Chemistry 9 Long Questions and Answers – Chapters 1 to 8

Long Questions Answers

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Chemistry 9 Long Questions and Answers – Chapters 1 to 8

Chemistry is a fundamental branch of science that explores the nature, composition, and transformations of matter. For 9th-grade students, understanding chemistry through long-answer questions helps in building a strong foundation for further studies. Below are detailed answers to important long questions from Chapters 1 to 8 of Chemistry.

Chapter 1: Nature of Science in Chemistry

Q1: Define chemistry and explain its importance in daily life.

Answer:
Chemistry is the branch of science that deals with the study of matter, its composition, properties, and the changes it undergoes. It plays a crucial role in daily life in the following ways:

  • Medicine: Chemistry helps in the production of life-saving drugs and vaccines.

  • Food Industry: Preservatives, flavor enhancers, and nutritional supplements are all products of chemistry.

  • Agriculture: Fertilizers and pesticides increase food production.

  • Energy Production: Fuels such as petrol, diesel, and natural gas are chemical substances used for energy generation.

  • Environmental Protection: Chemistry helps in wastewater treatment and pollution control.

Chapter 2: Matter

Q2: Differentiate between elements, compounds, and mixtures with examples.

Answer:

Property Element Compound Mixture
Definition A pure substance consisting of only one type of atom. A pure substance made of two or more different elements chemically combined. A combination of two or more substances physically mixed.
Composition Single type of atom Two or more elements Two or more substances
Separation Cannot be broken down chemically Can be broken down into simpler substances Can be separated by physical methods
Examples Oxygen (O₂), Gold (Au) Water (H₂O), Carbon dioxide (CO₂) Air, Saltwater

Chapter 3: Atomic Structure

Q3: Explain Dalton’s atomic theory and its limitations.

Answer:
Dalton’s atomic theory was proposed by John Dalton in 1808. The main postulates of the theory are:

  1. All matter is made up of tiny, indivisible particles called atoms.

  2. Atoms of a given element are identical in mass and properties.

  3. Atoms cannot be created or destroyed in chemical reactions.

  4. Atoms combine in simple whole-number ratios to form compounds.

Limitations of Dalton’s Atomic Theory:

  • Atoms are divisible, as they contain protons, neutrons, and electrons.

  • Isotopes of the same element have different masses, contradicting Dalton’s theory.

  • Atoms do not always combine in simple whole-number ratios (e.g., organic compounds).

Chapter 4: Periodic Table and Periodicity of Properties

Q4: What is the periodic table? Discuss its significance and periodic trends.

Answer:
The periodic table is an arrangement of elements in order of increasing atomic number, such that elements with similar properties appear in the same group.

Significance of the Periodic Table:

  • Helps in predicting the properties of elements.

  • Provides a systematic way to study elements.

  • Helps in understanding the trends in chemical behavior.

Periodic Trends:

  • Atomic Radius: Decreases across a period, increases down a group.

  • Ionization Energy: Increases across a period, decreases down a group.

  • Electronegativity: Increases across a period, decreases down a group.

Chapter 5: Chemical Bonding

Q5: What is a chemical bond? Explain ionic and covalent bonding with examples.

Answer:
A chemical bond is the force that holds atoms together in a molecule or compound.

Ionic Bonding:

  • Involves the transfer of electrons from one atom to another.

  • Occurs between a metal and a non-metal.

  • Example: Sodium chloride (NaCl), where Na donates an electron to Cl.

Covalent Bonding:

  • Involves the sharing of electrons between atoms.

  • Occurs between two non-metals.

  • Example: Water (H₂O), where oxygen shares electrons with hydrogen.

Chapter 6: Stoichiometry

Q6: What is stoichiometry? Explain with an example.

Answer:
Stoichiometry is the calculation of reactants and products in a chemical reaction based on the balanced chemical equation.

Example:
Consider the reaction:

2H2+O2→2H2O2H₂ + O₂ \rightarrow 2H₂O

  • This equation means that 2 moles of hydrogen react with 1 mole of oxygen to form 2 moles of water.

  • If we have 4 moles of hydrogen, we need 2 moles of oxygen to produce 4 moles of water.

Chapter 7: Electrochemistry

Q7: What is electrolysis? Explain its applications.

Answer:
Electrolysis is the process of using electricity to drive a non-spontaneous chemical reaction.

Applications of Electrolysis:

  • Electroplating: Used to coat metals with a thin layer of another metal, such as gold or silver.

  • Purification of Metals: Impure metals like copper are refined using electrolysis.

  • Production of Chemicals: Electrolysis is used in the production of chlorine and hydrogen gas.

Chapter 8: Energetics

Q8: Explain the difference between exothermic and endothermic reactions with examples.

Answer:
Exothermic Reactions:

  • Release energy in the form of heat.

  • The temperature of the surroundings increases.

  • Example: Combustion of fuels (e.g., burning of methane).

Endothermic Reactions:

  • Absorb energy from the surroundings.

  • The temperature of the surroundings decreases.

  • Example: Photosynthesis, where plants absorb sunlight.

Conclusion

Understanding chemistry through long-answer questions allows students to develop a deeper knowledge of concepts such as atomic structure, bonding, periodic properties, and chemical reactions. These answers serve as a helpful guide for students preparing for their exams and practical applications in the field of science.

By mastering these fundamental concepts, students can excel in chemistry and apply their knowledge to real-world scientific problems. 🚀 Happy learning!