Unit 1: States of Matter and Phase Changes — Long Questions

Chemistry is the branch of Science which deals with the properties, composition and the structure of matter. It also studies the physical and chemical changes in matter and the laws or principles which govern these changes.

(a) Rate of reaction
Ans. Rate of reaction is studied in physical chemistry.

(b) Digestion of food in human body
Ans. Digestion of food in human body is studied in biochemistry.

(c) Properties of Plasma
Ans. Properties of plasma are studied in physical chemistry.

(d) Ecosystem
Ans. Ecosystem is studied in environmental chemistry.

(e) Reactions taking place during fire works
Ans. Inorganic chemistry deals with the study of reactions taking place during fireworks.

(f) Measurement of the absorption of wavelength with the help of ultraviolet spectrometer.
Ans: Analytical chemistry deals with the measurement of the absorption of wavelength with the help of ultraviolet spectrometer.

Definition

Elements may exist in more than one structural forms which can exhibit quite different physical and chemical properties. These forms are called allotropic forms and phenomenon is called allotropy.

For example -

(i) Allotropic forms of oxygen:
Oxygen exists in two allotropic forms namely oxygen (O₂) and ozone (O₃).

(ii)Allotropic forms of carbon:
Carbon exists in three allotropic forms diamond, graphite and Buckminster fullerene.

a. Diamond
Diamond has a giant macromolecular structure.

b. Graphite
Graphite has a layered structure of hexagonal rings of carbon.

c. Buckminster fullerene
Buckminster fullerene (C₆₀) consists of spheres made of atoms arranged in pentagons and hexagons. Fullerenes are stable at high temperatures and high pressures. Being covalent in nature, they are soluble in organic solvents. The fullerene structure is unique in that the molecule is not charged, has no boundaries and has no unpaired electrons. They have a cage like structure. Fullerene C₆₀ has a low melting point. It is soft and cannot conduct electricity.

(iii) Allotropic forms of sulphur

Sulphur also exists in two crystalline allotropic forms i.e. rhombic and monoclinic;

1. Rhombic: It contains S₈ molecules arranged in a rhombic crystal lattice. It is more stable allotropes under standard condition

2. Monoclinic: It contains S₈ molecule arranged in a monoclinic crystal lattice.

Coal vs Diamond

Coal

• Coal is a combustible black or brownish-black sedimentary rock composed primarily of carbon along with hydrogen, sulphur, oxygen and nitrogen.
• Coal is used as a source of energy for heating and electricity generation due to its high carbon content.

Diamond

• Diamond is a form of carbon with a rigid three dimensional crystal lattice structure.
• Diamond is known for its hardness, transparency and high refractive index. Due to which, it is use in jewelry and industrial applications.

Supercritical fluids are highly compressed state of matter which shows both properties of gases and liquids.

Difference between supercritical fluids and ordinary liquids:

Supercritical fluids

• They diffuse quickly.
• They have higher solvating power which means they can dissolve a wide range of substances.
• They have lower viscosity allowing them to flow more easily.
• They are more compressible than ordinary liquids.

Ordinary liquids

• They diffuse slowly.
• They have low solvating power which means they can dissolve a fewer substance.
• They have high viscosity.
• They are less compressible than supercritical fluids.

Definition

The solubility of a solute is the amount of solute which can dissolve in 100g of a solvent at a particular temperature.

Solubility change with change in temperature

Change in temperature has different effects on the solubility of different compounds.

i) Solubility increase with increase in temperature:

Usually the solubility increases with the increase in temperature but it cannot be taken as a general rule. There are a large number of compounds whose solubility in H₂O increases with the increase in temperature e.g. potassium nitrate (KNO₃), silver nitrate (AgNO₃) and potassium chloride (KCl) etc. Similarly, the solubility of copper sulphate and sodium nitrate also increase with increase in the temperature. On dissolving a solute in a solvent if heat is absorbed, it means that solutes- solutes forces are stronger and heat is required to break these forces. For such solutes, solubility increace with the increase in temperature.

ii) Solubility decrease with increase in temperature:

The solubility of compounds like Lithium carbonate (Li₂CO₃) and calcium chromate (CaCrO₄) decrease with the increase in temperature. The solubility of gases in water also decreases with the increase in temperature. On dissolving solute in a solvent if heat is released, it means that solute solvent interactions are stronger then solute-solute forces. For such solids solubility decrease with the increase of temperate. Similarly, the solubility of calcium hydroxide decreases with the increase in temperature.

iii) Temperature has no effect on solubility

The solubility of sodium chloride in H₂O does not increase appreciably with the increase in temperature. On adding a solute in a solvent, if neither heat is absorbed nor released, temperature has minimum effect on solubility.

i. Gaseous Molecules:

In gaseous molecules, the molecules have rapid and random movements. They move freely and quickly, colliding with each other and the walls of the container. Due to this free movement, gases expand to fill their container. They have weak intermolecular forces and make gases easily compressible. Their densities are very low.

ii. Liquid Molecules:

In liquid molecules, the molecules are also in continous state of motion but the movement is more restricted as compared to gases. Liquid molecules have significant intermolecular forces between them allowing them to flow and take the shape of the container. But they do not expand to fill the entire volume like gases. Liquids are therefore not easily compressible and their densities have high values.

Organic chemistry

i) Definition
It is the branch of chemistry that deals with the compounds of carbons and hydrogen (hydrocarbons) and their derivatives other than its simple salts like carbonates, bicarbonates, oxides and carbides.

ii) Application
In this branch, we study the structure, formation, properties, composition and reactions of carbon containing compounds. Organic compounds are found in all forms of life and are also essential for life.

Inorganic chemistry

i) Definition
It is the study of the synthesis composition, properties and structure of elements and compounds that contain little or no carbon. hydrogen (hydrocarbons)

ii) Application
Inorganic compounds are used as medicines, fertilizers, catalysts, pigments, coatings and much more.

Potassium nitrate is purified through crystallization by following steps:

i) Prepare the Solution: Dissolve the impure potassium nitrate in hot water. The solubility of potassium nitrate increases with temperature allowing more of the compound to dissolve.

ii) Filtering: Filter the hot solution to remove any insoluble impurities or undissolved particles. This step helps in obtaining a clear solution.

iii) Cooling the Solution: Slowly cool down the filtered solution. As the temperature decreases, the solubility of potassium nitrate decreases as well as leading to the formation of crystals.

iv) Crystallization: Crystals of potassium nitrate will start to form as the solution cools. These crystals are purer than the original compound since impurities are less likely to be incorporated the crystal lattice.

v) Isolation of Crystals: Once a sufficient amount of crystals has formed, separate them from the remaining liquid using techniques like filtration or decantation.

vi) Drying: Finally, dry the purified potassium nitrate crystals to remove any remaining water resulting in a pure crystalline compound. Put solids commonly appear as beautifully shaped crystals.

This process of crystallization helps in purifying potassium nitrate by separating it from impurities present in the initial sample.

Graphene is highly valuable in the field of electronics and it is often called a "miracle material" because of its unique characteristics. It is useful in electronics like:

• It is a single layer of carbon atoms arranged in a hexagonal lattice, making it incredibly strong.
• It is a light weight.
• It is a good conductor of electricity and heat.
• It is a transparent material.
• It is highly flexible material.

Graphene is exceptionally strong about 200 times stronger than steel. This strength combined with its light weight nature make it highly desirable for various applications.

Examples Graphene-based transistors, sensors and flexible electronic devices are just a few examples of how this material is revolutionizing the electronics industry.

Uses Due to its transparency, it is use in touch-screen, solar cells and other optoelectronic devices.

Chemistry is the science which deals with the properties, composition and the structure of matter. It also studies the physical and chemical changes in matter and the laws or principles which govern these changes.

Need of Branches of Chemistry

Chemistry is divided into many distinct branches. These branches have distinct areas of study for the scientists to focus on and to achieve breakthroughs and advancements.

1. Physical Chemistry

This branch investigates how substances behave at atomic or molecular levels. It provides clear explanation as to how fundamental physical laws governing our world cause atoms and molecules to show specific characteristics and in turn react to give huge structures related to life.

Uses Physical chemistry is also used to predict and change the rates of reaction and thus optimize the conditions to carry out the reaction on industrial scale.

2. Inorganic Chemistry

It is the study of the synthesis, composition, properties and structure of elements and compounds that contain little & no carbon.

Uses Inorganic compounds are used as fertilizers, medicines, catalysts, pigments, coatings and much more.

3. Organic Chemistry

It is the branch of chemistry that deals with the carbon compounds (hydrocarbons and their derivatives) other than its simple salts like carbonates, bicarbonates, oxides and carbides. In this branch, we study the structure, formation, properties, composition and reactions of carbon containing compounds.

Uses Organic compounds are found in all forms of life and are also essential for life.

4. Environmental Chemistry

It is the scientific study of the chemical and biochemical phenomena that occur in this planet. In this we study the sources, reactions, effects and fates of chemical species in the air, soil and water environments.

Uses Without this, it would be imposible to study the effects that humans have on the environment through the release of chemicals. It helps in understanding the causes, effects and solutions of different types of pollution.

5. Analytical Chemistry

This branch of chemistry deals with the analysis of different substances. It involves separation, identification and determination of the concentration of the material things.

Uses Nowadays the field of analytical chemistry generally involves the use of modern instruments to analyze the matter.

6. Biochemistry

It is the branch of chemistry in which we understand life through chemical processes. It is the study of chemical substances and vital processes occurring in living organisms.

Uses Biochemistry provides insights into the structure and function of molecules such as proteins, carbohydrates, lipids and nucleic acids.

7. Nuclear Chemistry

Nuclear chemistry deals with the reactions taking place in the nucleus of an atom. It deals with radioactivity, nuclear processes and transformation in the nuclei of atoms.

8. Polymer Chemistry

Polymer chemistry focuses on the properties, structure and synthesis of polymers and macromolecules.

Uses Many materials present in the living organisms including proteins, cellulose and nucleic acids are naturally occurring polymers.

9. Geochemistry

The study of chemical composition of Earth and its sources and minerals is called geochemistry.

Uses It is used in minerals exploration, geochemistry mapping today has application in environmental monitoring, forestry and medical research.

10. Medicinal Chemistry

In this branch of chemistry, the chemist tries to design and synthesize a medicine or drugs which is beneficial for mankind.

Uses It includes the discovery, delivery, absorption and metabolism of drugs in human body.

11. Astrochemistry

It is the study of molecules and ions recurring in space and interstellar space.

Uses In this discipline we study the abundance and reactions of molecules and ions in the universe and interaction of these species with radiation.

Elements

• An element is the simplest form of matter. It is a pure substance containing the same kind of atoms.
• It is not possible to break down an element into simpler particles by ordinary chemical reactions.
• When an element exists in the form of aggregate of atoms, it is represented by a symbol. For example, sodium and calcium are represented by their symbols Na and Ca.
• Gaseous elements exist in the form of independent molecules, for example nitrogen (N₂), oxygen (O₂) and chlorine (Cl₂). Noble gases however, exist as monoatomic molecules.
• For example, Helium (He) and Argon(Ar)

Compounds

• A compound is a pure substance. It is formed by the chemical combination of two or more atoms of different elements.
• In a compound, the atoms of elements must combine together by a fixed ratio by weight. For example, in water (H₂O) hydrogen and oxygen are present in a fixed ratio of 1:8 by weight.
• It is possible to break a compound into its constituent elements by a chemical reaction. For example, ammonia can be converted back to nitrogen and hydrogen by a suitable chemical reaction.
• The properties of a compound are always different from the elements from which it is formed. For example, the properties of water are different from those of hydrogen and oxygen.
• Compounds exist in the form of molecules, for example hydrogen chloride (HCl), ammonia (NH₃) and water (H₂O). Compounds may also exist as network arrangement of their atoms. For example ionic compounds like NaCl and covalent compounds like sand (SiO₂)

Mixtures

• Mixture is an impure compound. A sample of matter having more than one type of elements or compounds mixed together in any ratio, is called a mixture.
• Each component of a mixture retains its identity and specific properties.
• A mixture may be homogenous or heterogeneous. For example, the solution of common salt in water is a homogenous mixture while a sample of rock is a heterogeneous mixture.
• The components of a mixture are not chemically bound together and they can be separated by physical method.
• The properties of a mixture are the sum of those of its components.