Tag: chemistry

Questions Related to chemistry

Which of the following are covalent solids?

chemistry solid state classification of crystalline solids classification of solids introduction to solids

  1. Iron

  2. Diamond

  3. Sodium chloride

  4. Graphite

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Correct Option: B,D
Explanation:

Covalent solids form crystals that can be viewed as a single giant molecule made up of an almost endless number of covalent bonds. 

Each carbon atom in diamond and graphite is covalently bound to four other carbon atoms oriented toward the corners of a tetrahedron. Because all of the bonds in this structure are equally strong, covalent solids are often very hard and they are notoriously difficult to melt. Diamond is the hardest natural substance and it melts at $355^oC$.

Hence, the correct options are $B$ and $D$

Passage of current through graphite is due to :

chemistry solid state classification of crystalline solids classification of solids introduction to solids

  1. free electrons

  2. mobile electrons

  3. $p\pi-p\pi$ bonded electrons

  4. lone pair of electrons

Show answer
Correct Option: B
Explanation:

In graphite, each carbon atom uses only 3 of its 4 outer energy level electron in covalently bonding to there other carbon atoms in a place. In graphite, electrons are spread out between the structure.

Statement: Diamond glitters because of its high refractive index.

State whether the given statement is true or false
chemistry solid state classification of crystalline solids classification of solids introduction to solids

  1. True

  2. False

Show answer
Correct Option: A
Explanation:
The diamond glitters because of its high refractive index. The refractive index of diamond is $2.414$. 
Higher is the refractive index, the more brilliance a substance has. This is because the substance can bend light rays to a higher degree. The brilliance of the diamond is also dependent on the cut if a diamond which in turn depends on the diamond cutter's skill. Greater number of refractive surfaces result in more glitter.

Hence, the given statement is $\text{true}$
Statement: Increase in pressure in ionic solids may decrease its co-ordination number.

State whether the given statement is true or false.
chemistry solid state classification of crystalline solids classification of solids introduction to solids

  1. True

  2. False

Show answer
Correct Option: A
Explanation:

Pressure and temperature also influence the structure of ionic solids. The structures of chlorides, bromides and iodides of sodium, potassium and rubidium having $6:6$ Co-ordination at normal temperature and pressure changes to $8:8$ co-ordination like CsCl structure at high pressure, Thus, high pressure increases co-ordination number. Furthermore, CsCl structure changes to NaCl structure at $760$ K. Thus, high temperature decreases co-ordination number.


Hence, the given statement is $true$

Ice is an example of ............ crystal.

chemistry solid state classification of crystalline solids classification of solids introduction to solids

  1. liquid

  2. molecular

  3. ionic

  4. covalent

Show answer
Correct Option: B
Explanation:

Molecular Crystals: 

In these crystals, molecules occupy the lattice points of the unit cells except in solidified noble gases in which the units are atoms, where the binding is due to van der Waal's forces and dipole-dipole forces. Since van der Waal's forces are non-directional, the structure of the crystal is determined by geometric consideration only.
Ice is the common example in which dipole-dipole forces of attraction (hydrogen bonding) are active. Many organic and inorganic crystals involve hydrogen bonds. Although these are comparatively weaker but play a very important role in determining the structures of substances. Example, polynucleotides, proteins etc.

Hence, the correct option is $\text{B}$

Statement: The melting point of all substances decreases with pressure increase.

State whether the given statement is true or false.
chemistry solid state classification of crystalline solids classification of solids introduction to solids

  1. True

  2. False

Show answer
Correct Option: B
Explanation:

Melting point increases with increase in pressure. This is because , due to increased pressure molecules tend to remain in solid state. (This is the basic principle on which liquification of gas works)


Hence, the given statement is $false$.

Statement: Ionic solids do not possess molecules.

State whether the given statement is true or false.
chemistry solid state classification of crystalline solids classification of solids introduction to solids

  1. True

  2. False

Show answer
Correct Option: A
Explanation:

In ionic solids, atoms are present as ions, where cations and anions are arranged in various structure giving rise to a variety of lattices. Thus, they do not have molecules.


Hence, the given statement is $\text{true}$

Dry ice is an example of_________.

chemistry solid state classification of crystalline solids classification of solids introduction to solids

  1. ionic cystal

  2. supercooled liquid

  3. molecular crystal

  4. covalent crystal

Show answer
Correct Option: C
Explanation:

Molecular solid is a solid composed of molecules held together by the van der Waals forces. Because these dipole forces are weaker than covalent or ionic bonds, molecular solids are soft and have relatively low melting temperature. Pure molecular solids are electrical insulators but they can be made conductive by doping. Examples of molecular solids include hydrocarbons, ice, sugar, fullerenes, sulfur and solid carbon dioxide.

Assertion (A): Covalent crystals have a higher melting point.
Reason (R): Covalent bonds are stronger than ionic bonds.

Choose the appropriate answer :
chemistry solid state classification of crystalline solids classification of solids introduction to solids

  1. Both (A) and (R) are correct and (R) is the correct explanation of (A)

  2. Both (A) and (R) are correct but (R) is not the correct explanation of (A)

  3. (A) is correct but (R) is incorrect

  4. (A) is incorrect but (R) is correct

  5. Both (A) and (R) are incorrect

Show answer
Correct Option: A

The cation-anion bond have the largest nature of covalent character for:

chemistry solid state classification of crystalline solids classification of solids introduction to solids

  1. NaBr

  2. SrS

  3. CdS

  4. BaO

Show answer
Correct Option: C
Explanation:

More is the deformation in anion, more is the covalent character. 
Pseudo inert gas cation e.g. $Cd^{2+}$ causes more polarisation of ion and so, it has higher covalent character.