Q1: What is the particle size range that characterises a colloid? (a) Less than 1 nm (b) 1 to 1000 nm (c) Greater than 1000 nm (d) Greater than 10000 nm
Solution:
Ans: (b) Colloids have particle sizes ranging from 1 to 1000 nm in diameter, which makes them intermediate between true solutions and suspensions.
Q2: Which method is used to separate a liquid from a solution containing dissolved solids? (a) Sublimation (b) Centrifugation (c) Distillation (d) Coagulation
Solution:
Ans: (c) Distillation separates a liquid from dissolved solids by heating until the liquid vaporises, then cooling the vapour back to liquid form.
Q3: What is the formula for calculating mass by mass percentage? (a) (Volume of solute / Volume of solution) × 100 (b) (Mass of solvent / Mass of solution) × 100 (c) (Mass of solute / Volume of solution) × 100 (d) (Mass of solute / Mass of solution) × 100
Solution:
Ans: (d) Mass by mass percentage is calculated by dividing the mass of solute by the total mass of solution and multiplying by 100.
Q4: Which scientist is credited with developing Oral Rehydration Solution (ORS)? (a) Dilip Mahalanabis (b) John Tyndall (c) Isaac Newton (d) Marie Curie
Solution:
Ans: (a) Dilip Mahalanabis, an Indian paediatrician, developed ORS which revolutionised rehydration therapy and saved millions of lives worldwide through WHO popularisation.
Q5: Which alloy is composed of approximately 80% copper and 20% zinc? (a) Bronze (b) Stainless steel (c) Brass (d) Aluminium alloy
Solution:
Ans: (c) Brass is an alloy made from approximately 80% copper and 20% zinc, making it stronger and more corrosion-resistant than pure copper.
Fill in the Blanks
Q1: A solution that cannot dissolve any more solute at a given temperature is called a _____ solution.
Solution:
Ans: saturated
Q2: The substance that gets dissolved in a solution is called the _____.
Solution:
Ans: solute
Q3: The process in which a solid changes directly into vapour without passing through the liquid state is called _____.
Solution:
Ans: sublimation
Q4: The scattering of light by particles in a colloid or suspension is called the _____ effect.
Solution:
Ans: Tyndall
Q5: The component in a colloid in which the dispersed phase is suspended is called the _____ medium.
Solution:
Ans: dispersion
True or False
Q1: A homogeneous mixture has a uniform composition throughout.
Solution:
Ans: True Homogeneous mixtures have uniform composition where every part looks and tastes the same, like sugar dissolved in water.
Q2: The solubility of gases in liquids generally increases with increase in temperature.
Solution:
Ans: False The solubility of gases in liquids generally decreases with increase in temperature, contrary to solid solutes which increase in solubility.
Q3: Particles of a suspension are larger than 1000 nm in diameter.
Solution:
Ans: True Suspensions have particles larger than 1000 nm in diameter, which are visible to the naked eye and settle on standing.
Q4: Fractional distillation is used to separate components with boiling point differences greater than 25°C.
Solution:
Ans: False Fractional distillation separates components with small differences in boiling points less than 25°C, while regular distillation requires at least 25°C difference.
Q5: Alloys are homogeneous mixtures of two or more metals or a metal and a non-metal.
Solution:
Ans: True Alloys are homogeneous mixtures that are stronger and more corrosion-resistant than pure metals, like brass, bronze, and stainless steel.
Match the Following
Column A
Column B
1. Crystallization
A. Separates immiscible liquids by density difference
2. Paper chromatography
B. Separates by rapid spinning using centrifugal force
3. Separating funnel
C. Separates coloured substances by movement rates on paper
4. Centrifugation
D. Separates by differences in solubility at different temperatures
5. Coagulation
E. Uses alum to clump fine particles together
Solution:
Ans:
1 - D: Crystallization separates substances based on their different solubilities at varying temperatures, forming pure crystals on cooling saturated solutions.
2 - C: Paper chromatography separates coloured substances like dyes and inks by their different movement rates as solvent rises through paper.
3 - A: Separating funnel separates immiscible liquids like oil and water based on their density differences, with denser liquid settling at bottom.
4 - B: Centrifugation separates mixtures by spinning them at high speed, causing heavier particles to settle while lighter liquid remains on top.
5 - E: Coagulation uses substances like powdered alum to make fine suspended particles clump together, which then settle by gravity for separation.
Short Answer Questions
Q1: Explain what a solution is and identify its two main components with an example.
Solution:
Ans: A solution is a homogeneous mixture of two or more substances. It has two main components: the solute and the solvent. The solute is the substance that gets dissolved, such as sugar. The solvent is the substance that dissolves the solute, such as water. When sugar dissolves in water, sugar is the solute and water is the solvent, forming a sweet solution.
Q2: Define solubility and explain how temperature affects the solubility of solid solutes and gases in liquids.
Solution:
Ans: Solubility is the maximum amount of solute that can dissolve in 100 mL or 100 g of solvent at a given temperature. Temperature has different effects on different types of solutes. The solubility of solid solutes in liquid solvents generally increases with temperature. However, the solubility of gases in liquids generally decreases with increase in temperature, showing opposite behaviour.
Q3: Describe the Tyndall Effect and provide two everyday examples where this phenomenon can be observed.
Solution:
Ans: The Tyndall Effect is the scattering of light by particles in a colloid or suspension, making the path of the light beam visible. This effect does not occur in true solutions. Examples include a beam of light entering a dark room through a small hole being scattered by dust particles, and sunlight passing through gaps in leaves of a dense tree, making the light beam visible.
Q4: What is the difference between a homogeneous mixture and a heterogeneous mixture? Give one example of each.
Solution:
Ans: A homogeneous mixture has a uniform composition throughout, where every part looks and tastes the same, such as sugar dissolved in water being equally sweet from first sip to last. A heterogeneous mixture has non-uniform composition that varies from one part to another, such as sand and water where sand particles are visible and settle with time.
Q5: Explain the process of crystallization and mention its practical applications.
Solution:
Ans: Crystallization is the process of forming crystals from a saturated solution. The process involves preparing a saturated solution by heating, filtering to remove impurities, then cooling slowly. Pure crystals separate out on cooling in a regular geometric pattern. It is used for separating two solids when one is present in small quantity and for purification of solids, such as obtaining salt crystals from seawater.
Long Answer Questions
Q1: Compare and contrast solutions, colloids, and suspensions based on their particle size, visibility, settling behaviour, and the Tyndall Effect.
Solution:
Ans: Solutions, colloids, and suspensions differ significantly in their properties. Solutions have particle size less than 1 nm, are truly homogeneous, particles are not visible, do not settle, cannot be separated by filtration, and do not show Tyndall Effect. Colloids have particle size from 1 to 1000 nm, appear homogeneous but are heterogeneous, particles are not visible, do not settle, cannot be filtered, and show Tyndall Effect. Suspensions have particles greater than 1000 nm, are heterogeneous, particles are visible to naked eye, settle on standing, can be separated by filtration, and show Tyndall Effect.
Q2: Analyze the three methods of expressing concentration of a solution, explaining when each method is most appropriately used with suitable examples.
Solution:
Ans: Concentration can be expressed in three ways. Mass by mass percentage shows grams of solute in 100 grams of solution, calculated as (mass of solute/mass of solution) × 100, used for milk powder and packaged foods. Mass by volume percentage shows grams of solute in 100 mL of solution, calculated as (mass of solute/volume of solution) × 100, used for medicines like glucose IV solution. Volume by volume percentage shows mL of solute in 100 mL of solution, calculated as (volume of solute/volume of solution) × 100, used for perfumes, cosmetics, and vinegar.
Q3: Evaluate the importance of separation techniques in industrial processes by discussing distillation and coagulation with their practical applications.
Solution:
Ans: Separation techniques are crucial in industrial processes. Distillation separates homogeneous mixtures by heating until the liquid with lower boiling point vaporises, then cooling the vapour back to liquid through condensation. Fractional distillation is used in petroleum refineries to separate crude oil into useful products like LPG, petrol, kerosene, and diesel based on small differences in boiling points. Coagulation adds coagulants like powdered alum to make fine suspended particles clump together, which then settle by gravity. This is used in water treatment plants to purify water and in food industry for making paneer from milk.
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