Download (Association of American Medical Colleges) (AAMC) organizes MCAT Medical College Admission For Medical Entrance Exam Chemical Paper V Model Paper with Answers
Question 1
The boiling point of benzene is 80OC. Estimate its molar heat of vaporization. Assume that it
obeys Trouton's rule.
a) 25.64 kJ mol-1
b) 31.064 kJ mol-1
c) 29.96 kJ mol-1
d) 39.54 kJ mol-1
e) 40.67 kJ mol-1
Correct Answer: b) 31.064 kJ mol-1
Explanation:
From the Trouton's law H/Tb = 88 J mol-1 K-1
The given data is Tb = 80OC = 80+273 = 353 K
Therefore, H = (88J mol-1 K-1) (353 K) = 31064 J mol-1 = 31.064 kJ mol-1
Question 2
The force of attraction between gaseous particles is
a) Strong
b) Weak
c) Very strong
d) Very weak
e) Negligible
Correct Answer: e) Negligible
Explanation:
Due to very high kinetic energy, gaseous particles easily escape from the attractions of other particles
and tend to maintain very long distances from each other. So, the attraction between gaseous
particles is negligible.
Question 3
The coordination number of hcp structure is
a) 6
b) 4
c) 8
d) 12
e) 2
Correct Answer: d) 12
Explanation:
Each sphere in hcp structure is in contact with 12 neighbouring spheres. Six spheres are on its own
layer, three on the above layer and remaining three on the below layer. So, the coordination number
of hcp structure is 12. For BCC structure it is 8. For ZnO it is 4.
Question 4
Diamond is an example for
a) Ionic crystals
b) Metallic crystals
c) Covalent crystals
d) Molecular crystals
e) None of these
Correct Answer: c) Covalent crystals
Explanation:
In diamond, atoms are linked together by continuous system of covalent bonds. In ionic crystals,
atoms are held together by ionic bonds. In metallic crystals, atoms are held together by metallic
bonds. In molecular crystals, molecules are held together by weak Van der Waals forces.
Question 5
Select the incorrect phrase(s) about the significance of salt bridge
I. Connects the solutions of two half-cell reactions.
II. It keeps the solution of two half-cells electrically charged.
III. Prevents liquid-liquid junction potential.
a) I & II
b) I & III
c) II & III
d) II only
e) III only
Correct Answer: d) II only.
Explanation:
It keeps the solution of two half-cells electrically neutral. In anodic half-cell, positive ions will
accumulate around the anode due to deposition of negative ions by oxidation. To neutralise these
positive ions, sufficient number of negative ions are provided by salt bridge. Similarly for cathodic half-
cell, it is vice-versa.
Question 6
Hess's law is related to ________ of the system.
a) Free energy change
b) Entropy change
c) Enthalpy change
d) Internal energy
e) None of these
Correct Answer: c) Enthalpy change
Explanation:
Hess's law states that the enthalpy or heat energy change accompanying a chemical reaction is
independent of the pathway between the initial and final states. H for a single reaction can be
calculated from the difference between the enthalpy (heat) of formation of the product and reactant.
H0reaction = H 0
0
f (products) ? Hf (reactant)
Question 7
7) Which one of the following molecules is held together by dative bond?
a) AlBr3
b) NaCl
c) Al2 Cl6
d) C2 H6
e) H2 O2
Correct Answer: c)Al2 Cl6
Explanation:
In Al2 Cl6 lone pairs of electron from chlorine are donated to electron deficient aluminium in such a
way that it is held together by dative bond, where aluminium acts as an electron acceptor and chlorine
acts as an electron donor.
AlBr3 is a neutral ionic molecule. NaCl- ionic bond, C2 H6 - covalent bond,H2 O2? Hydrogen bond.
Question 8
Arrange the following atoms and ions in the increasing order of atomic size
Mg, Mg2+, Al, Al3+
a) Al3+> Al > Mg2+> Mg
b) Mg2+ Mg > Al3+> Al
c) Mg > Mg2+ > Al > Al3+
d) Mg > Al > Mg2+> Al3+
e) Al3+> Mg2+ > Al > Mg
Correct Answer: d) Mg > Al > Mg2+> Al3+
Explanation:
Atomic radii decrease across the period. Cations are smaller than their parent atoms. Among these
isoelectronic ions, the one with larger positive nuclear charge will have the smaller radius. So, here
the largest atom is Mg and the smallest one is Al3+.
Question 9
Which of the following groups has ?I effect?
a) -CH3
b) -C2 H5
c) -C(CH3)3
d) ?C6 H5
e) Both a and c
Correct Answer: d) ?C6 H5
Explanation:
The polarisation of the bond is due to electron withdrawing or electron donating effect of adjacent
atoms or groups. Such a type of electron displacement along a carbon chain is called Inductive effect.
Eg: C ?>--- C ?>--- C ?>--- C6 H5 The electron withdrawing nature of groups or atoms is called
negative inductive effect. C6H5 is the only group, which has ?I effect. Since --C6 H5 is electron-
withdrawing group, it pulls up the electrons towards itself. Thereby it creates a partial positive charge
in adjacent carbon atoms and partial negative charge in phenyl group (C6 H5).
Question 10
An example for interpolation error is
a) Incorrect identification of indicator's color change in titration
b) Guessing the correct value between two calibrated marks on the metre scale
c) Zero setting of the needle in analog display
d) Calibration of measured instrument
e) None of these
Correct Answer: b) Guessing the correct value between two calibrated marks on the metre scale
Explanation:
Guessing the correct value between two calibrated marks on the metre scale is an example for
interpolation error. It is one of the two types of human or personal errors.
Incorrect identification of indicator's color change in titration ? Operative error. Zero setting of the
needle in analog display ? static error. Calibration of measured instrument - Instrument error.
Question 11
The one which is most commonly used as a detection of developed colorless chromatogram
spots in T.L.C plate is
a) Iodine
b) Phosphorus
c) Water
d) Copper salts
e) Ammonia
Correct Answer: a) Iodine
Explanation:
The spots of colorless compounds can be detected by placing the T.L.C plate in a closed jar
containing few crystals of iodine. Spots of compounds, which absorb iodine, will indicate as a brown
color.
Question 12
The Henderson-Hasselbalch equation for acid is
a) pH = pKa- log ([A-] / [HA])
b) pH = pKa + log ([HA] / [A-])
c) pH = pKb + log ([B] / [HB+])
d) pH = pKa+ log ([A-] / [HA])
e) pH = pKa+ 2log ([A-] / [HA])
Correct Answer: d) pH = pKa+ log ([A-] / [HA])
Explanation:
The Henderson-Hasselbalch equation explains whether a compound will exist in its acidic form or in
its basic form at a particular pH. [A-] = Molar concentration of a conjugate base. [HA] = Molar
concentration of an undissociated weak acid (M).
Question 13
An azeotropic mixture is also called
a) Increased boiling mixture
b) Decreased boiling mixture
c) Constant boiling mixture
d) Either a or b
e) None of these
Correct Answer: c) Constant boiling mixture
Explanation:
A pure chemical compound boils at a constant temperature and distils over completely at the same
temperature without any change in composition. It is also known as constant boiling mixture.
Question 14
A system is said to be in equilibrium at all the times. Such a process is called
a) Irreversible process
b) Equilibrium process
c) Static process
d) Quasi-static process
e) Reversible process
Correct Answer: d) Quasi-static process
Explanation:
A quasi-static process is the one in which the system may be considered to be in equilibrium at all
times.
Question 15
Which one of the following is an intensive property?
a) Volume
b) Density
c) Mass
d) Energy
e) None of these.
Correct Answer: b) Density
Explanation:
Density is the only intensive property of the above-mentioned properties. All other properties are
extensive properties. Intensive property of a system is that which is independent of the amount of the
substance present in the system. Extensive property of a system depends upon the amount of
substance or substances present in the system.
This post was last modified on 19 October 2021