F.Sc. Part 1 Chemistry.Ch.08.Test (Malik Xufyan)

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5
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Experimental Techniques – Solved Paper
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Atomic Structure – Unsolved Paper
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INDEX

Chapter#8:Chemical equilbrium Malik Chemistry
Jhang Institute for Advanced74
Name : CH # Chemical Equilbrium Class 11th
Chemistry Test # 08, CH # 08 (Complete) Marks : 85
Time : 2 & Half Hour Objective & Subjective JIAS Test System
Section-I= Objective
1. Choose the correct answer 17x1=17
Sr # Statement A B C D
1. Acetic acid is week electrolyte because Its molecular mass is
high
It is covalent
compound
It is highly unstable It does not
dissociate much
or its ionization is
small
2. Cl -
ion is conjugate base of HCl HOCl HClO3
HClO4
3. The Ph of an aqueous solution of a 0.1 M solution
of a week monoprotic acid which is 1 percent
ionized is
1 2 3 11
4. Which of the following salts when dissolved in
water will hydrolyse
NaCl KCl NH4
Cl Na2
SO4
5. KC
and KP
has same value for Synthesis of ammonia Synthesis
of HI
Synthesis of sulphur
trioxide
Dissociation of PCl5
6 Optimum condition for the synthesis of ammonia Catalyst iron Temp 400 o
C Pressure 200-300 atm All of these
7. If Kc
is high then equilibrium position is Towards left Towards
right
Remain unchanged None of these
8. Which material possess the highest pOH Soft Drinks Bananas Milk of magnesia Sea water
9. Which is not a property of Kc
? May or may not have unit Depends upon
temperature
Depends upon
equilibrium conc. Of
reactants and products
Associated with
activation energy
not with extent of
reaction
10. Which statement is not correct? Conjugate base of a week
acid is strong
Greater is Ka
value ,greater
is Kb
value
Greater is molar conc.
of H+
smaller is pH
Smaller is pKa
,stronger is the acid
11. The pOH of 10-8
Molar solution of HCl in water is 8 Between 7
and 8
6 -8
12. When NH4
Cl is added to NH4
OH solution, the
dissociation of ammonium hydroxide is reduced.
It is due to
Common ion effect Hydrolysis Oxidation Reduction
13. Equilibrium constant depends upon Actual quantities of
reactants and products
Temperature Pressure of a catalysts Presence of inert
material
14. Which of the statement is correct? pKw
increase with
increase of temperature
pKw
decrease
with
increase of
temperature
pKw
=14 at all
temperatures
pKw
= pH at all
temperatures
15. The most favourable condition for the manufacture
of ammonia is
High temperature and
high pressure
Low
temperature
and low
pressure
High temperature
and low pressure
Low temperature
and high pressure
16. The chemical equilibrium of a reversible reaction
is not influenced by
Catalyst Temperature Pressure Concentration
17. In a reversible chemical reaction equilibrium is
said to have been established when
Conc. of reactants and
products are equal
Opposing
reaction cease
Temp of opposing
reaction are equal
Speed of opposing
reaction become
equal

Jhang Institute for Advanced Studeies 75
Section-lI: Short questions
2. Attempt only Eight questions. 8x2=16
i. Explain the term reversible reaction and state of equilib-
rium?
ii. Reversible reactions attain the position of equilibrium.
Which is dynamic in nature and not static .Explain?
iii. Why do rates of forward reactions slow down when a re-
versible reaction approaches the equilibrium stage?
iv. How some reactions are effected by volume at equilibri-
um stage?
v. The change of temperature disturbs both equilibrium po-
sition and constant of reaction?
vi. Define pH and pOH. How are they related with pkw
?
vii. What is Lowry bronsted idea of acids and bases?
viii. What are buffer solutions? Why do we need them in
daily life?
ix. How does the mixture of sodium acetate and acetic acid
give us the acidic buffer?
x. Explain the term buffer capacity?
xi. How do you calculate the solubility of a substance from
the value of solubility product?
xii. Write Kc
of this reaction
N2
+3H2
2NH3
3. Attempt only Eight questions. 8x2=16
i. Calculate the pH of 10-4
mole dm-3
of HCl?
ii. Describe the effect of common ion on solubility by giving
examples?
iii. When the concentration soft salt is increased in an acidic
buffer than the pH of the solution increases. Why?
iv. What will be the effect of change in pressure on NH3
syn-
thesis?
v. A catalyst does not affect the equilibrium constant com-
ment on it?
vi. Why is the formation of ammonia carried out at about
400 o
C when a lower temperature would favour the for-
mation of ammonia?
vii. How equilibrium constant ‘Kc
‘is used to predict the di-
rection of reaction?
viii. What is chemical equilibrium mixture?
ix. Why aqueous solution of salt derived from a very week
acid and a week base may not be neutral?
x. In some reversible reactions direction of reaction is
changed by change in pressure? Give reason.
xi. What is the effect of presence of common ion on solubil-
ity? Give examples.
4. Attempt only six questions.
i. How equilibrium constant explains the extent of reaction
?
ii. Define law of mass action and also define Kc
?
iii. State Le –Chatelier principal. Explain the effect of tem-
perature for endothermic reaction ?
iv. The solubility of glucose in water is increased by increas-
ing temperature .reason?
v. Write graphical representation of temperature and pres-
sure for NH3
synthesis.
vi. What are the ways to maximize the yield of ammonia?
vii. What happens to the acidic and basic properties of aque-
ous solutions when PH varies from zero to 14?
viii. Define common ion effect and also give examples?
Section-lIl: Long Questions.
Attempt any THREE questions. 8 x 3 = 24
5) a) Write a detailed note on preparation of sulphur triox-
ide?
b) The solubility of CaF2
In water at 25o
C is found to
be 2.05 x 10-4
mol dm-3
.What is the value of Ksp
at this temperature?
6) a) Write relationship between Ka
, Kb
and Kw
?
b) N2
and H2
combine to give NH3
.The values of Kc
in this reaction at 500o
C IS 6.02 x10-2
. Calculate
the value of Kp
for this reaction.
7) a) Define and explain law of mass action and derive the
expression for the equilibrium constant (Kc
).
b) What is percentage ionization of acetic acid in a
solution in which 0.1 mole of it has been dis-
solved per dm3
of the solution?
8) (a) What is solubility product? Explain it with examples
and applications.
(b) What are buffer solution and how can we pre-
pare buffer solution and write its importance.
9) (a) Write note on Henderson equation for pH of Buffer.
(b) What do you know about synthesis of Ammonia
with the help of Le-Chatelier’s Principle?

Section-l: Short questions
2. Attempt only EIGHT questions 8 x 2= 16
i. Explain the term reversible reaction and state of equilibrium?
Ans:
Those reactions in which the reactants products are converted into each other under same set of conditions.
The state of reversible reaction, in which forward and reverse rates are equal.(Rf
=Rr
)
State of equilibrium: The state of a chemical reaction in which its forward and reverse reactions occur at
equal rates so that the concentration of the reactants and products does not change with time. It is called
dynamic equilibrium.
ii. Reversible reactions attain the position of equilibrium which is dynamic in nature and not static
.Explain?
Ans:At equilibrium, there is no net change in the equilibrium mixture. The forward and reverse reactions
are taking place with exactly the same rate. This makes the equilibrium dynamic
iii. Why do rates of forward reactions slow down when a reversible reaction approaches the equilibri-
um stage?
Ans:According to the law of mass action the rate of forward reaction is directly proportional to molar
concentration of reactants it means that greater the concentration of reactants higher the rate of for-
ward reaction and lesser the concentration of reactants, lower the rate of forward reaction.
It start of the reaction the concentration of reactants is high but when the reaction reaches at equilib-
rium state the concentration reactants become low due to lower concentration of reactant, the rate of
forward reaction slow down at equilibrium state.
iv. How some reactions are effected by volume at equilibrium stage?
Ans:Change in volume will disturb the equilibrium only when total moles of reactants are not equal to
that of products. Thus change in volume will speed up either forward or reversed depending upon the
situation but the system in order readjust the equilibrium move in opposite direction to the minimize
the effect of the change. As a result of which Kc
will not change.
v. The change of temperature disturbs both equilibrium position and constant of reaction?
Ans:In a reversible reaction two reactions are taking place simultaneously i.e. endothermic and exother-
mic. Increase of temperature favours endothermic reaction because it requires heat and decrease of
temperature favours exothermic reaction.
vi. Define pH and pOH. How are they related with pkw
?
Ans: The pH of a solution is defined as the negative logarithm of [H+
].
pH = -log[H+
]
pOH of a solution is defined as the engative log of [OH-
].
pOH = -log[OH-
]
According to this equation:
[H+
][OH-
] = Kw
Taking logarithm of both sides of the equation
log[H+
] log[OH-
] = log Kw

Changing the signs (multiplying by -1) gives
-log [H+
] –log[OH-
] = -logKw
From the definitions
pH + pOH = pKw
vii. What is Lowry Bronsted idea of aids and bases?
Ans: According to this concept:
Acid: Acids those species which donate the proton or have the tendency to donate
Example: HA + H2
O H3
O+
+ A-
Acid Conjugate base of HA
Base: bases are those species which accept the proton or have the tendency to accept the proton.
H2
O + A-
OH-
+ HA
Base Conjugate acid of base A-
viii. What are buffer solutions? Why do we need them in daily life?
Ans: Buffer solution:
Buffers can resist the charge of its pH value.
Need of Buffer solutions:
• Therefore they are required in chemical analysis, pharmaceuticals, electroplating, photography, bever-
age industry, microbiology molecular biology, soil science and in quantitative analysis.
• Our blood is best example of buffer solution having pH 7.35. If it decreases upto 7 or goes upto 8 death
may occur.
ix. How does the mixture of sodium acetate and acetic acid give us the acidic buffer?
Ans: Consider a mixture of CH3
COOH and CH3
COONa is a buffer mixture or buffer solution, the ioniza-
tion equations of CH3
COONa and CH3
COOH are as follows:
CH3COOH + H2O CH3COO-
+ H3O+
CH3COONa CH3COO-
+ Na+
CH3
COOH is a weak acid and ionizes very small, while CH3
COONa is a strong electrolyte and it
ionizes in water to greater extent and provides acetate ion. According to the preparation of acidic
buffer solution a weak acid and a its salt with strong base. It produces acidic buffer with pH < 7 like
CH3
COOH.CH3
COONa.
x. Explain the term buffer capacity?
Ans: Buffer capacity: The amount of acid or base which a buffer can absorb without significant charge in
pH is called buffer capacity. Buffer capacity is the ability of buffer to resist the change in its pH value.
xi. How do you calculate the solubility of a substance from the value of solubility product?
Ans: Consider a sparingly soluble salt PbCl2
dissolved in water. Equilibrium will be established b/w the
ionic solid salt and dissolved ions.
PbCl2 (aq)
Pb(aq)
2+
+ 2Cl(aq)
-
According to law of mass action:

Since PbSO4
is sparingly soluble, therefore, its concentration will remain constant.
Kc
[PbSO4
] = [Pb2+
] [SO4
2-
]
Ksp = [Pb2+
][SO4
2-
] = 1.6 × .10-8
at 25o
C.
Where Ksp
[PbSO4
] = Ksp
= solubility product
Similarly for PbCl2
Ksp
= [Pb2+
] [Cl-
]2
xii. Write Kc
of this reaction
N2
+ 3H2
2NH3
Ans: N2
+3H2
2NH3
Initial conc. a + b 0 (t = 0)
(moles)
Equilibrium conc. a-b + b-3x 2x (t = teq
)
(moles)
3. Attempt only 8 questions 8 X 2 = 16
i. Calculate the pH of 10-4
mole dm-3
of HCl?
Ans:
HCl ionizes as
HCl H+
+ Cl–
Since HCl is a strong acid, and it is 100% dissociated. Hence 10 –4
mol/dm3
of HCl produces
10 –4
mol/dm3
of H+
ions.
Thus
[H+
] = 10 –4
mol/dm3
So
pH = – log [H+
]
pH = – log [10 –4]
pH = 4
ii. Describe the effect of common ion on solubility by giving examples?
Ans: The presence of a common ion decreases the solubility of a slightly soluble ionic compound. In order
to explain it, considera saturated solution of PbCrO4
which is a sparingly soluble ionic salt.
PbCrO4 (aq)
Pb2+
(aq)
+ CrO4
2-
(aq)
Now add Na2
CrO4
, which is a soluble salt. CrO4
2-
(aq)
is the common ion. It combines with Pb2+
to form

more insoluble PbCrO4
. So equilibrium is shifted to the left to keep Ksp
constant.
iii. When the concentration of salt is increased in an acidic buffer than the PH of the solution increas-
es. why?
Ans:When CH3
COONa salt is added to CH3
COOH solution then the dissociation of CH3
COOH is sup-
pressed due to common ion effect CH3
COO-
.
CH3COOH + H2O CH3COO-
+ H3O+
CH3COONa CH3COO-
+ Na+
If one goes on the adding CH3
COONa n CH3
COOH solution then the added concentration of CH-
3COO-
decrease the dissociation of CH3COOH and the pH of solution increases.
iii. What will be the effect of change in pressure on NH3
synthesis?
Ans: Pressure is inversely proportional to volume. When the pressure is increased then volume will be
decreases. Molecules of reactants close to each other and react with each other to form ammonia.
Increase the pressure to decrease the volume of the reaction vessel. Four moles of the reactants combine
to give two moles of the products. High pressure will shift the equilibrium will shift it to the forward
direction. According to Le-Chatlier’s principle: with high pressure more ammonia will be obtained.
iv. A catalyst does not affect the equilibrium constant comment on it ?
Ans: A catalyst does not affect the equilibrium position of the reaction. It increases the rates of both for-
ward and backward reactions and this reduces the time to attain the state of equilibrium. Actually, a
catalyst lowers the energy of activation of both forward and reverse steps by giving new path to the
reaction.
v. Why is the formation of ammonia carried out at about 400 o
c when a lower temperature would
favour the formation of ammonia?
Ans:No doubt, the yield of NH3
is favoured at lower temperature, but the rate of its formation does not
remain favourable. The rate becomes so slow and the process is rendered uneconomical. One needs
a compromise to optimize the yield and the rate. The temperature is raised to a moderate level and a
catalyst is employed to increase the rate. If one wants to achieve the same rate without catalyst, then
it requires much higher temperature, which lowers the yield. Hence the optimum condition are the
pressure of 200-300 atm and temperature around 673 K (400o
C).
vi. How equilibrium constant ‘Kc
‘is used to predict the direction of reaction?
Ans: we know that
a) The ratio is less than Kc
. This implies that more of the product is required to attain the equilibrium;
therefore, the reaction will proceed in the forward direction.
b) The ration is greater than Kc
. It means that the reverse reaction will occur to attain the equilibrium.
c) When the ratio is equal to Kc
, then the reaction is at equilibrium.
vii. What is chemical equilibrium mixture?
Ans: Chemical equilibrium mixture:
If reversible reaction is allowed to continue for a considerable long time, without changing the con-
dition, there is no further change in composition of the reaction mixture. The reaction is said to have
attained a state of chemical equilibrium. This reaction mixture is chemical equilibrium mixture.
Example: Ammonia and hydrogen iodide
NH3
+ HI NH4
I
viii. Why aqueous solution of salt derived from a very week acid and a week base may not be neutral?

Ans:
A salt formed between a weak acid and a weak base can be neutral, acidic, or basic depending on the rela-
tive strengths of the acid and base.
If Ka
(cation) > Kb
(anion) the solution of the salt is acidic.
If Ka
(cation) = Kb
(anion) the solution of the salt is neutral.
If Ka
(cation) < Kb
(anion) the solution of the salt is basic.
ix. In some reversible reactions direction of reaction is changed by change in pressures? Give reason.
Ans: Pressure and volume are inversely proportional to each other. For gaseous reactions, if we increase
the pressure then volume will be decrease, equilibrium position of reversible reaction will be disturbed
and reaction will move to the forward direction. E.g,
2SO2(g)
+ O2 (g)
2SO3(g)
x. What is the effect of presence of common ion on solubility? Give examples.
Ans:The presence of common ion decreases the solubility of a slightly soluble ionic compound. In order
to explain it, consider a saturated solute soluble ionic result salt.
PbCrO4(aq)
Pb2+
(aq)
+ CrO4
2-
(aq)
Now add Na2
CrO4
, which is a soluble salt. CrO4
2-
is the common ion. It combines with Pb2+
to form
PbCrO4
. So equilibrium is shifted to the left to keep Ksp
constant.
4. Attempt any 6 questions 6 x 2 = 12
iv. How equilibrium constant explains the extent of reaction?
Ans: (a) if the equilibrium constant is very large, this indicates that the reaction is almost complete.
(a) If the value of Kc
is small, it reflects that the reaction does not proceed appreciably in the forward
direction.
(b) If the value of Kc
is very small, this shows a very little forward reaction.
v. Define law of mass action and also define Kc
?
Ans: Law of mass action:
it states that the rate at which the reaction proceeds s directly proportional to product of the active
masses of the reactants.
Kc
: The constant Kc
is called the equilibrium constant of the reaction. Kc
is the ratio of two rate constants.
Conventionally, while writing equilibrium constant, the products are written as nominator and reac-
tants as denominator.
vi. State Le –Chatelier principal. Explain the effect of temperature for endothermic reaction?
Ans: Le-Chatelier’s Principle:

it states that if a stress is applied to a system at equilibrium, the system acts in such a way so as to
nullify, as far as possible, the effect of that stress.
Effect of temperature for endothermic reaction: According to Le-Chatelier’s Principle, therefore a
temperature increase favours the endothermic reactions. Increase the temperature moving to forward
direction and decrease the temperature moving to backward direction.
KI (s)
KI(aq)
H = 21.4 Kj mol-
Hence solubility of KI in water must increase with increase in temperature.
vii. The solubility of glucose in water is increased by increasing temperature. Give reason?
Ans:According to Le-Chatelier’s Principle, if there is endothermic reaction, increase the temperature in-
crease the solubility of substance in water. So solubility of glucose in water is endothermic reaction,
increasing the temperature increasing the solubility of glucose in water.
viii. Write graphical representation of temperature and pressure for NH3
synthesis .
Ans:
ix. What are the ways to maximize the yield of ammonia?
Ans: High pressure, lower temperature and continual removal of ammonia will give the maximum yield
of ammonia. Industrial conditions are between 200-300 atm at about 400o
C.
N2
+ 3H2
2NH3
x. What happens to the acidic and basic properties of aqueous solutions when pH varies from zero to
14?
Ans:
W h e n
pH = 7 solution is neutral
pH > 7 solution is acidic
pH < 7 solution is basic
xi. Define common ion effect and also give examples?
Ans: Common ion effect:

The decrease in ionization of a weak electrolyte by adding another strong electrolyte having common
ion.
Example: ionization of NaOH is decreased by passing NH4
Cl through NH4
OH solution. Another example
of NH4
OH and NH4
Cl:
NH4
OH NH4
+ + OH-
NH4
Cl NH4
+ + Cl-
Common ion
Section-lIl: Long Questions
Attempt any THREE questions. 8 x 3 = 24
5) a) Write a detailed note on preparation of sulphur trioxide?
b) The solubility of CaF2
In water at 25 C is found to be 2.05 x10-4
mol dm-3
. What is the value of Ksp
at this
temperature?
6) a) Write relationship between Ka
, Kb
and Kw
?
b) N2
and H2
combine to give NH3
.The values of Kc
in this reaction at 500o
C is 6.02 x 10-2
. Calculate the
value of Kp
for this reaction.
7) a) Define and explain law of mass action and derive the expression for the equilibrium constant (Kc
).
b) What is percentage ionization of acetic acid in a solution in which 0.1 mole of it has been dissolved per
dm3
of the solution?
8) (a) What is solubility product? Explain it with examples and applications.
(b) What are buffer solution and how can we prepare buffer solution and write its importance?
9) (a) Write note on Henderson equation for pH of Buffer.
b) What do you know about synthesis of Ammonia with the help of Le-Chatelier’s Principle?

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