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d-and f-Block Elements - Some Applications of d- and f-Block Elements

Grade 12CBSEChemistry

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Transition metals and their compounds are vital in the iron and steel industry, where iron is alloyed with other dd-block elements like CrCr, NiNi, MnMn, VV, and WW to produce various types of steels.

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Transition metals are excellent catalysts due to their ability to adopt multiple oxidation states and form coordination complexes. Important examples include V2O5V_2O_5 in the Contact Process for H2SO4H_2SO_4 and FeFe in the Haber Process for NH3NH_3.

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The Wacker process utilizes PdCl2PdCl_2 as a catalyst for the oxidation of ethyne to ethanal.

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Ziegler-Natta catalysts, which consist of TiCl4TiCl_4 and Al(CH3)3Al(CH_3)_3, are used for the polymerization of ethene into high-density polyethylene.

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Silver bromide (AgBrAgBr) is used in photographic industry due to its light-sensitive properties.

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Complexes like KMnO4KMnO_4 and K2Cr2O7K_2Cr_2O_7 are extensively used as powerful oxidizing agents in analytical chemistry (titrations) and industrial synthesis.

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Lanthanoid alloys, specifically 'Mischmetall', consist of approximately 95%95\% lanthanoid metal (mostly CeCe, LaLa, NdNd) and 5%5\% iron, along with traces of SS, CC, CaCa, and AlAl. It is used in cigarette lighter flints and magnesium-based alloys for bullets and shells.

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Transition elements play a critical role in biological systems. For example, FeFe is present in hemoglobin (oxygen transport), and CoCo is present in Vitamin B12B_{12} (cyanocobalamin).

📐Formulae

2SO2+O2→V2O52SO32SO_2 + O_2 \xrightarrow{V_2O_5} 2SO_3

N2+3H2→Fe2NH3N_2 + 3H_2 \xrightarrow{Fe} 2NH_3

MnO4−+8H++5e−→Mn2++4H2OMnO_4^- + 8H^+ + 5e^- \rightarrow Mn^{2+} + 4H_2O

Cr2O72−+14H++6e−→2Cr3++7H2OCr_2O_7^{2-} + 14H^+ + 6e^- \rightarrow 2Cr^{3+} + 7H_2O

TiCl4+Al(C2H5)3 (Ziegler-Natta Catalyst)TiCl_4 + Al(C_2H_5)_3 \text{ (Ziegler-Natta Catalyst)}

💡Examples

Problem 1:

Explain why transition metals and their compounds act as good catalysts.

Solution:

Transition metals act as catalysts because: 1. They can show variable oxidation states, allowing them to form unstable intermediate compounds. 2. They provide a large surface area for reactants to be adsorbed, which increases the concentration of reactants on the surface and lowers the activation energy.

Explanation:

In the Haber process, FeFe provides a surface where N2N_2 and H2H_2 bonds are weakened, while V2O5V_2O_5 in the Contact process changes its oxidation state from +5+5 to +4+4 and back to facilitate the oxidation of SO2SO_2.

Problem 2:

What is Mischmetall and what is its primary application?

Solution:

Mischmetall is an alloy consisting of about 95%95\% Lanthanoid metals (chiefly CeCe, LaLa, and NdNd) and about 5%5\% FeFe, with traces of SS, CC, CaCa, and AlAl.

Explanation:

Because of its pyrophoric nature (it produces sparks when struck), it is primarily used in making flints for cigarette lighters and in tracer bullets.

Problem 3:

Name the catalyst used in the manufacture of polyethylene and identify the transition metal present in it.

Solution:

The catalyst used is the Ziegler-Natta catalyst, which is a combination of TiCl4TiCl_4 and Al(C2H5)3Al(C_2H_5)_3. The transition metal present is Titanium (TiTi).

Explanation:

This catalyst is essential for the production of high-density polyethylene (HDPEHDPE) at low pressures and temperatures.