ACIDIC STRENGTH & BASIC STRENGTH

Acidic Strength & Basic Strength

ACIDIC STRENGTH & BASIC STRENGTH

EXERCISE # I
1. Write correct order of acidic strength of following compounds :
O O
|| ||
(i) (a) NO 2 - CH 2 - C - O - H (b) F - CH 2 - C - O - H
O O
|| ||
(c) Ph - CH 2 - C - O - H (d) CH 3 - CH 2 - C - O - H
O O
|| ||
(ii) (a) CH 3 - CH 2 - CH - C - O - H (b) CH 3 - CH - CH 2 - C - O - H
| |
F F

O
||
(c) CH 2 - CH 2 - CH 2 - C - O - H
|
F
O O
|| ||
(iii) (a) Cl - CH 2 - C - O - H (b) Cl - CH - C - O - H
|
Cl
Cl O
| ||
(c) Cl - C - C - O - H
|
Cl

(iv) (a) CH3–CH2–O–H (b) CH 3 - CH - O - H

|
CH3 CH 3
(c) CH3–C–O–H
CH3
(v) (a) (b) (c)
COOH COOH COOH
COOH COOH CH 2 - COOH
(vi) (a) | (b) CH2 (c) |
COOH COOH CH 2 - COOH

(vii) (a) H–F (b) H–Cl (c) H–Br (d) H–I

(viii) (a) CH4 (b) NH3 (c) H2O (d) H–F

(ix)(a) F–CH2–CH2–O–H (b) NO2–CH2–CH2–O–H

Å
(c) Br–CH2–CH2–O–H (d) NH3 - CH2 - CH2 - O - H

(x) (a) CH3COOH (b) CH3CH2OH (c) C6H5OH (d) C6H5SO3H

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2. Explain which is a stronger acid.

O O
|| ||
(a) CH3CH3 or BrCH2NO2 (b) CH 3 - C - CH 3 or CH 3 - C - CH 2CN

OH

(c) or (d) or

O=C–CH 3

3. Which of the following would you predict to be the stronger acid ?

(a) Benzoic acid or para-nitrobenzoic acid (b) CH3–CH2–CH2–OH or CH3–CH = CH – OH
(c) CH3 – CH = CH – CH2 – OH or CH3 – CH = CH – OH
4. Arrange the given phenol & its derivative in their decreasing order of acidity :

(I) C6H5–OH (II) F OH (III) Cl OH (IV) O2N OH

Select the correct answer from the given code:

(A) IV > III > I > II (B) IV > II > III > I (C) IV > III > II > I (D) IV > I > III > II
5. Which one of the following is the most acidic?

(A) (B) (C) (D) CH2=CH–CH3

6. Which of the following is weakest acid?

(A) (B) (C) (D)

7. Arrange pH of the given compounds in decreasing order:

(1) Phenol (2) Ethyl alcohol (3) Formic acid (4) Benzoic acid
(A) 1 > 2 > 3 > 4 (B) 2 > 1 > 4 > 3 (C) 3 > 2 > 4 > 1 (D) 4 > 3 > 1 > 2
8. Arrange acidity of given compounds in decreasing order:
(I) CH3–NH–CH2–CH2–OH (II) CH3–NH–CH2–CH2–CH2–OH
Å
(III) (CH 3 )3 N - CH 2 - CH 2 - OH
(A) III > I > II (B) III > II > I (C) I > II > III (D) II > I > III

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9. Consider the following compound

O
||
CH 3CCOOH

I II III
Which of the above compounds reacts with NaHCO3 giving CO2
(A) I, II and III (B) I and III (C) II and III (D) I and II
10. Say which pka belong to which functional group in case of following amino acids :

(i) cysteine : 1.8, 8.3 & 10.8

(ii) glutamic acid : : 2.19, 4.25, 9.67

11. Record the following sets of compounds according to increasing pKa ( = – log Ka)

(a) , , cyclohexane carboxylic acid.

(b) 1-butyne, 1-butene, butane

(c) Propanoic acid, 3-bromopropanoic acid, 2-nitropropanoic acid
(d) Phenol,o-nitrophenol, o-cresol
(e) Hexylamine, aniline, methylamine
12. Write correct order of acidic strength of following compounds:

O–H O–H O–H O–H

NO2 NO2 NO2 NO2
(i) (a) (b) (c) (d)

NO2 NO2 NO2

O–H O–H O–H

(ii) (a) (b) (c)

NO2 Cl CH3

O–H O O–H O–H O–H

N
\ (iii)(a) O (b) O (c) (d)
N
O N
O O

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O–H O–H O–H O–H

(iv) (a) (b) (c) (d)

O–H O–H O–H

Cl
(v) (a) (b) (c)
Cl
Cl
O O
C–O–H C–O–H
CH3
(vi)(a) (b)

O O O
C–O–H C–O–H C–O–H
(vii) (a) (b) (c) NO2

NO2
N
O O
13. Select the strongest acid in each of the following sets :
OH OH OH OH

(i) (a) (b) (c) (d)

CH3 NO2 Cl NH2

OH OH OH OH

(ii) (a) (b) (c) (d)

NO2 F CH3

OH OH OH OH
OMe
(iii)(a) (b) (c) (d)
OMe
OMe
OH OH OH
NO2 OH
NO2
(iv)(a) (b) (c) (d)
NO2 NO2 NO2
NO2 NO2
NO2

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 Acidic Strength & Basic Strength

14. The strongest acid is :

(A)HF (B) CH3CO2H (C) HF + SbF5 (D) H2S
15. The weakest acid (does not show acidic character) is :
(A)HC º CH (B) CH2 = CH2 (C) Me3CH (D) Ph3CH
16. Which of the following is most acidic :
COOH COOH COOH COOH

(A) (B) (C) (D)

CH3
NO2 CH3
Paragraph for Question 17 to 18
The most important condition for resonance to occur is that the involved atoms in resonating structure
must be coplanar or nearly coplanar for maximum delocalisation. If this condition does not fulfil,
involved orbitals cannot be parallel to each other and as a consequence delocalisation cannot occcur.
Bulky groups present on adjacent atoms inhibit the planarity of atoms involved in resonance. This
phenomenon is known as steric inhibition of resonance. Steric inhibition of resonance has profound
effect on
(1) Physical properties (2) Acidity and basicity (3) Reactivity of organic compounds
17. Arrange the following in the decreasing order of basicity :
NH2 CH3–N– CH3 NH2 NH2

(I) (II) (III) (IV)

NO2
NO2
(A) I > II > III > IV (B) IV > III > II > I (C) II > I > IV > III (D) I > IV > III > II
18. Which of the following is most acidic :
COOH COOH COOH COOH

(A) (B) (C) (D)

CH3
CH3 CH3
19. How many following compounds are more acidic than water ?

(a) SO3H (b) HCl (c) CH3 – C º CH (d) CO 2H

OH
OH
(e) (f) (g) (h)
NO2
(i) NaOH
20. Select correct order regarding acidic strength of given compounds :
(1) o-methylbenzoic acid (2) m-methylbenzoic acid
(3) p-methylbenzoic acid (4) benzoic acid
(A)1 > 2 > 3 > 4 (B) 4 > 3 > 2 > 1 (C) 1 > 4 > 2 > 3 (D) 3 > 2 > 4 > 1
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EXERCISE # II
1. Write decreasing order of basic strength of following :
– – – –
(i) (a) CH3 (b) NH2 (c) OH (d) F
– – – –
(ii) (a) F (b) Cl (c) Br (d) I

(iii) (a) NH3 (b) MeNH2 (c) Me2NH (d) Me3N (in H2O)

(iv) (a) NH3 (b) MeNH2 (c) Me2NH (d) Me3N (Gas phase)

(v) (a) R–NH2 (b) Ph–NH2 (c) R - C - NH 2

||
O
O
(vi) (a) (b) (c)
NH NH N

Me

NH2 NH2

(vii)(a) (b) (c)

NH

N N N
(viii) (a) (b) (c)
O2N Me F

NH2 NH2 NH2 NH2

(ix) (a) (b) (c) (d)

Å Cl CH 3 H
NH3

2. Write decreasing order of basic strength of following :

·· ·· ··
(i) (a) CH3–CH2– N H 2 (b) CH3–CH= NH (c) CH3–Cº N

· · ·· · · · · · ·
(ii) (a) CH 3 - C - NH 2 (b) CH3–CH2– NH 2 (c) CH 3 - C - N H 2 (d) NH 2- C - N H 2
|| || ||
O NH
··
N
··
H

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NH2

(iii) (a) (b) (c)

N N
H

NH2 NH2 NH2 NH2

(iv) (a) (b) (c) (d)

NO2 CN OMe NH2

NH2 NH2 NH2

NO2
(v) (a) (b) (c)
NO2
NO2

NH2 NH2
Me Me
(vi) (a) (b)
Me Me
N N
O O O O

O
NH–C–CH3 NH2 NH–CH2–CH3

(vii)(a) (b) (c)

(viii) (a) (b) (c) (d)

(ix) (a) (b) (c) (d)

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3. Select the strongest base in following compound :
O S
(i) (a) (b) (c) (d)
N N N N
H H H
NH2

(ii) (a) (b) (c) (d)

NH
N N
H
N
(iii) (a) (b) (c) (d)
N N N N

H H CH3 Et

Ph H Me
+
N¯Li N N N

(iv) (a) (b) (c) (d)

4. Arrange the following compound in decreasing order of their basicity.

(i) (a) H2C = CHNa (b) CH3CH2Na (c) CH3CH2ONa (d) HC º CNa

(ii) (a) NH2 (b) CH2 – NH2 (c) NH2 (d) C – NH2
NO2 O

(iii) (a) HO¯ (b) NH3 (c) H2O (d) HSO4¯

5. Correct decreasing order of basic strength -

NH2 NH2 NMe2

N N H–N N
H–N
N
H
(I) (II) (III)

Of following compound -
(A) III > II > I (B) II > I > III (C) I > II > III (D) III > I > II

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6. Consider the following bases:

(I) o-nitroaniline (II) m-nitroaniline (III) p-nitroaniline
The decreasing order of basicity is:
(A) II > III > I (B) II > I > III (C) I > II >III (D) I > III > II
7. Consider the basicity of the following aromatic amines:
(I) aniline (II) p-nitroaniline (III) p-methoxyaniline (IV) p-methylaniline
The correct order of decreasing basicity is:
(A) III > IV > I > II (B) III > IV > II > I (C) I > II > III > IV (D) IV > III > II > I
8. Which one of the following is least basic in character?

(A) (B) (C) (D)

9. In each of the following pair of compounds, which is more basic in aqueous solution?
Give an explanation for your choice:
(a) CH3NH2 or CF3NH2

(b) CH3CONH2 or H2N NH2

(c) CH3CH2CH2NH2 or CH3CN
(d) C6H5N(CH3)2 or 2,6-dimethyl-N-N-dimethylaniline
10. Choose the member of each of the following pairs of compunds that is likely to be the weaker base.
(a) H2O or H3O+ (b) Cl¯, SH¯ (c) F¯, OH¯, NH¯,
2 CH¯
3 (d) HF, H2O, NH3
(e) OH¯, SH¯, SeH¯
11. Explain which compound is the weaker base.

(a) or (b) CH2 = CH – CH = CH – CH2– or CH2 = CH – CH2–

COO¯ COOH
(c) | or | (d) or
COOH COOH

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12. Arrange the basic strength of the following compounds.

(a) OH¯ CH3COO¯ Cl¯

(i) (ii) (iii)
(b) CH º C¯ CH2 = CH¯ CH3CH 2¯
(i) (ii) (iii)
(c) CH2 = CHCH2NH2 CH3 CH2 CH2 NH 2 CH º C – CH2NH2
(i) (ii) (iii)

(d)

(i) (ii) (iii)

13. Arrange the following compounds in order of increasing basicity.

(a) CH3NH2, CH3 NH 3Å , CH3NH¯ (b) CH3O¯, CH3NH¯, CH3CH¯2

14. Which of the following is most basic :

N N
N N N
N N
(A) (B) (C) (D)
N

15. Basicity order of N in following compound is :

CH3 CH3
O
Nb
H2N– C– CH 2 CH2 – NH – C– CH 3
c
NH
a
N
CH3 d CH3

(A) b > d > a > c (B) a > b > d > c (C) a > b > c > d (D) a > c > b > d

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16. The conjugate base of serotonin (used as tranquilisers) is given as follows :

CH2–CH2–NH2
–
O

••
N
H

How many basic groups present in following compound ?

17. The structure of saccharin is given as follows :
O
C
NH [Provided N is the donor atom in all cases]
S
O O
How many following compounds are more basic than saccharin ?
O
C
(i) CH3– C – NH2 (ii) H2N– C – NH 2 (iii) CH3 – C – NH2 (iv) N–H
C
NH NH O
O
CH2–NH2
(v) (vi) N

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EXERCISE # III
1. In given reaction Gas liberated is/are

O O–H
C
14
NaHCO3

SO3H

(A) CO2 & SO3 (B) SO3 & 14CO2 (C) 14CO2 only (D) SO2 only
2. Arrange marked atom in decreasing order of acidic strength
2
H O
3 1
H N–H

(A) 1 > 2 > 3 (B) 3 > 2 > 1 (C) 2 > 1 > 3 (D) 2 > 3 > 1
3. Column - I Column-I
OH

(A) (P) React with NaOH

OH

(B) (Q) React with NaHCO3

OH

(C) (R) React with NaH

NO2

OH
NO2
(D) (S) React with Na

NO2
(T) React with NaNH2

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4. Compound which can give effevescences with NaHCO3

OH O OH
COOH
(i) (Salicylic acid) (ii) (Squaric acid)
O OH
SO3H OH
O2N NO2
(iii) (Benzene sulphonic acid) (iv) (Picric acid)

NO2

OH
(v) Ph–CH=CH–COOH (cinnamic acid) (vi)

OH CH2–OH OH OH
NO2
(vii) (viii) (ix) (x)
NO2
NO2
5. Statement-1 : For the given two compounds-I is more acidic than compounds-II.
NO2 CN
H3C CH3 H3C CH3

OH OH
(I) (II)

and
Statement-2 : Due to presence of –CH3 group at ortho positions to –NO2 ; the plane of –NO2
deviates, w.r.t plane of ring.
(A) Statement-1 is True, Statement-2 is True ; Statement-2 is a correct explanation for Statement-1.
(B) Statement-1 is True, Statement-2 is True ; Statement-2 is NOT a correct explanation for Statement-1.
(C) Statement-1 is True, Statement-2 is False.
(D) Statement-1 is False, Statement-2 is True.

6. Statement 1 : is more basic than

O N O O
N
(I) H
(II)

and
Statement 2 : Lone pair electrons on nitrogen in compound (I) does not participate in resonance.
(A) Statement-1 is True, Statement-2 is True ; Statement-2 is a correct explanation for Statement-1.
(B) Statement-1 is True, Statement-2 is True ; Statement-2 is NOT a correct explanation for Statement-1.
(C) Statement-1 is True, Statement-2 is False.
(D) Statement-1 is False, Statement-2 is True.

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7. Match Column-I with Column-II.

Column - I (Facts) Column - II (Reasons)
(A) Guanidine H2N–C–NH2 is example (P) Resonance stabilisation of conjugate acid
of strong base NH of strong base.
(B) Carbanion stability CCl3 > CF3 (Q) Due to s-character of central atoms
(C) Alkyne is more acidic than alkene (R) Due to d-orbital resonance
(D) Acidity : (S) Due to formation of aromatic anion

< (T) Stability of conjugate base due to more

number of identical resonating structure

8. Match Column-I with Column-II.
Column - I (Compounds) Column - II (pKa)

(A) HO F (P) 7.15

(B) HO Cl (Q) 10.14

(C) HO NO2 (R) 9.98

(D) HO CH3 (S) 9.38

(T) pKa is more than phenol

(Comprehension) (Q.9 to Q.11)
Observe the following feasible reactions :

COOH ONa COONa OH

(i) + +

NO 2 NO 2

OH ONa
NO2 NO2
(ii) + NaHCO3 ¾® + H2CO3

NO 2 NO 2

ONa OH

(iii) + H2CO3 ¾® + NaHCO3

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 Acidic Strength & Basic Strength
Answer the following question :
9. Which of the following is the correct order of acidic strength.

COOH OH OH COOH OH OH
NO2 NO2
(A) > > H2CO3 > (B) > > > H2CO3

NO 2 NO 2

COOH OH OH
NO2
(C) > H2CO3 > > (D) None

NO 2

10. Which of the following compound does not react with NaHCO3

OH OH OH COOH

(A) (B) (C) (D)

NO 2
CH3 NO2 NO2

11. Identify the feasible reactions

COOH COONa

(A) + NaHCO3 ¾® + H2O + CO2

NH2 NHNa

(B) + NaHCO3 ¾® + H2O + CO2

OH ONa

(C) + NaHCO3 ¾® + H2O + CO2

COONa COOH COOH COO¯

(D) + ¾® +

NO2 NO2

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12. Identify the non-feasible reaction

••
ˆˆ† CH3—C º C + NH3
(A) CH3–C º CH + NH2¯ ‡ˆˆ

ˆˆ† CH3CH2ONa + H2
(B) CH3CH2—OH + NaH ‡ˆˆ

ˆˆ† CH3ONa + H2O

(C) CH3—OH + NaOH ‡ˆˆ

ˆˆ† HCºCNa + H2O

(D) HCºCH + NaOH ‡ˆˆ
13. Select the number of compounds in which deprotonation gives aromatic anion :
O
HO–CH2 O
O O
O
HN NH H
(A) (B) HO (C) (D)
O O HO OH N O
Barbituric acid Ascorbic acid |
(Vitamin-C) H
Paragraph for Questions 14 and 15

Aqueous
Layer
(Salt - B)
Aqueous
OH Organic Layer
NaOH

Aqueous
COOH NaHCO3
Organic
Layer
Aqueous Layer (Compound - C)
(Salt - A)
Mixture of
3-compounds
in hexane
14. Identify salt 'A' ?
– + – +
O Na COO Na +
– Na

(A) (B) (C) (D) All of these

15. Identify compound 'C' ?

OH COOH OH

(A) (B) (C) (D)

COOH

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ANSWER KEY

EXERCISE # I

1. (i) a > b > c > d, (ii) a>b>c, (iii) c > b > a, (iv) a > b > c,
(v) c > b > a, (vi) a > b > c (vii) d > c > b > a , (viii)d > c > b > a,
(ix) d > b > a > c, (x) d > a > c> b

2. (a) 2 ; (b) 2 ; (c) 1 ; (d) 1 3. (a) 2 ; (b) 2 ; (c) 2 4. (C) 5. (B)

6. (B) 7. (B) 8. (A) 9. (A)

10. (i) cysteine : (ii) glutamic acid :

11. (a) 3 < 2 < 1 ; (b) 1 < 2 < 3 ; (c) 3 < 2 < 1 ; (d) 2 < 1 < 3 ; (e) 2 < 3 < 1

12. (i) d > c > a > b, (ii) a > b > c, (iii) c > a > b > d, (iv) d > b > c > a,

(v) a > b > c, (vi) b > a (vii) c > a > b

13. (i) b , (ii) a, (iii) b , (iv) b 14. (C) 15. (C) 16. (B)
17. (C) 18. (B) 19. (4) 20 (C)

EXERCISE # II
1. (i) a > b> c> d, (ii) a > b > c > d, (iii) c > b> d> a , (iv) d > c > b > a

(v) a > b > c, (vi) c > b > a (vii) c > a > b, (viii) b > c > a, (ix) c > d > b > a

2. (i) a > b > c, (ii) d > c > b > a, (iii) b > c > a, (iv) d > c > b > a,

(v) b > a > c, (vi) b > a, (vii) c > b > a, (viii) d > a > b > c

(ix) d > c > b > a

3. (i) d, (ii) b, (iii) a, (iv) a

4. (i) b > a > d > c, (ii) b > a > c > d, (iii) a > b > c > d

5. (A) 6. (A) 7. (A) 8. (A)

9. (a) i , (b) ii , (c) i , (d) ii 10. (a) 2 ; (b) 1 ; (c) 1 ; (d) 1 ; (e) 3

11. (a) 2; (b) 1;(c) 2; (d) 2 12. (a) 1 > 2 > 3 ; (b) 1 < 2 < 3 ; (c) 3 < 1 < 2 ; (d) 2 < 1 < 3

13. (a) 2 < 1 < 3 ; (b) 1 < 2 < 3 14. (C) 15. (B)
••
16. 3, 3 basic groups are NH 2 ; –NH–;O — 17. (6)

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EXERCISE # III
1. (C) 2. (C)

3. (A) – R, S, T ; (B) – P, R, S, T ; (C) – P, Q, R, S, T ; (D) – P, Q, R, S, T

4. (i) , (ii) (iii) (iv), (v) (ix) 5. (D) 6. (A)

7. (A) – P,T ; (B) – R; (C) – Q ; (D) – S, T 8. (A) – R ; (B) – S; (C) – P ; (D) – Q, T

9. (A) 10. (A) 11. (A, D) 12. (D)

13. (A, B, C, D) 14. (B) 15. (C)

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