AHSEC| CLASS 12| CHEMISTRY| SOLVED PAPER - 2022| H.S. 2ND YEAR
2022
CHEMISTRY
(Theory)
Full Marks: 70
Pass Marks: 21
Time: Three hours
The figures in the margin indicate
full marks for the questions.
1. A metal crystallies in a body-centred cubic structure. If ‘a’ is the edge length of its unit cell, ‘r’ is the radius of the sphere, what is the relationship between ‘r’ and ‘a’? 1
2. Arrange the following compounds in the increasing
order of their boiling points: CH3 -CHO, CH3 -CH2
-OH, CH3 -CH2 -CH3 1
3. Write down the formula of
Tetraamineaquachloridocobalt(III) chloride.
1
Ans:- [CQ(NH3)4(H2O)CI]CI2
4. Write the IUPAC name of the following compound: 1
Ans:- Benzylic propeneol.
5. What will be the impact on Kf when the
molality of a solution is doubled? 1
Ans:- When the molality of a solution is doubled, the
effect on Kf will remain unchanged.
6. Which is a stronger oxidizing agent- 1
Ans:- Bi.
7. pKb of aniline is more than that of
methylamine. Why? 1
Ans:- In aniline, the lone pair of electrons on the
N-atom delocalizes over the benzenering. As a result, the electron density on
nitrogen decreases. On the other hand, in CH3NH2,+l effect
of CH3 group increases the electron density on the N-atom. Hence
aniline is less basic than methylamine. Therefore, the Kb value of
aniline is less than that of methylamine.
8. Which of the following compounds can undergo
Hell-Volhard-Zelinsky reaction? 1
(i) Benzoic
acid (ii) Propanoic acid
Ans:- (ii) Propanoic acid.
9. The freezing point depression constant for water is
1.860Cm-1. If 5.0g of Na2So4 is
dissolved in 45g of water, then freezing point is charged by 3.800C.
Calculate the Van’t Hoff factor for Na2So4. 2
Or
State Henry’s
law. Why do gases nearly always tend to be less soluble in liquids as the
temperature is raised? 2
Ans:- Henry's
law states that at a constant temperature the mass of a gas dissolved per unit
volume of solvent is directly proportional to the pressure of the gas in
equilibrium with the solution.
If m is the
mass of the gas dissolved in unit volume of the solvent and p is the pressure
of the gas in equilibrium with the solution, then
m
p
Or m = k.p.
Where is the
constant of proportionality.
The solubility
of gases in liquids decreases with increase in temperature. Because solution is
an exothermic process.
10. Calculate the pH at which the potential of hydrogen
electrode will be 0.059V. 2
Ans:- Given, 2H+ + 2e-1 –>H2
Ecell =
E0cell – 0.059log 1/H+ Ecell = E0cell
– 0.059PH
0.059 = 0.0 – 0.059PH
PH = -1
Or
The Chemistry
of corrosion of iron is essentially an electrochemical phenomenon. Explain the
reaction occurring during the corrosion of iron in the atmosphere. 2
11. Why H2 and O2 do not react at
room temperature? Write the rate equation for the reaction A2+B2
-->2C, if the overall order of the reaction
is zero. 1+1=2
Ans:- H2
and O2 do not react at room temperature because the activation
energy for that reaction is high which is not provided at room temperature.
Since, the
overall order of the reaction is zero, hence the rate equation for the reaction
A2 + 3B2 –> 2C, is Rate, = K[A]0[B]0
Or
A first order
reaction has a rate constant of 0.0051 min-1. If we begin with 0.10M
concentration of the reactant, what concentration of reactant will remain in
solution after 3 hours? 2
12. Answerer any two:
(a) Write the
mathematical expression for the Freundlich absorption isotherm and draw the
graph log x/y vs log P.
2
Ans:-
The plot of the extent of adsorption (x/m) against the pressure of a gas (P) at
a constant temperature (T) is called an adsorption isotherm.
Freundlich
adsorption isotherm for the adsorption of gases on solids:
x/m
= K P1/n
It can also be
written as
Log x/m = log
k+1/n log P
Where x = mass of adsorbate
M = mass of
adsorbent
P = Pressure of
the gas
N = Constant and
is greater than 1.
(b) How do
emulsifiers stabilize emulsion? Name two emulsifiers. 2
Ans:- Emulsifiers
stabilize an emulsion by reducing the interfacial tension between the two
liquids that make up the emulsion. glue, soap etc.
(c) Define
shape-selective catalysis. Give an example.
1+1=2
Ans:- The
catalytic reaction which depends on the pore structure and pore structure of
the catalyst or the size of the catalyst and reactant and product molecules is
called size-selective catalysis.
13. Why is it that only sulphide ores are concentrated by
froth floatation processes? What is the role of depressants in the froth
floatation process of dressing of ores?
1+1=2
Ans:- Since the sulphide particles are preferentially
wetted with oil and further processing by gangue coaters is selected depending
on the concentration of the sulphide ore.
A depressant
suppresses the formation of scum with a particular compound in the froth
flotation process by chemically reacting with it. Thus, it helps in the
separation of two metal sulphides viz: ZnS and PbS In case of ore containing,
NaCN is used as a depressant. It forms a layer of Zn complex, Na2 [Zn(CN)4]
with ZnS on the surface of ZnS and hence prevents it from foaming.
ZnS + 4NaCN –>
Na2 [Zn(CN)4] + Na2S
14. Answer any two:
(a) Ti4+
compounds are colourless in aqueous solution but Ti3+
compounds are violet coloured. Explain.
2
Ans:- If
Ti4+ has no electron in the d-orbital, no d-d transition is possible
and hence it is colourless. But in Ti3+ one electron is in
d-orbital. So, it's coloured.
(b) What is
meant by ‘disproportionation’ of an oxidation state? Give an example. 2
Ans:- 'Disproportionation',
is a redox reaction in which a compound in an intermediate oxidation state is
converted into two compounds, one in a higher and one in a lower oxidation
state.
(c) Actinoid
contraction is greater than lanthanoid contraction. Why? 2
Ans:- The
actinides in general exhibit a greater range of oxidation states than the cap
of the lanthanides. This is due to the fact that in the case of actinides the
5f, 6d and 7s levels are of comparable energy.
15. (i) Write the IUPAC name of the following
compound: 1
[Pt(NO2)(NH3)BrCI]
Ans:-
Triamminebromochloronitroplatinum (iv) chloride.
(ii) How many
geometrical isomers will be possible for [Pt(Py)(NH3)BrCI] compound? 1
Ans:- 3
no. of geometrical isomers will be possible.
Or
Write the
hybridization state of central atom of the following co-ordination complexes
along with their magnetic properties.
2
[Cu(NH3)4]2+
and [Ni(CO)4]
Ans:- Hybridization
state of the central atom of - [Cu(NH3)4]2+
= dsp2 , [N1(CO)4] = Sp3
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