Question Bank For CBSE Class 9th Chemistry

Unlock the World of Chemistry: Your Comprehensive Question Bank for CBSE Class 9th!

• What factors affect the rate of evaporation from a liquid surface?

Factors include temperature, surface area, humidity, and air movement.

• Explain why the rate of evaporation increases with an increase in temperature.

With an increase in temperature, the kinetic energy of the particles increases, leading to more particles overcoming the attractive forces of the liquid and escaping into the vapor phase.

• Give examples of each state of matter found in daily life.

Examples include solid (ice), liquid (water), and gas (steam).

• Define the term 'density' and explain how it varies with the state of matter.

Density is defined as mass per unit volume. Generally, the density of solids is higher than that of liquids, and the density of liquids is higher than that of gases.

• Describe the process of condensation and give an example.

Condensation is the conversion of a vapor or gas into a liquid. Example: Water vapor condensing on a cold surface to form dew.

• Explain the concept of sublimation with examples.

Sublimation is the process in which a substance transitions directly from the solid phase to the gas phase without passing through the liquid phase. Example: The sublimation of iodine crystals.

• Differentiate between centrifugation and chromatography in terms of principle and application.

Centrifugation separates particles based on their density and size using centrifugal force, while chromatography separates components based on their differential partitioning between the mobile and stationary phases.

• How does the principle of chromatography help in separating different components of a mixture?

Chromatography separates components based on their different affinities for the mobile and stationary phases, allowing them to travel at different rates and become separated.

• Define an element and give examples.

An element is a substance made up of only one type of atom that cannot be broken down further by chemical means. Examples include oxygen, carbon, and gold.

• Explain the difference between an element and a compound.

An element consists of only one type of atom, while a compound consists of two or more different types of atoms chemically bonded together.

• Define an atom. What are its main constituents?

An atom is the smallest unit of an element that retains its chemical properties. Its main constituents are protons, neutrons, and electrons.

• Describe the structure of an atom according to the Bohr model.

According to the Bohr model, electrons orbit the nucleus in fixed energy levels or shells.

• Define a chemical formula. Give examples.

A chemical formula represents the types and numbers of atoms present in a compound. Examples include H2O (water), CO2 (carbon dioxide), and NaCl (sodium chloride).

• Explain the difference between a molecular formula and an empirical formula.

A molecular formula shows the actual number of atoms of each element in a molecule, while an empirical formula shows the simplest whole-number ratio of atoms in a compound.

• State and explain the law of conservation of mass with an example.

The law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction. Example: In the reaction between hydrogen gas and oxygen gas to form water, the total mass of reactants equals the total mass of products.

• What is the law of definite proportions? Provide an example.

The law of definite proportions states that a chemical compound always contains the same elements in the same proportions by mass. Example: Water (H2O) always consists of two hydrogen atoms for every one oxygen atom.

• Define a mole. How many particles are there in one mole of a substance?

A mole is a unit of measurement used in chemistry to express amounts of a substance. One mole contains Avogadro's number (approximately 6.022 × 10^23) of particles.

• Calculate the number of moles in 24 grams of magnesium (Mg). (Atomic mass of Mg = 24 g/mol)

Number of moles = Mass of substance (g) / Molar mass (g/mol) = 24 g / 24 g/mol = 1 mole

• Describe Dalton's atomic theory. What are its main postulates?

Dalton's atomic theory states that all matter is made up of tiny, indivisible particles called atoms, and atoms of a given element are identical in properties.

• Explain Thomson's model of the atom. What was its major contribution?

Thomson's model proposed that atoms are made up of positively charged material with negatively charged electrons embedded within it, similar to raisins in a pudding. This model introduced the idea of subatomic particles.

• Define an ion. How are cations and anions formed?

An ion is an atom or molecule that has gained or lost one or more electrons, thus acquiring a net electric charge. Cations are formed by losing electrons, while anions are formed by gaining electrons.

• What is the difference between an atom and an ion?

An atom is electrically neutral, while an ion has a net electric charge due to the gain or loss of electrons.

• Explain the difference between mass and weight.

Mass is the amount of matter present in an object, while weight is the force exerted on an object due to gravity.

• Give examples of physical and chemical changes, distinguishing between them.

Physical changes do not alter the chemical composition of a substance, while chemical changes result in the formation of new substances with different chemical properties. Example of a physical change: melting of ice. Example of a chemical change: rusting of iron.

• Describe the process of melting with an example.

Melting is the process in which a solid changes into a liquid upon heating. Example: Ice (solid water) melts to form liquid water when heated above its melting point.

• Explain the concept of latent heat of fusion.

Latent heat of fusion is the amount of heat energy required to change a unit mass of a substance from the solid phase to the liquid phase at its melting point, without changing its temperature.

• Differentiate between a homogeneous mixture and a heterogeneous mixture with examples.

A homogeneous mixture has uniform composition throughout and its components are not visibly distinguishable. Example: Saltwater. A heterogeneous mixture has non-uniform composition, and its components are visibly distinguishable. Example: Sand and water.

• Define solute and solvent in the context of a solution.

Answer: A solute is the substance that is dissolved in a solvent to form a solution. The solvent is the substance in which the solute is dissolved.

• Discuss the conservation of mass during a chemical reaction with an example.

The law of conservation of mass states that the total mass of the reactants in a chemical reaction equals the total mass of the products. Example: When iron rusts, the total mass of iron and oxygen before the reaction is equal to the total mass of iron oxide formed after the reaction.

• Explain the difference between exothermic and endothermic reactions.

Exothermic reactions release heat energy to the surroundings, while endothermic reactions absorb heat energy from the surroundings.

• Describe the process of distillation. How is it used to separate mixtures?

Distillation is a process used to separate components of a mixture based on differences in their boiling points. The mixture is heated to vaporize the more volatile component, and the vapor is then condensed back into a liquid and collected.

• Explain the principle behind fractional distillation with an example.

Fractional distillation is used to separate components of a mixture that have similar boiling points. It involves repeated vaporization and condensation steps using a fractionating column. Example: Separation of crude oil into its components such as gasoline, diesel, and kerosene.

• Define a molecule. How does it differ from an atom?

A molecule is a group of two or more atoms held together by chemical bonds. It differs from an atom, which is the smallest unit of an element that retains its chemical properties.

• Differentiate between a covalent bond and an ionic bond.

A covalent bond is formed by the sharing of electrons between atoms, typically between non-metal atoms. An ionic bond is formed by the transfer of electrons from one atom to another, typically between a metal and a non-metal.

• Define isotopes. Provide an example.

Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons. Example: Carbon-12 (12C) and Carbon-14 (14C) are isotopes of carbon.

• Explain the concept of relative atomic mass. How is it calculated?

Relative atomic mass is the average mass of an atom of an element relative to the mass of an atom of carbon-12, which is assigned a mass of exactly 12 atomic mass units (u). It is calculated by taking into account the abundance of each isotope of the element.

• Discuss the difference between physical and chemical properties of matter with examples.

Physical properties can be observed or measured without changing the chemical composition of a substance, such as color, density, and melting point. Chemical properties describe the ability of a substance to undergo chemical reactions and form new substances, such as flammability and reactivity with acids.

• Explain why gases are highly compressible compared to solids and liquids.

Gases are highly compressible because the particles in a gas are far apart and move freely. When pressure is applied, the particles can be pushed closer together, reducing the volume occupied by the gas.

• Define a colloid. Give examples of colloidal systems.

A colloid is a heterogeneous mixture in which the dispersed particles are larger than molecules but smaller than those in a suspension, and they do not settle out. Examples include milk, fog, and whipped cream.

• Explain the process of sieving and give an example of its application.

Sieving is a method used to separate particles of different sizes by passing a mixture through a sieve, which allows smaller particles to pass through while retaining larger particles. Example: Separation of sand and gravel in construction work.

• Define the term 'valency' of an element. How is it determined?

Valency is the combining capacity of an element, determined by the number of electrons an atom can gain, lose, or share to achieve a stable electron configuration.

• Explain the concept of the electronic configuration of atoms with an example.

Electronic configuration describes the distribution of electrons in the electron shells or energy levels of an atom. For example, the electronic configuration of carbon is 2,4, indicating that it has 2 electrons in the first shell and 4 electrons in the second shell.

• Discuss the limitations of the Rutherford model of the atom.

Answer: The Rutherford model could not explain the stability of atoms, the arrangement of electrons in atoms, or the spectrum of hydrogen.

• Describe the modern atomic model, including the roles of protons, neutrons, and electrons.

The modern atomic model depicts the atom as consisting of a nucleus containing protons and neutrons, with electrons arranged in energy levels or shells around the nucleus.

• Define the terms 'atomic number' and 'mass number' of an atom. How are they related?

The atomic number of an atom is the number of protons in its nucleus. The mass number is the total number of protons and neutrons in the nucleus. They are related by the equation: Mass number = Atomic number + Number of neutrons.

• Explain the significance of isotopes in the study of atomic structure.

Isotopes provide valuable information about the structure of atoms, such as the existence of subatomic particles like neutrons. They also have practical applications in fields such as medicine and industry.

• Describe the process of sublimation with examples.

Sublimation is the transition of a substance directly from the solid phase to the gas phase without passing through the intermediate liquid phase. Examples include the sublimation of dry ice (solid carbon dioxide) and the sublimation of iodine crystals.

• Discuss the concept of critical temperature and critical pressure in relation to the states of matter.

The critical temperature is the highest temperature at which a substance can exist as a liquid, regardless of pressure. The critical pressure is the minimum pressure required to liquefy a gas at its critical temperature.

• Explain the difference between endothermic and exothermic reactions with examples.

Endothermic reactions absorb heat energy from the surroundings and feel cold. Example: Photosynthesis. Exothermic reactions release heat energy to the surroundings and feel hot. Example: Combustion.

• Discuss the role of catalysts in chemical reactions. Provide an example.

Catalysts are substances that speed up the rate of a chemical reaction without being consumed in the process. They provide an alternative reaction pathway with lower activation energy. Example: The catalytic converter in automobiles helps convert harmful gases into less harmful ones.

• Define the terms 'molecular formula' and 'structural formula' of a compound. Provide examples.

The molecular formula of a compound shows the actual number of atoms of each element present in one molecule of the compound. Example: The molecular formula of glucose is C6H12O6. The structural formula shows the arrangement of atoms and bonds in the molecule. Example: The structural formula of ethanol is CH3CH2OH.

• Explain how to determine the molecular mass of a compound using its chemical formula.

To determine the molecular mass of a compound, multiply the atomic masses of each element present in the compound by the respective number of atoms and then sum them up.

• Describe the differences between isotopes and isobars.

Isotopes are atoms of the same element with different numbers of neutrons and the same number of protons, while isobars are atoms of different elements with the same mass number but different atomic numbers.

• Explain how isotopes are useful in radiometric dating.

Radiometric dating relies on the decay of radioactive isotopes in minerals to determine the age of rocks and fossils. By measuring the ratio of parent isotopes to daughter isotopes, scientists can calculate the age of the sample.

• Discuss the factors that affect the rate of evaporation of a liquid.

Factors affecting the rate of evaporation include temperature, surface area, humidity, and air movement. Higher temperatures, larger surface areas, lower humidity, and increased air movement all increase the rate of evaporation.

• Explain why evaporation causes cooling.

Evaporation causes cooling because the process requires energy. When liquid molecules evaporate from the surface, they take away energy in the form of heat from the remaining liquid, leading to a decrease in temperature.