Coordination Compounds 1-mark questions(objective)

1. A compound has an empirical formula CoCl3.5NH3. When an aqueous solution of this compound is mixed with excess of silver nitrate, 2 moles of AgCl precipitates per mole of the compound. Hence the compound is

(a) [Co(NH3)5Cl2]Cl (b) [Co(NH3)5Cl]Cl2

1. The oxidation state of cobalt in the following comples is [Co(NH3)4Cl2]Cl:

a) +1 b)+2 c)+3 d)0

5. The number of unpaired electrons in d⁶, low spin, octahedral complex is : a) 4

b) 2 c) 1 d) 0

6. Which ion would you expect to have the largest splitting of d-orbitals?

a) [Fe(CN)6]^4- (b)[Fe(CN)6]^3- (c)[Fe(H2O)6]²⁺ (d)[Fe(H2O)6]³⁺

7. Statement-1: [Co(NH3)3Cl3] does not give white precipitate with AgNO3 solution.

Statement-2: Chlorine is not present in the ionisable part of the given complex.

a) If both the statements are true and statement-2 is the correct explanation of statement-1.

b) If both the statements are true but 2 is not the correct explanation of statement-1.

c) If statement-1 is True and statement-2 is False.

d) If statement-1 is False and statement-2 is True.

2-marks questions(objective)

1. The magnetic moment of a complex ion is 2.83 BM. The complex ion is a) [Cr(H2O)6]³⁺ (b) [Cu(CN)4]^2- (c) [V(H2O)6]³⁺ (d) [MnCl4]

2-2. Which of the following complex has five unpaired electrons

a) [Mn(H2O)6]²⁺ (b) [Mn(CN)6]^3- (c) [CrCl3(H2O)3] (d) [Ag(NH3)2]⁺

3. Among the following ions, which one has the highest paramagnetism ? a) [Cr(H2O)6]³⁺

b) [Fe(H2O)6]²⁺

c) [Cu(H2O)6]²⁺

d) [Zn(H2O)6]²⁺

Case- based ( 3 marks)

The colour in the coordination compounds can be readily explained in terms of the crystal field theory. Consider, for example, the complex [Ti(H2O)6]³⁺, which is violet in colour. This is an

octahedral complex where the single electron (Ti³⁺ is a 3d¹ system) in the metal d orbital is in the t2g

level in the ground state of the complex. The next higher state available for the electron is the empty eg level. If light corresponding to the energy of yellow-green region is absorbed by the

complex, it would excite the electron from t2g level to the eg level (t2g1 eg0 → t2g0 eg1 ). Consequently, the complex appears violet in colour. The crystal field theory attributes the colour of the

coordination compounds to d-d transition of the electron.

1. Which of the following species is expected to be colourless?

(a) [Ti(H2O)6]³⁺ (b) [Ti(NO3)4] (c) [Cr(NH3)2]⁺ (d) [Fe(CN)6]

4-e) Among TiF62- , CoF63-, Cu2Cl2 and NiCl42- (atomic numbers of Ti = 22, Co = 27, Cu = 29, Ni = 28), the colourless species are

(a) CoF₆³⁻and NiCl²₄⁻ (b) TiF₆²⁻ and CoF₆³⁻ (c) Cu2Cl2 and NiCl²₄⁻ (d) TiF62- and Cu2Cl2 f) Which of the following statements is not correct?

a) TiCl4 is a colourless compound.

b) [Cr(NH3)6)]Cl3 is a coloured compound.

c) K3[VF6] is a colourless compound.

d) [Cu(NCCH3)4][BF4 ] is a colourless compound

2-marks questions(subjective)

1. What is the coordination number and the oxidation state of the metal in each of the following complexes?

(a) [AgCl2]^- (b) [Cr(H2O)5Cl]²⁺ (c) [Co(NCS)4]^2–

(d)[Co(NH3)3(NO2)3] (e)[Fe(EDTA)]^– (f) [Cu(en)2]SO4

2. Write down the formulae of the following compounds (a) diamminetriaquahydroxidochromium (III) nitrate (b) tetrakis(pyridine)platinum(II) tetraphenylborate(III) (c) dibromidotetracarbonyliron (II)

(d) ammonium diamminetetrakis(isothiocyanato)chromate(III).

3. Predict the hybridisation and geometry of the following complexes.

(a) [NiBr4]^2– (b) [AuCl4]^– (c) [Pt(NH3)4]²⁺

4. The magnetic moment of [MnBr4]^2– is 5.9 B.M. What is the geometry of this complex ion?

3-marks questions(subjective)

1. Complete the following statements for the coordination entity (complex ion) [CrCl2(OX)2] 3-(a) OX is abbreviation for ____________

(b) The oxidation number of chromium is ____________

2. Write down the IUPAC nomenclature of the given complex along with its hybridisation and structure.

3. Explain [Co(NH3)6]³⁺ is an inner orbital complex whereas [Ni(NH3)6]²⁺ is an outer orbital complex.

4. Draw figure to show the splitting of d orbitals in an octahedral crystal field.

5-marks questions(subjective)

1. For each of the following complexes, draw a crystal field energy-level diagram, assign the electrons to orbitals, and predict the number of unpaired electrons:

(a) [CrF6 ]^3– (b) [V(H2O)6]³⁺ (c) [Fe(CN)6]^3– (d) [Cu(en)3]²⁺ (e) [FeF6]^3–.

2. Write down the IUPAC name for each of the following complexes and indicate the oxidation state, electronic configuration and coordination number. Also give magnetic moment of the complex: (i) K[Cr(H2O)2(C2O4)2].3H2O (iii) CrCl3(py)3 (v) K4[Mn(CN)6] (ii) [Co(NH3)5Cl]Cl2 (iv) Cs[FeCl4]

SOLUTIONS

1-mark questions(objective)

1. (b), As the moles of AgCl precipitated is 2 so there must be two chloride ions outside the sphere.

Thus the compound would be [Co(NH3)5Cl]Cl2. 2. (c), x+(-2) = +1 ➔X= +3

3. (b), while naming complex compounds alphabetical order is followed.

4. (b), ethylene diamine has two nitrogen which can bind through central metal atom/ion.

5. (a), coordination no. is 4 and hybridisation is dsp² 6. (d), all the electrons will pair up in d⁶ low spin complex.

7. (a), strong ligand and high charge on metal ion results in higher splitting of d-orbitals.

8. (a).

2-marks questions(objective)

1. (c), for magnetic moment to be 2.83 BM there must be 2 unpaired electrons.

V³⁺ ion has d² configuration.

2. (a), Mn⁺² has d⁵ configuration.

3. (b), Fe²⁺ has max no. of unpaired electrons i.e. 4 Case- based (3 marks)

1. (b), Ti⁴⁺has d⁰ configuration. There will be no d-d transition.

2. (d), Ti⁴⁺ and Cu⁺ ion has d⁰ and d¹⁰ configuration. Thus there will not be any d-d transition.

3. (c), V³⁺ has d¹ configuration. So there will be d-d transition and it will be coloured.

2-marks questions(subjective)

1. The coordination number of the central atom/ion is determined by the number of sigma bonds between the ligands and the central atom/ions i.e. the number of ligand donor atoms to which the metal is directly attached. The oxidation number of the central atom is defined as the charge it would carry if all the ligands are removed along with the electron pairs that are shared with the central atom. Complex Coordination Number and Oxidation State respectively are:

(a) 2 ,1 (b) 6, 3 (c) 4 ,2

(d) 6, 3 (e) 6, 3 (f) 4, 2

2. (a) [Cr(NH3)2(H2O)3(OH)](NO3)2 (b) [Pt(Py)4][B(ph)4]2

(d) (NH4)[Cr(NH3)2(NCS)4].

3. (a)sp³ , tetrahedral (b) dsp² , square planar (c) dsp² , square planar.

4. Since the coordination number of Mn²⁺ ion in this complex ion is 4, it may be either tetrahedral (sp³ hybridisation) or square planar (dsp² hybridisation) as shown below at (b) and (c). But the fact that the magnetic moment of the complex ion is 5.9 B.M. shows that it should be tetrahedral in shape rather than square-planar.

3d 4s 4p

(a) Mn²⁺ ion (3d⁵)

(b) [MnBr4]^2–

(sp³

hybridisation–

tetrahedral shape)

3d 4s 4p

(n = 5,  = 5.9 B.M) Br ^– Br ^– Br ^– Br ^– sp³ hybridisation-tetrahedral shape

×× ×× ×× ××

(dsp² hybridisation–

square planar shape)

3d 4s 4p

(n=3, =3.8 B.M)

Br ^– Br ^– Br^– Br ^– dsp² hybridisation–

square planar shape ×× ×× ×× ×× ××

3-marks questions(subjective)

46 1. (a) oxalato (b) +3 (c) 6

K2[Cr(NO)(NH3)(CN)4] ; µ = 1.73 B.M.

(Potassium amminetetracyanonitrosoniumchromate(I)

Cr is in +1 oxidation state and possess d²sp³ hybridisation with one unpaired electron.

 = ⁿ⁽ⁿ⁺²⁾= ¹⁽¹⁺²⁾ = ³ = 1.73 BM.

5-marks questions(subjective) 1.

47 2.

UNIT –X : Halokanes and Haloranes Haloalkane & Haloarene

Question Bank Read the given passage and answer the questions that follow:

The substitution reaction of alkyl halides occurs in SN¹ or SN² mechanism whatever mechanism alkyl halide follow for substitution reaction to occur, the polarity of the carbon-halogen bond is responsible for the substitution reaction. The rate of SN¹ reactions are governed by the stability of carbocation where as for SN² reactions steric factor is the deciding factor. If the starting material is a chiral compound, we may end up with an inverted product or racemic mixture depending upon the type of mechanism followed by alkyl halide. Cleavage of ethers with HI is also governed by steric factor and stability of carbocation which indicates that in organic chemistry, these two major factors help us in deciding the kind of product formed.

1. The order of reactivities of the following alkyl halides for a SN² reaction is

(a) CH3F > CH3Cl > CH3Br > CH3I (b) CH3F > CH3Br > CH3Cl > CH3-I (c) CH3Cl > CH3Br > CH3F > CH3I (d) CH3I > CH3Br > CH3Cl > CH3F

2. The stereochemistry of the product formed if optically active alkyl halide undergoes substitution reaction by S^N¹ mechanism is -

(a) Optically active inverted product (b) Optically active retention product (c) Racemic mixture

4. n-propyl bromide on treatment with ethanolic potassium hydroxide produces (a) propane (b). propene (c) propyne (d) propanol

Answer

1 d 3 c

2 c 4 b

Multiple Choice Question 1. Which of the following are secondary bromides?

(a) CH3CH2Br (b) (CH3)3CCH2Br (c) CH3CH(Br)CH2CH3 (d)(CH3)2CBr 2. IUPAC name of (CH3)3CCl

(a) 3-Chlorobutane (b) 2-Chloro-2-methylpropane (c) t-butyl chloride (d) n-butyl chloride

3. C – X bond is strongest in

(a) CH3F (b) CH3Cl (c) CH3Br (d) CH3I

4. The best method for the conversion of an alcohol into an alkyl chloride is by treating the alcohol with :

(a) PCl5

(b) dry HCl in the presence of anhydrous ZnCl2

5. A Grignard reagent may be made by reacting magnesium with (a) CH3COOH (b) CH3 CH3 (c) CH3CH2 I (d) CH3CH2OH

6. Reaction used to prepare alkyl iodide from alkyl bromide by using NaI in acetone is (a) Willamson’s reaction (b) Swart reaction

7. Which of the reaction given below is an example of Swart Reaction a) C2H5Cl + KOH + H2O → C2H5OH

b) C2H5Br + AgF → C2H5F

c) C2H5Br + Na (dry ether) →n- butane d) CH3CH=CH2 + HBr → CH3CH(Br)CH3

8.

A hydrocarbon that does not gives only one monochloro product on photo chlorination is

In these questions a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.

a) Assertion and reason both are correct statements and reason is correct explanation for assertion.

b)Assertion and reason both are correct statements but reason is not correct explanation for assertion.

c) Assertion is correct statement but reason is wrong statement.

d)Assertion is wrong statement, but reason is correct statement.

1. Assertion: Iodoalkanes undergo nucleophilic substitution more readily than bromoalkanes

Reason: Iodine is a better leaving group due to its larger size which makes the covalent bond weaker.

2. Assertion: SN² reaction is a bimolecular reaction

Reason: Both alkyl halide and nucleophiles are involved in the slow step.

3. Assertion: Haloalkanes react with KCN to form cyanoalkanes.

Reason: KCN completely ionises in solution.

4. Assertion: Alkyl halides are polar molecule but immiscible in water.

Reason: Alkyl halides form hydrogen bonding with water.

Answers

1 a 2 A 3 a 4 a

Very short answer type Questions (Each question carries one mark)

1. Out of CH2=CH—CH2Cl and CH3CH2CH2Cl which one undergoes SN¹mechanism faster?

Ans : CH2=CH—CH2Cl undergoes faster SN¹ reaction because allyl carbocation gets stabilised by resonance

(2) Name the instrument used for measuring the angle by which the plane polarised light is rotated.

Ans. Polarimeter

(3) What is racemic mixture?

Ans : Mixture in which two enantiomers are present in equal proportion with net zero optical rotation.

(4) Mention the product obtained by hydrolysis of 2,4,6-trinitrochlorobenzene?

Ans : 2,4,6-trinitrophenol commonly known as picric acid is obtained

Short Answer type Questions : (Each question carries 2 marks) 1. Write short notes on

(a) Fittig reaction (b) Wurtz reaction Ans : (a) Fittig reaction :

(b) Wurtz reaction

2. Mention two difference between SN¹ and SN²

Ans:

SN² SN¹

Rate of reaction = k[Alkyl halide] [Nucleophile] Rate of reaction = k.[Alkyl halide]

Bimolecular reaction Unimolecular reaction

Only inversion of configuration takes place. Both retention and inversion of configuration takes place.

Optically active alkyl halide gives optically active product.

Optically active alkyl halide gives racemic mixture.

3. (a) Arrange the following compounds in the decreasing order of rate of reaction towards SN1

reaction

C6H5CH2Br, C6H5CH(C6H5)Br, C6H5CH(CH3)Br, C6H5C(CH3)(C6H5)Br

(b)In the following pair of halogen compounds, which would undergo SN² reaction faster?

Answer : (a)

(b) will undergo faster SN²

Short Answer type Question: (Each question carries 3 marks)

1. Among the isomeric alkyl bromide of molecular formula C4H9Br (i) Write the compound which is optically active

(ii) Write the compound which is more reactive towards SN² reaction (iii) Write the compounds which is more reactive towards SN¹ reaction.

Answer: (i) CH3CH2CH(Br)CH3 , Contains a chiral centre at carbon containing Br (ii) CH3CH2CH2CH2Br , Primary alkyl halide

(iii)(CH3)3CBr , Tertiary alkyl halide 2. Give reasons

a. C―Cl bond length in chlorobenzene is shorter than C-Cl bond length in CH³―Cl b. Boiling point of n-butyl chloride is more than t-butyl chloride

c. Grignard reagents should be prepared under anhydrous conditions Answer

a) In chlorobenzene, there is partial double bond character b/w carbon and halogen due to + resonance effect.

b) Strong Van-der-waal interaction due to more surface area in n-butyl chloride compared to t-butyl chloride.

c) Grignard reagent is highly reactive and its forms alkane in presence of moisture.

3. Account for the following .

(a) The dipole moment of chlorobenzene is lower than that of cyclohexyl chloride.

(b) Alkyl halides though polar immiscible in water

(c)Sulphuric acid not used during the reaction of alcohols with KI Ans :

(a) Due to resonance chlorine gets partial positive charge in chlorobenzene resulting in lowering of dipole moment

(b) The force of interaction between alkyl halide and water is less compared to dipole interaction between alkyl halide and hydrogen bonding in water.

4. Write the major product in the following reaction :

Answer

(a)

(b)

(c)

5. Write the product when

a) Chlorobenzene is treated with Cl2 and AlCl3

b) Chloroethane is treated with magnesium in dry ether c) Methyl bromide is treated with AgNO2

(a)

(b) CH3CH2Cl + Mg (in dry ether) ---> CH3CH2MgCl (c) CH3Br + AgNO2 --- > CH3NO2 + AgBr

Long Answer type Question ( Carrying 5 marks ) 1. (a) Identify A,B,C,D

(b) Carry out the following conversion (i) Ethanol to butane

(ii) Propene to propan-1-ol (iii) Toluene to benzyl iodide

Ans : (a) A ➔ H2C=CH2 B ➔ CH3CH2OH C ➔ CH3CH2NC D ➔ CH3CH2CN (b) (i) CH3CH2OH +SOCl2 ----> CH3CH2Cl +Na (dry ether) ----> CH3-CH2-CH2-CH3

(ii) CH3-CH=CH2 + HBr + H2O2 --- > CH3-CH2CH2-Br +KOH +H2O ---> CH3-CH2CH2-OH

(iii)C6H5-CH3 + Br2 + UV radiation --- > C6H5-CH2-Br +NaI + Acetone ---> C6H5-CH2-I

In document KENDRIYA VIDYALAY SANGATHAN GUWAHATI REGION (Page 42-55)