Chapter-8
d and f block Elements
Question. Silver atom has completely filled d orbitals in its ground state. How can you say that it is a transition element?
Answer: It forms AgF2 a dark brown crystalline solid
Question. Transition elements exhibit their highest oxidation state in their oxides not in Flourides.Why?
Answer: Because oxygen can form covalent multiple bonds.
Question. Explain why, Zn (II) salts are white while Mn (VII) are deep purple in colour?
Answer: due to charge transfer between O2- ion to Mn7+
Question. KMnO4 is used in acidic medium quite frequently than in its aqueous or alkali for oxidizing purpose. Why?
Answer: In acidic medium MnO4
- involves the addition of 5e- or Eo = +1.52v
Question.Give reasons:
i) Zr and Hf have identical sizes
ii) In the titration of FeSO4 with KMnO4 in the acidic medium dil.H2SO4 is used instead of dil HCl
Answer: i) Due to lanthanoid contraction
ii) dil.HCl is reducing agent and liberates chlorine on reacting with KMnO4 soln.
Question.Calculate the spin only magnetic moment of Iron present in the following compound.
[Fe(H20)5NO] 2+
Answer: 5.92 BM
Question. K2 [PtCl6] is a well known compound whereas the corresponding Ni compound is not known. State the reason for it.
Answer: The oxidation state of Pt in K2 [PtCl6] is +4, which is a stable oxidation state for Pt. The same oxidation state Ni is very difficult because of (I.E1 + I.E 2+ I.E 3+I.E 4)
Question. Among the ionic species Sc 3+ ,Ce 4+ and Eu2+ Which one is a good oxidizing agent?
Answer: Ce 4+ is a good reducing agent because it can readily change to the most stable oxidation state by gaining one electron. Others cannot do so.
Question. Why are Fe 3+ and Cu 2+ prominent in their aqueous solutions?
Answer: Because of high hydration enthalpies.
Question. There is a dip in the melting point curve at Mn, though the preceding element also has similar electronic configuration. Why?
Answer: Due to 3d 5 half filled configuration which are tightly held by more effective nuclear charge of Mn
Question. CrO3 is an acid anhydride. Explain.
Answer: It dissolves in water to give chromic acid.
CrO3 + H2O H2 CrO4
Question. Though both Cr 2+ and Mn 3+ have d4 configuration, yet Cr2+ is reducing and Mn3+ is oxidizing. Explain Why?
Answer: Because of the stable half filled configuration of t2g sets Cr3+
1 - MARK QUESTIONS
1. Why is that orange solution of K2Cr2O7 turns yellow on adding NaOH ? 1
2. Arrange CrO, CrO3 and Cr2O3 in increasing order of acidic strength. 1
3. Why does Ti4+ ion show diamagnetic nature? 1
4. Which metal in the first series of transition metal exhibits +1 oxidation state most frequently and why? 1
5. Which element of the first transition series shows the highest number of oxidation states? 1
6.. K2[PtCl6] is a well known compound, Where as the corresponding Ni compound is not known. State a reason for it. 1
7. Why does vanadium pentoxide act as a catalyst? 1
8. Why hydrated CuSO4 is blue while its anhydrous form is colourless. 1
9. Why is HCl not used to acidify a permanganate solution in volumetric estimation of Fe2+ and oxalate ion. 1
2 - MARKS QUESTIONS
10. Why is copper (I) sulphate diamagnetic and Copper (II) Sulphate paramagnetic ? Explain. 2
11. HgCl2, SnCl2, cannot exist together in an aqueous solution. Why? 2
12. Describe giving reason which one of the following pairs has the property indicated and why?
(a) Fe or Cu has higher melting point
(b) Co2+ or Ni2+ has lower magnetic moment 2
13. Give reason:
(a) Transition metals sometimes exhibit very low oxidation states such as +1 and 0
(b) Sc shows only +3 oxidation state 2
14. Why Hg(I) ion exist as Hg2 2+ ion while Cu(1) ion exist as Cu1+. Explain. 2
15. A serious accident took place in a laboratory when a student tried to dissolve KMnO4 in conc. Sulphuric acid instead of dil. Sulphuric acid. What went wrong ? Explain.
3 - MARKS QUESTIONS
16. An aqueous blue coloured solution of a transition metal sulphate reacts with H2S in acidic medium to give a black precipitate (A) Which is insoluble in warm aqueous solution of KOH. The blue solution on treatment with KI in weakly acidic medium turns yellow and produces a white precipitate (B). Identify the transition metal ion; write the chemical reaction involved in the formation of A and B. 3
17. An aqueous solution of a compound (A) is acidic towards litmus and (A) sublimes at about 3000C. (A) on treatment with an excess of NH4SCN gives a red coloured compound (B) and on treatment with a solution of K4(Fe (CN)6) gives a blue coloured compound (C). (A) on heating with excess of K2Cr2O7 in the presence of concentrated H2SO4 evolves deep red vapour of (D). On passing the vapours of (D) into a solution of NaOH and d then adding the solutions of acetic acid and lead acetate a yellow precipitate of compound (E) is obtained. Identify A to E and give chemical equations involved. 3
18. When a white crystalline compound X is heated with K2Cr2O7 and conc. H2SO4, a reddish brown gas A is evolved. On passing A into caustic soda solution, a yellow coloured solution of B is obtained. Neutralizing the solution B with acetic acid and on subsequent addition of lead acetate, yellow ppt. C is obtained. When X is heated with NaOH solution, a colorless gas is evolved and on passing the gas into K2HgI4 solution, a reddish brown ppt. D is obtained. Identify A, B, C, D and X. write the equations of the reactions involved. 3
19. A metal oxide of iron and chromium is fused with sodium carbonate in the presence of air to form a yellow colour compound A. on acidification, the compound A forms an orange coloured compound B which is a strong oxidizing agents. Identify the compounds A and B and write balanced equations for each step. 3
20. State the reasons for the following:
i. Mercury is transported in iron containers.
ii. Ce(III) is readily oxidized to Ce(IV)
iii. Actinoids have a stronger tendency to form complexes than lanthanoids 3
1 Mark Questions
1. Ce4+ has a noble gas electronic configuration, but it is used as an oxidizing agent in volumetric analysis. Give reason.
2 State why Flourine stabilizes higher oxidation states?
3. CrO4 2- is a strong oxidizing agent while MnO4 2- is not. Why?
4. Why is Cu2Cl2 colourless and CuCl2 coloured?
5. Which is stronger base La(OH)3 or Lu(OH)3? Why?
6. It is found that Ce4+ is a good oxidizing agent whereas Sm2+ is a good reducing agent. State the reason for this difference.
7. Actinoid contraction is greater from element to element than lanthanoid contraction. Why?
8. Mn2+ is more stable than Mn3+. Give the reason?
9. Observe the following equation and identify the phenomenon takes place: 3MnO42- + 4H+ → 2MnO4- + MnO2 + 2H2O
10. Cr2O72- → 2CrO42- How does this equilibrium can be shifted to right?
2 Marks Questions
11. An yellow translucent solution is obtained on passing H2S gas through an acidified solution of KMnO4. Identify the solution and write the balanced chemical equation.
12. Electronic configuration of Cu(I) is [Xe]3d10 and that of Cu(II) is [Xe]3d9. Which is more stable in aqueous solution? Why?
13. Electronic configuration of four metals A,B and C are give below:
A: 1S2 2S2 2P6 3S2 3P6 4S1 3d10
B: 1S2 2S2 2P6 3S2 3P6 4S2 3d10
C: 1S2 2S2 2P6 3S2 3P6 4S2 3d5
Identify the transition metals among them.
14. Zr (4d series) and Hf (5d series) have similar radi and have similar physical and chemical properties. Explain why?
15. In a given series the difference in the ionization enthalpies between any two successive d block elements is very much less than that in case of s and p block elements. Give the explanation.
16. Cu+ is unstable in aqueous solution and disproportionate as 2Cu+ → Cu2+ + Cu
Why does Cu+ disproportionate in aqueous solution?
17. Observe the following reaction:
2Fe3+ + 2I- 2Fe2+ + I2
2Fe2+ +S2O82- 2Fe3+ +2SO42-
(i) Identify the role of Fe3+ in this reaction
(ii) Which property of Fe is used up here.
18. Among the oxides of Chromium CrO3 is acidic, Cr2O3 is amphoteric and CrO is basic. State reasons for these observations.
19. For the first row of transition metals the E, values are Elements V Cr Mn Fe Co Ni Cu
ELEMENT v cR Mn Fe Co Ni Cu
E-,(M2+/ M) in volts -1.18 -0.91 -1.18 -0.44 -0.28 -0.25 +0.34
Observe the values and write the reasons for irregularities.
20. Give reasons for the following:
(i) Mn2+ is more stable than Mn3+
(ii) The colour of CuCr2O7 in water is green.
3 Marks Questions
21. The structure of chromate ion and dichromate ion are given below;
They are interconvertible in aqueous solution depending upon PH of the solution. Give the possible reason for this phenomenon along with the balanced chemical equations.
22. When an orange coloured crystalline compound ‘A’ was heated with common salt and concentrated H2SO4, an orange red coloured gas ‘B’ was evolved. The gas ‘B’ on passing through NaOH solution gave an yellow solution C
(i) Identify A,B and C.
(ii) Write balanced chemical equation involved in the reactions.
23. Observe the following graph and answer the questions given below:
Mp/103K Ag Au
1 Atomic Number
(i) Why melting point of transition elements generally increases towards middle in each series.
(ii) Why Mn and Tc in 3d and 4d series respectively have low values of melting points.
(Hint: d5 – stable electronic configuration; electrons held tightly by nucleus; delocalization is less and metallic bond is weak)
(iii) Why the last members of each series show low values of melting points?
26. A mixed oxide of iron and chromium FeOCr2O3 is fused with Sodium Carbonate in presence of air to form a yellow coloured compound (A). On acidification the compound (A) forms an orange coloured compound (B) which is a strong oxidizing agent.
(i) Identify the compounds (A) and (B)
(ii) Write balanced chemical equations for each step.
5 Marks Questions
27. (a) A blackish brown coloured solid (A) when fused with alkali metal hydroxides in presence of air produces a dark green compound (B), which on electrolytic oxidation in alkaline medium gives a dark purple compound (C). Identify (A), (B) and (C) and write balanced chemical equations for the reactions involved.
(d) What happens when an acidic solution of the green coloured compound (B) is allowed to stand for some time? Give the equation of the reaction involved. What is this type of reaction called?
(Hint: MnO42- changes to MnO4-)
28. (A) reacts with H2SO4 to form purple coloured solution (B) which reacts with KI to form colourless compound (C). The colour of (B) disappears with acidic solution of FeSO4. With concentrated H2SO4 (B) forms (D) which can decompose to give a black compound (E) and O2. Identify (A) to (E) and write equations for the reactions involved.
