Write any three applications of d - and f -block elements.

Applications of the d- block elements: Iron and its amalgam, steel, are utilized broadly in the development industry. Titanium is utilized as a part of the manufacture of air ship and spaceship. Niobium composites are utilized as a part of fly motors. Silver bromide is utilized as a part of photography. Many d- block or transition metals and their compounds are utilized as impetuses in the chemical reactions. Applications of f-block elements: Lanthanide alloys (mischmetal) utilized for the creation of instrumental steels and heat resistance. Carbides, Borides, and nitrides of lanthanides are utilized as refractories. Lanthanide oxides are utilized in cleaning glass as abrasives. Thorium is utilized as a part of cancer treatment and in glowing gas mantles.

Give the steps involved in the preparation of potassium dichromate ( K 2 Cr 2 O 7 ) from chromite ore.

Potassium dichromate is prepared from chromite ore ( FeCr 2 O 4 ) by the following steps. (i) Concentration of chromite ore: The chromite ore is powdered and concentrated by gravity separation method. (ii) Preparation of sodium chromate: The concentrated ore is roasted with excess of sodium carbonate in a reverberatory furnace at 1200 K in the presence of air. Chromic oxide of the ore is converted to sodium chromate. 4 FeCr 2 O 4 + 8 Na 2 CO 3 + 7 O 2 → 1200 K 8 Na 2 CrO 4 + 2 Fe 2 O 3 + 8 CO 2 (iii) Conversion of sodium chromate into sodium dichromate. 2 Na 2 CrO 4 + conc . H 2 SO 4 → Na 2 Cr 2 O 7 + Na 2 SO 4 + H 2 O (iv) Conversion of sodium dichromate to potassium dichromate: Na 2 Cr 2 O 7 + 2 KCl → K 2 Cr 2 O 7 + 2 NaCl . Potassium dichromate being less soluble than sodium chloride is obtained in the form of orange coloured crystals and can be removed by filtration.

Outer electronic configuration of Cu 2 + ion is 3 d 9 . Calculate its spin only magnetic moment.

The outer electronic configuration of Cu 2 + ion is 3 d 9 , therefore it has one unpaired electron. The spin only magnetic moment can be calculated as given below: μ = n n + 2 = 1 1 + 2 = 1 . 73 B M .

In d -block elements the radii of elements of third transition series are similar to those of the elements of second transition series. Give reason.

The second and third transition series of d -block elements have almost similar atomic radii. It is due to lanthanoid contraction. This arises due to poor shielding effect of d and f electrons.

Give reasons for the following : Write the step involved in the preparation of Na 2 CrO 4 from chromite ore.

Dichromates are generally prepared from chromate, which in turn are obtained by the fusion of chromite ore FeCr 2 O 4 with sodium or potassium carbonate in free access of air. The reaction with sodium carbonate occurs as follows: 4 FeCr 2 O 4 + 8 Na 2 CO 3 + 7 O 2 → 8 Na 2 CrO 4 + 2 Fe 2 O 3 + 8 CO 2 . The yellow solution of sodium chromate is filtered and acidified with sulphuric acid to give a solution from which orange sodium dichromate

Give reasons for the following : Scandium (Z= 21) does not exhibit a variable oxidation state and yet it is regarded as a transition element.

Transition metals show a variable oxidation state due to the presence of unpaired electrons. The atomic number of scandium is 21. Here is the electronic configuration of scandium Ar 3 d 1 4 s 2 . Scandium shows only a +3 oxidation state because it attains a stable electronic configuration like noble gas Argon. Therefore, it does not exhibit a variable oxidation state and yet it is regarded as a transition element.

Give reasons for the following : Transition metals and many of their compounds act as catalysts.

The transition metals and their compounds are known for their catalytic activity. This activity is ascribed to their ability to adopt multiple oxidation states and to form complexes. Vanadium(V) oxide (in Contact Process), finely divided iron (in Haber’s Process), and nickel (in Catalytic Hydrogenation) are some of the examples. Catalysts at a solid surface involve the formation of bonds between reactant molecules and atoms of the surface of the catalyst (first-row transition metals utilise 3d and 4s electrons for bonding). This has the effect of increasing the concentration of the reactants at the catalyst surface and also weakening of the bonds in the reacting molecules (the activation energy is lowering). Also, because the transition metal ions can change their oxidation states, they become more effective as catalysts.

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EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR CHEMISTRY>Chapter -1 - The d- and f-Block Elements>Kerala Board-2018>Q 1

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What is the structure of chromate ion ( ${({CrO}_{4})}^{2 -}$ )?

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