Tag: chemistry

Questions Related to chemistry

The heat of neutralisation of $HCl$ by $NaOH$ is -55.9 KJ/mole. If the heat of neutralisation of $HCN$ by$ NaOH$ is -12.1 KJ/mole, the energy of dissociation of $HCN$ is:

chemistry energetics and thermochemistry bond energies and enthalpy changes bond enthalpies enthalpies for different types of reactions

  1. -43.8 KJ

  2. 43.8 KJ

  3. 68 KJ

  4. -68 KJ

Show answer
Correct Option: B
Explanation:

Heat of dissociation $=(55.9-12.1)=43.8\ KJ$

Which of the following statement is not correct about molecular crystals?

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

  1. They are generally soft and easily compressible.

  2. They are good conductors of electricity as the electrons are delocalised in the bonds.

  3. They have low melting and boiling points.

  4. They consist of polar or non-polar molecules.

Show answer
Correct Option: B
Explanation:

In molecular crystals, atoms are bounded by weak van der Walls forces. They have no free electrons in them. So, they are electrical insulators.

Hence, the correct answer is option B.

Examples of few solids are given below. Find out the example which is not correctly matched.

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

  1. Ionic solids - $NaCl$, $ZnS$

  2. Covalent solids - $H _2,I _2$

  3. Molecular solids - $H _2O _{(s)}$

  4. Metallic solids - $Cu$, $Sn$

Show answer
Correct Option: B
Explanation:

In ${ H } _{ 2 }\quad and\quad { I } _{ 2 }$, molecules are attracted by weak van der Waals attractions. So, they are molecular solids. 

Hence, option B is not a correct match.  

Which of the solids show the following properties?
(i) Electrical conductivity 
(ii) Malleability
(iii) Ductility
(iv) Fairly high melting point

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

  1. Ionic solids

  2. Covalent solids

  3. Metallic solids

  4. Molecular solids

Show answer
Correct Option: C
Explanation:

In the given options, both ionic and metallic solids are electrical conductors and have high melting point. But only metallic solids are malleable and ductile. 

So, the correct answer is option C.

Ionic solids conduct electricity in molten state but not in solid state because:

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

  1. in molten state free ions are loosely bound which are not free to move in the solid state

  2. in solid state ionic solids are hard, brittle and become soft in molten state

  3. all solids conduct electricity in molten state

  4. in solid state ions are converted to atoms which are insulators.

Show answer
Correct Option: A
Explanation:

In solid state, atoms in ionic solids are bonded by strong ionic bonds. They are able to move freely. So, they do not conduct electricity in solid state. While in molten form, the ions and electrons are free to move. So, they conduct electricity in molten state.

So, the correct answer is option A. 

Which of the following forms a molecular solid when solidified?

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

  1. Calcium fluoride

  2. Silicon dioxide

  3. Carbon dioxide

  4. Sodium chloride

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Correct Option: C
Explanation:

In the given options, Calcium Fluoride and Sodium Chloride are the ionic crystals due to presence of ionic bond in them.

Silicon dioxide is network solid due to strong intermolecular covalent bond.
In carbon dioxide, the molecules are bonded by weak van der Walls force. Hence, they are molecular solids.
So, the correct answer is option C.

Solid $X$ is a very hard solid which is electrical insulator in solid as well as in molten state and has extremely high melting point. What type of solid is it?

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

  1. Ionic solid

  2. Covalent solid

  3. Metallic solid

  4. Molecular solid

Show answer
Correct Option: B
Explanation:

Covalent solids have high melting point due to their interconnected covalent bonds. Since there are no free electrons present in covalent solids, so they do not conduct electricity in solid state as well as molten state. Some of the examples are Diamond and Quartz.

So, correct answer is option B.

Graphite cannot be classified as:

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

  1. conducting solid

  2. network solid

  3. covalent solid

  4. ionic solid

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Correct Option: D
Explanation:

Since graphite is an allotrope of carbon hence, each atom is linked to each other through a covalent bond. Therefore, graphite is a covalent solid. 


Hence, it cannot be classified as an ionic bond.

Hence, the correct answer is option $\text{D}$.

Which of the following is not the characteristic of ionic solids?

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

  1. Very low value of electrical conductivity in the molten state

  2. Brittle nature

  3. Very strong forces of interactions

  4. Anisotropic nature

Show answer
Correct Option: A
Explanation:

In molten state, the ionic solids have free ions in them. Ions help in the conduction of electricity. Due to these free ions the electrical conductivity of ionic compounds in molten state is very high. 

So, option A is not correct regarding the characteristics of ionic compounds.
So, option A is correct answer.

Which of the following is network solid?

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

  1. $SO _{2(solid)}$

  2. $I _2$

  3. Diamond

  4. $H _2O _{(ice)}$

Show answer
Correct Option: C
Explanation:

A network solid or covalent network solid is a chemical compound (or element) in which the atoms are bonded by covalent bonds in a continuous network extending throughout the material. In a network solid there are no individual molecules, and the entire crystal or amorphous solid may be considered a macromolecule.

In diamond, the carbon atoms are held together by strong covalent bonds. It is a giant molecule. Thus, it is a network solid.
So, option $C$ is correct.