Class XII_Delhi_Chemistry_Set-1
19.
(a)
(b)
What type of semiconductor is obtained when silicon is doped with boron?
What type of magnetism is shown in the following alignment of magnetic
moments?
3
(c)
What type of point defect is produced when AgCl is doped with CdCl2?
Ans.
(a)
(b)
(c)
When silicon is doped with boron, p-type semiconductor is obtained.
The magnetism shown in the alignment of magnetic moments is ferromagnetism.
Impurity defect is produced when AgCl is doped with CdCl2.
20.
Determine the osmotic pressure of a solution prepared by dissolving 2.5 × 10–2 g of
K2SO4 in 2L of water at 25°C, assuming that it is completely dissociated.
(R = 0.0821 L atm K–1 mol–1, Molar mass of K2SO4 = 174 g mol–1)
3
Ans. w2 = 2.5 × 10–2 g (Mass of K2SO4) and M2 = 174 g mol–1 (Molar mass of K2SO4)
V = 2L, R = 0.0821 L atm K–1 mol–1 and T = 25°C = 298 K
w 2 RT
Osmotic pressure,  M V
2
2.5 102  0.0821 298 61.1645 102


 1.76 103 atm.
174  2
348
21.
Calculate the emf of the following cell at 298 K:
Fe(s) Fe2+  0.001M  || H + (1M) | H 2 (g) (1bar), Pt(s)
 Given E°cell =  0.44 V 
Ans.
At anode: Fe → Fe2+ + 2eAt cathode: 2H+ + 2e- → H2
So, total number of electrons (n) transferred = 2
Given: Eocell = +0.44 Volt
Temperature (T) = 298 K
aoxi
 2.303RT 
E cell  Ecell  
 log
aRed
 nF 
aoxidation
0.0591V
0.001
 0.05916V 
Ecell  Ecell  
 E cell  0.44 
log
 log
n
areduction
2
1


Therefore, Ecell = 0.44(–0.02955 × – 3) = 0.44 + 0.08865 = 0.53 Volt.
3
Class XII_Delhi_Chemistry_Set-1
22.
How would you account for the following?
(i)
Transition metals exhibit variable oxidation states.
(ii)
Zr (Z = 40) and Hf (Z = 72) have almost identical radii.
(iii)
Transition metals and their compounds act as catalyst.
3
OR
Complete the following chemical equations:
(i)
Cr2O72  6Fe2  14H 
Ans.
(ii)
2CrO24  2H 
(iii)
2MnO4  5C2O42  16H 
(i)
The variable oxidation states of transition elements are due to the participation of
ns and (n−1)d-electrons in bonding. Lower oxidation state is exhibited when nselectrons take part in bonding. Higher oxidation states are exhibited when (n − 1)
d-electrons take part in bonding.
(ii)
This is because the atomic radii of 4d and 5d transition elements are nearly same.
This similarity in size is consequence of lanthanide contraction. Because of this
lanthanide contraction the radii of Hf becomes nearly equal to that of Zr.
(iii)
Transition elements act as good catalyst in chemical reaction because they can
lend electrons or withdraw electrons from the reagent, depending on the nature of
the reaction. The ability of transition metals to be in a variety of oxidation states,
the ability to interchange between the oxidation states and the ability to form
complexes with the reagents and be a good source for electrons make transition
metals good catalysts.
OR
Complete the following equations:
(i)
(ii)
2CrO42- + 2H+ → Cr2O72- + H2O
(iii)
2MnO4- + 5C2O42- + 16H+ → 2Mn2+ + 10CO2 + 8H2O
23.
Write the IUPAC names of the following coordination compounds:
(i)
[Cr(NH3)3Cl3]
(ii)
K3[Fe(CN)6]
(iii)
[CoBr2(en)2]+, (en = ethylenediamine)
Ans.
IUPAC Nomenclature:
(i)
Triamminetrichlorochromium (III)
(ii)
Potassium hexacyanoferrate (III)
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Class XII_Delhi_Chemistry_Set-1
(iii)
Dibromidobis (ethane-1, 2-diammine) cobalt (III) ion
24.
Give the structures of A, B and C in the following reactions:
NH3
H 2O/H
CuCN
(i)
C6 H5 N 2 Cl  
 A 
 B 
C

NaNO2  HCl
H 2O/H 
Sn  HCl
(ii)
C6 H5 NO2 
 A 
 B 
C
273 K

Ans.
(i)
3
(ii)
25.
Write the names and structure of the monomers of the following polymers:
(i)
Buna – S
(ii)
Neoprene
(iii)
Nylon-6, 6
Ans.
The monomers of the following polymers are as follows:
(i)
(ii)
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Class XII_Delhi_Chemistry_Set-1
(iii)
26.
After watching a programme on TV about the adverse effects of junk food and soft drinks
on the health of school children, Sonali, a student of Class XII, discussed the issue with
the school principal. Principal immediately instructed the canteen contractor to replace
the fast food with the fibre and vitamins rich food like sprouts, salad, fruits etc. This
decision was welcomed by the parents and the students.
3
After reading the above passage, answer the following questions:
(a)
What value are expressed by Sonali and the Principal of the school?
(b)
Give two examples of water-soluble vitamins.
Ans.
(a)
(b)
27.
(a)
(b)
(c)
Ans.
(a)
(b)
(c)
The values showed by Sonali are awareness regarding adverse effect of junk food
and concern for the health of her school mates.
The value showed by the principal is responsible behavior in listening to Sonali’s
views and taking prompt action in replacing junk food with healthy food.
The water soluble vitamins are vitamin B-complex and vitamin C.
Which one of the following is a food preservative?
Equanil, Morphine, Sodium benzoate
Why is bithional added to soap?
Which class of drugs is used in sleeping pills?
3
Sodium benzoate is used as a food preservative whereas equanil is a tranquillizer
and morphine is a narcotic analgesic.
Bithional is an antiseptic so it is added to soaps to reduce odours producing
bacterial decomposition of organic matter on the skin.
Tranquillizers relieve stress, fatigue by inducing sense of well being, so they are
used in the making of sleeping pills.