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Important Questions for Class 12 Chemistry Chapter 1 – The Solid State

Here are the important questions for Class 12 Chemistry Chapter 1 – Solid State with Answers. These important questions are derived from the CBSE board curriculum and correspond to the most recent Class 12 chemistry syllabus. By practicing these Class 12 key questions, students will be able to swiftly review all of the concepts discussed in the chapter and prepare for the Class 12 Annual Examinations as well as other entrance exams such as NEET and JEE.

Important Questions with Answers: The Solid State

Ques. Why are solids incompressible?

Ans. Solids are incompressible because their constituent particles (atoms, ions, or molecules) are tightly packed, with very small interparticle spaces. If we make an effort to compress, repulsive interactions will dominate in the electron clouds of the constituent particles.

Ques. Why are solids rigid?

Ans. Solids are rigid because their constituent particles are tightly packed. They have no translatory movement and can only oscillate about the average position.

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

Ans. Iron oxide  (FeO) is not produced in stoichiometric compositions. It appears in the non-stochiometric composition of Fe0.95O. Because some Fe2+ ions are missing from the crystal lattice of ferrous oxide (FeO), Fe3+ ions compensate for the loss of positive charge. The lattice’s electrical neutrality can be maintained with fewer Fe3+ ions.

Ques. Why does table salt, NaCl, sometimes appear yellow in color?

Ans. The yellow color of sodium chloride results from a metal excess defect, which causes electrons to occupy anionic sites. These sites are referred to as F-centers. When electrons absorb radiation from visible light, they become excited. These excited electrons generate radiations that correlate to yellow color.

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

Ans. The yellow color of sodium chloride results from a metal excess defect, which causes electrons to occupy anionic sites. These sites are referred to as F-centers. When electrons receive radiation from visible light, they become excited. These excited electrons generate radiations that correspond to a yellow color.

Ques. Why does the electrical conductivity of semiconductors increase with a rise in temperature?

Ans. This is demonstrated through the use of band theory. In semiconductors, the energy gap between valence and conduction bands is tiny. The electron’s kinetic energy increases as temperature rises. This means that more electrons can transfer from valence to conduction bands. As a result, electrical conductivity increases as temperature rises.

Ques. Under which situations can an amorphous substance change to crystalline form?

Ans. This can be done by slowly heating and then cooling over a long period of time. If an amorphous solid is kept at a temperature slightly below its melting point for a longer period of time, the individual molecules, atoms, or ions can gradually reorganize into a more ordered crystalline form.

Ques. Calculate the density of a cubic crystal from its structure.

Ans. The edge of a cubic crystal is estimated from X-ray research, as well as the crystal type (simple cubic, body-centered cubic, or face-centered cubic). If you know how many particles are in a unit cell, you can calculate the crystal’s density.

Let, for a cubic unit cell, the edge length be = a cm

The volume of the cubic unit cell = a³ cm³

Density of the unit cell = (Mass of the unit cell / Volume of the unit cell)l

Mass of the unit cell = Number of atoms in unit cell × Mass of each atom

⇒ Mass of the unit cell= Z × Mass of each atom

Let M be the atomic mass of an element.

Mass of one atom = Atomic mass number (M) /Avogadro’s number (NA)

Therefore,

Density of unit cell (ρ) = {Z × (M/NA)} / a3 = (Z × M) / (a3 × NA)

Ques. Match the types of defect given in Column I with the statement given in Column II

Column (I) Column (II)
(a) Impurity defect (i) NaCl with anionic sites called F-centers
(b) Metal excess defect (ii) FeO with Fe3+
(c) Metal deficiency defect (iii) NaCl with Sr2+ and some cationic sites vacant

Ans. (a)- (iii)
(b)- (i)
(c)- (ii)

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