CLASS: XII
MARKS: 70
UNITS: SOLUTIONS
TIME: 3 HRS
ELECTROCHEMISTRY
CHEMICALB KINETICS
GENERAL INSTRUCTIONS:
Read the following instructions
carefully.
(a) There are 33 questions in this question
paper with internal choice.
(b) SECTION A consists of 16
multiple-choice questions carrying 1 mark each.
(c) SECTION B consists of 5 short
answer questions carrying 2 marks each.
(d) SECTION C consists of 7 short answer
questions carrying 3 marks each.
(e) SECTION D consists of 2
case-based questions carrying 4 marks each.
(f) SECTION E consists of 3 long
answer questions carrying 5 marks each.
(g) All questions are compulsory.
(h) Use of log tables and
calculators is not allowed.
SECTION A:
The following questions are multiple-choice questions with one correct
answer. Each question carries 1 mark. There is no internal choice in this
section
1. The unit of ebullioscopy constant is:
a) K kg mol-1
b)
K-1 kg mol
c)
K kg-1 mol-1
d)
K kg-1 mol
2.
A 5%
solution of cane-sugar (molecular weight = 342) is isotonic with 1% solution of
substance A. The molecular weight of X is
a) 342
b) 171.2
c) 68.4
d) 136.8
3.
Which of the following solutions will have the
highest conductivity at 298 K?
(a) 0.01 M HCl
(b) 0.1 M HCl
(c) 0.01 M CH3COOH
(d) 0.1 M CH3COOH
4. If E°Fe2+/Fe =
-0.441 V and E°Fe2+/Fe2+ = 0.771 V, the
standard EMF of the reaction,
Fe + 2Fe3+ → 3Fe2+ will
be
(a) 1.212 V
(b) 0.111 V
(C) 0.330 V
(d) 1.653 V
5.
Which of the following associated with isotonic
solutions is not correct?
a) They will have the same osmotic pressure
b) They will have the same vapour pressure
c) They
have same weight concentrations
d) Osmosis does not take place when the two
solutions are separated by a semipermeable membrane
6.
Which of the following statement is true?
(a) molecularity of reaction can be zero or a
fraction.
(b) molecularity has no meaning for complex
reactions.
(c) molecularity of a reaction is an
experimental quantity
(d) reactions with the molecularity three are
very rare but are fast.
7.
Which of the following solutions has the highest
vapour pressure?
a) 0.2 𝑚 urea
b) 0.1 𝑚 glucose
c) 0.1 𝑚
MgSO4
d) 0.1 𝑚
BaCl2
8. If the initial concentration of substance A is
1.5 M and after 120 seconds the concentration of substance A is 0.75 M, the
rate constant for the reaction if it follows zero - order kinetics is:
(a)
0.00625 molL-1s -1
(b) 0.00625 s -1
(c) 0.00578 molL-1s
-1
(d) 0.00578 s -1
9.
Galvanised iron sheets are coated
with
(a) Carbon
(b) Copper
(c) Zinc
(d) Nickel
10.
The e.m.f. of the cell Zn/Zn2+ (0.01 M)
|| Fe2+ (0.001 M) Fe at 298 K is 0.2905 volt. Then
the value of equilibrium constant for the cell reaction is:
(a) e0.32/0.0295
(b) 100.32/0.0295
(c) 100.26/0.0295
(d) 100.32/0.0591
11.
4.5 g of aluminium (at. mass 27) is deposited at cathode from
Al3+ solution by a certain quantity of electric
charge. The volume of hydrogen produced at STP from H+ ions in solution by the same quantity of electric
charge will be:
(a) 44.8 L
(b) 11.2 L
(c) 22.4 L
(d) 5.6 L
12.
For a chemical reaction, X + 2Y → Z, if the rate of
appearance of Z is 0.50 moles per litre per hour, then the rate of
disappearance of Y is
(a) 0.5 mol
L-1 hr-1
(b) 1.0 mol
L-1 hr-1
c) 0.25
mol L-1 hr-1
(d) cannot
be predicted
In
questions 13 to 16 Given are two statements labelled as Assertion (A) and
Reason (R) Select the most appropriate answer from the options given below:
(a) Both
A and R are true and R is the correct explanation of A
(b) Both
A and R are true but R is not the correct explanation of A
(c) A
is true but R is false
(d) A
is false but R is true
13.
Assertion (A): Molarity of a solution in liquid state
changes with temperature.
Reason (R): The volume of a solution changes with change in temperature.
14.
Assertion: Aquatic species are more comfortable
in cold waters rather than in warm waters. Reason: Different gases have
different KH values at
the same temperature.
15.
Assertion (A): During electrolysis of aqueous
copper sulphate solution using copper electrodes hydrogen gas is released at
the cathode.
Reason (R): The electrode potential of Cu2+ /Cu is greater than that
of H +/H2
16.
Assertion (A): The half- life for a zero order
reaction is independent of the initial concentration of the reactant.
Reason (R): For a zero order reaction, Rate =
k
Section
B
This
section contains 5 questions with internal choice in one question. The
following questions are very short answer type and carry 2 marks each.
17.
Equimolal solutions of NaCl and BaCl2
are prepared in water. Freezing point of NaCl is found to be -20C,
What freezing point do you expect for BaCl2 solution? 2
18.
Plot a
graph between vapour pressure and mole fraction of a solution obeying Raoult’s
Law at constant temperature? 2
19.
Calculate the emf of the following cell at 298 K
: Cr(s) / Cr3+ (0.1M) // Fe2+ (0.01M) / Fe(s) [Given : EoCell = + 0.30 V]
OR
The conductivity of 10-3 mol/L acetic acid at 25oC is 4.1 x 10 -5
S cm-1. Calculate its
degree of dissociation, if 
for acetic acid at 250 C is 390.5 S cm2 mol-1. 2
20.
What
are Fuel cells? Write the electrode reactions of a H2- O2 fuel cell.
What advantages do fuel cells have
over conventional methods of generating electrical energy? 2
21.
The activation energy of a reaction is 75.2
kJmol-1 in the absence of
a catalyst and it lowers to 50.14 kJmol-1 with a catalyst. How many times will
the rate of reaction grow in the presence of a catalyst if the reaction
proceeds at 25oC? 2
Section
C:
This
section contains 7 questions with internal choice in one question. The
following questions are short answer type and carry 3 marks each.
22.
The following data were obtained during the
first order thermal decomposition of N2O5(g) at a constant volume: 2N2O5 g ® 2N2O4 g +O2 g
Calculate the rate constant. 3
23.
A) Name and state the law correlating the
pressure of the gas & its solubility in a liquid.
B) What happens to the vapour pressure of a
liquid if a volatile liquid is added to it.
C) How is elevation in b.pt., when a
non-volatile solute is added, related to lowering of vapour pressure. 3
24.
The element A and B formed purely
covalent compounds having molecular formula AB2 and AB4.
When dissolved in 20 gram of benzene 1 gram of AB2 lowers the
freezing point by 2.3 K and of AB4 by 1.3 K. Calculate atomic mass
of A and B. The molar depression constant for freezing is 5.1 KKg mol-1 3
25.
Calculate
the maximum work done that can be obtained from the Daniell cell Zn/Zn2+//Cu2+/Cu.
Given that E°Zn2+/Zn and E°Cu2+/Cu are -0.76 and +0.34 V
respectively. 3
26.
(a) Can we construct an electrochemical cell
with two half-cells composed of ZnSO4 solution and zinc electrodes? Explain
your answer.
(b) Calculate the λ0m for Cl- ion from the
data given below: Λ0m
MgCl2 = 258.6 Scm2mol–1 and λ 0m Mg2+ = 106 Scm2mol–1
c) The cell constant of a conductivity cell is
0.146 cm-1. What is the
conductivity of 0.01 M solution of an electrolyte at 298 K, if the resistance
of the cell is 1000 ohm? 3
27. A first order gas phase reaction: A2B2(g)
→ 2A(g) + 2B(g) at the temperature 400°C has the rate constant k = 2.0 × 10-4 sec-1.
What percentage of A2B2 is decomposed on heating for
900 seconds? (Antilog 0.0781 = 1.197) 3
28.
(i) Solutions of two electrolytes ‘A’ and ‘B’
are diluted. The limiting molar conductivity of ‘B’ increases 1.5 times while
that of ‘A’ increases 25 times. Which of the two is a strong electrolyte?
Justify your answer.
(ii) The products of electrolysis of aqueous
NaCl at the respective electrodes are:
Cathode: H2 Anode:
Cl2 and not O2. Explain. 3
Section
D:
The
following questions are case -based questions. Each question has an internal
choice and carries 4 marks each. Read the passage carefully and answer the
questions that follow.
29.
Read the given passage and answer the questions
that follow:
A Lead storage battery is the most important
type of secondary cell having a lead anode and a grid of lead packed with PbO2
as cathode. A 38% solution of sulphuric acid is used as electrolyte.
(Density=1.294 g mL-1)
The battery holds 3.5 L of the acid. During the discharge of the battery, the
density of H2SO4 falls to 1.139 g mL-1.
(20% H2SO4 by mass)
a)
Write the reaction taking place at the cathode
when the battery is in use.
b)
How much electricity in terms of Faraday is
required to carry out the reduction of one mole of PbO2?
c)
What is the molarity of sulphuric acid before
discharge?
OR
Write the products of electrolysis when dilute sulphuric acid is
electrolysed using Platinum electrodes. 4
30.
Read the given passage and answer the questions
that follow
In corrosion, a metal is oxidised by loss of
electrons to oxygen and formation of oxides. Corrosion of iron (commonly known
as rusting) occurs in presence of water and air. The chemistry of corrosion is
quite complex but it may be considered essentially as an electrochemical
phenomenon. At a particular spot of an object made of iron, oxidation takes
place and that spot behaves as anode and we can write the reaction
Electrons released at anodic spot move through
the metal and go to another spot on the metal and reduce oxygen in the presence
of H+ (which is believed to be available from H2CO3 formed due to dissolution
of carbon dioxide from air into water. Hydrogen ion in water may also be
available due to dissolution of other acidic oxides from the atmosphere). This
spot behaves as cathode with the reaction
The overall reaction: 2Fe(s) + O2 (g) + 4H+
(aq) à 2Fe2 +(aq) + 2 H2O (l), Eo(cell) =1.67 V
The ferrous ions are further oxidised by
atmospheric oxygen to ferric ions which come out as rust in the form of
hydrated ferric oxide (Fe2O3 . x H2O) and with further production of hydrogen
ions.
a)
Write the cathode half- reaction during rusting of iron.
b)
Iron does not rust when a coating of zinc cracks in a
galvanised iron pipe, whereas it rusts when a coating of tin done on its
surface cracks. Give reasons.
c)
What is meant by galvanisation? 4
Section
E
The following questions are long answer types and carry 5 marks each.
31.
i) Graphically explain the effect of temperature
on the rate constant of reaction? How can this temperature effect on rate
constant be represented quantitatively?
ii) The decomposition of a hydrocarbon follows
the equation
Calculate Ea.
OR
i) In
the reaction
Q + R → Products
The time taken for 99% reaction of Q is twice
the time taken for 90% reaction of Q. The concentration of R varies with time
as shown in the figure below:
What is the overall order of the reaction?
Give the units of the rate constant for the same. Write the rate expression for
the above reaction.
ii) Rate constant for a first order reaction has
been found to be 2.54 x 10-3s-1.
Calculate its three-fourth life. 5
32.
(a)
Why is glycol and water mixture used in car radiators in cold countries?
(b) Give reason
When 30 ml of ethyl alcohol and 30ml of water are mixed, the volume of
resulting solution is more than 60ml.
(c) What is cryoscopic
constant? Give the expression to obtain the cryoscopic constant of a solvent.
(d) What do you
mean by a minimum boiling azeotrope? Give an example. 5
33.
A) Explain
construction & working of a standard hydrogen electrode.
B) Give
reasons: (i) Why does the voltage of a mercury cell remain constant throughout
its life? (ii) Dry cells do not have a long life.
C) What is a
salt bridge? Give its functions. 5
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