AHSEC| CLASS 12| CHEMISTRY| SOLVED PAPER - 2015| H.S. 2ND YEAR
2015
CHEMISTRY
(Theory)
Full Marks: 70
Pass Marks: 21
Time: Three hours
The figures in the margin indicate full marks for the questions.
1. Answer the following: 1x8=8
(i) Which point
defect lowers the density of a crystal?
Ans:- Schottky
defect lowers the density of a crystal.
(ii) Liquid-liquid
sols are known as Emulsion. (Fill in
the blank)
(iii) Which
metal foils are used for wrapping chocolates?
Ans:- Aluminium.
(iv) In the first
transition series of elements, which element shows highest oxidation state?
Ans:- Mn.
(v) Write the
formula for the co-ordination compound: tetracarbonylnickel (o).
Ans:- [Ni(CO)4]
(vi) Mention
one use of tetrachloromethane.
Ans:- Tetrachloromethane
is used as a solvent in the manufacture of pharmaceuticals.
(vii) Give
the IUPAC name of the following compound:
CH2=CH-CH2-CHO
Ans:- But-3enal.
(viii) Name
one water soluble vitamin.
Ans:- Vitamin C.
2. State Henry’s law.
At the same
temperature, hydrogen gas is more soluble in water than helium gas.
Which one of
them will have higher value of KH? 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 a unit volume of solvent and p is the pressure of the
gas in equilibrium with the solution, then
where is the
proportionality constant.
The KH
value of helium will be higher than that of hydrogen gas.
3. Define molar conductivity of an electrolytic solution.
How does molar conductivity vary with concentration for weak electrolyte? 2
Ans:- Molar conductivity is defined as the conductance of a solution of molarity 1 when the solution is bounded between two electrodes spaced by unit distance. It is defined by
M= molarity of
the solution
S.I unit of
molar conductivity is S.m2/mol.
The molar
conductivity of a weak electrolyte is lower than that of a strong electrolyte
at any given concentration, because of their lower degree of dissociation. But
the degree of dissociation of weak electrolytes increases with dilution. As a
result, the molar conductivity of a weak electrolyte increases with dilution.
Or
The limiting
molar conductance’s of sodium chloride, hydrochloric acid and sodium acetate
are 126.45, 426.16 and 91.0. Scm2mol-1 respectively at
298 K. Calculate the limiting molar conductance of acetic acid at 298K.
4. Distinguish between calcination and roasting. 2
Ans:- The difference between calcination and roasting is
shown below:
|
Roasting |
Calcination |
|
(i) It is the
process in which ore is heated n presence of excess o2 or air. |
(i) Ore is
heated in absence or limited supply of o2 or air. |
|
(ii) This method
is employed for Sulphide ores. |
(ii) This method
is employed for carbonate ores. |
Ans:- A transition element can be defined as an
element whose atoms in the ground state or in the normal oxidation state of the
ion are partially filled with d-orbitals (partially filled) i.e. between 1 and
9 electrons.
The general
electronic configuration of the transition element is: [Inert gas] (n-1)d1-10ns1-2.
6. What are alloys? Name the metals used for the
formation of bronze. 2
Ans:- An alloy is a homogeneous mixture of different
metals or metals and nonmetals.
The metals used
in the manufacture of bronze are copper and tin.
Or
Explain the
following: 1+1=2
(i) Transition
metals and their compounds can act as catalyst.
Ans:- This
is due to the variable oxidation states. They have large surface area and can
form intermediates with reactants that are easily converted into products.
(ii) In the titration
of FeSO4 with KMnO4 in acidic medium, dilute HCL is not
used.
Ans:- Dil
H2SO4 is an oxidising agent and oxidises F2SO4
to Fe2(SO4)3. Dil HCL is a reducing agent and
liberates chlorine on reacting with KMnO4 solution. Thus, part of the
oxygen produced from KMnO4 is used up by HCL.
7. Give one example each of the following: 1+1=2
(i) Ionisation
isomerism
Ans:- [Co(NH3)5
Br]So4 and [Co(NH3)5 So4] Br.
(ii) Geometrical
isomerism
Or
Using valence
bond theory, show that [Ni(CN)4]2- complex ion is
diamagnetic in nature. [Atomic number of Ni is 28].
8. Explain why: (Any Two) 1+1=2
(i) Phenols
are acidic in nature.
Ans:- The
acidic nature of phenol is due to the presence of polar O-H group. The hydroxyl
group of phenol is directly attached to the SP2 hybridized carbon of
the benzene ring which acts as an electron sharer with the drawing group. Due
to the high electronegativity of the SP2 hybridized carbon of phenol
to which the –OH is attached, the electron density on the oxygen decreases.
This increases the polarity of the O-H bond resulting in ionization of phenol.
As a result, H+ can be easily released from aqueous solution as
shown below –
This release of
H+ ion gives acetic character to phenol because the phenoxide ion is
resonance stabilised.
(ii) Ethers
have lower boiling points than alcohols.
Ans:- The
boiling point of ether is lower than the boiling point of alcohol. This is
because -
Ethers have
low polarity and no H-atom is attached to the oxygen, resulting in no visible
bonding by intermolecular hydrogen bonding. But in alcohols due to the presence
of intermolecular hydrogen bonding, the molecules are held together and due to
this their boiling point increases.
(iii) Propan-2-ol
is more basic than propan-1-ol.
Ans:- In
propan-2-ol the carbon atom carrying the -or group is attached to two alkyl
groups due to which the electron density is maximum on the oxygen. Therefore,
the (+) inductive effect of the two alkyl groups of propan-2-ol makes it more
basic than propan-1-ol.
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