1. HALF COURSE TEST - II (MAILING)
CHEMISTRY
SOLUTIONS
1. We know that
5770
693
.
0
t
693
.
0
K
2
/
1


year–1
[2]
Let the relative number of C
14
6
atoms C12
at t = 0 be N0, then relative number of C
14
6
atoms after t
years = 0.617 N0.
So putting these values in the equation
N
N
log
t
303
.
2
K 0

[2]
0
0
N
617
.
0
N
log
693
.
0
5770
303
.
2
t


[4]
t = 4026.76 years
2. The kinetic equation for a second order reaction in which both reactants have same initial
concentration.
K =
)
x
a
(
a
x
t
1


[3]
Initial concentration of ester and base (a) = 0.01 M, K = 6.36 litre mol–1
min–1
t = 20 minutes. On
substituting the values
6.36 =
)
x
01
.
0
(
01
.
0
x
x
1


[3]
x =
272
.
2
01272
.
0 [2]
Fraction of ester hydrolysis =
01
.
0
272
.
2
01272
.
0
a
x


= 0.56
3. Sulphide ions in alkaline solution react with solid sulphur and to form S2
–2
and S3
–2
ions as
i) S(s) + S2–
S2
2–
K1 = 1.7
ii) 2S(s) + S2–
S3
2–
K2 = 5.1
iii) and S2
2–
+ S(s) S3
2–
K3 = ?
equation (iii) = equation (ii) – equation (i)
So K3 =
7
.
1
1
.
5
K
K
1
2

= 3
4. Molarity of N2H4 =
500
1000
32
16
.
0

= 0.01 M
N2H4 + H2O N2H5
+
+ OH–
Initially 0.01 M –– –– ––

2. IAI
 2
2
7
10
x
2
1
.
0
x
10
6
.
1
10
8
.
1




 
At equilibrium (0.01 – x)m –– xM xM
Kb =
)
x
01
.
0
(
x
x


x = 2 × 10–4
M
% of N2H4 reacting with water =
01
.
0
100
10
2 4

  = 2.1
5. λ =
mv
h
13.4 × 10–10
=
v
10
1
.
9
10
626
.
6
31
34





∴ v = 5.43 × 105
m/s [2]
We know that
2.18 × 106
×
n
Z = vn
2.18 × 106
×
n
1 = 5.43 × 105
⇒ n = 4 [2]
First excited state means n = 2
1
1

= 109637






 2
2
4
1
2
1
λ1 = 4864 o
A
[2]
Longest wavelength means transition from 2 → 1
2
1

= 109737






 2
2
2
1
1
1
λ2 = 1216 o
A
[2]
6. C3H8 + 5O2 ⎯ → 3CO2 (g)+ 4H2O(l)
CH4 + 2O2 ⎯ → CO2 (g)+ 2H2O(l)
CO +
2
1 O2 ⎯ → CO2 (g) [2]
Let a,b and c ml be the volumes of C3H8,CH4 and CO respectively.
than a + b + c = 100
where a = 36.5 [2]
Volume of CO2 formed = 3a + b + c
= 3 × 36.5 + (100 – 36.5)
= 173 ml [2]
7. Let the moles of Na2C2O4 be ‘a’ and that of KHC2O4.H2C2O4 be ‘b’ and the volumes of KMnO4
and NaOH consumed be V litre.
equivalent of KMnO4 = equivalent of Na2C2O4 + equivalent of KH2O4.H2C2O4
0.1 × V =
4
b
2
a

----------------- (i) [3]
equivalent of NaOH = equivalent of KHC2O4.H2C2O4
0.1V =
3
b ----------------- (ii) [3]
⇒ from (i) & (ii)
a : b = 1 : 6 [1]

3. IAI
 2
2
7
10
x
2
1
.
0
x
10
6
.
1
10
8
.
1




 
8. i) (a) sp3
d2
Xe
F
F
O
F
F
 
Square pyramidal
[2] (b) sp3
d
P
Br
Br
Br
Cl
Cl
TBP
[2]
(c) sp3
d
P
Br
Br
Cl
Cl
Cl
TBP
[2] (d) sp3
d
Xe
F
F
F
F
 
Square planar
 
[2]
ii) (a) NH3 < PH3 < AsH3 < SbH3 [2]
(b) BeCO3 < MgCO3 < CaCO3 < BaCO3 [2]
9. 2 P (g) ⎯ → 4Q(g) + R (g) + S (l)
at initial P0 0 0 0
at time t (P0-x) 2x
2
x Ps
at time ∞ 0 2P0
2
P0
Ps [2]
given P0 –x + 2x +
2
x + Ps = 317
and 2P0+
2
P0
+ PS = 617
putting Ps = 32.5
we get P0 = 233.8
x = 33.8 [4]
Now K =
x
P
P
log
t
303
.
2
0
0

=
8
.
33
8
.
233
8
.
233
log
30
303
.
2

K = 5.2 × 10-3
min-1
[2]
T1/2 =
3
10
2
.
5
6932
.
0
K
6932
.
0



= 133.3 min [2]
10. AgCl (s) Ag+
(aq) + Cl-
(aq) K1 = KSP
Ag+
(aq) + 2NH3 (aq) [Ag(NH3)2]+
(aq) K2 = Kf
––––––––––––––––––––––––––––––––––––––––––––––––––––––
AgCl (s) + 2NH3 (aq) [Ag(NH3)2]+
(aq) + Cl-
(aq) K = '
K [2]
0.1 0 0 at initial
(0.1-2x) x x at equilibrium
K’
= K1 × K2 = [4]
⇒
 
x
2
1
.
0
x

= 0.0536, ⇒ x = 4.9 × 10-3
M
hence the solubility of AgCl (s) in 0.100 M NH3 (aq) is 4.9 × 10-3
mole/litre [2]

4. IAI
 2
2
7
10
x
2
1
.
0
x
10
6
.
1
10
8
.
1




 
11. a) Butane 2,3 dione exist in the trans from, due to flipping which is highly stable hence
exclusively exist in keto form. But in case of cyclopentanone no such kind of flipping is possible hence
form enol in which it is stable through H – bonding.
b) OH OH
OMe
OH
OMe
[3]
12. A O3, H2O [1]
B LiAlH4 [1]
C. Conc. H2SO4, H+
[1]
D NaNH2 in Liq. NH3 [1]
E CH3I [1]
F H2SO4, Hg+2
[1]
13. a) CH3
CH3
NO2
Conc. HNO3
Conc. H2SO4
Sn/HCl
CH3
NH2
CH3COCl
CH3
NH2
NO2
CH3
N2Cl
NO2
NaNO2/HCl
0-5
o
C
H3PO2
CH3
NO2
Sn/HCl
CH3
NH2 [3]
CH3
NHCOCH3
Conc. HNO3
Conc. H2SO4
CH3
NO2
Hydrolysis
NHCOCH3
[4]
b) SO3H
Conc. Boiling H2SO4
SO3H
Conc. Boiling H2SO4
SO3H
NaOH , Fuse
OH
OH
[2]
6