Exam (elaborations) Chemistry (Important Questions)

QUESTION BANK
HIGHER SECONDARY – SECOND YEAR
CHEMISTRY - VOLUME II – ENGLISH MEDIUM


UNDER THE GUIDANCE OF:

Dr. ANITHA
CHEIF EDUCATIONAL OFFICER
CHENNAI

COORDINATOR:

TMT.R.C.SARASWATHI, M.Sc.,M.Ed.,M.Phil
HEADMISTRESS
GOVERNMENT GIRLS HR.SEC.SCHOOL
ASHOK NAGAR , CHENNAI – 83

REVEIWERS:
1. THIRU. RAJU.A., PG. ASST.,
GOVT. GIRLS HR.SEC.SCHOOL
VILLIVAKKAM, CH-49.
2. THIRU.DURAICHANDRAN. PG. ASST .,
CHINMAYA VIDHYALAYA HSS,
CHINMAYA NAGAR, CH-92.

COMPILER:

TMT.A. HELEN JAYANTHI., P.G.ASST.,
ST. RAPHAEL’S GHSS,
SANTHOME, CHENNAI -4

, TEAM MEMBERS:
THIRU.G.SOUNDARARAJAN TMT.M.INDHUMATHI,
P.G.ASST., HEADMISTRESS
CHENNAI HR. SEC. SCHOOL, GOVT. HR. SEC. SCHOOL,
ALWARPET, CH-18 KUMPINIPET, ARAKKONAM.
TMT.M. VIMALA TMT.A. HELEN JAYANTHI
P.G.ASST. GOVT., GIRLS P.G.ASST.,
HR. SEC. SCHOOL, ST. RAPHAEL’S GHSS,
ASHOK NAGAR, CH-83 SANTHOME, CHENNAI -4

TMT. A . JEYA P.G.ASST., TMT.V.POONGODI
GOVT. GIRLS HR. SEC. SCHOOL, P.G.ASST.,
ASHOK NAGAR, CH-83 GUNTUR SUBIAH PILLAI GHSS.
T.NAGAR,CH-17
TMT.R PRABHA P.G.ASST., THIRU. N. SHANMUGANANDAM
JAI GOPAL GARODIA GOVT GIRLS P.G.ASST.,
HR SEC SCHOOL ICF. HR. SEC. SCHOOL,
CHOOLAIMEDU,CH- ICF COLONY, CHENNAI -38
TMT. J.R LAKSHMI KANTHAM TMT.C. LATHA P.G.ASST
P.G.ASST., JAI GOPAL GARODIA GOVT GIRLS
THE CHILDREN’S GARDEN HR SEC SCHOOL,
HR SEC SCHOOL VIRUGAMBAKKAM, CH_92
MYLAPORE, CHENNAI -4
TMT. K.S. R SARASWATHY, TMT.T.K. JAGATHEESWARI,
P.G.ASST., P.G.ASST.,
LADY WILLINGDON GOVT HR SEC RAJAH MUTHIAH HR SEC SCHOOL,
SCHOOL, TRIPLICANE, CH-5 R A PURAM,CH-28.
TMT.V. IMMACULATE, P.G.ASST., TMT.V.SORNA PREMA RANI,
HOLY ANGEL’S A.I. HR SEC P.G.ASST.,
SCHOOL, PCKG GOVT HR SEC SCHOOL,
T NAGAR, CH - 17 KODAMBAKKAM, CH - 25
TMT.V. SATHIYALATHA, P.G.ASST., TMT.V. D.JEYA, P.G.ASST.,
GOVT.MADARASA-I-AZAM HR.SEC. ANJUHAM HR SEC SCHOOL,
SCHOOL, WEST MAMBALAM, CH - 33
ANNA SALAI , CH - 2.

, 1

UNIT – 8 IONIC EQUILIBRIUM
I.Text Book Questions and Answers
1. What are Lewis acids and bases? Give two examples for each.

S.No Lewis Acids Lewis Bases
1 Species that accepts an electron pair Species that donates an electron pair
2 Ex: BF3, AlCl3 Ex: NH3, H2O



2. Discuss the Lowry-Bronsted concept of acids and bases .
• An acid is a proton donar.
HCl + H2O ⇌ H3O+ + Cl-
• A base is a proton acceptor.
NH3 + H2O ⇌ NH4+ + OH¯
• The species that remains after the donation of a proton is a base (Base1) and is called the
conjugate base of the Bronsted acid (Acid 1) .
• The species that remains after the acceptance of a proton is an acid (Acid2) and is called the
conjugate acid of the Bronsted base (Base2) .
• Lowry – Bronsted (acid – base) reaction is represented as
Acid1 + Base2 ⇌ Acid2 + Base1

Conjugate acid - base pair
________________________________________________________


HCl + H2O ⇌ H3O+ + Cl-
Proton donar (acid 1) Proton acceptor (Base 2) Proton donar (acid 2) Proton acceptor (Base 1)


Conjugate acid - base pair


• In other words, chemical species that differ only by a proton are called conjugate acid – base pairs.
• Limitations of Lowry-Bronsted Theory
Substance like BF3, AlCl3 do not have a proton but they are acids.

3. Identify the conjugate acid base pair for the following reaction in aqueous solution
i) HS- (aq) + HF ⇌ F- (aq) + H2 S (aq)


Conjugate acid - base pair



HS-( aq) + HF(aq) ⇌ F-(aq) + H2S(aq)
Base2 Acid1 Base1 Acid2

Conjugate acid - base pair

, 2



ii) HPO42- + SO32- ⇌ PO43- + HSO3-

Conjugate acid - base pair


HPO42- + SO32- ⇌ PO43- + HSO3-
Acid1 Base2 Base1 Acid2


Conjugate acid - base pair



iii) NH4+ + CO32- ⇌ NH3 + HCO3-

Conjugate acid - base pair


NH4+ + CO32- ⇌ NH3 + HCO3-
Acid1 Base2 Base1 Acid2

Conjugate acid - base pair


4. Account for the acidic nature of HClO4 in terms of Bronsted – Lowry theory, identify its
conjugate base.
HClO4 + H2O ⇌ H3O+ + ClO4-
• The conjugate base of HClO4 is ClO4-.
• When oxidation number of an element in an oxy acid increases then its acidic nature increases.
• The oxidation number of chlorine in HClO4 is 7, which weakens the bond between O-H bond and
increases the acidity.

5. When aqueous ammonia is added to CuSO4 solution, the solution turns deep blue due to the
formation of tetramminecopper (II) complex, [Cu(H2O) 4 ]2+(aq) + 4NH3 (aq) ⇌ [Cu(NH3)4 ] 2+(aq),
among H2O and NH3 which is stronger Lewis base.
• In complexes, central metal ion act as a lewis acid which has a tendency to accept lone pair of electron
from lewis base (ie) ligands.
• In the presence of a strong lewis base, the lewis acid (ie) the central metal ion undergoes ligand
exchange reaction with weak lewis base.
• In the above equation, NH3 replaces H2O molecule to form the deep blue complex, so NH3 is the
strong lewis base.

6. The concentration of hydroxide ion in a water sample is found to be 2.5 x10-6 M. Identify
the nature of the solution.
GIVEN: [OH − ] = 2.5 x 10−6 M
pOH = −log [OH − ]
= −log [2.5 x 10−6 ]
= 6 − log 2.5 = 6 – 0.3979 = 5.6021
pH = 14 - pOH
pH = 14 − 5.6021 = 8.3979.
pH = 8.3979. Since the pH is greater than 7, the solution is basic.