants
  4. reactants and products does not change
Show answer

Correct answer: (b) reactants is more than that of the products

Heat is given out, so the products hold less energy than the reactants and $\Delta H$ is negative.

80.In endothermic reaction, the heat content of the (UHS MDCAT 2024)

  1. Reactants and products is equal
  2. Reactants is more than that of products
  3. Products is more than that of reactants
  4. Reactants & Products will not change
Show answer

Correct answer: (c) Products is more than that of reactants

An endothermic reaction takes heat in, so the products hold more energy than the reactants.

81.ΔH can be measured indirectly by applying (KMU MDCAT 2024)

  1. Avogadro's law
  2. Faraday's law
  3. Gas's law
  4. Hess's law
Show answer

Correct answer: (d) Hess's law

Hess’s law lets an enthalpy change be got from any convenient route between the same two states.

82.DeltaH° for sublimation of one mole of iodine: H2(g) + I2(g) → 2HI(g) DH = 51.8kJ/mol H2(g) + I2(s) → 2HI(g) DH = -10.5kJ/mol (NUMS MDCAT 2024)

  1. 41.3 kJ/mol
  2. 62.3 kJ/mol
  3. 53.5 kJ/mol
  4. 36.5 kJ/mol
Show answer

Correct answer: (b) 62.3 kJ/mol

Subtracting the second equation from the first leaves the sublimation, $51.8-(-10.5)$, that is $62.3\,\mathrm{kJ\,mol^{-1}}$.

83.The enthalpy change when one mole of water is formed by the reaction of an acid with an alkali under standard conditions is known as the: (MDCAT 2024)

  1. enthalpy of formation
  2. enthalpy of reaction
  3. enthalpy of combustion
  4. enthalpy of neutralization
Show answer

Correct answer: (d) enthalpy of neutralization

Acid plus alkali making one mole of water is the enthalpy of neutralization.

84.The enthalpy change when1 Mole of water is formed by the reaction of acid with an alkali under standard conditions is known as: (UHS MDCAT 2024)

  1. Enthalpy of formation
  2. Enthalpy of reaction
  3. Enthalpy of combustion
  4. Enthalpy of neutralization
Show answer

Correct answer: (d) Enthalpy of neutralization

That is the enthalpy of neutralization.

85.One slice of bread with a tablespoon of peanut butter on it contains 20g carbohydrate, 10g protein, and 9g fat. Calculate total energy consumed in this intake. (KMU MDCAT 2024)

  1. 158kcal
  2. 173kcal
  3. 201kcal
  4. 218kcal
Show answer

Correct answer: (c) 201kcal

Carbohydrate and protein give $4\,\mathrm{kcal}$ a gram and fat $9$, so $80+40+81$ is $201\,\mathrm{kcal}$.

86.Identify standard enthalpy of formation for the following reaction: (NUMS MDCAT 2024)

  1. H2(g) + 1/2 O2(g) → H2O(l)
  2. CO(g) + 1/2 O2(g) → CO2(g)
  3. 2Al(s) + Fe2O3(s) → Al2O3(s) + 2Fe(s)
  4. S(s) + 3/2 O2(g) → SO3(g)
Show answer

Correct answer: (a) H2(g) + 1/2 O2(g) → H2O(l)

Only the first makes one mole of a compound from its elements in their standard states.

87.When 1 mole of ice melts at 0°C and constant pressure of 1 atmosphere, 6025 J of heat is absorbed by the system. The molar volume of ice and water are 0.020 and 0.018 dm³, respectively. Calculate ΔE. (1dm³.atm=101.33J) (KMU MDCAT 2024)

  1. 6010.20J
  2. 6015.20J
  3. 6020.20J
  4. 6025.20J
Show answer

Correct answer: (d) 6025.20J

The volume falls slightly on melting, so the surroundings do a little work and $\Delta E$ is a shade above the heat absorbed.

88.Calculate the work done when 1 mole of an ideal gas expands from 15 dm³ to 20 dm³ against a constant external pressure of 2 atmospheres. (KMU MDCAT 2024)

  1. -10 atm.dm³
  2. -5 atm.dm³
  3. 5 atm.dm³
  4. 10 atm.dm³
Show answer

Correct answer: (a) -10 atm.dm³

$w=-P\Delta V=-2\times5$, which is $-10\,\mathrm{atm\,dm^3}$; the sign says the gas did the work.

89.Expansion takes place when gas evolves during reaction between carbohydrates and dilute HCl. Predict energy change and work done: (NUMS MDCAT 2024)

  1. w is positive, q is negative
  2. w is negative, q is positive
  3. q is positive, no work done
  4. w is positive, q is positive
Show answer

Correct answer: (b) w is negative, q is positive

The gas pushes back the surroundings, so the system does work and the sign of $w$ is negative while heat is absorbed.

Electrochemistry

90.Placing a rod of iron metal in a solution of CuSO4: (NUMS MDCAT 2024)

  1. Cu will be deposited
  2. Fe is precipitated out
  3. Cu and Fe both dissolve
  4. No reaction taken place
Show answer

Correct answer: (a) Cu will be deposited

Iron is above copper in the reactivity series, so it displaces copper from the solution.

91.The oxidation number of Mn in $\mathrm{KMnO_4}$ is: (MDCAT 2024)

  1. $+2$
  2. $+1$
  3. $-7$
  4. $+7$
Show answer

Correct answer: (d) $+7$

$+1$ for K and $-2$ for each of four oxygens leaves $+7$ for manganese.

92.Oxidation number of 'Mn' in KMnO4 is (UHS MDCAT 2024)

  1. 0
  2. +1
  3. -7
  4. +7
Show answer

Correct answer: (d) +7

Potassium is $+1$ and the four oxygens are $-8$, so manganese must be $+7$.

93.Which of the following is NOT a correct feature of electrolytic cells? (UHS MDCAT 2024)

  1. Reduction occurs at cathode
  2. Oxidation occurs at anode
  3. Alternating current source is connected to electrodes
  4. Electrochemical reaction takes place
Show answer

Correct answer: (c) Alternating current source is connected to electrodes

An electrolytic cell is driven by direct current; alternating current would reverse the electrodes every half cycle.

94.Which step is irrelevant with respect to balancing redox equations by the oxidation number method? (MDCAT 2024)

  1. split the reaction into two half reactions
  2. assign oxidation numbers to all the atoms involved in the equation
  3. identify the element undergoing a change in oxidation number
  4. equalize the number of electrons lost and gained
Show answer

Correct answer: (a) split the reaction into two half reactions

Splitting into half reactions belongs to the ion-electron method, not to the oxidation number method.

95.Which step is irrelevant with respect to balancing of redox equations by oxidation number method? (UHS MDCAT 2024)

  1. Split the reaction into two half reactions
  2. Assign oxidation number to all the atoms involved in the equation
  3. Identify the element undergoing a change in oxidation number
  4. Equalize the number of electrons lost and gained
Show answer

Correct answer: (a) Split the reaction into two half reactions

Splitting into half reactions belongs to the ion electron method, not to the oxidation number method.

96.Which one of the following is a strong electrolyte in solution? (KMU MDCAT 2024)

  1. Acetic acid
  2. Ammonium hydroxide
  3. Carbonic acid
  4. Potassium iodide
Show answer

Correct answer: (d) Potassium iodide

Potassium iodide is an ionic salt fully dissociated in water; the other three are weak acids or a weak base.

97.The electrode potential of the standard hydrogen electrode is chosen as (KMU MDCAT 2024)

  1. -1 V
  2. 0 V
  3. 1 V
  4. 2 V
Show answer

Correct answer: (b) 0 V

The standard hydrogen electrode is the zero against which every other electrode potential is measured.

98.Zn rod acts as cathode when coupled with magnesium electrode because reduction potential of: (NUMS MDCAT 2024)

  1. Zn > Mg
  2. Zn < Mg
  3. Zn = Mg
  4. Zn = 0
Show answer

Correct answer: (a) Zn > Mg

The electrode with the higher reduction potential is reduced, and that is the cathode.

Chemical Bonding

99.Which of the following is NOT a feature of the Valence Shell Electron Pair Repulsion theory? (MDCAT 2024)

  1. it determines the shape of a molecule
  2. pairs of electrons repel each other
  3. it helps in understanding the interaction of medicinal drug molecules
  4. only lone pairs participate in determining the geometry of molecules
Show answer

Correct answer: (d) only lone pairs participate in determining the geometry of molecules

Bond pairs count as well as lone pairs; it is the whole set of electron pairs that fixes the shape.

100.Which of the following is NOT a feature of Valence Shell Electron Pair Repulsion theory? (UHS MDCAT 2024)

  1. It determines the shape of molecule
  2. Pairs of electrons repel each other
  3. It helps in understanding interaction of medicinal drug molecules
  4. Only lone pairs participate in determining geometry of molecules
Show answer

Correct answer: (d) Only lone pairs participate in determining geometry of molecules

VSEPR counts lone pairs and bond pairs alike; the lone pairs merely repel more strongly.

101.Total number of electron pairs present in the valence shell of central atom in water are (KMU MDCAT 2024)

  1. 2
  2. 3
  3. 4
  4. 5
Show answer

Correct answer: (c) 4

Oxygen in water has two bond pairs and two lone pairs, four pairs in all.

102.The unhybridized p orbital in sp2 hybridization is (KMU MDCAT 2024)

  1. In the same plane
  2. Out of the plane
  3. Parallel to sp2 orbitals
  4. Perpendicular to sp2 orbitals
Show answer

Correct answer: (d) Perpendicular to sp2 orbitals

The three sp2 orbitals lie in a plane and the leftover p orbital stands at right angles to it.

103.Which of the following has a coordinate bond? (UHS MDCAT 2024)

  1. NaCl
  2. CaO
  3. NH3BF3
  4. H2O
Show answer

Correct answer: (c) NH3BF3

Nitrogen gives both electrons of the bond to the empty orbital of boron.

104.Predict the highest bond energy of the following single bond: (NUMS MDCAT 2024)

  1. C-H
  2. C-N
  3. C-O
  4. C-C
Show answer

Correct answer: (a) C-H

The bond to the small hydrogen atom is the shortest and strongest of the four.

105.Identify the following compound having shortest bond length: (NUMS MDCAT 2024)

  1. Methyl amine
  2. Formamide
  3. Formic acid
  4. Ethanol
Show answer

Correct answer: (c) Formic acid

The carbon oxygen double bond of the carboxyl group is the shortest bond among these.

106.Which one of the following molecules has a zero-dipole moment? (KMU MDCAT 2024)

  1. BF3
  2. NF3
  3. NH3
  4. H2O
Show answer

Correct answer: (a) BF3

Boron trifluoride is trigonal planar, so its three bond dipoles cancel exactly.

s- and p-Block Elements

107.Which of the following has the smallest atomic radius? (MDCAT 2024)

  1. Mg
  2. S
  3. P
  4. Na
Show answer

Correct answer: (b) S

Across a period the nuclear charge rises and the radius falls, and sulphur is the furthest right of the four.

108.Which of the following is not basic in nature? (MDCAT 2024)

  1. aluminium oxide
  2. potassium oxide
  3. magnesium oxide
  4. sodium oxide
Show answer

Correct answer: (a) aluminium oxide

Aluminium oxide is amphoteric, reacting with acids and with alkalis alike.

109.Which of the following has smallest atomic radius (UHS MDCAT 2024)

  1. Mg
  2. S
  3. P
  4. Na
Show answer

Correct answer: (b) S

Atomic radius shrinks across a period, and sulphur lies furthest right of the four.

110.The difference of lithium from the other alkall metals is mainly because of: (UHS MDCAT 2024)

  1. Large radius and low charge density
  2. Small radius and low charge density
  3. Large radius and high charge density
  4. Small radius and high charge density
Show answer

Correct answer: (d) Small radius and high charge density

The lithium ion is very small and its charge is concentrated, so it polarizes and behaves unlike its group.

111.Which of the following is not Basic in nature (UHS MDCAT 2024)

  1. Aluminum oxide
  2. Magnesium oxide
  3. Potassium oxide
  4. Sodium oxide
Show answer

Correct answer: (a) Aluminum oxide

Aluminium oxide is amphoteric; the other three are the basic oxides of group I and II metals.

112.Third period element that initially reacts rapidly with oxygen to form a protective oxide coating that prevents further reactions is (KMU MDCAT 2024)

  1. Al
  2. Ar
  3. Na
  4. Si
Show answer

Correct answer: (a) Al

Aluminium takes an oxide film at once, and the film then seals the metal beneath it.

113.In CH3Cl, bond length of C-Cl is 176.7pm and covalent radius of Cl is 99.4pm. Covalent radius of carbon is: (NUMS MDCAT 2024)

  1. 66.3 pm
  2. 276.1 pm
  3. 175.4 pm
  4. 77.3 pm
Show answer

Correct answer: (d) 77.3 pm

The bond length is the sum of the two radii, so $176.7-99.4$ leaves $77.3\,\mathrm{pm}$.

114.Correct order of decreasing electron affinities of group VII is: (NUMS MDCAT 2024)

  1. F > Cl > Br > I
  2. Cl > F > Br > I
  3. F < Cl < Br < I
  4. Cl < F < Br < I
Show answer

Correct answer: (b) Cl > F > Br > I

Fluorine is so small that the incoming electron is crowded, so chlorine has the greater electron affinity.

115.The difference of lithium from the other alkali metals is mainly because of its: (MDCAT 2024)

  1. large radius and low charge density
  2. small radius and low charge density
  3. large radius and high charge density
  4. small radius and high charge density
Show answer

Correct answer: (d) small radius and high charge density

The small $\mathrm{Li^+}$ ion concentrates its charge, which is why lithium resembles magnesium more than it resembles sodium.

116.Which of the following alkali metal forms only normal oxide with O2? (KMU MDCAT 2024)

  1. K
  2. Li
  3. Na
  4. Rb
Show answer

Correct answer: (b) Li

Lithium alone gives the simple oxide; sodium gives a peroxide and the rest give superoxides.

117.The solubility of the sulphates of the alkaline earth metals generally: (MDCAT 2024)

  1. increases down the group
  2. decreases down the group
  3. increases then decreases down the group
  4. does not change down the group
Show answer

Correct answer: (b) decreases down the group

The lattice energy falls more slowly than the hydration energy down the group, so the sulphates become less soluble.

118.The solubility of sulphates of alkaline metals generally (UHS MDCAT 2024)

  1. Increase down the group
  2. Decrease down the group
  3. Increase then decrease down the group
  4. Doesn't change down the group
Show answer

Correct answer: (b) Decrease down the group

The lattice energy falls more slowly than the hydration energy down group II, so the sulphates get less soluble.

119.When a metal carbonate is heated at 100°C, which will readily decompose? (NUMS MDCAT 2024)

  1. BaCO3
  2. MgCO3
  3. BeCO3
  4. SrCO3
Show answer

Correct answer: (c) BeCO3

Thermal stability of the carbonates rises down the group, so the beryllium salt goes first.

Transition Elements

120.The electronic configuration of chromium (proton number 24) is: (MDCAT 2024)

  1. $[\mathrm{Ar}]3d^44s^2$
  2. $[\mathrm{Ar}]3d^54s^1$
  3. $[\mathrm{Ar}]3d^54s^2$
  4. $[\mathrm{Ar}]3d^64s^0$
Show answer

Correct answer: (b) $[\mathrm{Ar}]3d^54s^1$

A half-filled $3d$ set with one $4s$ electron is the more stable arrangement.

121.Which of the following is NOT a property of transition elements? (MDCAT 2024)

  1. high melting points
  2. good conductors of electricity
  3. hard metals
  4. their ions and compounds are colourless
Show answer

Correct answer: (d) their ions and compounds are colourless

Transition metal ions are typically coloured, because of $d$-$d$ electron transitions.

122.Which of the following is NOT an Alloy (UHS MDCAT 2024)

  1. Steel
  2. Brass
  3. Bronze
  4. Graphite
Show answer

Correct answer: (d) Graphite

Graphite is an element, not a mixture of metals.

123.Electronic configuration of chromium (Proton number 24) is: (UHS MDCAT 2024)

  1. [Ar] 3d4 4s2
  2. [Ar] 3d5 4s2
  3. [Ar] 3d5 4s1
  4. [Ar] 3d6 4s2
Show answer

Correct answer: (c) [Ar] 3d5 4s1

A half filled d subshell is stable, so chromium is $[\mathrm{Ar}]3d^5 4s^1$.

124.Cu2+ salt solution is blue in colour due to transition of electrons from (KMU MDCAT 2024)

  1. d to d orbital
  2. p to d orbital
  3. p to p orbital
  4. s to p orbital
Show answer

Correct answer: (a) d to d orbital

The d subshell is split by the ligands, and an electron moving between the split levels absorbs visible light.

125.Potassium ferrocyanide is which type of salt? (KMU MDCAT 2024)

  1. Complex
  2. Double
  3. Mixed
  4. Normal
Show answer

Correct answer: (a) Complex

It gives no simple iron ions in solution, because the iron is held in the complex ferrocyanide ion.

Fundamental Principles of Organic Chemistry

126.Homocyclic organic compounds are subdivided into two types, namely: (MDCAT 2024)

  1. alicyclic and aromatic
  2. alkenes and alkynes
  3. aromatic and non-aromatic
  4. saturated and unsaturated
Show answer

Correct answer: (a) alicyclic and aromatic

Rings of carbon only are either alicyclic, like cyclohexane, or aromatic, like benzene.

127.Pyridine belongs to which class of organic compounds? (KMU MDCAT 2024)

  1. Alicyclic
  2. Heterocyclic
  3. Homocyclic
  4. Hydrocarbon
Show answer

Correct answer: (b) Heterocyclic

Pyridine has a nitrogen atom in its ring, so it is heterocyclic.

128.Which of the following elements cannot be detected directly in a given organic compound? (KMU MDCAT 2024)

  1. Chlorine
  2. Nitrogen
  3. Oxygen
  4. Phosphorous
Show answer

Correct answer: (c) Oxygen

Oxygen has no test of its own; its presence is worked out from the difference in the analysis.

129.CnH2nO is the general formula of: (UHS MDCAT 2024)

  1. Ether
  2. Carboxylic acid
  3. Ketones
  4. Carbolic acid
Show answer

Correct answer: (c) Ketones

A ketone of formula $\mathrm{C_nH_{2n}O}$ carries one carbonyl group inside the chain.

130.Name of ketone functional group is (KMU MDCAT 2024)

  1. Amino
  2. Carbonyl
  3. Carboxyl
  4. Formyl
Show answer

Correct answer: (b) Carbonyl

The group in a ketone is the carbonyl group.

131.1-Butene and 2-butene show which type of isomerism? (MDCAT 2024)

  1. functional group
  2. position
  3. metamerism
  4. chain
Show answer

Correct answer: (b) position

The chain and the functional group are the same in both; only the position of the double bond differs.

132.Which type of isomerism is displayed by compounds having the same structural formula but a different position of atoms on the two sides of a carbon-carbon double bond? (MDCAT 2024)

  1. chain
  2. metamerism
  3. geometric
  4. tautomerism
Show answer

Correct answer: (c) geometric

Restricted rotation about the double bond gives the cis and trans forms, which is geometric isomerism.

133.Which type of isomerism is displayed by compounds having same structural formula but different position of atoms on both sides of carbon bond? (UHS MDCAT 2024)

  1. Chain
  2. Metamerism
  3. Geometric
  4. Tautomerism
Show answer

Correct answer: (c) Geometric

Groups fixed on either side of a double bond give the cis and trans, or geometric, isomers.

134.Select the alkene showing geometrical isomerism: (NUMS MDCAT 2024)

  1. 3-methyl-1-butene
  2. Methyl cyclopentane
  3. 2,3-dimethyl-2-butene
  4. 3-methyl-2-pentene
Show answer

Correct answer: (d) 3-methyl-2-pentene

Each carbon of its double bond carries two different groups, which is what geometrical isomerism needs.

Chemistry of Hydrocarbons

135.The homolytic fission of C-H bond in an alkane result in (KMU MDCAT 2024)

  1. Alkyl free radical
  2. Carbanion
  3. Carbocation
  4. Methylpropane
Show answer

Correct answer: (a) Alkyl free radical

Homolysis gives each atom one electron of the pair, leaving an alkyl free radical.

136.The carbon atom carrying positive charge and attached to three other atoms or groups is called (KMU MDCAT 2024)

  1. Carbanion
  2. Carbene
  3. Carbocation
  4. Oxonium
Show answer

Correct answer: (c) Carbocation

A positively charged carbon with three attachments is a carbocation.

137.Addition of HBr to isobutylene mainly gives (KMU MDCAT 2024)

  1. isobutyl bromide
  2. n-butyl bromide
  3. sec-butyl bromide
  4. tert-butyl bromide
Show answer

Correct answer: (d) tert-butyl bromide

By Markovnikov’s rule the bromine goes to the more substituted carbon, giving the tertiary halide.

138.Identify the alkene which gives only one type of aldehyde upon ozonolysis: (NUMS MDCAT 2024)

  1. 1-pentene
  2. 2-methyl propene
  3. 2-butene
  4. 2,3-dimethyl-2-butene
Show answer

Correct answer: (c) 2-butene

But-2-ene is symmetrical, so both halves give the same aldehyde, acetaldehyde.

139.In Friedel-Crafts acylation an acyl group is introduced into the benzene ring in the presence of the catalyst: (MDCAT 2024)

  1. $\mathrm{AlCl_3}$
  2. $\mathrm{H_2SO_4}$
  3. sunlight
  4. $\mathrm{V_2O_5}$
Show answer

Correct answer: (a) $\mathrm{AlCl_3}$

Anhydrous aluminium chloride is the Lewis acid that generates the acylium electrophile.

140.In Friedel Craft acylation an acyl group is introduced in benzene ring in the presence of catalyst: (UHS MDCAT 2024)

  1. AlCl3
  2. H2SO4
  3. Sunlight
  4. V2O5
Show answer

Correct answer: (a) AlCl3

Anhydrous aluminium chloride generates the acylium ion that attacks the ring.

141.Which of the following is an example of a substituent group which releases electrons to the benzene ring? (MDCAT 2024)

  1. $-\mathrm{CN}$
  2. $-\mathrm{NR_3^+}$
  3. $-\mathrm{NH_2}$
  4. $-\mathrm{NO_2}$
Show answer

Correct answer: (c) $-\mathrm{NH_2}$

The lone pair on nitrogen is donated into the ring, which is why $-\mathrm{NH_2}$ activates it.

142.Which of the following is an example of substituent group which release electrons to benzene ring : (UHS MDCAT 2024)

  1. -CN
  2. -NR3+
  3. -NH2
  4. -NO2
Show answer

Correct answer: (c) -NH2

The lone pair of the amino group is fed into the ring; nitro and cyano groups pull electrons out.

143.The most readily sulphonated compound is: (NUMS MDCAT 2024)

  1. Benzene
  2. Chlorobenzene
  3. Nitrobenzene
  4. Toluene
Show answer

Correct answer: (d) Toluene

The methyl group feeds electrons into the ring and so activates it towards the electrophile.

Alkyl Halides

144.Identify the correct ascending order of reactivity of alkyl halides: (MDCAT 2024)

  1. Cl, Br, I, F
  2. F, Cl, Br, I
  3. Br, I, F, Cl
  4. I, F, Cl, Br
Show answer

Correct answer: (b) F, Cl, Br, I

The weaker the carbon-halogen bond the better the leaving group, and that bond weakens from fluorine to iodine.

145.Identify the correct statement related to substitution and elimination of alkyl halides: (MDCAT 2024)

  1. strong bases cause substitution in preference to elimination
  2. the role of leaving groups in elimination is similar to that in substitution
  3. substitution is favoured more than elimination by decreasing solvent polarity
  4. a decrease in temperature will favour elimination more than substitution
Show answer

Correct answer: (b) the role of leaving groups in elimination is similar to that in substitution

Both reactions need the halide to leave, so a better leaving group speeds up either one; strong bases and higher temperatures favour elimination.

146.Alkyl halides involving C-X bond breakage and C-Nu bond formation simultaneously would follow which one of the following mechanisms? (MDCAT 2024)

  1. $\mathrm{S_N1}$
  2. $\mathrm{S_N2}$
  3. E1
  4. E2
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Correct answer: (b) $\mathrm{S_N2}$

In $\mathrm{S_N2}$ the nucleophile attacks as the halide leaves, in one step through a single transition state.

147.Dehydrohalogenation of alkylhalide is carried out in presence of (KMU MDCAT 2024)

  1. Alcoholic KOH
  2. Aqueous KOH
  3. Conc. H2SO4
  4. Zn dust
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Correct answer: (a) Alcoholic KOH

Alcoholic potash favours elimination; aqueous potash would substitute and give the alcohol.

Alcohols and Phenols

148.Which of the following alcohols can give the iodoform reaction? (MDCAT 2024)

  1. methanol
  2. 1-butanol
  3. 1-propanol
  4. ethanol
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Correct answer: (d) ethanol

The test needs a $\mathrm{CH_3CH(OH)}-$ group, and of these only ethanol has one.

149.Which of the following alcohol can give Iodoform reaction? (UHS MDCAT 2024)

  1. Methanol
  2. 1-Butanol
  3. 1-Propanol
  4. Ethanol
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Correct answer: (d) Ethanol

Only an alcohol with a $\mathrm{CH_3CH(OH)}$ group gives iodoform, and ethanol is the one here.

150.Which of the following has the highest boiling point? (KMU MDCAT 2024)

  1. ethyl alcohol
  2. isopropyl alcohol
  3. n-propyl alcohol
  4. tert-butyl alcohol
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Correct answer: (c) n-propyl alcohol

The straight chain has the largest surface for its dispersion forces, so n-propyl alcohol boils highest.

151.The reaction of an alcohol with sodium produces (KMU MDCAT 2024)

  1. Aldehyde
  2. Alkoxide
  3. Ethane
  4. Ethene
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Correct answer: (b) Alkoxide

Sodium displaces the hydrogen of the hydroxyl group and leaves the sodium alkoxide.

152.Oxidation of secondary alcohol gives (KMU MDCAT 2024)

  1. Carboxylic acid
  2. Ether
  3. Ketone
  4. Phenol
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Correct answer: (c) Ketone

A secondary alcohol has one hydrogen on the carbinol carbon, so oxidation stops at the ketone.

153.The increasing order of reactivity of alcohols towards nucleophile is: (NUMS MDCAT 2024)

  1. 2-methyl-2-pentanol < 3-methyl-2-pentanol < 2-methyl-1-pentanol
  2. 2-methyl-1-pentanol > 3-methyl-2-pentanol > 2-methyl-2-pentanol
  3. 2-methyl-2-pentanol > 3-methyl-2-pentanol > 2-methyl-1-pentanol
  4. 2-methyl-2-pentanol < 2-methyl-1-pentanol < 3-methyl-2-pentanol
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Correct answer: (a) 2-methyl-2-pentanol < 3-methyl-2-pentanol < 2-methyl-1-pentanol

Attack by a nucleophile is easiest where the carbon is least crowded, that is at the primary alcohol.

154.The most reactive alcohol towards Lucas reagent is: (NUMS MDCAT 2024)

  1. 2-butanol
  2. 2-methyl-1-butanol
  3. 2-methyl-2-butanol
  4. 2,2-dimethyl-1-butanol
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Correct answer: (c) 2-methyl-2-butanol

Lucas reagent works fastest on a tertiary alcohol, and only the third is tertiary.

155.Which of the following is correct regarding phenol? (MDCAT 2024)

  1. phenol and water are equally acidic
  2. phenol is less acidic than carboxylic acid
  3. phenol is less acidic than water
  4. phenol is less acidic than ethanol
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Correct answer: (b) phenol is less acidic than carboxylic acid

Phenol is more acidic than water and ethanol because its anion is stabilized by the ring, but weaker than a carboxylic acid.

Aldehydes and Ketones

156.$\mathrm{C_nH_{2n}O}$ is the general formula of: (MDCAT 2024)

  1. ethers
  2. carboxylic acids
  3. ketones
  4. carbolic acid
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Correct answer: (c) ketones

Aldehydes and ketones share this formula; of the options only the ketones fit.

157.The blue colour of Fehling's solution is changed to red when warmed with an aldehyde due to the formation of: (MDCAT 2024)

  1. $\mathrm{NO_2}$
  2. $\mathrm{Cu_2O}$
  3. $\mathrm{Ag_2O}$
  4. $\mathrm{SO_2}$
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Correct answer: (b) $\mathrm{Cu_2O}$

The aldehyde reduces copper(II) to a red precipitate of copper(I) oxide.

158.The reaction of HCN with formaldehyde is a: (MDCAT 2024)

  1. nucleophilic addition reaction
  2. nucleophilic substitution reaction
  3. electrophilic addition reaction
  4. electrophilic substitution reaction
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Correct answer: (a) nucleophilic addition reaction

The cyanide ion adds to the carbon of the polar carbonyl group, giving a cyanohydrin.

159.The blue color of Fehling solution is changed to red when warmed with an aldehyde due to formation of which of the following? (UHS MDCAT 2024)

  1. NO2
  2. Cu2O
  3. AgO
  4. SO2
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Correct answer: (b) Cu2O

The aldehyde reduces the copper(II) of Fehling’s solution to a red precipitate of copper(I) oxide.

160.Reaction of HCN with formaldehyde is a: (UHS MDCAT 2024)

  1. Nucleophilic addition reaction
  2. Nucleophilic substitution reaction
  3. Electrophilic addition reaction
  4. Electrophilic substitution reaction
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Correct answer: (a) Nucleophilic addition reaction

The cyanide ion attacks the electron poor carbonyl carbon, so the step is nucleophilic addition.

161.Compound A + I2 + Na2CO3 → Compound B + RCOONa + NaI + H2O. Identify compound B: (NUMS MDCAT 2024)

  1. Acetone
  2. Acetic acid
  3. Acetamide
  4. Acetic anhydride
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Correct answer: (a) Acetone

A methyl ketone gives iodoform with iodine and alkali, and the ketone here is acetone.

162.Which aldehyde is more reactive towards nucleophilic addition? (KMU MDCAT 2024)

  1. Acetaldehyde
  2. Butyraldehyde
  3. Formaldehyde
  4. Propionaldehyde
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Correct answer: (c) Formaldehyde

Formaldehyde has no alkyl group feeding electrons to the carbonyl carbon, so it is the most open to attack.

Carboxylic Acids

163.The common name of 2-hydroxypropanoic acid is: (MDCAT 2024)

  1. tartaric acid
  2. lactic acid
  3. phthalic acid
  4. formic acid
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Correct answer: (b) lactic acid

That is lactic acid, the acid of sour milk and of tired muscle.

164.Common name of 2-hydroxy propanoic acid is: (UHS MDCAT 2024)

  1. Tartaric acid
  2. Lactic acid
  3. Phthalic acid
  4. Formic acid
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Correct answer: (b) Lactic acid

2-hydroxypropanoic acid is lactic acid, the acid of sour milk.

165.Acetic acid can be prepared by the hydrolysis of (KMU MDCAT 2024)

  1. Ethanal
  2. Ethanol
  3. Methanoic acid
  4. Methyl cyanide
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Correct answer: (d) Methyl cyanide

Hydrolysis of methyl cyanide gives acetic acid and ammonia.

166.Select the carboxylic acid with highest melting point: (NUMS MDCAT 2024)

  1. Ethanoic acid
  2. Propanoic acid
  3. Butanoic acid
  4. Pentanoic acid
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Correct answer: (a) Ethanoic acid

Ethanoic acid packs into the tightest crystal of the four, so it melts highest.

167.Compound X + Na2CO3 → Compound Y + CO2 + H2O. The compound X is: (NUMS MDCAT 2024)

  1. CH2=CH-CH2-CH3
  2. CH3CH2CHO
  3. CH3C(O)OCH3
  4. CH3CH2COOH
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Correct answer: (d) CH3CH2COOH

Only a carboxylic acid is strong enough to displace carbon dioxide from a carbonate.

168.When carboxylic acids are heated with an alcohol in the presence of sulphuric acid, one of the following is formed: (MDCAT 2024)

  1. amides
  2. acyl chlorides
  3. esters
  4. acid anhydrides
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Correct answer: (c) esters

That is esterification, with the sulphuric acid as catalyst and water as the other product.

169.When carboxylic acid are heated with alcohol in the presence of sulphuric acid one of the following is formed (UHS MDCAT 2024)

  1. Amides
  2. Acyl chloride
  3. Esters
  4. Acid Anhydride
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Correct answer: (c) Esters

An acid and an alcohol with a little sulphuric acid give an ester and water.

Macromolecules

170.Which one of the following is not an amino acid? (MDCAT 2024)

  1. lactic acid
  2. glutamic acid
  3. glycine
  4. lysine
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Correct answer: (a) lactic acid

Lactic acid carries a hydroxyl group where an amino acid carries an amino group.

171.Which one of the following is not an amino acid (UHS MDCAT 2024)

  1. Folic acid
  2. Glutamic acid
  3. Glycine
  4. Lysine
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Correct answer: (a) Folic acid

Folic acid is a vitamin; the other three are amino acids.

Industrial Chemistry

172.Bakelite is formed upon polymerization of: (NUMS MDCAT 2024)

  1. Phenol + HCHO dilute base
  2. Phenol + NaOH H2O
  3. Phenol + H2SO4 H2O
  4. Phenol + CH3-C(=O)-Cl H2SO4
Show answer

Correct answer: (a) Phenol + HCHO dilute base

Bakelite is the condensation polymer of phenol with formaldehyde.

Other MDCAT past papers