Ncert Solution Class 12 Chemistry Chapter 1 Questions And Answers, Notes & Numericals PDF

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Ncert Solution Class 12 Chemistry Chapter 1 Questions And Answers, Notes & Numericals PDF, chemistry practical class 12, The Solid State Notes | Class 12 chemistry notes, Ncert chemistry class 12 intext questions solutions chapter 1


The Solid State Notes | Class 12 chemistry notes


1. Solids have definite mass, volume and shape due to the fixed positions of their constituent particles.

2. Amorphous and crystalline are two types of solids.

 3. On the basis of interaction between constituent particles, crystalline solids are divided into four categories: ionic, molecular, metallic and covalent solids.

 4. The three-dimensional arrangement of constituents or points in a crystalline solid is called a crystal lattice. 

5. The smallest repeating pattern of the crystal lattice is known as a unit cell. A unit cell is characterised by six parameters: edges a, b, c and angles a, ẞ and y..

6. Number of lattice points or atoms in a simple cubic unit cell is 1.

Face centred = 4 and body centred is 2.

7. A tetrahedral void is formed when spheres are tetrahedrally arranged in space while an octahedral void is formed by their octahedral arrangement.

8. Coordination number is the number of neighbouring atoms for an atom in a crystal. The coordination number of trigonal planar = 3, tetrahedral = 4, octahedral = 6 and body centred is 8.0 9. Atomic radii are related to edge length as follows:

9. Packing efficiency is the percentage of total space filled by the particles.

10. Packing efficiency for

  • (a) hcp and Ccp structure = 74%
  • (b) Body-centred = 68%
  • (c) Simple cubic lattice = 52,4% 

11. Imperfections in solids are electronic or point defects.

12. Semiconductors are of two types-n-type and p-type.

13. n-type semiconductors are formed by adding small amounts of elements of group 15 to the pure elements of group 14 such as Si and Ge.

14. p-type semiconductors are formed by adding small amounts of elements of group 13 to the pure elements of group 

15. Paramagnetic substances show magnetic behaviour only under the influence of the applied magnetic field. 

16. Ferromagnetic substances exhibit magnetism even when the applied magnetic field is removed. 

17. Antiferromagnetic substances have no magnetic moment since the electronic spins mutually cancel under the influence of an external magnetic field. 

18. Ferrimagnetic substances exhibit some magnetic character due to the alignment of the electron spins in parallel and antiparallel directions in unequal numbers.


Ncert Solution Class 12 Chemistry Chapter 1

Class12th 
Chapter No01
ProvidingQuestions And Answers, Notes & Numericals PDF
Chapter NameThe Solid State
BoardCBSE
Book NCERT
SubjectChemistry
Medium English
Study MaterialsFree VVI Study Materials are Available
Download PDF class 12 Chemistry Ncert Solutions Chapter 1 pdf

Ncert chemistry class 12 intext questions solutions chapter 1


Question 1. Why are solids rigid?

Solution. In a solid state, the constituent particles are not free to move. They can only oscillate about their mean positions due to strong attractive forces between the particles. That is why solids have a closely packed arrangement and rigid structure. 

(The three states of matter differ in intermolecular forces and mode of packing of molecules, so define solids on of basis of these) 

Question 2. Why do solids have a definite volume?

Solution. The constituents particles in solids are bound to their mean positions by strong forces of attraction. The interparticle distances remain unchanged even at increased or reduced pressure. Therefore, solids have a definite volume) 

Question 3. Classify the following as amorphous or crystalline solids: Polyurethane, naphthalene, benzoic acid, Teflon, potassium nitrate, cellophane, polyvinyl chloride, fibreglass, and copper.

Amorphous and crystalline solids differ in the properties such as cleavage property, melting point, shape, anisotropy etc., so classify the given substances, on the basis of these properties.

Solution.

Amorphous solidsCrystalline solids
Polyurethane Benzoic acid
NaphthalenePotassium nitrate
TeflonCopper
Cellophane
Polyvinyl chloride
Fibre glass

Question 4. Why is glass considered a supercooled liquid?

Fluidity is the property of glass in which it resembles liquid, so give an answer on the basis of the fluidity of glass.

Solution. Liquids have the characteristic property i.e., the tendency to flow. Glass also shows this property, though it flows very slowly. Glass panes fixed to windows or doors of old buildings are invariably found to be slightly thicker at the bottom than the top. This is because the glass flows down very slowly and makes the bottom portion slightly thicker. Therefore, glass is considered a supercooled liquid. 

Question 5. The refractive index of a solid is observed to have the same value in all directions. Comment on the nature of this solid. Would it show cleavage property?

Amorphous solids have the same physical properties in all directions, and hence, are called isotropic. The refractive index is also a physical property. So give the nature of solid on this basis. Also, give cleavage property of such solids.

Solution. A solid that has the same value of refractive index directions is isotropic and hence amorphous in nature. It would along all not show a clean cleavage when cut with a knife. Instead, it would break into pieces with an irregular surface. 

Question 6. Classify the following solids into different categories based on the nature of the intermolecular forces operating in them:

Potassium sulphate, tin, benzene, urea, ammonia, water, zinc sulphide, graphite, rubidium, argon, and silicon carbide. 

On the basis of intermolecular forces, solids are classified as ionic. covalent, molecular and metallic solids. So classify the given substance into these classes. Solution. Ionic solids Potassium sulphate, and zinc sulphide (as they have ionic bonds).

Covalent solids Graphite, and silicon carbide (as they are covalent giant molecules).

Molecular solids Benzene, urea, ammonia, water, argon (as a covalent bond). Metallic solids Rubidium, tin (as these are metals).

Question 7. Solid ‘A’ is a very hard electrical insulator in solid as well as in molten state and melts at extremely high temperatures. What type of solid is it?

Consider the properties of the above-mentioned types of solids (as in Q.6),

Solution. Since, the solid ‘A’ is an insulator in solid as well as in molten state, it shows the absence of ions in it. Moreover, it melts at extremely high temperatures, so it is a giant molecule. These are the properties of covalent solids. So, it is a covalent solid.

Question 8. Ionic solids conduct electricity in the molten state but not in the solid state. Explain. The movement of ions is responsible for conducting electricity and in the solid state, no ion is present.

Solution. In ionic solids, electrical conductivity is due to the movement of ions. In a solid state, ions cannot move and remain held together by strong electrostatic forces of attraction. Therefore, they behave as insulators.

Question 9. What types of solids are electrical conductors, malleable and ductile?

For a solid being an electrical conductor, the presence of free electrons is the necessary condition. So consider the type of solids in which free electrons are present. Solution. Metallic solids.

Question 10. Give the significance of a ‘lattice point’. 

Solution. The lattice point denotes the position of a particular constituent (atom, ion or molecule) in a crystal lattice. The arrangement of the lattice points in space is responsible for the shape of a particular crystalline solid.

Question 11. Name the parameters that characterise a unit cell. Edges and angles between the edges are the parameters that characterise a unit cell, so mention them. 

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Solution. A unit cell is characterised by

(i) its dimensions along the three edges, a, b and c. (ii) angles between the edges, a (between b and c) B (between a and c) and y (between a and b). Thus, a unit cell is characterised by six parameters, a, b, c, a, ẞ and Y.



Question 12.

Distinguish between

  • (i) hexagonal and monoclinic unit cells. 
  • (ii) face-centred and end-centred unit cells.

(i) Hexagonal and monoclinic unit cells differ in axial distances, axial angles, examples etc. So distinguish on the basis of these. 

(ii) Distinguish on the basis of the position of the lattice point and number of atoms per unit cell as the given unit cells differ in these.

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Question 13. Explain how many portions of an atom are located at 

(i) corner?

(ii) body-centre of a cubic unit cell is part of its neighbouring unit cell? 

Recall the structure of a body-centred cubic unit cell, in which a corner atom is shared by eight unit cells while that present at the body centre is not shared by any other unit cell and give an answer. Solution.

(1) A point lying at the corner of a unit cell is shared equally by eight unit cells and therefore, only one-eighth H of each such point belongs to the given unit cell.

(ii) A body-centred point belongs entirely to one unit cell since it is not shared by any other unit cell.

Question 14. What is the two-dimensional coordination number of a molecule in a square close-packed layer? 

(i) Coordination number is the number of nearest neighbours of a particle. 

(ii) Square close packing in two vo dimensions,

PRE DSJ CHE XII V01 C06 E02 040 S01 edited

Solution. Four (4), as each atom is surrounded by four other atoms.

Question 15. A compound forms a hexagonal close-packed structure. What is the total number of voids in 0.5 mol of it? How many of these are tetrahedral voids?

To find a total number of voids, we have to calculate the number of octahedral and tetrahedral voids which depend upon the number of atoms in 0.5 mol (N) so first calculate the number of atoms in 0.5 moles and then find no. of octahedral voids (=N), No. of tetrahedral voids (=2N) and total voids.

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Question 19. What type of defect can arise when a solid is heated? ch physical property is affected by it and in what way?

Heating decreases the density, hence vacancy defect is created. 

Solution. When a solid is heated, a vacancy is created in the crystal. On heating, some of the lattice sites are vacant and the density of the solid decreases as the number of ions per unit volume decreases. 

Question 20. What type of stoichiometric defect is shown by

(i) ZnS (ii) AgBr

In ZnS and AgBr there is a large difference between the size of ions so recall the defect which arises in such a condition. Also, recall the exceptional behaviour of AgBr.

Solution.

(1) ZnS shows Frenkel defect because its ions have a large difference in size.

(ii) AgBr shows both Frenkel and Schottky defects.

Question 21. Explain how vacancies are introduced in an ionic solid when a cation of higher valence is added as an impurity in it.

1

Recall the definition of impurity defects with examples and remember, a solid as a whole is neutral.

Solution. When a cation of higher valence is added as an impurity to an ionic solid, some vacancies are created. This can be explained with the help of an example. When strontium chloride (SrCl₂) is added as an impurity to ionic solid sodium chloride (NaCl), two vacant sites are created by the removal of one Nation. One vacant site is replaced by Sr²+ ion but the other remains vacant. The reason is that the crystal as a whole is to remain electrically neutral.

Question 22. Ionic solids, which have anionic vacancies due to metal excess defects, develop colour. Explain with the help of a suitable example.

Free unpaired electrons (or F-centres) are responsible for the colour of solids. Explain the generation of F-centre by taking an example of NaCl with an excess of Na metal.

Solution. We can explain the metal excess defect with the example of sodium chloride crystals. When NaCl crystals are heated in an atmosphere of sodium vapour, the Na atoms are deposited on the surface of the crystal. The CI ions diffuse to the surface of the crystal and combine with Na atoms to give NaCl. This happens by the loss of electrons by Na atoms to form Na ions. 

The released electrons occupy anionic sites by diffusing into the crystals. These electrons absorb energy from visible light and emit radiations corresponding to yellow colour. These electrons are called F-centres (from the German word Farbenzenter meaning colour centre)

Question 23. A group 14 element is to be converted into #type semiconductor by doping it with a suitable impurity. To which group should this impurity belong?

n-type means excess electrons ie., negative charge, so impurity should belong to the higher group. Solution. n-type semiconductor means an increase in conductivity due to the presence of an excess of electrons. Therefore, a 14-group element should be doped with a 15-group element e.g., arsenic or phosphorus.

Question 24. What type of substances would make better permanent

magnets, ferromagnetic or ferrimagnetic? Justify your answer. Ferromagnetic substances are strongly and permanently magnetised whereas ferrimagnetic substances are weakly (temporarily) magnetised.

Solution. Ferromagnetic substances make better permanent magnets than ferrimagnetic substances, The metal ions of a ferromagnetic substance are grouped into small regions known as domains and these are randomly oriented. When a magnetic field is applied, all domains are oriented in the direction of the magnetic field. 

Now the ferromagnetic substance behaves as a magnet. When the applied magnetic field is removed, the magnetic character is retained. Thus, the ferromagnetic substance becomes a permanent magnet. This property (of being permanently magnetised) is not found in ferrimagnetic substances. They lose their magnetic property on heating.


Ncert exemplar class 12 chemistry | pradeep chemistry class 12


Question 1. Define the term ‘amorphous’. Give a few examples of amorphous solids.

Amorphous is a Greek word meaning no form i.e., have irregular shape Define on this basis and give examples. 

Solution. An amorphous solid consists of particles of irregular shape In such a solid, the arrangement of constituent particles has only short-range order. In such an arrangement, a regular and periodically

repeating pattern is observed over short distances only. Examples are glass rubber, plastics etc.

Question 2. What makes glass different from a solid such as quartz?

Under what conditions could quartz be converted into glass? 

Solution. Glass is an amorphous solid in which the constituent particles (SiO, tetrahedra) have only a short-range order. Quartz is a crystalline form of silica in which SiO, units are arranged in such a way that they have long-ranged order. Quartz can be converted into glass by melting it and cooling it rapidly. 

Question 3. Classify each of the following solids as ionic, metallic, molecular, network (covalent) or amorphous.

(i) Tetraphosphorus dioxide (P4O10) (vii) Graphite
(ii) Ammonium phosphate, (NH4)3PO4(viii) Brass
(iii) Sic(ix) Rb
(iv) i2(x) LiBr
(v) P4(xi) Si
(vi) Plastic

logic means contain ions, metallic means are metals, network solids are giant molecules, molecular solids contain covalent bonds, and amorphous solids have short-range order, so classify the given solid on the basis of intermolecular forces.

Solution.

(1) Molecular solid (as contains covalent bonds)(viii) Metallic solid (metal) 
(ii) ionic solid (as contains ions) (ix) Metallic solid (metal)
(iii) Network (covalent) solid (as giant molecule)(x) Ionic solid (gives ions)
(iv) Molecular solid (contains (xi) Network (covalent) solid (giant molecule)
(v) Molecular solid (contains covalent bond) 
(vi) Amorphous solid (short-range order)
(vii) Network (covalent) solid (giant molecule)

Question 4. (i) What is meant by the term ‘coordination number?

(ii) What is the coordination number of atoms

(a) in a cubic close-packed structure? (b) in a body-centred cubic structure? U

(1) The number of neighbouring particles for a particle is its coordination number.

CHEN12043600

Solutions

(i) Coordination number It is defined as the number of nearest neighbours of a particle in a close-packed structure. 

(ii) (a) 12 (as each atom is attached to 12 other atoms.)

(b) 8 (because each atom is attached to 8 other atoms.)

Question 5. The stability of a crystal is reflected in the magnitude of its melting points’, Comment. Collect melting points of solid water, ethyl alcohol, diethyl ether and methane from a data book. What can you say about the intermolecular forces between these molecules?

The melting point of a solid is related to the attraction force between its molecules. The higher the melting point of a solid, the greater will be the forces of attraction between its molecules.

Solution.

(i) Stability of a crystal depends upon the magnitude of the force of attraction between the constituent particles. Greater the attraction. force, more will be the stability of the crystal. Hence, the point of the solid will be higher.

(ii) The melting point of different substances are:

(a) Water=273 K 

(b) Ethyl alcohol = 155.7K

(c) Diethyl ether = 156.8K

(d) Methane = 90.5 K

The intermolecular forces in molecules of water and ethyl alcohol are mainly hydrogen bonding. The magnitude is more in water than in ethyl alcohol which is evident from the values of their melting point.

The force in the molecules of diethyl ether are dipolar forces while in methane, only weak van der Waals’ forces of attraction exist. The values of melting point are the evidence for the same.

Question 6. How will you distinguish between the following pair of terms:

(i) hexagonal close-packing and cubic close-packing?

(ii) crystal lattice and unit cell?

(iii) tetrahedral void and octahedral void?

Solution.

(1) In hexagonal close packing (hcp), the spheres of the third layer are vertically above the spheres of the first layer. It means that the tetrahedral voids of the second layer are covered by the spheres of the third layer. The AB AB AB….. type. 

In cubic close packing (hcp), the spheres of the third layer cover the octahedral voids of the second layer. But the spheres of the fourth melting layer are aligned with those of the first layer. The pattern is ABC ABC…… type.

(ii) Crystal lattice is the three-dimensional arrangement of identical points in space which represents how the constituent particles (atoms, ions, molecules) are arranged in a crystal. The unit cell is the smallest portion of a crystal lattice which, when repeated in different directions, generates the entire lattice.

(iii) Tetrahedral voids are surrounded by four spheres that lie at the vertices of a regular tetrahedron. There are 2 tetrahedral voids per atom in a crystal. Octahedral voids are surrounded by six spheres and formed by a combination of two triangular voids of the first and second layers. There is one octahedral void per atom in a crystal.

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or 12 and 16 to stimulate the average valence of four as in Ge or Si. Typical compounds of groups 13-15 are InSb, AIP and GaAs.

Gallium arsenide (GaAs) semiconductors have a very fast response and have revolutionised the design of semiconductor devices. ZnS, CdS, CdSe and HgTe are examples of groups 12-16 compounds.

In these compounds, bonds are having the same ionic character as with covalent. The ionic character depends on. electronegativities of the two elements.


Short Answer Type


Question 1. Why are liquids and gases categorised as fluids? 

Solution. Liquids and gases have the tendency to flow, i.e., their molecules can move freely from one place to another. Therefore, they are known as fluids.

Question 2. Why are solids incompressible? 

Solution. The distance between the constituent particles is very less in solids. On bringing them still closer repulsion will start between electron clouds of these particles. Hence, they cannot be brought further close together.

Question 3. In spite of the long-range order in the arrangement of particles, why are the crystals usually not perfect? 

Solution. Crystals have long-range repeated patterns of arrangement of constituent particles but in the process of crystallisation some deviations from the ideal arrangement (i.e., defects) may be introduced, therefore, crystals are usually not perfect.

Question 4. Why does table salt NaCl sometimes appear yellow colour?

Solution. The yellow colour in NaCl is due to metal excess defect due to which unpaired electrons occupy anionic sites, known as F-centres. These electrons absorb energy from the visible region for excitation which makes the crystal appear yellow.

Question 5. Why is FeO(s) not formed in stoichiometric composition? 

Solution. In the crystals of FeO, some of the Fe2+ cations are replaced. by Fe3+ ions. Three Fe²*ions are replaced by two Fe¹+ ions to make up for the loss of positive charge. Eventually, there would be less amount of metal as compared to stoichiometric composition.

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