JH SIR DPP

1. PAGE NO. # 1
ETOOS ACADEMY Pvt. Ltd
F-106, Road No.2 Indraprastha Industrial Area, End of Evergreen Motor,
BSNL Lane, Jhalawar Road, Kota, Rajasthan (324005) Tel. : +91-744-242-5022, 92-14-233303
* Marked Questions are having more than one correct option.
DPP No.# 48
1. Calculate the change in pH when a 0.1 M solution of CH3
COOH in water at 25ºC is diluted to a final concentration
of 0.01 M. [Ka
= 1.85 × 10–5
]
(A) +0.5 (B) +0.4 (C) +0.7 (D) +0.6
2. At 25ºC , the dissociation constants of CH3
COOH and NH4
OH in an aqueous solution are almost the same.
The pH of a solution of 0.01 N CH3
COOH is 4 at 25ºC. The pH of 0.01 N NH4
OH solution at the same
temperature would be :
(A) 4 (B) 3 (C) 10 (D) 11
3. The acid dissociation constants of H2
S and HS–
are 10–7
and 10–13
respectively. The pH of 0.1M aqueous
solution of H2
S will be :
(A) 2 (B) 2 (C) 4 (D) 5
4.* Which of the following increase with dilution at a given temperature?
(A) pH of 103
M acetic acid solution (B) pH of 103
M aniline solution
(C) degree of dissociation of 103
M acetic acid (D) degree of dissociation of 10–3
M aniline
5. How much water must be added to 300 mL of a 0.2 M solution of CH3
COOH for the degree of dissociation of
the acid to double ? (Assume Ka
of acetic acid is of order of 10–5
M)
6. Saccharin (Ka
= 2  10 12
) is a weak acid represented by formula HSac. A 4  10 4
mole amount of
saccharin is dissolved in 200 cm3
solution of pH 3 .Assuming no change in volume , calculate the concentration
of Sac
ions in the resulting solution at equilibrium.
7. Calculate [H+
] of a solution that contains 0.1M HCOOH (Ka
= 1.8 x 10-4
) and 0.1 M HOCN (Ka
= 3.2 x 104
)
8. Find [OH–
] in a solution made by dissolving 0.005 mol each of NH3
(Kb
= 1.8 × 10–5
) and pyridine
(Kb
= 1.5 × 10–9
) in enough water to make up 1 L of the solution. What are the concentration of ammonium
and pyridinium ions.
9. What is the concentration of acetic acid which can be added to 0.5 M formic acid so that the % dissociation
of neither acid is changed by the addition. Ka
for acetic acid is 2 × 10-5
, Ka
for formic acid = 2.4 × 10-4
.
10. Hydrazine, N2
H4
, can interact with water in two stages.
N2
H4
(aq) + H2
O(l) N2
H5
+
(aq) + OH–
(aq) Kb1
= 8.1 × 10–7
N2
H5
+
(aq) + H2
O (l) N2
H6
2+
(aq) + OH–
(aq) Kb2
= 9 × 10–16
(i) What are the concentrations of OH–
, N2
H5
+
and N2
H6
2+
in a 0.010 M aqueous solution of hydrazine ?
(ii) What is pH of the 0.010 M solution of hydrazine?
PHYSICAL CHEMISTRY
DAILY PRACTICE PROBLEMS
D P P
COURSE NAME : UMANG (UP) DATE : 02.09.2013 to 07.09.2013 DPP NO. 48 & 49
TARGET
JEE (ADVANCED) : 2014

2. PAGE NO. # 2
ETOOS ACADEMY Pvt. Ltd
F-106, Road No.2 Indraprastha Industrial Area, End of Evergreen Motor,
BSNL Lane, Jhalawar Road, Kota, Rajasthan (324005) Tel. : +91-744-242-5022, 92-14-233303
DPP No. # 49
1.(a) Which of the following salts is alkaline in water?
(A) CuSO4 . 5H2O (B) K2SO4 (C) NaNO3 (D) Na2B4O7 . 10H2O
(b) Which of the following salts undergoes anionic hydrolysis?
(A) CuSO4 (B) NH4Cl (C) FeCl3 (D) Na2CO3
2.(a) The pH value will be highest for the aqueous solution of
(A) NaCl (B) Na2CO3 (C) NH4Cl (D) NaHCO3
(b) Which of the following salts does not undergo hydrolysis?
(A) NH4NO3 (B) FeCl3 . 6H2O (C) KCl (D) KCN
3. Find the concentration of H+
, HCO3

& CO3
2
in a 0.01 M solution of H2
CO3
if the pH of this is 4.1.
Ka
(H2
CO3
) = 4  107
; Ka
(HCO3

) = 4.8  1011
.
4.(a) Potassium Cyanide is the deadliest poison known. Calculate the percent hydrolysis in a 0.06 M solution
of KCN. [Ka
(HCN) = 6 × 10-10
]
(b) Calculate the degree of hydrolysis of 0.1 M sodium acetate solution if pH is 8.9 .
5. A solution contains 0.10 M H2
S and 0.25 M HCl. Calculate the concentration of [S2
] and [HS
] ions in the
solution. For H2
S, 1aK = 1.0 ×10–7
, 2aK = 1.3 × 10–13
6. Determine the [S2
] in a saturated (0.1M) H2
S solution to which enough HCl has been added to produce
a [H+
] of 2 x 104
. K1
= 107
, K2
= 1014
.
7. Ka
for butyric acid is 2.0  106
. Calculate pH and hydroxyl ion concentration of 0.02 M aqueous solution of
sodium butyrate .
8. Calculate the mass of NH4
Cl required to be dissolved in 500 ml water to have pH = 4.5,
if Kb
for NH4
OH is 10–6 .
9. Calculate hydrolysis constants for each of the following salt solutions. Compute also the pH of the solution
and the percentage of hydrolysis.
(i) 0.05 M NaAc ; Ka
(HAc) = 2 × 10–5
.
(ii) 0.008 M NH4
Cl ; Kb
(NH3
) = 2 × 10–5
.
(iii) 0.5 M Na2
S ; Ka
(HS—
) = 1.0 × 10–15
[ log (0.475) = - 0.32 ].
(iv) 0.64 M KCN : Ka
(HCN) = 4.0 × 10–10
.
ANSWER KEY
DPP No.# 48
1. (A) 2. (C) 3. (C) 4.* (ACD) 5. 900 mL.
6. [Sac–
] = 4 × 10–12
M 7. [H+
] = 7.071 × 10-3
8. [OH–
] = [NH+
4
] = 3 × 10–4
M ; [C5
H6
N+
] = 2.5 × 10–8
M.
9. C1
a1
= C2
a2
 1a CK 1
= 2a CK 2
Þ 2 × 10–5
× C1
= 2.4 × 10–4
× 0.5 = C1
= 6 M.
10. (i) [OH–
] = 9 × 10–5
M, [N2
H5
+
] = 9 × 10–5
; (ii) pH = 9.96, [N2
H6
2+
] = 9 × 10–16
.
DPP No. # 49
1.(a) (D) (b) (D) 2.(a) (B) (b) (C)
3. [H+
] = 8 × 10–5
, [HCO3
–
] = 8 × 10–5
, [CO3
2–
] = 3 × 10–11
.
4.(a) h =
C
Kh
= CK
K
a
w
 =
06.0106
10
10
14
 

= 1.66 × 10–2
= 1.66 %.
(b) 8 × 10-5
. 5. [ HS -
] = 4 × 10 -8
M ; [ S2 -
] = 2.08 × 10 -20
M.
6. [S2-
] = 2.5 × 10-15
. 7. pH = 9, [OH¯ ] = 10–5
. 8. 2.675 gm.
9. Kh
pH %Hydrolysis
(i) 5 × 10–10
8.7 0.01%
(ii) 5 × 10-10
5.7 0.025%
(iii) 10.0 13.68 95%
(iv) 2.5 × 10–5
11.60 0.625%