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The Solid State Class 12th Chemistry Part I CBSE Solution

Class 12th Chemistry Part I CBSE Solution
Intext Questions Pg-4
  1. Why are solids rigid?
  2. Why do solids have a definite volume?
  3. Classify the following as amorphous or crystalline solids: Polyurethane, naphthalene,…
  4. Why is glass considered a super cooled liquid?
  5. Refractive index of a solid is observed to have the same value along all directions.…
Intext Questions Pg-6
  1. Classify the following solids in different categories based on the nature of…
  2. Solid A is a very hard electrical insulator in solid as well as in molten state and melts…
  3. Ionic solids conduct electricity in molten state but not in solid state. Explain.…
  4. What type of solids are electrical conductors, malleable and ductile?…
Intext Questions Pg-12
  1. Give the significance of a ‘lattice point’,
  2. Name the parameters that characterize a unit cell
  3. Hexagonal and monoclinic unit cells Distinguish between
  4. Face-centred and end-centred unit cells. Distinguish between
  5. Explain how many portions of an atom located at (i) corner and (ii) body-center of a cubic…
Intext Questions Pg-21
  1. What is the two dimensional coordination number of a molecule in square close-packed…
  2. A compound forms hexagonal close-packed structure. What is the total number of voids in…
  3. A compound is formed by two elements M and N. The element N forms ccp and atoms of M…
  4. Which of the following lattices has the highest packing efficiency (i) simple cubic (ii)…
  5. An element with molar mass 2.7×10-2 kg mol-1 forms a cubic unit cell with edge length 405…
Intext Questions Pg-29
  1. What type of defect can arise when a solid is heated? Which physical property is affected…
  2. What type of stoichiometric defect is shown by? (i) ZnS (ii) AgBr…
  3. Explain how vacancies are introduced in an ionic solid when a cation of higher valence is…
  4. Ionic solids, which have anionic vacancies due to metal excess defect, develop colour.…
  5. A group 14 element is to be converted into n-type semiconductor by doping it with a…
  6. What type of substances would make better permanent magnets, ferromagnetic or…
Exercises
  1. Define the term 'amorphous'. Give a few examples of amorphous solids.…
  2. What makes a glass different from a solid such as quartz? Under what conditions quartz…
  3. Classify each of the following solids as ionic, metallic, molecular, network (covalent) or…
  4. What is meant by the term 'coordination number'?
  5. What is the coordination number of atoms: (a) in a cubic close-packed structure? (b) in a…
  6. How can you determine the atomic mass of an unknown metal if you know its density and the…
  7. 'Stability of a crystal is reflected in the magnitude of its melting points'. Comment.…
  8. Hexagonal close-packing and cubic close-packing? How will you distinguish between the…
  9. Crystal lattice and unit cell? How will you distinguish between the following pairs of…
  10. Tetrahedral void and octahedral void? How will you distinguish between the following pairs…
  11. Face-centred cubic How many lattice points are there in one unit cell of each of the…
  12. Face-centred tetragonal How many lattice points are there in one unit cell of each of the…
  13. Body-centred How many lattice points are there in one unit cell of each of the following…
  14. The basis of similarities and differences between metallic and ionic crystals. Explain…
  15. Ionic solids are hard and brittle. Explain
  16. simple cubic Calculate the efficiency of packing in case of a metal crystal for…
  17. body-centred cubic Calculate the efficiency of packing in case of a metal crystal for…
  18. face-centred cubic (with the assumptions that atoms are touching each other). Calculate…
  19. Silver crystallises in fcc lattice. If edge length of the cell is 4.07 × 10-8 cm and…
  20. A cubic solid is made of two elements P and Q. Atoms of Q are at the corners of the cube…
  21. Niobium crystallises in body-centred cubic structure. If density is 8.55 g cm-3, calculate…
  22. If the radius of the octahedral void is r and radius of the atoms in close packing is R,…
  23. Copper crystallises into a fcc lattice with edge length 3.61 × 10-8 cm. Show that the…
  24. Analysis shows that nickel oxide has the formula Ni0.98O1.00. What fractions of nickel…
  25. What is a semiconductor? Describe the two main types of semiconductors and contrast their…
  26. Non-stoichiometric cuprous oxide, Cu2O can be prepared in laboratory. In this oxide,…
  27. Ferric oxide crystallises in a hexagonal close-packed array of oxide ions with two out of…
  28. Ge doped with In Classify each of the following as being either a p-type or a n-type…
  29. Si doped with B. Classify each of the following as being either a p-type or a n-type…
  30. Gold (atomic radius = 0.144 nm) crystallises in a face-centred unit cell. What is the…
  31. Between a conductor and an insulator In terms of band theory, what is the difference?…
  32. Between a conductor and a semiconductor? In terms of band theory, what is the difference?…
  33. Schottky defect Explain the following terms with suitable examples:…
  34. Frenkel defect Explain the following terms with suitable examples:…
  35. Interstitials Explain the following terms with suitable examples:…
  36. F-centres. Explain the following terms with suitable examples:
  37. Aluminium crystallises in a cubic close-packed structure. Its metallic radius is 125 pm.…
  38. If NaCl is doped with 10-3 mol % of SrCl2, what is the concentration of cation vacancies?…
  39. Ferromagnetism Explain the following with suitable examples:
  40. Paramagnetism Explain the following with suitable examples:
  41. Ferrimagnetism Explain the following with suitable examples:
  42. Antiferromagnetism Explain the following with suitable examples:
  43. 12-16 and 13-15 group compounds. Explain the following with suitable examples:…
Intext Questions Pg-4
Question 1.

Why are solids rigid?


Answer:
  • Solids can be defined as any substance that has a definite shape, has mass and occupies volume.
  • The intermolecular spaces between the molecules forming the solid structures are smaller.
  • The intermolecular forces are strong.
  • The constituent particles (atoms, molecules, nuclei, etc.) has a fixed position and they can oscillate only about their mean position.
  • They are incompressible and rigid.

Question 2.

Why do solids have a definite volume?


Answer:

Solids have strong intermolecular forces of attraction. The constituent particles of solids cannot move from their position they can only vibrate from their mean position. That is why 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, fibre glass, copper.


Answer:



Explanation: Amorphous solids are not true solids, in these solids the constituent particles (atoms, ions or molecules) have short range order of arrangement.


In crystalline solids the constituent particles have long range order of arrangement)



Question 4.

Why is glass considered a super cooled liquid?


Answer:

Glass is an amorphous solid and all the amorphous solids have a tendency to flow, though very slowly. Hence glass is considered a super cooled liquid and that becomes the reason why the glass windows become slightly thicker at the bottom that at the top over a period of time.

Explanation: All amorphous solids have tendency to flow as rubber, plastic.



Question 5.

Refractive index of a solid is observed to have the same value along all directions.

Comment on the nature of this solid. Would it show cleavage property?


Answer:

Isotropic solids have the same value of the reflective index in all the direction. All isotropic solids are amorphous solids. Amorphous solids cut into two pieces with irregular surfaces. Therefore, amorphous solids do not show cleavage. Anisotropic solid is a solid material in which the physical properties do not depend on its orientation.

Explanation: Amorphous solids do not show cleavage property because of an irregular arrangement of particles. When amorphous solids are cut with the sharp-edged tool the newly generated surfaces are irregular and not smooth.


Intext Questions Pg-6
Question 1.

Classify the following solids in different categories based on the nature of

intermolecular forces operating in them:

Potassium sulphate, tin, benzene, urea, ammonia, water, zinc sulphide,

graphite, rubidium, argon, silicon carbide.


Answer:



Explanation: Ionic solids are those in which constituents particles are cations and anions which are held together by columbic force of interactions


e.g.- K2SO4⇒ K+ + SO4—


Metallic solids are metals in which metal ions (also called kernals) are held together by metallic bonds.)


Molecular solids are made up on molecules or inert gases.


In covalent solids constituent particles are atoms which are held together by continuous system of covalent bonds.


Note: Though in solid argon the constituent particles are atoms even it is categorised as molecular solid because the particles are held together by vander waal forces so all solids of zero group elements are placed under the category of molecular solids.)



Question 2.

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


Answer:

The solid ‘A’ is a covalent solid, such as diamond. As it is an electrical insulator in both solid and molten form and melts at an extremely high temperature.

Explanation-In covalent solids the constituent particles (i.e. atoms) form a network of covalent bonds which make them very hard and also very high melting points.


Further they are electrical insulator in solid as well as in molten state because they do not contain any ion (like ionic solids) or free electrons (like metallic solids) in solid or in molten state.


(Note- For any compound to show electrical conductivity either free electrons or free ion must be available.)



Question 3.

Ionic solids conduct electricity in molten state but not in solid state. Explain.


Answer:

The ionic solids conduct electricity in molten state as the constituent particles of ionic solid are not free to move in solid state, thus ionic solids are insulators in their solid state. While the ions become free to move in the molten state



Question 4.

What type of solids are electrical conductors, malleable and ductile?


Answer:

Metallic solids have these properties.

Explanation: They are electrical conductors, are malleable and ductile, which means it could be drawn into thin wires. The metals are orderly free collection of positive ions surrounded by and held together by a sea of free electrons. These free and mobile are responsible for high electrical and thermal conductivity of metals.



Intext Questions Pg-12
Question 1.

Give the significance of a ‘lattice point’,


Answer:

The points in a crystal lattice where atoms or ions can be placed are called as lattice points. Lattice Points can be vacant or filled.

The number of lattice points can be different as well as can be arranged in different ways which give rise to the different crystal lattice.


Given below is a diagram of the crystal lattice and the lattice points:




Question 2.

Name the parameters that characterize a unit cell


Answer:

There are a total of six parameters that characterize a unit cell.

i. Dimensions of a unit cell (also called the edges): a, b and c.


ii. The angles between the edges: α, β and γ


The variation of these 6 parameters leads to different shapes and sizes of the unit cell, shown as below:



Where a, b and c are technically the vectors of the unit cell. The angle α is between edges b and c; the angle β is between the edges α and γ; γ is the angle between a and b.



Question 3.

Distinguish between

Hexagonal and monoclinic unit cells


Answer:




Question 4.

Distinguish between

Face-centred and end-centred unit cells.


Answer:




Question 5.

Explain how many portions of an atom located at (i) corner and (ii) body-center of a cubic unit cell is part of its neighbouring unit cell.


Answer:

The portion of an atom of the corner of a cubic unit cell is shared by eight adjacent unit cells as shown below:



Therefore, a portion of the atom at the corner = 8 × 1/8 = 1 atom.


(ii) The atoms present at the center of the body is not shared by its neighbouring unit cell.


Therefore, portion of the atom at the center = 1 atom



Intext Questions Pg-21
Question 1.

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


Answer:

In a two dimensional square closed packed layer, a molecule touches four neighbour atoms. Therefore, 4 is the two dimensional coordinate number of a molecule in square closed packing.

Explanation-In two dimensional square close-packed layer each sphere is in contact with four of its neighbours hence its coordination number is four.



Question 2.

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


Answer:

Number of atoms in close packing = 0.5 mol

1 mol has 6.022x1023 particles


So that


Number of close- packed particles = 0.5 × 6.022 × 1023 = 3.011 × 1023


Number of tetrahedral voids = 2 × number of atoms in close packing plug the value we get


Number of tetrahedral voids = 2 × 3.011 × 10 23 = 6.022 × 10 23


Number of octahedral = number of atoms in close packing


So that


Number of octahedral voids = 3.011 × 10 23


Total number of voids = tetrahedral voids + octahedral voids


= 6.022 × 10 23 + 3.011 × 10 23


= 9.03 × 10 23



Question 3.

A compound is formed by two elements M and N. The element N forms ccp and atoms of M occupy 1/3rd of tetrahedral voids. What is the formula of the compound?


Answer:

The formula can be determined by using the following method

Let the number of atoms of the element N = n


Number of tetravalent voids = 2n


It is given that the atoms of element M occupy 1/3 of the tetrahedral voids.


So that the number of atoms of M = (1/3) × 2n


Ratio of the number of atoms of M and N


M:N =2n/3:n


Multiplying the 3 and divide by n we get


M:N = 2:3


Hence, the formula of the compound is M2N3 .



Question 4.

Which of the following lattices has the highest packing efficiency

(i) simple cubic

(ii) body-centred cubic and

(iii) Hexagonal close-packed lattice?


Answer:

(i)



In a simple cubic lattice the atoms are located only at the corners of the cube.


Let us assume the edge length or the side of the cube = a


And the radius of each particle = r


The relation between radius and edge a


Can be given as a = 2r


The volume of the cubic unit cell = side3 = a3


= (2r3)


= 8r3


Number of atoms in unit cell 


The volume of the occupied space 


And we know that, the packing efficiency 




= 52.36%


(ii) 


Let us assume the edge length or the side of the cube = a


And the radius of each particle = r


The diagonal of a cube is always a 


The relation between radius and the edge will be = 4r


Divide by root 3 we get A 


Total number of atoms in body centred cubic


Number of atoms at the corner


Number of atoms at the centre = 1


Total number of atoms = 2


The volume of the cubic unit cell = side3


= a3


= (4r/a√3)3


The volume of the occupied space 


Packing efficiency 




= 68%


(iii) Let the base of the hexagon is a and the height is c


Each angle in hexagonal will be 60 degree at the base


Packing efficiency of


Hexagonal close- packed lattice 



a = 2r c  = 1.633a




= 74%


Thus, hexagonal close- packed lattice has the highest packing efficiency of 74%.



Question 5.

An element with molar mass 2.7×10-2 kg mol-1 forms a cubic unit cell with edge length 405 pm. If its density is 2.7×103 kg m-3, what is the nature of the cubic unit cell?


Answer:

Given information:-

Molar mass of the element = 2.7×10-2 kg mol-1


Edge length, a = 405 pm


Density, d = 2.7×103 kg m-3


Using the formula, d 


Putting the values given at their appropriate place, we get



= 3.99 which is approximately equal to 4


Therefore, it is an fcc unit cell.


Intext Questions Pg-29
Question 1.

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


Answer:

When a solid is heated, vacancy defect is produced in the crystal. On heating, some ions or atoms leave the lattice site completely, which means the lattice site becomes empty or vacant. As a result of this defect, density of the substance decreases. Thus density is the physical property that is effected by the vacancy defect.



Question 2.

What type of stoichiometric defect is shown by?

(i) ZnS (ii) AgBr


Answer:

i) ZnS shows Frankel defect


Explanation: Frankel defect arises when an atom or smaller ion leaves its place in the lattice, creating a vacancy and becomes an interstitial by lodging in a nearby location. This occurs in ZnS due to the comparatively smaller size of Zn2+ .


ii) AgBr shows frankel as well as schottky defect.


Explanation: AgBr shows both types of defects, i.e. schottky and Frenkel Defects. Since, Schottky Defects arises because of mission of constituent particles, thus it decreases the density of ionic compound.



Question 3.

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


Answer:

To explain this, let us take an example of NaCl doped with SrCl, impurity when SrCl2 is added to NaCl solid as an impurity, two Na+ ions will then be replaced and one of their site will be occupied by Sr2- while the other will remain vacant. Thus, we can say that when a cation of higher valance is added as an impurity to an ionic soil, two or more cations of lower valency are replaced by a cation of higher valence to maintain electrical neutrality. Hence, some cationic vacancies are created.



Question 4.

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


Answer:

To explain this, let us take an example of NaCl. When NaCl crystal is heated in presence of Na vapour, some Cl- ions leave their lattice sites to combine with Na to form Na+ (Na+ + Cl-⇒ NaCl) then diffuse into the crystal to occupy the anion vacancies. These sites are called as the F- centres. These electrons absorb energy from the visible light, get excited to higher energy level and when they fall back to the ground state they impart yellow colour to the NaCl crystal.



Question 5.

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


Answer:

Silicon and germanium both have valance electrons and they belong to group 14th of the periodic table. Arsenic and phosphorus belong to group 15th of the periodic table and they have valence electrons equal to 5. When silicon or germanium is adopted with phosphorus or arsenic, four electrons of phosphorus or arsenic out of five; make covalent bonds with four electrons of silicon or germanium leaving one electron free; which increases the electrical conductivity of silicon or germanium. Since the electrical conductivity of silicon and phosphorus is increased because of negatively charged particles (electron), thus this is known as n – type semiconductor.



Question 6.

What type of substances would make better permanent magnets, ferromagnetic or ferrimagnetic ? Justify your answer.


Answer:

Metal ions of ferromagnetic substances are randomly oriented in normal condition and substances do not act as a magnet. But when metal ions are grouped together in small regions, called as domains, each domain acts as a tiny magnet and it produces a strong magnetic field. In such condition ferromagnetic substances act like a magnet. When the ordering of the domain in group persists even after removal of the magnetic field a ferromagnetic substance becomes a permanent magnet. While domains are grouped in parallel and anti – parallel direction but in unequal number in ferromagnetic compounds. Thus, ferromagnetic substances, such as Ni, Co, Fe would make better permanent magnets rather than ferromagnetic substances.



Exercises
Question 1.

Define the term 'amorphous'. Give a few examples of amorphous solids.


Answer:

Solids having constituent particles with irregular with shapes and short range order are called amorphous solids. Amorphous solids are isotropic in nature and melt over a range of temperature. Thus, amorphous solids are also referred as pseudo solids or super cooled liquids. They do not do not have definite heat of fusion. These solids give irregular surfaces, cut with sharp tool. Glass, rubber, etc. are some examples of amorphous solid.



Question 2.

What makes a glass different from a solid such as quartz? Under what conditions quartz could be converted into glass?


Answer:

It is the arrangement of constituent particles of glass which makes it different from quartz. The constituent particles of glass have short range order while quartz has constituent particles in long range order both by heating and cooling rapidly can be converted into glass.


Question 3.

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

(i) Tetra phosphorus decoxide (P4O10) (vii) Graphite

(ii) Ammonium phosphate (NH4)3PO4 (viii) Brass

(iii) SiC (ix) Rb

(iv) I2 (x) LiBr

(v) P4 (xi) Si

(vi) Plastic


Answer:

(i) Tetra phosphorous decoxide (P4O10): molecular

Explanation: Molecular solids are made up on molecules or inert gases.


(ii) Ammonium phosphate (NH4)3PO4: Ionic


Explanation: Ionic solids are those in which constituents particles are cations and anions which are held together by coulombic force of interactions


e.g.- K2SO4⇒ 2K+ + SO4—


(iii) SiC: Covalent (network)


Explanation: In covalent solids constituent particles are atoms which are held together by continuous system of covalent bonds.


(iv) I2 :molecular


Explanation: Molecular solids are made up on molecules or inert gases.


(v) P4: Molecular


Explanation: Molecular solids are made up on molecules or inert gases.


(vi) Plastic: Amorphous


Explanation: Amorphous solids are not true solids, in these solids the constituent particles (atoms, ions or molecules) have short range order of arrangement.


(vii) Graphite: Covalent (network)


Explanation: In covalent solids constituent particles are atoms which are held together by continuous system of covalent bonds.


(viii) Brass: Metallic


Explanation: Metallic solids are metals in which metal ions (also called kernals) are held together by metallic bonds.)


(ix) Rb: Metallic


Explanation: Metallic solids are metals in which metal ions (also called kernals) are held together by metallic bonds.)


(x) LiBr: Metallic


Explanation: Metallic solids are metals in which metal ions (also called kernals) are held together by metallic bonds.)


(x) Si : Covalent (network)


Explanation: In covalent solids constituent particles are atoms which are held together by continuous system of covalent bonds.


Question 4.

What is meant by the term 'coordination number'?


Answer:

Coordination number is the number of nearest neighbours of any constituent particles present in the crystal lattice.



Question 5.

What is the coordination number of atoms:

(a) in a cubic close-packed structure?

(b) in a body-centred cubic structure?


Answer:

(a) In a cubic close- packed structure is 12.

(b) In a body- centered cubic structure is 8.



Question 6.

How can you determine the atomic mass of an unknown metal if you know its density and the dimension of its unit cell? Explain.


Answer:

The atomic mass of an unknown metal can be determined by knowing its density and the dimension of unit cell.

Let ‘a’ be the edge length of a unit cell of a crystal.


‘d’ is the density of the metal


‘m’ is the atomic mass of the metal.


‘z’ is the number of atoms in the unit cell.


Now, the density of the unit cell 


As we know that, mass of the unit cell = Number of atoms in the unit cell × atomic mass


And the volume of the unit cell = (Edge length of the cubic unit cell)3


Therefore, d --------- (i)


 ---------------- (ii)


Now, since mass of the metal (m)



Therefore, from equation (ii) we have



 --------------- (iii)


If the edge lengths are different (say a, b and c), therefore, equation (iii) can be written as


 ----------- (iv)


Thus, using equation (iii) and the atomic mass of an unknown metal can be determined.



Question 7.

'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?


Answer:

The melting points of the given substance are as follows:

Solid water – 273 K


Ethyl alcohol – 158.8 K


Diethyl ether – 156.85 K


Methane – 89.34 K


As we can see the melting point of solid water is highest and melting point of methane is lowest among the given substance. This says that intermolecular force in solid water is strongest and the intermolecular force in methane is weakest.



Question 8.

How will you distinguish between the following pairs of terms:

Hexagonal close-packing and cubic close-packing?


Answer:




Question 9.

How will you distinguish between the following pairs of terms:

Crystal lattice and unit cell?


Answer:




Question 10.

How will you distinguish between the following pairs of terms:

Tetrahedral void and octahedral void?


Answer:




Question 11.

How many lattice points are there in one unit cell of each of the following lattice?

Face-centred cubic


Answer:

One unit cell of a face- centered cubic has 8 lattice points are corners and 6 lattice points at faces, total 14 lattice points.



Question 12.

How many lattice points are there in one unit cell of each of the following lattice?

Face-centred tetragonal


Answer:

One unit cell of face- centered tetragonal has 8 lattice points are corners and 6 lattice points at faces, total 14 lattice points.



Question 13.

How many lattice points are there in one unit cell of each of the following lattice?

Body-centred


Answer:

One unit cell of body centered has 8 lattice points are corners and 1 lattice points at faces, total 9 lattice points.



Question 14.

Explain

The basis of similarities and differences between metallic and ionic crystals.


Answer: