1.1 What is Chemistry?

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

Composition determination represents finding out percentages of elements and compounds in a sample of matter.

Structure of matter means the arrangement of atoms in matter.

Both physical and chemical changes may be brought about by the interaction of energy.

Branches of Chemistry

To understand the widely spread complex subject of chemistry and to concentrate on its specific aspects, chemistry is divided into many distinct branches.

Physical Chemistry

Investigates how substances behave at atomic or molecular levels.

Example:

Studying how temperature affects the rate of a chemical reaction, like how iron rusts faster in humid conditions.

Inorganic Chemistry

Study of compounds that do not contain carbon-hydrogen bonds.

Example:

Studying table salt (NaCl), acids like sulfuric acid (H₂SO₄), and bases like sodium hydroxide (NaOH).

Organic Chemistry

Deals with carbon compounds other than simple salts like carbonates, oxides and carbides.

Example:

Studying methane (CH₄) in natural gas, ethanol (C₂H₅OH) in alcoholic drinks, and glucose (C₆H₁₂O₆) in our food.

Environmental Chemistry

Scientific study of chemical and biochemical phenomena that occur in the environment.

Example:

Studying how acid rain forms from sulfur dioxide emissions and its effects on buildings and ecosystems.

Analytical Chemistry

Deals with the analysis of different substances, involving separation, identification and determination of concentration.

Example:

Testing drinking water for impurities or determining the amount of vitamin C in orange juice.

Biochemistry

Understanding life through chemical processes occurring in living organisms.

Example:

Studying how enzymes digest food in our stomach or how DNA stores genetic information.

Nuclear Chemistry

Deals with the reactions taking place in the nucleus of an atom.

Example:

Studying how uranium-235 undergoes fission in nuclear reactors to produce energy.

Polymer Chemistry

Focuses on the properties, structure and synthesis of polymers and macromolecules.

Example:

Studying polyethylene in plastic bags, nylon in clothing, and rubber in tires.

1.3 Element, Compound and Mixture

Comparison Table

Property Element Compound Mixture
Definition Simplest form of matter with same kind of atoms Pure substance formed by chemical combination of different elements in fixed ratio Impure substance with two or more elements/compounds mixed in any ratio
Composition Only one type of atom Two or more types of atoms in fixed proportion Two or more substances in any proportion
Separation Cannot be broken down by chemical means Can be broken into elements by chemical reactions Can be separated by physical methods
Properties Has its own unique properties Properties are different from constituent elements Properties are similar to its components
Examples Oxygen (O₂), Gold (Au), Iron (Fe) Water (H₂O), Salt (NaCl), Carbon dioxide (CO₂) Air, Soil, Milk, Salt water
Chemical Bond No chemical bond between atoms of same element Chemical bonds exist between different atoms No chemical bonds between different substances

Key Points:

  • Elements are pure substances with same type of atoms (e.g., O₂, Fe)
  • Compounds are pure substances with elements in fixed ratios (e.g., H₂O always has H:O = 2:1 by atoms)
  • Mixtures are impure substances with components in any ratio (e.g., air has variable amounts of gases)
  • Elements and compounds have uniform composition, mixtures may not

1.4 Solution, Colloidal Solution and Suspension

Comparison Table

Property True Solution Colloidal Solution Suspension
Particle Size Less than 1 nm 1 nm to 1000 nm More than 1000 nm
Visibility Particles not visible even with microscope Particles visible under ultramicroscope Particles visible to naked eye
Filterability Passes through filter paper Passes through filter paper Does not pass through filter paper
Tyndall Effect Does not show Shows clearly May show
Stability Very stable, particles don’t settle Fairly stable, particles don’t settle Unstable, particles settle on standing
Examples Sugar in water, Salt in water Milk, Blood, Starch solution Muddy water, Chalk in water

Saturated Solution: Contains maximum solute that can dissolve at a given temperature.

Unsaturated Solution: Can dissolve more solute at the same temperature.

Solubility: Maximum amount of solute that can dissolve in 100g solvent at a given temperature.

Practical Example:

When making lemonade, if you add sugar and it completely dissolves, you have an unsaturated solution. If you keep adding sugar until some remains undissolved at the bottom, you’ve made a saturated solution.

Exercises and Solutions

Multiple Choice Questions

1. Hazardous effects of shopping bags are studied in:
(a) Geochemistry
(b) Inorganic chemistry
(c) Analytical Chemistry
(d) Environmental chemistry
Answer: (d) Environmental chemistry

Solution: Environmental chemistry deals with the study of chemical phenomena in the environment, including pollution caused by plastics and shopping bags.

2. Which liquid among the following is a colloidal solution?
(a) Milk
(b) Slaked lime used for white wash
(c) Vinegar solution
(d) Mixture of AgCl in water
Answer: (a) Milk

Solution: Milk is a colloidal solution where fat globules are dispersed in water. It shows Tyndall effect and particles don’t settle on standing.

3. Which of the following is a heterogeneous mixture?
(a) A solution of calcium hydroxide in water
(b) A solution of potassium nitrate in water
(c) Hot chocolate
(d) Concrete mixture
Answer: (d) Concrete mixture

Solution: Concrete mixture is heterogeneous because you can see different components (sand, cement, gravel) separately. The other options are homogeneous mixtures.

Constructed Response Questions

1. Why is there a need to divide Chemistry into many branches? Give three reasons.
Solution:

Chemistry is divided into many branches because:

  1. Complexity: Chemistry is a vast subject covering everything from atoms to living organisms. Dividing it makes study manageable.
  2. Specialization: Different branches allow scientists to specialize in specific areas like medicines, environment, or materials.
  3. Focused Research: Each branch has its own techniques and principles, allowing for deeper understanding and advancements in that specific area.
2. Most of the molecules we study in biochemistry are organic in nature. Where does the difference exist in organic and biochemistry branches of Chemistry?
Solution:

Organic Chemistry studies all carbon compounds (except carbonates, oxides, carbides) including those not found in living things like plastics, fuels, etc.

Biochemistry specifically studies chemical processes and substances in living organisms like digestion, respiration, DNA, enzymes, etc.

While both study carbon compounds, biochemistry focuses only on those related to life processes.

Descriptive Questions

1. Mention the name of the branch of Chemistry in which you will study each of the following topics:

(a) Rate of a reaction
(b) Digestion of food in human body
(c) Properties of plasma
(d) Ecosystem
(e) Reactions taking place during fireworks
(f) Measurement of the absorption of wavelength with the help of ultraviolet spectrometer

Solution:

(a) Physical Chemistry – Studies reaction rates and kinetics

(b) Biochemistry – Studies chemical processes in living organisms

(c) Physical Chemistry – Studies different states of matter including plasma

(d) Environmental Chemistry – Studies chemical interactions in ecosystems

(e) Inorganic Chemistry – Fireworks involve reactions of metal salts

(f) Analytical Chemistry – Uses instruments like spectrometers for analysis

2. Differentiate between the areas which are studied under inorganic and organic chemistry.
Solution:
Inorganic Chemistry Organic Chemistry
Studies compounds that do NOT contain carbon-hydrogen bonds Studies compounds that DO contain carbon-hydrogen bonds (except carbonates, oxides, carbides)
Includes metals, minerals, salts, acids, bases Includes fuels, drugs, plastics, food components
Examples: NaCl, H₂SO₄, NaOH, CaCO₃ Examples: CH₄, C₂H₅OH, C₆H₁₂O₆, proteins
Generally involves ionic bonds Generally involves covalent bonds
Reactions are usually fast Reactions are usually slower

Investigative Questions

1. Preparation of solutions leads to an important process in chemistry which enables us to purify a compound through crystallization. Describe a process in which potassium nitrate is purified by crystallizing it in water.
Solution:

Process for purifying potassium nitrate by crystallization:

  1. Preparation of Saturated Solution: Add impure potassium nitrate to hot water while stirring until no more dissolves, creating a saturated solution.
  2. Filtration: Filter the hot solution to remove insoluble impurities using filter paper and funnel.
  3. Cooling: Allow the filtered solution to cool slowly. As temperature decreases, solubility of KNO₃ decreases.
  4. Crystal Formation: Pure potassium nitrate crystals form as the solution becomes supersaturated upon cooling.
  5. Separation: Separate crystals from the remaining solution (mother liquor) by filtration.
  6. Drying: Dry the crystals between filter papers or in air to remove moisture.

Why it works: Impurities either remain dissolved in the solution or are filtered out because different substances have different solubilities at various temperatures.

2. Design an experiment to separate the components of a mixture containing iron filings, sand, and salt.
Solution:

Experiment to separate iron filings, sand, and salt:

  1. Step 1 – Magnetic Separation: Use a magnet to separate iron filings from the mixture. The magnet will attract and remove iron filings.
  2. Step 2 – Dissolution: Add water to the remaining mixture (sand + salt). Salt dissolves in water but sand does not.
  3. Step 3 – Filtration: Filter the mixture. Sand remains on the filter paper as residue. Salt solution passes through as filtrate.
  4. Step 4 – Evaporation: Heat the salt solution to evaporate water. Salt crystals will be left behind.
  5. Step 5 – Drying: Dry the sand and salt separately.

Principle Used: Different physical properties (magnetic property, solubility, particle size) are utilized to separate the components.