Solved Exercise, Chem-12, Ch-06


Q.01: Fill in the blanks:

(i) The property of paramagnetism is due to the presence of ______ electrons. (unpaired)

(ii) MnO41 ion has ______ colour and Cr2O72 has _____ colour. (purple, orange red)

(iii) When potassium chromate is treated with an acid _____ is produced. (K2Cr2O7)

(iv) The d-block elements are located between _____ and ______ block elements. (s & p)

(v) Oxidation number of Fe in K4[Fe(CN)6] is _____ while in K3[Fe(CN)6] it is _____. (+2, +3)

(vi) The presence of _______ in a metal promotes corrosion. (impurities)

(vii) If copper is in contact with aluminium, ______ gets corroded. (aluminium)

(viii) Complexes having sp3d2 hybridization have _______ shape. (octahedral)

(ix) In naming the complexes, all the ligands are named in ______. (alphabetical order)

(x) In an aqueous solution, CrO4 2 and Cr2O7 2 exist in the form of ______. (equilibrium)

Q.02: Indicate True or False:

(i) A substance which is attracted into a magnetic field is said to be diamagnetic. (FALSE)

CORRECT: A substance which is attracted into a magnetic field is said to be paramagnetic.

(ii) Compounds of the transition elements are mostly coloured. (TRUE)

(iii) Fe3+ ions are blue when hydrated. (FALSE)

CORRECT: Fe3+ ions are brown when hydrated.

(iv) An extreme case of paramagnetism is called diamagnetism. (FALSE)

CORRECT: An extreme case of paramagnetism is called ferromagnetism.

(v) Tin plating is used to protect iron sheets from corrosion. (TRUE)

(vi) In galvanizing, zinc prevents corrosion of iron. (TRUE)

(vii) Tin plated iron gets rusted more rapidly when the protective coating is damaged than the unplated Iron. (TRUE)

(viii) The name of anionic ligands in a complex ends in suffix ‘O’. (TRUE)

(ix) Pig iron contains greater percentage of carbon than steel. (TRUE)

(x) Complex compounds having dsp2 hybridization have tetrahedral geometry. (FALSE)

CORRECT: Complex compounds having dsp2 hybridization have square planar geometry.

Q.03: Multiple choice questions.

(i) Which of the followings is a non-typical transition element?                        

(a) Cr         

(b) Mn       

(c) Zn         

(d) Fe

ANSWER: (c) Zn

EXPLANATION: Zinc belongs to group IIB (Zn, Cd & Hg) which are regarded as non-typical transition elements because they do not have a partially filled d-subshell as element or in any of their ionic states. Neither do they have properties of transition elements except complex formation.

(ii) Which of the followings is a typical transition element?

(a) Sc         

(b) Y           

(c) Ra         

(d) Co

ANSWER: (d) Co

EXPLANATION: Cobalt is a typical transition element because it belongs to group VIIIB. Sc & Y are non-typical transition elements belonging to group IIIB, while Radium is a radioactive alkaline earth metal.

(iii) f-block elements are also called:

(a) Non-typical transition elements

(b) Outer transition elements

(c) Normal transition elements.  

(d) None is true

ANSWER: (d) None is true

EXPLANATION: f-block elements are called inner transition elements. So, none of the given options is true.

(iv) The strength of binding energy of transition elements depends upon: 

(a) Number of electron pairs

(b) Number of unpaired electrons

(c) Number of neutrons

(d) Number of protons

ANSWER: (b) Number of unpaired electrons

EXPLANATION: The number of unpaired electrons present in valence s and d orbitals take part in metallic bonding. The greater is the number of unpaired electrons, the greater is the binding energy and vice versa. Thus, the number of unpaired electrons affect the strength of binding energy.

(v) Group VIB of transition elements contains:               

(a) Zn, Cd, Hg               

(b) Fe, Ru, Os

(c) Cr, Mo, W                     

(d) Mn, Te, Re

ANSWER: (c) Cr, Mo, W

EXPLANATION: The elements Chromium, Molybdenum & Tungsten belong to group VIB of d-block transition elements. An indication about their group number is that these elements should utilize six electrons in bonding so they must show an oxidation state of +6.

(vi) Which is the formula of tetraamminechloro-nitro-platinum (IV) sulphate?

(a) [Pt(NH3)4(NO2)]S       

(b) [PtNO2Cl(NH3)4]SO4

(c) [PtCl(NO2)(NH3)4]SO4

(d) [Pt(NH3)4(NO2)Cl]SO4

ANSWER: (c) [PtCl(NO2)(NH3)4]SO4

EXPLANATION: In writing the formula of a complex ion, the usual practice is to place the symbol of the central metal atom first, followed by the formulas of the anionic ligands in alphabetical order, then neutral ligands in alphabetic order.

(vii) The percentage of C in different types of iron products is in the order of:         

(a) Cast iron >Wrought iron >Steel

(b) Wrought iron >Steel >Cast iron

(c) Cast iron >Steel >Wrought iron

(d) Cast iron = Steel >Wrought iron

ANSWER: (c) Cast iron >Steel >Wrought iron

EXPLANATION: Cast iron (2.5% — 4.5%) contains maximum percentage of carbon while wrought iron (0.12% — 0.25%) is the purest form of iron because it contains minimum percentage of carbon among three. Steel (0.25% — 2.5%) definitely comes in the middle of these two.

(viii) The colour of transition metal complexes is due to:

(a) d-d transition of electrons

(b) Paramagnetic nature of transition elements

(c) Ionization

(d) Loss of s-electrons

ANSWER: (a) d-d transition of electrons

EXPLANATION: In transition elements, d-orbitals are responsible for the colour development in their compounds. When these orbitals are involved in bonding, they split up into two energy levels, one set has higher energy than the other. The electrons residing in low energy d-orbitals absorb a part of visible light and jump to high energy d-orbitals. This process is called d-d transition. The energy difference of d-orbitals varies from ion to ion. Thus, every ion absorbs a different wavelength and transmits the remaining set of wavelengths that gives different colours to the ions.

(ix) Coordination number of Pt in [PtCl(NO2)(NH3)4]2+ is: 

(a) 2           

(b) 4           

(c) 1           

(d) 6

ANSWER: (b) 4

EXPLANATION: The charge on co-ordination sphere, +2, is the sum of the charge on central metal atom Pt and the ligands. i.e., Pt+Cl+NO2+4NH3 =+2. OR Pt-1-1-4(0) =+2 OR Pt =+4

(x) The total number of transition elements is:

(a) 10         

(b) 14         

(c) 40         

(d) 58

ANSWER: (d) 58

EXPLANATION: There are three d-series, each containing 10 elements, and two f-series each containing 14 elements. This makes a total of 58 transition elements, including both outer transition and inner transition elements.

Q.04: How does the electronic configuration of valence shell affect the following properties of the transition elements? (a) Binding energy (b) Paramagnetism (c) Melting points (d) Oxidation states

Ans: Consult textbook at page 100 — 102.

Q.05: Explain the following terms giving examples: (a) Ligands (b) Coordination sphere (c) Substitutional alloy (d) Central metal atom


(a) Legend: “The atoms or ions or neutral molecules which surround the central metal ion and donate electron pairs to it, are called ligands.” They may be anions or neutral molecules.

Examples: In K4[Fe(CN)6] & [Ag(NH3)2]Cl, CN and NH3 are the anionic and neutral ligands respectively. Ligands may be monodentate, if they have one donor atom. e.g. CN & NH3, or bidentate if they have two donor atoms. e.g., Oxalate ion is a bidentate ligand.

(b) Central Metal Ion: “A metal atom or ion (usually a transition element) surrounded by a number of ligands is called central metal atom or ion.”

Examples: In K4[Fe(CN)6] and [Ag(NH3)2]Cl, Fe2+ and Ag1+ are the central metal ions respectively.

(c) Substitutional Alloys:

Owing to the similarity in sizes, the atoms of one transition metal can easily replace the atoms of other metal in the lattices. The alloys formed in this way are termed as substitutional alloys.

Examples: Brass, bronze, coinage alloys etc.

Q.06: Describe the rules for naming the coordination complexes and give examples.

Ans: Consult textbook at page 105.

Q.07: What is the difference between wrought iron and steel. Explain the Bessemer’s process for the manufacture of steel.

Ans: The main difference between wrought iron and steel is that of carbon content. Wrought iron has the lowest carbon context ranging from 012% to 0.25%. thus, it is the purest form of iron. Steel has carbon content in the range of 0.25% to 2.5% along with some other metals as impurities which render specific properties to steel.

Bessemer’s Process: Consult textbook at page 108 — 109.

Q.08: Explain the following giving reasons:

Ans: When protective tin coating of tin-palted iron is damaged, it corrodes more quickly than non-plated iron. This is because when tin coating is damaged, both tin and iron come in contact with moisture and air. A galvanic cell is established, in which tin acts as cathode while iron as anode. The electrons flow from iron to tin, where they combine with H+ ions to release H2 gas. The OH ions at anode combine with Fe3+ ions to form Fe(OH)3 or rust, which dissolves in water rapidly to allow corrosion to penetrate further.

Ans: Aluminium corrodes when it comes in contact with a less active metal like copper, in the presence of moisture and O2. Water (moisture) ionizes to form H+ and OH ions. CO2 in atmosphere dissolves in water to form H2CO3 which also ionizes as: H2CO3 ⇌ H+ + HCO3. Both Al and Cu are immersed in a solution of H+, OH and HCO3 ions. A galvanic cell is established in which more active metal, aluminium, acts as anode while less active metal, copper, acts as cathode. The electrons move from Al to Cu, where they combine with H+ to release H2 gas. The remaining Al3+ ions combine with OH ions to form soluble Al(OH)3.In this way, Al starts corroding.

Ans: Galvanizing is done by dipping iron sheet in zinc chloride bath and heating. Iron sheet is then removed, rolled into molten zince bath and air cooled. In this way, a protective layer of zinc is formed on the surface of iron, which protects it from corrosion. When zinc layer is damaged, a galvanic cell is formed in the presence of moisture. Iron acts as cathode while zinc as anode. Electrons flow from zinc to iron. As a result, zinc decays while iron remains intact. This is called sacrificial corrosion.

Fe2+ + Zn ⟶ Zn2+ + Fe

In this way, galvanizing protects iron from rusting. This process is used in water pipes, etc.

Q.09: How chromate ions are converted into dichromate ions?

Ans: K2CrO4 andK2Cr2O7show similar properties because in equeous solutions, both CrO42  and Cr2O72 ions exist in equilibrium.

2CrO42 + 2H+ ⇌ Cr2O72 + H2O

If an alkali is added to such a solution, the OH ions will bind the H+ ions, and the equilibrium will shift towards left. As a result, dichromate ions will be converted into chromate ions. Similarly on adding an acid, the equilibrium will shift towards right and dichromate ions will be formed.

Q.10: Describe the preparation of KMnO4 and K2 CrO4.

Ans: (1) By oxidizing potassium chromite in the presence of an alkali:

2KCrO2 + 3Br2 + 8KOH ⟶ 2K2CrO4 + 6KBr + 4H2O

Ans: (2) By fusing Cr2O3 with alkali in the presence of an oxidant KClO3:

Cr2O3 + 4KOH + KClO3 ⟶ 2K2CrO4 + KCl + 2H2O

Q.11: Give systematic names to following complexes: (a) [Fe(CO)5] (b) [CO(NH3)6]Cl3(c) [Fe(H2O)6]2+ (d) Na3[CoF6] (e) K2[Cu(CN)4] (f) K2 [PtCI6]  (g) [Pt(OH)2(NH3)4]SO4 (h) [Cr(OH)3 (H2 O)3]

Ans: (a) [Fe(CO)5]: Pentacarbonyl iron (0)                              

(b) [Co(NH3)6]Cl3:Hexaammine cobalt (III) chloride

(d) Na3[CoF6]: Sodium hexafluoro cobaltate (III)

(f) K2[Pt(Cl)6]: Potassium hexachloroplatinate (IV)

(g) [Pt(OH)2(NH3)4]SO4: Tetramminedihydroxo platinum (IV) sulphate

(h) [Cr(OH)3(H2O)3]: Triaquatrihydroxo chromium (III)

Leave a Reply

Your email address will not be published. Required fields are marked *