NCERT Solutions Class 12 Chemistry Chapter 8

8.1 Introduction

The Periodic Table is used to categorise elements, and each of these elements is then further divided into other groupings. In this context, we will learn more about the d block and f block elements, which are also known as the transition elements and inner transition elements, respectively, in the groups from 3 to 11. The f-block elements’ 4f and 5f orbitals are stable in the latter of these two long periods. They are divided into lanthanides and actinides based on these criteria. An element’s position on the periodic table reflects its makeup and characteristics quite well.

The d- and f-block elements are thoroughly explained in this portion of NCERT Solutions Class 12 Chemistry Chapter 8. You may now solve exercise questions with a great deal of simplicity thanks to these answers. In addition, you will be better able to comprehend and revise the topics.

 d- and f- Block Elements: The d block elements, which are called transition elements, contain partially filled (n-1) d-orbitals. We have already discussed p- block elements in the previous class.

 8.2 Position of d-Block and f-Block Elements in the Periodic Table

Group 3–12 elements are covered in detail in Chapter 8 of the NCERT Solutions for Class 12 Chemistry. The elements in groups 3–12 that have their d-orbitals gradually filled over the course of each of the four long periods are found in the d-block of the periodic table. The d-block element’s position between the s and p-block elements is the only reason it has been given the name “transition.” Transition metals come in four series: the 3d series (Sc to Zn), the 4d series (Y to Cd), the 5d series (La, Hf to Hg), and the 6d series.

Transition Element

An element that possesses unfilled d orbitals in either its ground state or any of its oxidation states is referred to as a transition element. Due to their structure in both their ground state and common oxidation state, Zn, Cd, and Hg are not typical transition elements. However, as they are the final representatives of three transition series, their chemistry is investigated alongside that of transition metals.

8.3 Electronic Configuration of d-Block Elements:

Under NCERT Solutions Class 12 Chemistry Chapter 8, students learn about the following.

General electronic configurations of the d-block elements

For 3d series 3d1-104s1-2

For 4d series 4d1-105s1-2

For 5d series 5d1-106s1-2

For 6d series 6d1-107s1-2

Overall (n-1)d1-10ns1-2

In comparison to other orbitals, the transition elements d-orbitals extend farther from an atom’s centre (s and p). As a result, they are more affected by their environment than the atoms or molecules around them.

8.4 General Properties of d-Block Elements:

In this section of NCERT Solutions of Chapter 8 Chemistry Class 12, students learn about

• General Properties

The metallic properties of high tensile strength, ductility, malleability, high thermal and electrical conductivity, and metallic lustre are almost universally present in transition elements.

With the exception of Zn, Cd, and Hg, transition metals are much harder and less volatile. They have high melting and boiling points.

Except for Mn and Tc, which exhibit unusual behavior, the melting points of these metals generally increase as the atomic number decreases and reach a maximum at d5 in any row. They have high ionisation enthalpies.

In general, the stronger the resulting bonding is, the more valence electrons there are. Metals with a very high enthalpy of atomisation, or very high boiling point, end up being noble in their reactions because this property plays a significant role in determining the standard electrode potential of metal.

• Atomic and Ionic Size

In the given series, ions with the same charge often exhibit a progressive reduction in radius with rising atomic number. As a result, the ionic radius decreases and the net electrostatic attraction between the nuclear charge and the outermost electron increases. This is because every time the nuclear charge increases by one, a new electron enters a d-orbital, and the shielding effect of the d electron is ineffective.

The lanthanoid contraction that results from the filling of 4f before 5d orbitals essentially make up for the anticipated increase in atomic size with increasing atomic number.

• Density

The density of these elements generally rises asa result of the decrease in metallic radius and the increase in mass. Therefore, there may be noticeable increases in density from Ti to Cu.

• Ionisation Enthalpy

Ionization enthalpy rises along each series of the transition elements from left to right as a result of the increase in nuclear charge that comes along with the filling of the inner d orbitals. But there are lots of little variances.

• Oxidation State

The wide range of oxidation states present in transition elements is one of their distinguishing characteristics. In the middle of the series, or very close to it, is the element that offers the most oxidation states. From +2 to +7, Mn exhibits all oxidation states.

• Chemical Reactivity

The degree of chemical reactivity in transition metals varies greatly. While some of them are noble, which means they do not react with any acid, the majority of them are sufficiently electropositive to dissolve in mineral acid.

 8.5 Some Important Compounds of Transition Metals

Potassium Dichromate (K2 Cr2 O7)

Ore Ferrochrome or chromite (FeO· Cr2O3) or (FeCr2O4)

Preparation

4FeO.Cr2O3 + 8Na2CO3 + 7O2  → 8Na2CrO4 + 2Fe2O3 +8CO2

2Na2Cr04 + 2H+ → Na2Cr2O7  + 2Na+  + H2O

Na2Cr2O7 + 2KCl →  K2Cr2O7 + 2 NaCl

Dichromate of sodium is more soluble than that of potassium.

Depending on the pH of the solutions, chromates and dichromates can be converted into one another in aqueous solutions.

Properties 

Strong oxidising agents, sodium and potassium dichromates will oxidise iodide to iodine, sulphides to sulphur, tin (ll) to tin (IV), and iron (ll) salts to iron when acidified K2Cr27 is used.

Uses

1. K2Cr27 is used as an oxidising agent in volumetric analysis.
2. It is used in mordant dyes, the leather industry, and photography (for the hardening of the film).
3. It is used in the chromyl chloride test.
4. It is used in cleaning glassware.
5. Potassium Permanganate (KMnO 4)

Ore Pyrolusite (MnO2)

Preparation

2MnO2 + 4KOH + O2 → 2K2MnO4  + 2H2O

3MnO2-4  + 4H+ →  2MnO4-   + MnO2   + 2 H2O

Properties 

KMnO4 acts as a strong oxidising agent.

1. In the presence of dilute H2SO4, KMnO4 is reduced to manganous salt.

MnO-4 + 8H+ + 5e-   →  Mn2+   + 4H2O

Oxalates are converted to carbon dioxide (CO2), iron(II) to iron(ll), nitrites to nitrates, and iodides to iodine in an acidic KMnO4 solution. Because HCI combines with KMnO4 to produce Cl2, and HNO3 itself acts as an oxidising agent, only H2SO4 can be used to acidify KMnO4.

2. In alkaline medium, KMnO4 is reduced to insoluble MnO2.

MnO-4  + 3e-  + 2H2O →  MnO2   +  4 OH-

Alkaline or neutral KMnO4 solution oxidises I– to IO–3, S2O2-3 to SO2-4, Mn2+ to MnO2, etc.

Aqueous KMnO4 reacts with NH3 to liberate N2 gas.

2KMnO4 + 2NH3 → 2KOH + 2MnO2 + N2 + 2H2O

Uses

KMnO4 is used

(i) during the manufacture of CI2 in the lab.

(ii) as a disinfectant and oxidising agent.

(iii) making Baeyer’s reagent

3. Copper Sulphate (CUSO4 ·5H2O)

It is also known as blue vitriol.

Method of preparation It is produced when dilute H2SO4 reacts with copper scrap while being exposed to air.

2Cu + 2H2SO4 + O2 →  CuSO4  + 2H2O

Properties

1. It turns white when heated because water is lost during crystallisation.

CuSO4 breaks down into CuO and So3 at 1000 K.

CuSO4 →  CuO  + SO3

2. It gives the blue solution with NH4OH and the white ppt of Cu2I2 with KI.

Uses 

It is used in electroplating, dyeing as a mordant, and the Bordeaux mixture [Ca(OH)2 + CuSO4], among other things.4. Silver Nitrate (AgNO3)

It is also called Lunar caustic.

Method of preparation

It is prepared by heating silver with dilute nitric acid.

3 Ag + 4HNO3 →  3AgNO3 + NO  + 2H20

Properties

1. It is a colourless, crystalline compound that blackens when it comes in contact with organic substances (skin, cloth, etc.).
2. With potassium dichromate, it gives a red ppt of Ag2CrO4.
3. 3. On strong heating, it decomposes into metallic silver.

2 AgNO3  → 2Ag + 2NO2 + O2

4. Ammoniacal solution of silver nitrate is known as Tollen’s reagent.

Uses

It is used as a laboratory reagent, in the silvering of mirrors, in the preparation of inks and hair dyes, etc.

8.6 The Lanthanides

The 14 elements immediately following lanthanum, i.e., Cerium (58) to Lutetium (71), are called lanthanoids. They belong to the first inner transition series. Lanthanum (57) has similar properties. Therefore, it is studied along with lanthanoids.

8.7. General Properties of Lanthanoids

Properties of Lanthanides:

1. +3 oxidation state is most common, along with +2 and +4.
2. Except for Prmethiu, they are non-reactive.
3. The magnetic properties of lanthanoids are less complex  than those of actinoids.Students may understand the clear concept of p blocks elements by referring to NCERT solutions class 12 chemistry chapter 8.

8.8 The Actinides

Actinoids are the 14 elements with atomic numbers 90 (Thorium) through 103 (Lawrencium) that follow actinium (89). The second inner transition series includes them. Similar characteristics apply to actinium (89). As a result, it is researched alongside actinoids.

Properties of Actinoids:

1. Additionally, actinoids exhibit greater oxidation states, including +4,+5,+ and +7.
2. They emit radiation.
3. Compared to lanthanoids, actinoids have more complicated magnetic characteristics.
4. They react more quickly.

8.8 Applications of d- and f-Block Elements

There are numerous applications of d- and f- block elements. Some of them are as follows:

1. 1. The most essential construction material is iron and steel. In order to produce them, iron oxides must be reduced, impurities must be removed, carbon must be added, and alloying metals like Cr, Mn, and Ni must be added.
   2. Some compounds, including TiO for the pigment industry and MnO2 for use in dry cells with Zn, are produced for specific applications.
   3. Many of the substances that make up this block’s components or compounds are significant catalysts.
   4. A crucial chemical used in photography is AgBr. Ag and AgI can also be utilised in addition to AgBr.

• Some substances, including MnO4 and CrO42-, are effective oxidizers.

 While studying for their exams, students can refer to the NCERT solutions class 12 chemistry chapter 8 study material provided by Extramarks.

NCERT solutions class 12 chemistry chapter 8 Exercise & Answer Solutions

NCERT solutions class 12 chemistry, chapter 8, are explained in detail by the experts of Extramarks. Students can benefit from the detailed solutions provided by the experts. The solutions cover all of the concepts covered in Chapter 8, d- and f- Block Elements, such as the preparation and properties of transition and inner transition elements, as well as the detailed concept of lanthanides and actinides.Students may refer to Extramarks NCERT solutions for Class 12 Chemistry Chapter 8 by registering on the website. 

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