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Published on: 24/05/2021
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Questions + Answers key
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1.
Why is an amide more acidic than amine?
2.
(i) tert-Butylamine cannot be prepared by the action of NH3 on tert-butyl bromide. Explain why?
(ii) Suggest a convenient method for the preparation of tert-butylamine.
3.
How is 2, 4-dinitrophenylhydeazine prepared from chlorobenzene?
4.
Some halogen containing compounds are useful in daily life. Some compounds of this class are responsible for exposure of flora and fauna to more and more of UV light which causes destruction to a great extent. Name the class of these halo compounds. In your opinion, what should be done to minimise harmful effects of these compounds.
5.
Why are different colours observed in octahedral and tetrahedral complexes for the same metal and same ligands ?
6.
What is the relationship between observed colour of the complex and the wavelength of light absorbed by the complex ?
7.
CoSO4Cl.5 NH3 exists in two isomeric forms 'A' and 'B' gives white precipitate with BaCl2 but does not react with AgNO3. Answer the following questions.
(i) Identify 'A' and 'B' and write their structure formulas.
(ii) Name the type of isomerism involved
(iii) Give the IUPAC name of 'A' and 'B'.
8.
Using valence bond theory, explain the following in relation to the complexes given below :
\([Mn(CN)_6]^{3-}, [Co(NH_3)_6]^{3+}, [Cr(H_2O)_6]^{3+}, [FeCl_6]^{4-}\)
(i) Type of hybridisation
(ii) Inner or outer orbital complex.
(iii) Magnetic behaviour.
(iv) Spin only magnetic moment value.
9.
Using crystal field theory, draw energy level diagram, write electronic configuration of the central metal atom/ion and determine the magnetic moment value in the following :
(i) \([CoF_6]^{3-}, [Co(H_2O)_6]^{2+},[Co(CN)_6]^{3-}\)
(ii) \([FeF_6]^{3-}, \ [Fe(H_2O)_6]^{2+}, [Fe(CN)_6]^{4-}\).
10.
On heating compound(A) gives a gas (B) which is a constituent of air. This gas when treated with 3 mol of hydrogen (H2) in the presence of a catalyst gives another gas (C) which is basic in nature. Gas C on further oxidation in moist condition gives a compound (D) which is a part of acid rain. Identify compounds (A) to (D) and also give necessary equations of all the steps involved.
11.
On heating, lead (II) nitrate gives a brown gas 'A'. The gas 'A' on cooling changes to colourless solid 'B'. Solid 'B' on heating with NO changes to a blue solid 'C'. Identiy 'A', 'B' and 'C' and also write reactions involved and draw the structures of 'B' and 'C'.
12.
(a) what is meant by rate of a reaction.
(b) In a pseudo first order hydrolysis of ester in water, the following results are obtained:
| t in seconds | 0 | 30 | 60 | 90 |
| [Ester] M | 0.55 | 0.31 | 0.17 | 0.085 |
(i) Calculate the average rate of reaction between the time interval 30 to 60 seconds.
(ii) Calculate the pseudo first order rate constant for the hydrolysis of ester.
13.
Write down the reactions taking place in different zones in the blast furnace during the extraction of iron.
1.
The amide has the following resonating structures:

Due to the delocalisation of lone pair of electrons on N over C==O group, amino group acquires a positive charge which ma, es N-H bond weak. Moreover, the anion formed after removal of a proton is also stabilized by resonance as :
.png)
However, no such stabilization is possible in amines.
2.
(i) tert-Butyl bromide being a 3° alkyl halide on treatment with a base (i.e. NH3) prefers to undergo elimination rather than substitution. Therefore, the product is isobutylene rather than tert-butylamine.

1° amines containing tert-alkyl groups can be prepared by action of suitable Grignard reagents on O-methylhydroxylarnine. For example,
.png)
3.

4.
CFC (chlorofluoro carbons) are responsible for the destruction of ozone layer and UV light can reach earth which may cause skin cancer and affect flora and fauna.
These compounds should be banned and their use should be made to minimum extent.
5.
\({ \triangle }_{ t }=\left( \frac { 4 }{ 9 } \right) { \triangle }_{ 0 }\). Thus, \({ \triangle }_{ t }\) is smaller than \({ \triangle }_{ 0 }\). Hence, less energy (higher wavelength) is absorbed by tetrahedral complexes than by octahedral complexes of the same metal and ligands. Therefore, the observed colour are different.
6.
When white light falls on the complex, some part of it is absorbed. Greater the CFSE, greater is the energy absorbed or shorter is the wavelength absorbed \((E={hc\over\lambda })\). The observed colour is the complementary colour of the colour absorbed.
7.
(i) As isomer A reacts with AgNO3 to give a white precipitate, CI must be present in the ionization sphere. As it does not react with BaCI2, SO42- must be present in coordination sphere.
Formula of A = [Co(NH3)5SO4] CI (coordination no. of Co = 6) As reactions are reverse for isomer B, formula of B = [Co(NH3)5CI]S04
(ii) Ionization isomerism.
(iii) A = Pentaarnminesulphatocobalt (III) chloride ; B = Pentaamminechloridocobalt (ill) sulphate
8.
\([Mn(CN)_6]^{3-}\)
d2sp3, (ii) inner orbital complex, (iii) paramagnetic, (iv) 2.87 B.M.
(i) d2sp3 (ii) Inner orbital complex, (iii) diamagnetic, (iv) \(\mu=0\)
(i) d2sp3, (ii) Inner orbital complex, (iii) paramagnetic, (iv) 3.87 B.M.
(i) sp3d2, (ii) outer orbital complex (iii) paramagnetic (iv) 4.9 B.M.
9.
(i) \([CoF_6]^{3-}\)
\( [Co(H_2O)_6]^{2+}\)
\([Co(CN)_6]^{3-}\)
(ii) \([FeF_6]^{3-}\)
\(\ [Fe(H_2O)_6]^{2+}\)
\([Fe(CN)_6]^{4-}\)
It is diamagnetic due to the absence of unpaired electrons.
10.
(i) \({ NH }_{ 4 }{ NO }_{ 2 }(s)\underrightarrow { heat } { N }_{ 2 }+{ 2H }_{ 2 }O\)
'A' 'B'
(ii) \({ N }_{ 2 }+{ 3H }_{ 2 }\longrightarrow 2{ NH }_{ 3 }(g)\)
'C' basic
(iii) \({ 4NH }_{ 3 }+{ 5O }_{ 2 }\longrightarrow 4NO+{ 6H }_{ 2 }O\)
\(\\ 2NO+{ O }_{ 2 }\longrightarrow { 2NO }_{ 2 }\)
'D' (part of acid rain)
\({ 3NO }_{ 2 }+{ H }_{ 2 }O\longrightarrow 2{ HNO }_{ 3 }+NO\)
11.
\(2Pb{ { { { (NO }_{ 3 }) } } }_{ 2 }\xrightarrow { heat } 2PbO(s)+{ NO }_{ 2 }+{ O }_{ 2 }\)
Brown (A)
\({ 2NO }_{ 2 }(g)\overset { cooling }{ \rightleftharpoons } { N }_{ 2 }{ O }_{ 4 }(s)\)
(B) Colourless
\({ N }_{ 2 }{ O }_{ 4 }+2NO\overset { heat }{ \underset { 250k }{ \rightleftharpoons } } { 2N }_{ 2 }{ O }_{ 3 }(s)\)
(C) Blue solid

Resonating Structures of \({ N }_{ 2 }{ O }_{ 4 }\)
12.
(a) Rate of reaction is defined as change in cone. of reactants or products per unit time.Its unit is mol L-1 S-1.
Average rate: The rate of reaction measured over a long time interval is called average
rate of reaction: It is equal to Δx/Δt, e.g.
H2(g) + Cl2 (g) ⇾ 2HCI(g);
Rate of reaction = \(-{Δ[H_2]\over Δt}=-{Δ[Cl_2]\over Δt}=+{1\over 2}{Δ[HCl]\over Δt}\)
2HI (g) ⇾ H2 (g) + I2 (g)
Rate of reaction = \(-{Δ[HI]\over Δt}=+{Δ[H_2]\over Δt}=+{Δ[I_2]\over Δt}\)
Instantaneous rate: It is the rate of reaction when the average rate is taken over a very small interval of time. It is equal to dx/dt.
Instantaneous rate = Average rate as ∆t approaches zero.
(b) (t) Average rate = \(-\left(C_2-C_1\over t_2-t_1\right)=\left(0.17-0.31\over 60-30\right)=+{0.14\over 30}={10\over 100}\times{1\over 30}\)
= \({14\over 3}\) x 10-3 moI L-1 s-1
= 4.67 x 10-3 mol L-1 s1
(ii) \(k={2.303\over t}log{[A]_0\over [A]}={2.303\over 30}log{0.55\over 0.31}={2.303\over 30}[log 55-log 3]\)
\(={2.303\over 30}[1.7404 - 1.4914]={2.303\over 30}\times0.2490\)
= 1.91 x 10-2 s-1
13.
At 500-800 K
\(3Fe_{ 2 }{ O }_{ 3 }+CO\rightarrow 2Fe_{ 3 }{ O }_{ 4 }+CO_{ 2 }\)
\(Fe_{3 }{ O }_{ 4}+4CO\rightarrow 3Fe_+4CO_{ 2 }\)
\(Fe_{ 2 }{ O }_{ 3 }+CO\rightarrow 2Fe_{ }{ O }_{ }+CO_{ 2 }\)
At 900-1500 K
\(C+CO_{ 2 }\rightarrow 2CO\)
\(Fe_{} { O }_{ }+CO\rightarrow Fe_{ }{ }_{ }+CO_{ 2 }\)
\(C+O_{ 2}\rightarrow { }_{ }+CO_{ 2 }\)
At above 1570 K
\(Fe_{} { O }_{ }+C\rightarrow Fe_{ }{ }_{ }+CO_{ }\)
\(Ca{ CO }_{ 3 }\overset { \Delta }{ \rightarrow } Ca{ O }+CO_{ 2 }\)
\(Ca{ O }+SiO_{ 2 }\rightarrow CaSiO_{ 3 }(slag)\)
Ore, limestone, and coke
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