Download (Association of American Medical Colleges) (AAMC) organizes MCAT Medical College Admission For Medical Entrance Exam Chemical Paper II Model Paper with Answers
Question 1
Calculate the molarity (M), when 580g of NaClis added to 2L of water.
a) 5 M
b) 3 M
c) 2.5 M
d) 80 M
e) 10 M
Correct Answer: a) 5 M
Explanation:
Molarity (M) = (moles of solute/litres of solution)
Molecular weight of NaCl = 23+35= 58 g/mol
Moles of NaCl = 580/58 = 10 mol
Therefore, Molarity (M) = 10 mol/2 L= 5 M
Question 2
Which of the following gas is the most easily liquefied?
Gas
O2 N2 NH3 CH4
Van der Waals constant (a) 1.3 1.39 4.17 2.21
a) O2
b) N2
c) NH3
d) CH4
e) Can't be predicted using this value
Correct Answer: c) NH3
Explanation:
A gas with the greater `a' value wil liquefy easily. Here NH3 has greater `a' value than the other
gases. Therefore, it will liquefy easily.
Question 3
The coordination number of the Na+ in Rock salt is
a) 4
b) 3
c) 6
d) 8
e) 2
Correct Answer: c) 6
Explanation:
In Rock salt the coordination number of Na+ is six. Because each Na+ is surrounded by six Cl- ions
and each Cl- is surrounded by six Na+ ions.
Question 4
Choose the property, which depends only on, the amount of solute in a solution.
a) Osmotic pressure
b) Temperature
c) Heat capacity
d) Melting point
e) None of the above
Correct Answer: a) Osmotic pressure
Explanation:
Properties that depend only on the amount of the solute not on their identity are known as
colligative properties. In the above four, osmotic pressure alone depends on the amount of the
solute and the rest of properties are independent of amount of solute.
Question 5
Choose the strongest acid from the following.
a) HClO4
b) HClO3
c) HClO2
d) HOCl
e) None of the above
Correct Answer: a) HClO4
Explanation:
HClO4 is the strongest acid than the rest of the acids. The acidity is due to the presence of the more
electronegative oxygen. The acid with ore oxygen is the strongest acid and it has the highest
electronegativity. It can easily pull the electrons from the central atom and induces the central atom
to draw the electrons from the hydrogenated oxygen. This weakens the O-H bond and H+ ion leaves
the molecule easily.
Question 6
Which of the following represents a spontaneous reaction if T = +10 k?
a) H = +10, S = -30
b) H = +10, S = +30
c) H = -10, S = +30
d) H = -10, S = -30
e) Both b and d
Correct Answer: e) Both b and d
Explanation:
If the value of enthalpy is negative and the entropy is positive then the reaction is always
spontaneous (H = -10, S = +30). If both enthalpy and entropy are negative (H = -10, S = -30), and
T < H/ S then the reaction is spontaneous at low temperature.
Question 7
Choose the correct phrase(s) that can apply to first order reactions.
I) The overall rate of the reaction is proportional to the concentration of one of the reactants.
II) If the concentration of the reactant is doubled, the rate is doubled.
III) The unit of rate constant for a first order reaction is sec-1 or time-1.
a) I and III only
b) I and II only
c) I only
d) I, II and III
e) III only
Correct Answer: d) I, II and III
Explanation:
Rate of a first order reaction, depends only on one of the reactant's concentrations. When the
concentration of the reactant is increased by `n' times, the rate of reaction is also increased by `n'
times. The unit of rate constant for the first order reaction is sec-1 or time-1.
k1 = rate/ (a-x) = mol.lit-1sec-1/ mol.lit-1 = sec-1
Question 8
Predict whether the following half-cell reactions are Oxidation or Reduction.
a) I-Oxidation reaction, II- Reduction reaction
b) I-Reduction reaction, II- Oxidation reaction
c) Both I and II are Oxidation reactions
d) Both I and II are Reduction reactions
e) None of the above
Correct Answer: b) I- Reduction reaction, II- Oxidation reaction
Explanation:
Reduction reaction is one in which, an atom or an ion accepts an electron. Oxidation reaction is one
in which, an atom or an ion releases an electron. In the first reaction, Cu2+ ion accepts two
electrons. Therefore, it undergoes reduction. In the second reaction, Cu atom releases two
electrons. Therefore, it undergoes oxidation.
Question 9
Which of the following element has no neutrons in the nucleus?
a) Helium
b) Deuterium
c) Hydrogen
d) tritium
e) An alpha particle
Correct Answer: c) Hydrogen
Explanation:
Hydrogen has only one proton and one electron and no neutron is present. Deuterium has one
proton and one neutron. Tritium has one proton and two neutrons in its nucleus. An alpha particle is
also known as helium atom and it has two neutrons.
Question 10
Binding energy of an atom is
a) E = mc/
b) E = mc2
c) E = mc
d) E = m/c2
e) E = mc/v
Correct Answer: E = mc2
Explanation:
The atomic mass of any atom is less than the sum of the protons, neutrons and electrons present in
it. This defect in the mass is measured by the binding energy. Binding energy of an atom can be
calculated using the equation E = mc2, where E ? energy liberated, m ? loss of mass and c-
speed of light in vacuum.
Question 11
Which of the following are nucleophiles?
a) H+
b) H3O+
c) CO2
d) AlCl3
e) NH3
Correct Answer: e) NH3
Explanation:
Generally, electron pair donors are called as nucleophiles. In the case of ammonia, it has a lone of
pair of electrons. So, it can donate the electron to the other atoms. But, the rest of the atoms can't
donate a pair of electrons instead they can accept a pair of electrons. So, except ammonia all the
other molecules above are known as electrophiles.
Question 12
The ratio of relative abundance of two molecular ion peaks of a chlorine atom in mass
spectroscopy is
a) M+ : (M+2) = 1:3
b) M+ : (M+2) = 3:1
c) M+ : (M+2) = 1:2
d) M+ : (M+2) = 2:1
e) M+ : (M+2) = 1:1
Correct Answer: b) M+ : (M+2) = 3:1
Explanation:
The ratio of relative abundance of two molecular ion peaks of a chlorine atom in mass spectroscopy
is M+ : (M+2) = 1:3, because the natural abundance of chlorine is higher than other elements. The
natural abundance of chlorine is Cl35- 75.77% and Cl37t- 24.23%.
Question 13
Compound A reacts by first order kinetics. The rate constant of the reaction is 0.45 sec-1. Calculate
the half-life of the compound A in the reaction.
a) 4.62 seconds
b) 3.08 seconds
c) 1.54 seconds
d) 2.25 seconds
e) 0.9 seconds
Correct Answer: c) 1.54 seconds
Explanation:
Half-life period of the first order reaction can be calculated using the following formula, which is
derived from the first order rate law.
t1/2 = 0.693/k1 seconds.
Therefore, t1/2 = 0.693/ 0.45 sec-1 = 1.54 seconds.
Question 14
The standard EMF value of a reaction I is Eocell = -1.563 and for a reaction II it is Eocell = +0.86. Predict
the feasibility of these reactions.
a) Reaction I is not feasible, reaction II is feasible
b) Reaction I is feasible, reaction II is not feasible
c) Both the reactions are feasible
d) Both the reactions are not feasible
e) Can't be predicted using these values.
Correct Answer: a) Reaction I is not feasible, reaction II is feasible
Explanation:
In general, if Eocell is positive, the reaction is feasible. If Eocell is negative, the reaction is not feasible.
Here, the Eocell of the reaction I is negative, therefore the reaction is not feasible and Eocell of the
reaction II is positive, therefore the reaction is feasible.
Question 15
"No pairing occurs until al orbitals of a given sub level are half fil ed". The statement is known as
a) Exclusion principle
b) Uncertainty principle
c) Hund's rule
d) Aufbau principle
e) Bohr's theorem
Correct Answer: c) Hund's rule
Explanation:
Exclusion principle states that it is impossible for any two electrons in a given atom to have all the
four quantum numbers identical. Hund's rule states, "No pairing occurs until al orbitals of a given
sub level are half fil ed". Aufbau principle defines that in the ground state of the atoms the orbitals
are filled in order of their increasing energies. Uncertainty principle states that the position and
momentum of a particle can't be simultaneously measured with high precision.
This post was last modified on 19 October 2021