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The d-And-f-Block Elements

Short Answer Type

181.

Explain the following facts:
Transition metals form coloured complexes.

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182.

Give reasons:
Among transition metals, the highest oxidation state is exhibited in oxoanions of a metal.

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183.

Give reasons:
Ce⁴⁺ is used as an oxidising agent in volumetric analysis.

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184.

Give reasons:
Zn²⁺ salts are white while Cu²⁺ salts are blue.

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185.

Why La, Gd and Lu has low value of 3rd ionisation enthalpies?

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186. Why is cerium a good analytical reagent?

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187. Given below are the electrode potential values, E° for some of the first row of transition elements:
Elements V(23) Cr(24) Mn(25)Fe(26)Co(27)Ni(28) Cu(29)
E°_M²⁺/M(V) –1.18 – 0.91 – 0.44 – 0.28 –0.28 –0.25 +0.34
Explain the irregularities in these values on the basis of electronic structures of atoms.

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188.

Complete the following reaction equations:
(i) Cr₂O₇ ² + Sn²⁺ + H⁺ →
(ii) MnO₄^–+ Fe²⁺ + H⁺ →

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189.
Actinide cations are coloured? Why?

The cations of actinides are coloured because of the presence of unpaired electrons. The colour observed depends on the number of impaired electrons. The colours of some cations are given below:

Cation of actinide	U³⁺	Np³⁺	Pu³⁺	Am³⁺
Unpaired electrons	3	4	5	6
Colour observed	Red	Violet	Black violet	Pink

The colour is due to electronic transition within the 5f levels. The electronic transitions of actinides are about ten times more intense than those of lanthanides. The difference is due to difference in 4f and 5f electrons.

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